Preferred Citation: Warner, Richard E., and Kathleen M. Hendrix, editors California Riparian Systems: Ecology, Conservation, and Productive Management. Berkeley:  University of California Press,  c1984 1984. http://ark.cdlib.org/ark:/13030/ft1c6003wp/


cover

California Riparian Systems

Ecology, Conservation, and Productive Management

Edited by
Richard E. Warner and Kathleen M. Hendrix

UNIVERSITY OF CALIFORNIA PRESS
Berkeley · Los Angeles · Oxford
© 1984 The Regents of the University of California

TO
A. STARKER LEOPOLD, 1913–1983
Scientist
Conservationist
Mentor
Colleague
Friend
ALOHA NUI LOA, AND GODSPEED



Preferred Citation: Warner, Richard E., and Kathleen M. Hendrix, editors California Riparian Systems: Ecology, Conservation, and Productive Management. Berkeley:  University of California Press,  c1984 1984. http://ark.cdlib.org/ark:/13030/ft1c6003wp/

TO
A. STARKER LEOPOLD, 1913–1983
Scientist
Conservationist
Mentor
Colleague
Friend
ALOHA NUI LOA, AND GODSPEED

IN MEMORIAM

Rick Warner has died since completing this book. He finished it with the last of his ebbing great strength. He was a remarkable field scientist and activist who could be counted on to get things done correctly regardless of the difficulties. He was a strong moral force that will be sadly missed in the ongoing struggle to maintain a semblance of environmental quality.

HUEY JOHNSON


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A PICTORIAL OVERVIEW OF CALIFORNIA RIPARIAN SYSTEM CHARACTERISTICS

California riparian systems exhibit, in both structure and function, a mixture of regional uniqueness and global universality. An understanding of the nature and consequences of these characteristics can be very useful in interpreting observed field conditions and in designing and implementing management programs. Many of these characteristics are best described using on-site photography. The adage "one picture is worth a thousand words," is especially true here, where the diversity of species, topography, biogeography, climate, and geology found in California is so great. The set of photographs described below was selected to demonstrate and to assist in interpreting some of the more pervasive elements of structure and function in riparian systems both in California and elsewhere.

Frontispiece.—Valley oak (Quercuslobata ) forest on the lower floodplain of the Cosumnes River, San Joaquin County. The wild grape (Vitiscalifornica ) draping the branches in areas exposed to the sun gives this magnificent forest a cathedral-like aspect. (Photograph © 1983 by R.E. Warner.)

Page 1.—A stand of black cottonwood (Populus trichocarpa ) at about 4,000 ft. elevation along the Yuba River, Nevada County. This species is replaced at lower, drier, and warmer elevations by Fremont cottonwood (P . fremontii ), and at higher elevations by the quaking aspen (P . tremuloides ). (Photograph © 1983 by R.E. Warner.)

Page 45.—A stand of black willow (Salix gooddingii var. variabilis ) along the American River Parkway, Sacramento. Willows vary greatly in form, depending upon species. Some are small, prostrate shrubs; others robust shrubs and small trees; and others, like that illustrated here, are capable of developing into a dense forest, 50 ft. or more in height. (Photograph © 1983 by R.E. Warner.)

Page 109.—The California sycamore (Platanus racemosa ), here growing on the floodplain of the Sacramento River about 12 miles north of Sacramento, Yolo County. This species is strictly limited to streamside corridors and riverine floodplains, where it provides an attractive and ecologically valuable element to the riparian vegetation. Its tendency to produce cavities in trunks and major branches following limb loss makes it especially valuable to hole-nesting species of birds and mammals. (Photograph © 1983 by R.E. Warner.)

Page 159.—Valley oak forest in Caswell State Park, San Joaquin County. This area has been protected from human-use damage for several decades and is one of the most intact and ecologically diverse riparian systems in California. Even here, however, recent studies have demonstrated that tree size/frequency ratios and other determinants of vegetation structure are unusual. Thus, while valley oak forests of Caswell State Park are among the most intact of California riparian systems, even they are not "primeval," further supporting the growing suspicion that because of ubiquitous, long-term, human use impacts, there are essentially no pristine riparian systems left in the state. (Photograph © 1983 by R.E. Warner.)

Page 189.—A large specimen of the California buckeye (Aesculuscalifornica ) near the 100-year floodzone line on the Cosumnes River, Sacramento County. Less obligate a riparian species than the cottonwoods and willows, it is found concentrated in some riparian zones, especially riverine floodplain riparian systems, in the Central Valley. One finds, for example, a well-defined band of California buckeye in the lower floodplains of such rivers as the American, Cosumnes, Stanislaus, and Tuolumne. This band intermixes at its upper boundary with a broad band of valley oak and at its lower boundary with mixed cottonwood/Oregon ash (Fraxinuslatifolia ) forest. During earlier, less disturbed times this California buckeye zone must have been even more pronounced, as some of the largest, most massive specimens of the species are still present where human-use impacts have been limited. The species is also concentrated along perennial and intermittent streams of the Coast Ranges, often well above the riparian zone, but where local circumstances produce shaded slopes and enhanced soil moisture conditions. (Photograph © 1983 by R.E. Warner.)

Page 215.—Seeps are an inconspicuous but important type of riparian system, being essentially diminutive wet meadows. Studies of them have been neglected until recently. It is now becoming clear that they are often refugia for unique, riparian-dependent species of plants and animals. Like desert oases, seeps provide a special, insular biogeographical circumstance. This seep is located at about 1,520 ft. elevation near Placerville in El Dorado County. (Photograph by Cheryl Lemming Langley, with permission.)


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Page 241.—Along mountainous streams the banks and floodplains may be so steep, rocky, fractured, and/or unstable that the riparian zone is difficult to recognize. This segment of the upper Van Duzen River below Dinsmore (part of the state Wild and Scenic River System) illustrates this very well. Small pockets of riparian woodlands and meadows can be found where hydrologic and geologic circumstances permit. Other reaches may have only an occasional willow, alder, or other mesophyte growing amongst boulders and in the rocky, uneven streamside zone. (Photograph courtesy of Kerry J. Dawson, with permission.)

Page 287.—Yosemite Valley, Merced County, the floor of which contains grand and magnificent riparian systems. Carved from granite by glacial processes, the valley is a broad, nearly flat floodplain partially dammed by lateral and terminal moraines, where imported waters are delivered via a series of majestic waterfalls and cataracts. (Photograph © 1983 by R.E. Warner.)

Page 383 (upper).—Wet meadows comprise a significant part of the Yosemite Valley riparian zone. High soil moisture levels from the imported water supplies provide the necessary water for mesic riparian plants, while at the same time excluding the more xeric upland species found on adjacent slopes and higher sites. (Photograph © 1983 by R.E. Warner.)

Page 383 (lower).—Meadows constitute a major riparian resource wherever they occur, as the combination of high light intensity, soil moisture, nutrient availability, and amenability to fish and wildlife render them highly productive. They may be thought of as small riparian islands in the far less productive uplands. This meadow, at about 4,500 ft. elevation in the transition forest near Strawberry, Yuba County. Despite periodic meadow-hay cutting, grazing, and livestock yarding operations, it still retains much of its original structure and provides habitat for many wildlife species. (Photograph © 1983 by R.E. Warner.)

Page 437 (upper).—Vernal pools are another type of seasonal wetland with a strong riparian component. Precipitation is captured during winter rains in these impermeable-bottomed lowlands, creating shallow seasonal pondlets or "pools." As spring arrives and the imported water evaporates, concentric bands of wildflowers and other vegetation develop along the riparian zones of the pools. Many of these plant species are especially adapted to vernal pool circumstances. This vernal pool in the Vina Plains Preserve of The Nature Conservancy is just beginning to dry out with the onset of spring. (Photograph by Hella Hammid and The Nature Conservancy, with permission.)

Page 437 (lower).—Greater and Lesser Sandhill Cranes rising from the riparian floodplain grasslands of the Mokelumne River. For some five million years Sandhill Cranes have been flying south each winter to use this riparian resource for foraging and roosting. Recently, however, a strong trend to convert the riverine bottomlands to vineyards and other land uses incompatible to the cranes has developed. These land-use practices are so damaging to the native Sandhill Cranes that whole regional crane populations could be decimated. (Photograph © 1983 by R.E. Warner.)

Page 481 (upper).—Saratoga Springs is a unique type of desert riparian system in the southern end of Death Valley National Monument. Its imported water source is a series of springs emerging from the base of some rocky hills to the right. The encompassing sand dune ridges are maintained by the interaction of wind and stabilizing shrubs and grasses. The inner riparian zone is lush and green, being protected from wind by the dune barrier. The area receives less than five inches precipitation per year. (Photograph © 1983 by R.E. Warner.)

Page 481 (lower).—In this palm oasis the native riparian palm Washingtoniafilifera finds adequate moisture in a surface-emergent aquifer on the desert floor of Anza-Borrego Desert State Park. In such riparian systems water may appear only very rarely—or not at all—at ground level, sometimes limiting the ability of riparian shrubs and groundcover species to survive. Digging at the base of these trees produced wet, sandy soil. During wet years water has been recorded at ground level. (Photograph © 1983 by R.E. Warner.)

Page 537 (upper).—In the drier, warmer, more southerly portion of its range, the red alder (Alnusrubra ) is closely associated with and dependent upon riparian systems, occurring as a streamside species. In this photograph of a stream in the Coast Ranges about five miles south of Point Reyes Station, the species can be seen as relatively riparian-dependent, the trees closely following the watercourse. (Photograph © 1983 by R.E. Warner.)


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Page 537 (lower).—Further north, as climate tempers and precipitation increases, the species abandons its riparian dependency and is regularly found on moist, open slopes and along roadside berms. Here the species is growing vigorously in roadside gravels on coastal Vancouver Island, British Columbia. Precipitation in this region is between 100 and 200 inches per year. This varying dependency upon the riparian zone, resulting from changes in climatic circumstances, is seen in many riparian species. (Photograph © 1983 by R.E. Warner.)

Page 577 (upper).—A mature grove of Fremont cottonwood on the floodplain of the South Fork Kern River, Kern County. One of the finest remaining cottonwood/willow riparian systems in southern California, the area has now been preserved by The Nature Conservancy, and efforts are underway to rehabilitate portions that have been most seriously affected by grazing, clearing for agriculture, and other human-use impacts. (Photograph © 1983 by R.E. Warner.)

Page 577 (lower).—The floodplain riparian wetlands of the South Fork Kern River riparian system illustrate very well one of the major geologic principles in the formation and development of these unique systems. As can be seen here, there are large expanses of meadow as well as cottonwood/willow forest. The South Fork Kern River canyon was initially cut down several hundred feet below its present level, and at one time was a relatively steep-walled canyon. Subsequent downstream faulting and earth movement created a barrier across the watercourse. Today the canyon is filled with unconsolidated alluvial sediments and the resulting aquifer filled, raising water table height to at or near ground level. (Photograph © 1983 by R.E. Warner.)

Page 633 (upper).—It is easy to see how riparian systems can be major contributors to ecological diversity and productivity in arid and semi-arid regions. Little Panoche Creek provides a ribbon of mesic summer vegetation and shade through the otherwise arid, treeless uplands. This narrow band of riparian vegetation is heavily used by both wildlife and domestic livestock. (Photograph © 1983 by R.E. Warner.)

Page 633 (lower).—The world's second largest tree (the largest is found in similar circumstances), a coast redwood (Sequoiasempervirens ), in the Rockefeller Grove of Redwood State Park, Humboldt County. This immense specimen is growing on the floodplain riparian zone of Bull Creek and is one of the largest living beings on the face of the earth. Note from the photograph that its dimensions are: tree circumference—53 ft.; diameter—17 ft.; and height 346.5 ft. (Photograph © 1983 by R.E. Warner.)

Page 687 (upper).—An example of a very important but poorly understood riparian phenomenon common in the Central Valley. This "lake" or "slough" is formed by runoff erosion in upland areas immediately above the floodplain. The lower ends of these lakes empty onto the floodplain itself, and are at times blocked off and isolated from the floodplain by silt plugs, beaver dams, and other barriers. These lakes are generally perennial and host large populations of waterfowl, wading birds, and other wildlife. When left undisturbed by man, they are often exquisitely beautiful. The site illustrated here is along the lower Cosumnes River, Sacramento County. No special effort has been made to preserve these sites, and they are rapidly being lost to overgrazing, drainage, and forest clearing. (Photograph © 1983 by R.E. Warner.)

Page 687 (lower).—As the lowest-lying area of the Central Valley floodplain is reached, the character of the watercourses changes. Rivers and streams become slower moving, and sloughs, oxbows, lakes, and other secondary waterways with warm, nutrient-rich waters become prominent. Shortly before its confluence with the Mokelumne River, the lower Cosumnes River, shown here, becomes a series of slow-moving, warm water, high nutrient waterways. Wildlife is abundant here at all seasons. Indeed, this zone appears to be one of the most productive in the entire Central Valley ecosystem. (Photograph © 1983 by R.E. Warner.)

Page 721 (upper).—One of California's more remarkable watercourses, with its attenuated riparian zone. This small, perennial freshwater stream derives from springs and seeps in the mountains forming the western boundary of Death Valley in Death Valley National Monument. The water is fresh enough to support a population of the native (and endangered) species of pupfish, as it passes through the salt flats comprising the floor of Death Valley. (Photograph © 1983 by R.E. Warner.)

Page 721 (lower).—A closer view of the riparian zone of the small stream illustrated above. The narrow, dark line at the edge of the crystalline salt concretions is the riparian zone, a growth zone for several species of algae. This riparian algal growth zone, and algal mats on the bottom of the streambed, are the two major sites of primary production for this peculiar stream ecosystem. (Photograph © 1983 by R.E. Warner.)


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Page 747 (upper).—As a result of nearly two centuries of diverse, unplanned, and often destructive land-use practices, thousands of miles of smaller streams, creeks, and sloughs throughout California have been largely divested of their riparian resources. This is especially pronounced and observable in the San Joaquin Valley, where precipitation rate is low and the rate of natural recovery of riparian vegetation is slow. This small watercourse bordering Sandy Mush Road, San Joaquin County, formerly had a corridor woodland of Fremont cottonwood, willow, and riparian shrubs. Systems such as this have been variously grazed, burned, and cleared, until today little riparian vegetation remains. From an ecological point of view, the value of these systems is often reduced 90–95%. (Photograph © 1983 by R.E. Warner.)

Page 747 (lower).—Subsiding water tables are responsible for the loss of large areas of riparian vegetation. The willow-lined sloughs shown here are part of the formerly massive natural drainage system connecting the Kern River with Kern, Buena Vista, Goose, and Tulare lakes. Historically, overflow water moved via this system to the San Joaquin River for discharge to the Pacific Ocean. The terrestrial component of this extensive wetland system comprised a major riparian resource for that region and provided essential habitat for the endangered tule elk as well as many other species. Diversions for agricultural irrigation in the late 1800s, intensive groundwater pumping from agricultural wells in the early 1900s, and finally construction of Isabella Reservoir and further diversion of the Kern River water supplies removed so much water from the system that it dried up and its dependent riparian vegetation died. The photograph shows one of these dry sloughs in what is now the Tule Elk State Reserve. The trees are today but dead carcasses bordering the now-dry slough. (Photograph © 1983 by R.E. Warner.)

Page 783 (upper).—Rock riprap on the western bank of the Sacramento River north of Sacramento. This controversial structural erosion control measure is aesthetically defacing, ecologically damaging, expensive, and subject to failure. Yet it is one of the few structural bank erosion protection devices that has proven relatively effective over the years. Over time, as alternate bank protection strategies—e.g., river meander zones, integrated pest control on levees, integrated floodplain management, riparian vegetation reestablishment—become available and are accepted at policy and administrative levels, use of rock riprap and other controversial structural erosion control will diminish. Until then, because one of the principal mandates upon the Corps of Engineers remains the protection of life and property from flood damage, riprapping will continue to be used despite its well known negative values. (Photograph © 1983 by R.E. Warner.)

Page 783 (lower).—Rafting and other forms of boating recreation are developing into important uses of California's river systems. Here a group prepares to run the Merced River immediately below Yosemite National Park. Maintenance and restoration of riparian system values is very important to these user groups, as both the ecological and aesthetic values of the sport depend upon the health of the riparian zone. On such excursions, much time is spent picnicking, resting, and camping in the riparian zone. It is this type of recreational activity, in addition to recreational fishing, that feels most keenly the impact of structural bank protection measures such as riprapping. (Photograph © 1983 by R.E. Warner.)

Page 825 (upper).—Cattle foraging for food in the riparian zone of Little Panoche Creek. Note the absence of groundcover and shrubcover vegetation and presence of prominent browse lines on the Fremont cottonwood. Cattle are attracted to the riparian zone by the shade, (usually) high moisture, palatable vegetation, and (usually) free water. (Photograph © 1983 by R.E. Warner.)

Page 825 (lower).—Human disturbance has caused the cattle to leave immediate area. Note complete absence of cottonwood regeneration even though adult plants are present. In due course the remaining, heavily browsed trees will die, and this reach of stream will become devoid of tree cover. This pattern of gradual decline of ecological diversity and quality through livestock-induced destruction of riparian vegetation is common throughout the arid and semi-arid regions of California. (Photograph © 1983 by R.E. Warner.)

Page 867 (upper).—Many human-use riparian impacts are subtle and not readily apparent for many years. The effects of two different livestock management programs on adjacent reaches of the same watercourse are illustrated here. This photograph, looking west immediately upstream from the property line fence, shows a young, recovering riparian system with vigorous ground-and shrubcover growth. This vegetation, while deriving from a previously more heavily degraded riparian system and hence in no way "pristine," none-the-less indicates the regeneration potentials for such small streams. (Photograph © 1983 by R.E. Warner.)


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Page 867 (lower).—Looking downstream from the fenceline dividing the two properties, one sees denuded streambanks, remnant trees with browselines, and an almost complete absence of vegetation regeneration of any kind. This latter pattern of denudation from long-term overuse of the riparian zone is one of the more common riparian land-use patterns seen throughout California. (Photograph © 1983 by R.E. Warner.)

Page 905 (upper).—Some symptoms of hydrologic and vegetative instability damaging to riparian values: 1) cut or eroded streambanks, where roots are showing and the bank faces are unstable; 2) lack of ground- and shrubcover vegetation (grasses will often remain throughout a sequence of severe erosion damage); 3) grossly uneven size classes of trees. Here only a few decadent cottonwoods, willows, and sycamores remain after decades of overuse. (Photograph © 1983 by R.E. Warner.)

Page 905 (lower).—Some further symptoms of riparian erosion problems: 1) widening and shallowing of watercourse; 2) reduction in streamside vegetation cover, with reduced amounts of shade and increasing water temperatures; 3) significant numbers of dead and dying trees. Healthy streamside forests and woodlands have low rates of tree mortality, and tree carcasses are present but uncommon. Here dead mature willows are abundant; 4) lack of regeneration of dominant tree species; 5) loss of palatable mesic groundcover and shrubcover plants. (Photograph © 1983 by R.E. Warner.)

Page 957 (upper).—A good, relatively non-destructive use of riparian zones where competing human use interests exist. This golfcourse near Galt, Sacramento County, makes use of the aesthetic values of the Dry Creek riparian zone, while retaining intact most of its ecologic and hydrologic values. Golf carts trundle across bridges, making both sides of the system accessible for recreational use. (Photograph © 1983 by R.E. Warner.)

Page 957 (lower).—Some riparian systems are especially attractive and uniquely suited for dispersed recreation activities which, if properly designed, can protect and restore the systems while making them accessible for non-consumptive uses. Shown here is Orestimba Creek where it crosses Interstate 5 near Stockton. The floodplain supports a unique and beautiful stand of mature California sycamore. Unfortunately, the sycamore stand has been continuously grazed for several decades, the inevitable result being no sycamore or other riparian tree reproduction and loss of vegetative diversity and plant cover. If the present land-use practices prevail, the sycamore woodland will ultimately be destroyed. A park has been proposed for the site, which, if effectively implemented, could lead to long-term protection and recovery of the system. Presently the concept has low priority because the intrinsic riparian values and the potential symbiosis of park and natural system have not been fully factored into the planning process. (Photograph © 1983 by R.E. Warner.)


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FOREWORD

In the semi-arid environment that characterizes most of California, the narrow riparian strip of moist soil bordering watercourses, seeps, and springs supports the maximum abundance and variety of plant and animal life. This, of course, is most obvious in the desert or on the sagebrush flats in the Great Basin where the surrounding uplands are extremely dry. But apparently it was equally true of the Central Valley in 1844 when Colonel John Fremont traveled southward from Sutter's Fort on the American River, skirting the western foothills of the Sierra Nevada. With each river crossing he eulogized the beauties of the riparian vegetation: "We traveled for 28 miles over the same delightful country as yesterday, and halted in a beautiful bottom at the ford of the Rio de los Mukelemnes. . . . The bottoms on the stream are broad, rich, and extremely fertile. . . . A showy lupinus of extraordinary beauty, growing four to five feet in height, and covered with spikes in bloom, adorned the banks of the river, and filled the air with a light and grateful perfume." Not only did Fremont have a keen eye for rich soil and bright blossoms, but he commented as well on the numbers of deer and elk seen in the oak parklands and along the edges of the lowland tulares , or marshes. In the South Coast Ranges, the Spanish traveled the broad valleys and established most of their missions in riparian situations. Only in the wet and rugged North Coast Ranges did travelers shun the watercourses, largely because the valleys were V-shaped, with scant bottomlands.

In the process of settlement, the riverbottoms and alluvial terraces were the first areas to be homesteaded and adapted for tillage. Today virtually every acre of the Central Valley bottomlands has been cleared, drained, diked, leveled, or otherwise altered for cultivation. As reported in this volume, less than 10 percent of the original riparian vegetation remains, and over half of this remnant forest and woodland has been logged and otherwise degraded. Similarly, many other major California river valleys have been turned by the plow—the Russian, Napa, Salinas, Santa Maria, Santa Ana, and on—to take advantage of the fertile soils wherever they occur. Thousands of miles of diversion canals have permitted extension of cultivated fields and pastures to areas far removed from streamsides, even well into the desert. At the same time, these diversions have removed large amounts of water from the streams and rivers of origin, often greatly modifying their character. Today there are few arable acres left that are not producing crops or livestock.

The agricultural conquest has made a great contribution to the economy of California, but in the process some natural values have been sacrificed, at times unnecessarily. Riverine ecosystems often are unique, supplying habitats for animal and plant species that are narrowly restricted in their requirements. For example, the Yellow-billed Cuckoo and Bell's Vireo are two birds that nest exclusively in riparian thickets in the Central Valley and adjoining arid areas. The original, uncountably large populations of waterfowl and other wetland-dependent birds have been reduced to a pittance. Those that remain are still associated with and dependent upon the remnant wetlands. Many, like the large herons and egrets, colonize mature riparian trees. Others, like the Greater and Lesser Sandhill Cranes both feed and breed in riparian wetlands.

Aquatic mammals including the otter, beaver, and muskrat frequent streams and billabongs. According to Williams and Kilburn (this volume), of the 502 native species and subspecies of land mammals in California 25 percent (133 taxa) are limited to or largely dependent upon riparian systems. Of these, 21 species and subspecies are especially vulnerable to loss of habitat and are facing potential threats of extinction, principally through destruction of habitat.

Of the 120 species of reptiles and amphibians that occur in California, half of the reptiles and three-fourths of the amphibians are closely associated with riparian situations. And even the fishes in streams are sheltered by streamside vegetation and obtain much food from the insects that live on the banks and indirectly from the leaves and woody materials provided by riparian vegetation.


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When riparian vegetation is stripped away and the soil is seeded to monotypic crops, the native riparian ecosystem is effectively destroyed. Water impoundment or diversion can accomplish the same end. Logging and road building have exposed many streams to erosion and desiccation of the bank areas. Perhaps the most subtle but still highly degrading influence on riparian vegetation is unrestricted grazing by domestic livestock. All of the above forms of land exploitation are justifiable within limits. Yet it would seem both desirable and quite possible to preserve shelter strips along streams, wide enough to protect the riverbanks and riparian flora and fauna, but narrow enough to minimize loss of production. Rigorous protection of desert riparian systems, so few in number and so vital to wildlife, would also seem reasonable, especially because of their extreme vulnerability to human-use impacts.

Fortunately, there is an awakening public appreciation of the beauty, interest, and productive values of riverine forests, streamside woodlands, desert washes and oases, and their richly endowed ecosystems. Some of the most appreciated public parks are situated in old-growth riparian stands along the Sacramento and San Joaquin Rivers, Bidwell Park near Chico being an outstanding example. The stimulus of the California Riparian Systems Conference and this resultant volume of thoughtful and informative reports on many aspects of the problem is evidence of that new interest and concern. Hopefully, from this auspicious beginning there will emerge enduring public and private determination to perpetuate the rich values of riparian systems throughout California.

A. STARKER LEOPOLD
13 JUNE 1983


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PREFACE

This volume had its origin in the California Riparian Systems Conference, held at the University of California, Davis, 17–19 September 1981. The conference, one year in development and execution, was organized as a means of bringing together the wide range of riparian interests which have been evolving throughout California (and indeed throughout America) over the last decade. From the arid southern deserts to the rainy northcoast forest country, development and other land–use pressures have been destroying and degrading riparian systems at unprecedented rates. Field observations and inquiries throughout the state indicated that virtually every city and county has its own set of urgent riparian problems. Planners, city councils, boards of supervisors, local, state, and federal resource managers, developers, lawyers, conservationists, to mention a few, were all coping with riparian issues. Many of these issues were markedly similar in character, despite their disparate geographical locations.

The main goals of the conference were: a) to define major riparian concepts, problems, and opportunities; b) to promote discussion and information exchange among riparian interests; and c) to establish the technical and communicative base for a long-term, statewide riparian planning, management, and conservation strategy.

Seven hundred and eleven people, from not only California, but at least 10 other states and Washington, D.C., registered as conference participants, attesting both to the intensity and the wide geographical extent of interest in this subject. Sixteen federal and state agencies and two private organization (listed in the Acknowledgments) provided the funding and in-kind support necessary for a gathering of this size and complexity. Three plenary and 21 concurrent sessions permitted the presentation of approximately 150 technical papers.

Of these papers, 128 were ultimately accepted for publication, and then subjected—as required—to intensive post-conference technical and general editorial review. This review often involved extensive consultation with authors. Following editorial review, all manuscripts were retyped, proofread twice, and subjected to a final editorial review. It will be noted that there are two general formats, one for broadly scientific papers, the other for legal and related papers. This protocol facilitated most efficient reporting of reference material in the various disciplines.

The goals of the editors throughout were to provide a final product that is technically sound, accurate, and as free from jargon, imprecise terminology, and confusing graphics as possible. Our ultimate goal—which we believe we have achieved, but leave the reader to be final arbiter—has been a document of significantly higher professional quality than the usual conference proceedings, falling perhaps midway between that and rigorously peer-reviewed, heavily edited technical journals and monographs.

The task proved far more time consuming and costly than had been anticipated. In retrospect this is understandable, as the material derived from some 175 widely scattered authors and exceeded the equivalent of 3,000 manuscript pages in length. It is our hope that the combined efforts of authors, editors, and dedicated support staff have resulted in a document that will materially advance the long-term interests of riparian systems—both throughout California and in other areas where similar issues are being addressed.


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SOME RIPARIAN DEFINITIONS

The following definitions and the conceptual frame they provide were used both in the design of the conference and the preparation of this volume. While the editors did not attempt to achieve absolute uniformity of definition in order to accommodate strong author terminological preferences, considerable effort was made to minimize ambiguity and approach standardization of the most widely used descriptors. While all readers may not agree or be comfortable with all definitions, all will at least understand what the authors are trying to say.

It is important to discern at the outset that the "riparian" concept has had a specific ecological context for well over two thousand years. The present day riparian concept and its derivative terms (riparian, riparial, riparious) all come from the Latin Riparius , which itself derives from the Latin Ripa (Pl. Ripae ) meaning bank or shore, as of a stream or river. The original meaning has been largely retained through subsequent history, i.e., pertaining to the terrestrial, moist soil zone immediately landward of aquatic wetlands, other freshwater bodies, both perennial and intermittent watercourses, and many estuaries.

While the original Latin usage apparently related to freshwater/upland and estuarine/upland interfaces, the term has occasionally been applied to coastal shore zones. There is presently no clear concensus as to its applicability to coastal shorelines, but a conservative interpretation (which we prefer) would probably exclude them.

Despite numerous attempts, no single purely descriptive definition embracing riparian systems—that is, one that attempts to define by listing all the different types of riparian phenomena—has proven successful. There are far too many types of riparian systems to be encompassed in a single descriptive statement. Such all-inclusive descriptive definitions have inevitably proven both too unwieldy and less than totally encompassing of all significant riparian phenomena.

Last, it is useful to recognize that the term "riparian" isanadjective . The term, once defined, can thus usefully modify a multitude of other well-accepted terms. This process leads in a straight-forward manner to a set of riparian definitions that is functional and easily understood. The linch-pin or common denominator is of course the term "riparian." Once that has been adequately defined, everything else falls into place. Proceeding in a sequence that builds logically, the following definitions are offered.

RIPARIAN: pertaining to the banks and other adjacent terrestrial (as opposed to aquatic) environs of freshwater bodies, watercourses, estuaries, and surface-emergent aquifers (springs, seeps, oases), whose transported freshwaters provide soil moisture sufficiently in excess of that otherwise available through local precipitation to potentially support the growth of mesic vegetation.

AQUATIC: growing or living in or frequenting water; taking place in or on water.

ZONE: an area surrounde by boundary lines; a region or area set off as distinct from surrounding or adjoining parts.

WETLAND: a zone that is periodically, seasonally, or continuously submerged or which has high soil moisture; which may have both aquatic and riparian components, and which is maintained by transported water supplies significantly in excess of those otherwise available through local precipitation.

UPLAND: the ground above a floodplain; that zone sufficiently above and/or away from transported waters as to be dependent upon local precipitation for its water supplies.

POPULATION: a group of individuals of the same species inhabiting a specific zone or system.

HABITAT: the ecological and/or physical place determined and bounded by the needs and the presence of a specific plant or animal population, which contains a particular combination of environmental conditions sufficient for that population's survival. Similar or equivalent to "niche".


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VEGETATION: the total plant cover or plant life of a zone or area.

FAUNATION: the total animal life of a zone or area; the animal equivalent of vegetation.

ASSOCIATION: a collection of units or parts into a mass or whole (e.g., a group of animals, plants, or both). A statement of physical proximity or grouping, without necessarily requiring or implying interactions between units of the group, in contrast to "community", which does. Similar or equivalent to "aggregation."

COMMUNITY: an association of living organisms having mutual relationships among themselves and to their environment and thus functioning, at least to some degree, as an ecological unit.

SYSTEM: a group of related natural objects and/or forces within a defined zone; a regularly interacting or interdependent group of items forming a unified whole; a more general and less rigorous term than "ecosystem".

ENVIRONMENT: the complex of factors that act upon an organism or an ecological community and ultimately determine its form and survival.

ECOSYSTEM: the interacting complex of a community and its environment functioning as an ecological unit in nature. Differs from "system" in being a more rigorous definition that encompasses and requires assumptions of energetics, ecological interactions, species adaptations, and so forth.

A RIPARIAN ZONE is thus a delimited of riparian (moist soil) substrate, within whose boundaries may grow a RIPARIAN VEGETATION, which in turn may support a RIPARIAN FAUNATION. The riparian vegetation and riparian faunation in turn comprise one or more plant, animal, or biotic RIPARIAN ASSOCIATIONS, which, if the populations are known to interact and to have mutual relationships among themselves and their environments, constitute a RIPARIAN COMMUNITY. Each POPULATION of plant or animal so involved has its own population-specific HABITAT, determined and delimited by the specific physiological and ecological requirements of that population. All are part of and exploit a RIPARIAN ENVIRONMENT, and in so doing become parts of a RIPARIAN ECOSYSTEM. A RIPARIAN SYSTEM denotes, in a generalized way, a site-specific set of riparian phenomena without necessarily connoting an entire riparian ecosystem. Where the riparian plant and aminal life has been stripped off or otherwise destroyed, the remnant riparian system may consist of only the remaining geologic riparian zone. The riparian zone in turn may be reduced or even destroyed by the diversion or other loss of its transported water supplies.

Applying this terminology with respect to wetlands, there are permanently inundated AQUATIC WETLANDS (having water depths of two meters or less) with saturated soils and hydrophytic plants; and less frequently to never inundated RIPARIAN WETLANDS with moist soils and mesophytic plants. Riparian wetlands are bounded on their outer or drier sides by yet more xeric UPLANDS, which are usually higher in elevation and still further removed from the transported water supplies.


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ACKNOWLEDGMENTS

The enterprise resulting in the present volume spanned three years and involved the support and dedicated assistance of a wide array of organizations, institutions, and individuals. While space does not permit the enumeration of all to whom we are indebted, some must be identified because of their especially important contributions to the success of the venture.

Conference Organization and Execution

The funding and in-kind support of the following co-sponsors (listed alphabetically) was indispensible to the success of the California Riparian Systems Conference.

Conference Co-sponsors

California Department of Boating and Waterways
California Department of Conservation
California Department of Fish and Game
California Department of Food and Agriculture
California Department of Forestry
California Department of Parks and Recreation
California Department of Water Resources
California Resources Agency
Friends of the River
Natural Resource Biologists' Association (Friend of the Conference)
Riverlands Council
State Water Resources Control Board
The Reclamation Board
University of California (Davis) Water Resources Center
US Army Corps of Engineers
USDA Soil Conservation Service
USDI Bureau of Reclamation
USDI Fish and Wildlife Service
US Water Resources Council

Their confidence in the value of the enterprise and in our ability to bring it to fruition is deeply appreciated; without their support there could have been neither the conference nor the present volume.

During the year of organization preceeding the conference, day-to-day guidance was provided by the Conference Steering Committee. Committee members served as interested individuals rather than official agency representatives and gave unstintingly of their time and professional expertise as issues of planning and organization were dealt with. They also provided liason with their respective organizations, facilitating involvement and better understanding of the riparian interests and needs of these organizations.

Conference Steering Committee

Dana Abell*
Michael Aceituno*
Betty Andrews
E. Lee Fitzhugh
Randy Gray*
Glen Holstein
Joanne Jackson
Peter Moyle*
Anne Sands*
Ronald Schultze*
Kevin Shea*
John Speth*
Richard Warner (Chairman)*

* also served as conference session convener

The unwavering commitment to the success of the conference, and the significant professional and personal investments of effort each of these people made toward that end were impressive. Again, the conference could not have succeeded without this invaluable assistance. Some Steering Committee members also served as session conveners. They, and the other session conveners listed below had the important and difficult tasks of helping to formulate and then chairing specific sessions.


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Session Conveners

Dana Abell
Mike Aceituno
Harriet Allen
Bertin Anderson
Gary Bullard
James Burns
Mark Capelli
Randy Gray
Bruce Jones
Don Kelley
John Kramer
Philip Meyer
Peter Moyle
Bob Potter
John Renning
Hal Salwasser
Anne Sands
Ronald Schultz
Lauren Scott
Kevin Shea
Kent Smith
John Speth
Charles Van Riper III
Richard Warner

Promotion and execution of the conference itself was undertaken through the auspices of University Extension, University of California, Davis. Bill Hilden, then Assistant Dean for Business and Finance, was a bastion of sympathetic support and guidance. Promotion was handled with creativity and skill by Vicki Hines. Garrett Jones and Extension staff coordinated registration, facilities, and other on-site conference needs.

Betty Brandon and the staff of the USDA Soil Conservation Service Communication Center, Davis, provided unflagging and sympathetic help with various, often urgent, printing projects.

Roberta Walters, then Director of the Davis Art Center, took very able command of the riparian art exhibit and competition. Her professional skill was largely responsible—excepting, of course, the splendid participation of the contributing artists—for the success of that part of the conference.

Field Studies Center staff and interns Barbara Ott, Karin Van Klaveren, and Mary Tappel covered many bases with patience and unfailing good spirits throughout organization and execution of the conference. JoAnn Wildenradt lent her skill and grace as coordinator and hostess for food and drink.

The Present Volume

Bob Hamre, USDA Forest Service, Fort Collins, Colorado, kindly provided editorial counsel and copies of format and protocols used by that organization for manuscript preparation. These were utilized with but few modifications.

The University of California (Davis) Water Resources Center, in addition to being a conference co-sponsor, was responsible for the initial suggestion and the subsequent meetings which led to publication of this volume by the University of California Press. This and other assistance by Herbert Snyder, Otto Helwig, and the Water Resources Center staff is remembered with appreciation.

With very few exceptions, manuscript authors responded with understanding and often with appreciation to our editorial efforts. Their responses encouraged us in our negotiations with the prickly or unresponsive few who objected to proposed modifications of run-on sentences and dangling participles, or who sat in ruminative silence upon our requests for clearer graphics and more complete literature citations.

A significant number of authors also provided page costs to help defray the expense of putting their manuscripts into final camera-ready form. Readers should know of and appreciate—as we do—this additional contribution of the authors to the successful completion of this volume.

The Field Studies Center, Davis, provided overall coordination, logistic support, technical and support staff, office and library facilities, and materials and supplies throughout both phases of the enterprise. The Center also provided computer hardware and software for word processing, as well as secretarial and proofreading staff under the supervision of the assistant editor. Ronnie James, Carol Van Alstine, and Lisa Steinmann contributed patience and good humor as well as word-processing and proofreading skills. Melanie Minor and Nancy Gooch, interns from the University of California, Davis, helped with bibliographies, word processing, and other important chores.


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Throughout the enterprise, from initial conference concept to completion of the present volume, colleagues, friends, and family have provided unflagging guidance, support, and encouragement. One spouse and three children in particular made no material contribution, but without their loving understanding and tolerance for thrown-together meals, consultations into the wee hours of the morning, and enforced absences from home to accommodate their wife/mother's bizarre work schedule, we would be laboring still.

Finally, special acknowledgment is due the late A. Starker Leopold, who first called attention to the problem of riparian system decline nearly a decade ago, and who saw more clearly than most the ominous implication of this decline to our fish and wildlife resources. It is an enduring regret of the editors that he did not live to see the publication of this volume, which he so consistently encouraged.

To all those who helped bring this volume to publication, whether mentioned here or not, we express our most sincere thanks.

RICHARD E. WARNER
EDITOR
TECHNICAL COORDINATOR, CALIFORNIA RIPARIAN SYSTEMS CONFERENCE

KATHLEEN M. HENDRIX
ASSISTANT EDITOR
ASSISTANT COORDINATOR, CALIFORNIA RIPARIAN SYSTEMS CONFERENCE


1

1—
BIOGEOGRAPHY AND DYNAMICS OF CHANGE IN CALIFORNIA RIPARIAN SYSTEMS

figure


2

California Riparian Forests

Deciduous Islands in an Evergreen Sea[1]

Glen Holstein[2]

Abstract.—California riparian forests are dominated by deciduous trees and are thus anomolous in a state where most dominant woody plants are evergreen. Riparian zones provided refuges where riparian elements of the Arcto-Tertiary Geoflora could survive when its upland elements were decimated by the development of California's mediterranean-type climate. Water and nutrients imported to California's dry lowlands from wetter mountains by perennial streams permit high summer primary productivity in riparian communities while adjacent upland vegetation is severely drought stressed. High riparian productivity makes the cost of annual replacement of deciduous foliage affordable because such foliage is more photosynthetically efficient than that of evergreen upland dominants. Bird abundance and diversity in riparian communities are related to this high riparian productivity.

Introduction

Much of California has a mediterranean-type climate. In such climates rainfall and snowfall are maximal in winter, when minimal solar radiation limits plant growth. When the long days of summer potentially maximize growth, rainfall is minimal or nil and many plants are dormant or under severe drought stress. Thus moisture and solar radiation, two necessities for plant growth, are exactly out of phase (Major 1977).

Even near the moist northwest coast of California, fields of annual grasses in the hills above Redwood National Park (Humboldt County) are dead by late summer. Summer drought is also a major factor contributing to the uniqueness of California's alpine flora (Chabot and Billings 1972). Only at a few desert localities in California do some summer months have more rain than any single winter month, but here rainfall is so scanty and unpredictable at all times that vegetation is sparse and the flora limited to specialized drought resisters or evaders.

Most California vegetation is maximally productive in spring, when days are longer and warmer than in winter, and some moisture is still available. Stressful winter and summer conditions are thus both avoided. Productivity is less, however, than in ecosystems where light, warmth, and water are all simultaneously available in abundance. The productivity potential which is frequently unfulfilled in California because of summer drought stress is revealed by the increase in crop yield obtained there with irrigation, and by the productivity of the riparian vegetation which lines or once lined perennial streams. These streams carry the part of the winter water surplus which is slowly released from deep aquifers and melting mountain snow, making it available to lowland riparian vegetation in summer when little water is provided by the local climate. The resultant greater productivity and biomass of this vegetation is frequently obvious when contrasted with that of nearby communities which lack imported water. Riparian forests in central Asia ecologically similar to those of California's Central Valley are among the world's most productive natural ecosystems (Major 1977). When the current vacuum in California riparian research is filled, it is likely that riparian systems here will be found to be comparably productive.

Biogeography of Riparian Forest Components

Axelrod (1973) has provided compelling paleobotanical evidence that California's mediterranean-type climate is a relatively late phenomenon which first appeared in the upper Pliocene. This and other climatic perturbations caused the Arcto-Tertiary Geoflora, a zone of rich and diverse forest which was once continuous around the Northern Hemisphere, to retreat and become impoverished. Destructive impoverishment

[1] Paper presented at the California Riparian Systems Conference. [University of California, Davis, September 17–19, 1981].

[2] Glen Holstein is Lecturer, Botany Department, University of California, Davis.


3

of the Arcto-Tertiary Geoflora by spreading drought and cold was severe in western North America and Europe, but many of its elements survived in major refuges in eastern Asia, the Pontic region of southwest Asia, the Mexican highlands, and the southeastern United States. California's expanding mediterranean-type climate caused the replacement of many Arcto-Tertiary communities by drought-resistant vegetation known as the Madro-Tertiary Geoflora, which had long been adapted to local dry habitats (Axelrod 1975).

Riparian forests, as ecosystems in but not under the control of a mediterranean-type climate, seem likely refuges for Arcto-Tertiary elements within California, and Robichaux (1977) has shown in a review of their fossil record that most dominant California riparian forest taxa have modern ranges reduced from more widespread Tertiary distributions. These dominants all have relatives which are common in the Arcto-Tertiary derived deciduous forests of eastern North America (Axelrod 1960), and their dominance by deciduous trees and shrubs gives these vegetation types a similar aspect. Examination of the evolution and biology of the taxa dominant in California riparian forests provides further clues to the origin, evolution, and relationships of western North American riparian vegetation.

Acer (Maple)

This large genus, with 200 species of mostly deciduous trees, is one of the most important components of the temperate deciduous forests of the Northern Hemisphere, and its modern range coincides closely with those communities which are predominantly derived from the Arcto-Tertiary Geoflora (Hora 1981). It is by far the largest of the two genera in the Aceraceae and is the only one occurring naturally in North America, where it includes major upland dominants such as A . saccharum and widespread riparian species such as A . saccharinum and A . negundo .

The Aceraceae are part of the Sapindales (Cronquist 1968; Dahlgren 1975) or the essentially equivalent suborder Sapindineae of Thorne (1976), taxa which are otherwise largely dominated by entomophilous, evergreen, or drought-deciduous tropical to subtropical woody plants with compound leaves. The Hippocastanaceae are probably the closest relatives of the Aceraceae, and both of these families are unusual within the Sapindales because of their winter dormancy and largely north temperate distributions.

Acer consists mostly of winter-deciduous trees, but it is otherwise quite diverse and includes morphoclines both from compound to simple leaves and from flowers which are corollate and entomophilous to those which are reduced, apetalous, and wind pollinated. In both cases these cines reflect a shift from the primitive Sapindalean condition to a derived condition typical of the majority of dominant north temperate forest trees.

The four California species of Acer , A . glabrum , A . circinatum , A . macrophyllum , and A . negundo var. californicum , all can occur along streams, but only A . negundo (box elder) is primarily riparian. The other species are more common in mesic upland sites in the wetter parts of montane and coastal California, where gradients between riparian and upland vegetation are much more diffuse and less distinct than in the drier areas of the state.

A . macrophyllum is a particularly common and important tree throughout much of coastal and montane California, and it is listed by Roberts etal . (1977) along with Sequoiasempervirens , Umbellularia californica , and several more strictly riparian species as one of the common trees of California's north coastal riparian forests. In this region A . macrophyllum , S . sempervirens , and U . californica all occur from streambanks to the shaded, moist upland sites where they are most abundant.

A . negundo is frequent in riparian zones throughout the Mississippi basin and the Great Plains. Locally, it extends to the Atlantic coast and occurs along scattered streams and rivers in the southern Rocky Mountains, the Southwest, and California (fig. 1). Few other North American trees are transcontinental.

Within California A . negundo is locally common in riparian communities in the drier parts of the Coast Ranges and in the lower parts of the Sacramento and San Joaquin Valleys, where marine airflow through the Carquinez Straits somewhat moderates summer temperatures. Virtually nowhere in California, however, is it dominant. It is

figure

Figure 1.
Range of Acer  negundo  (AN) including Anegundo
var. californicum  (ANC) (after Little 1971).


4

normally a shade-tolerant subordinate tree in dense riparian vegetation dominated by Populus fremontii , P . trichocarpa , Salixgooddingii , S . laevigata , S . lasiandra , or S . lasiolepis . Association with P . fremontii is especially frequent.

Dispersal of A . negundo is by wind dispersed samaras, but these are produced in smaller quantities and are less easily dispersed than the lighter, comose seeds of Salix and Populus . As a result, box elder is less efficient at colonizing the new riparian habitats which are frequently created on sandbars and along ditches and canals.

A . negundo appears to be in decline in California since it is a relatively poor competitor which has been restricted to the most highly competitive riparian zones. It may now be at an early stage of the process by which climatic vicissitudes eliminated (e.g., A . saccharinum and Ulmusamericana ) (Axelrod 1977) or almost eliminated (e.g., Juglanshindsii ) other riparian taxa from California whose relatives are still common in the much more extensive riparian systems of eastern North America, which receive summer rain.

A . negundo is taxonomically isolated among North American maples since it is the only member of section Negundo on this continent. This section is distinct enough to be segregated as the genus Negundo Boehm. by some (Willis and Airy Shaw 1973). Its other species are Asian, and it combines the putatively primitive character (within Acer ) of compound leaves with dioecy and inflorescences which are apetalous and anemophilous in A . negundo but corollate in at least some Asian species (Rehder 1940).

Alnus (Alder)

Alnus is a morphologically homogeneous genus of 35 species of deciduous trees and shrubs of the Northern Hemisphere and the Andes, and it has monoecious, anemophilous catkins and nutlets which vary among species in the degree of development of marginal wings and the resultant relative importance of wind, water, and gravity dispersal (Sudworth 1908; Fowells 1965).

It shares a distinctive pattern of ecological adaptation with some other important California riparian genera like Salix . These consist primarily of large, obligately riparian trees in warm temperate climates but are increasingly dominated by widespread shrubs which are only facultatively riparian in colder boreal and montane regions. Unlike other genera with large California riparian trees, however, Alnus contributes no important trees to North America's eastern deciduous forest. The commonest alder there is the shrubby A . serrulata . The adaptations needed by alders which are temperate riparian trees and those which are boreal and montane shrubs may not be greatly different since snowmelt frequently saturates soils of cold regions during the brief growing season and creates conditions similar to those found only along streambanks and lakeshores in warmer climates. Alders can symbiotically fix nitrogen, which otherwise may be limiting in forest environments and elsewhere (Spurr and Barnes 1980).

Alnus is a member of the Betulaceae, a family of mostly north temperate deciduous and anemophilous trees and shrubs which is in the Fagales (Cronquist 1968; Dahlgren 1975; Thorne 1976), an order it shares with the Fagaceae, to which it is linked by several intermediate genera (Corylus , Carpinus , Ostrya , and Ostryopsis ) sometimes placed in Betulaceae and sometimes in the segregate families Corylaceae and Carpinaceae (Willis and Airy Shaw 1973). The Fagales are the most important single order of angiosperm trees in temperate regions and most member taxa have Arcto-Tertiary distributions.

Alnus has four California species: A . sinuata , A . tenuifolia , A . rubra , and A . rhombifolia . The first two are largely shrubs of the boreal/montane type mentioned previously, but they can occasionally grow large enough along streams to be riparian trees (Sudworth 1908). The second two are among California's most important riparian trees. All California alders are in subgenus Alnus except A . sinuata which is in Alnaster .

Alnusrubra (A . oregona ), the red alder, is associated with the North Coastal Coniferous Forest (Munz 1959) from the Alaska panhandle to the coast of San Luis Obispo County (Little 1971; Griffin and Critchfield 1972). Within its range (fig. 2) it is frequently the dominant riparian tree. This largest of American alders (Elias 1980) is also very common on moist slopes, especially after conifers have been removed by logging operations, but it is much more likely to form dense and distinctive riparian gallery forests which it overwhelmingly dominates than are trees such as Acermacrophyllum , which are also found from moist slopes to streamsides. A fine example of such a gallery forest is protected along Prairie Creek in Humboldt County at Prairie Creek Redwoods State Park.

Alnusrhombifolia (white alder) forms similar gallery forests throughout much of the rest of California south and east of the range of A . rubra (fig. 2), but it much more obligately restricted to streamsides than its coastal relative. As a result, it is the most reliable indicator of permanent water among California's riparian trees (Jepson 1910). A . rhombifolia is the usual dominant in California's montane riparian forests up to about 1,600 m., but it also is dominant near sea level along Alameda Creek in Alameda County's Niles Canyon and numerous other similar places. It is most common along fast-flowing mountain streams west of the crest of the Sierra Nevada and near the coast south of Sonoma County (Griffin and Critchfield 1972). White alders are absent from much of the Central Valley floor but are common along the Sacramento River in Shasta County (ibid .) and further south (Conard et al . 1977). Such


5

figure

Figure 2.
Ranges of Alnus  rubra  (ARU) and A . rhombifolia
(ARH) (after Little 1971, 1976).

montane-coastal distributions suggest intolerance for summer heat (e.g., Populustrichocarpa ), but this is unlikely in the case of A . rhombifolia since it is common in the vicinity of Redding, where summer temperatures are as high or higher than in most of the area where it is absent. The ecological factor which most controls the distribution of A . rhombifolia seems to be a need for constant saturation of its root zone by cool, well-aerated water.

The total range of A . rhombifolia extends from southern California to central Washington in the Peninsular, Transverse, Coast, Sierra Nevada, Klamath, and Cascade ranges, with an extension through the Columbia River Basin to northwestern Idaho (Little 1976). It is most common and its range most continuous in the Sierra Nevada, Klamath Mountains, and northern Coast Ranges of California. A . rhombifolia and A . rubra are morphologically similar and closely related, but hybrids between them do not seem to have been reported. They apparently diverged from a common ancestor at an unknown time in the Tertiary or Quaternary Periods and adapted to wet and riparian sites within the Sierran-Klamath and north coastal forests, respectively.

Betula (Birch)

Betula is the second genus in the Betulaceae when that family is narrowly defined to exclude the Corylaceae and Carpinaceae (Willis and Airy Shaw 1973). Its characters are similar to those of its sister genus, Alnus , which it resembles in its deciduous habit, its anemophilous catkins, its north temperate range, and its nutlets, which are more consistently winged and wind dispersed than those of Alnus . Betula also shares a similar range of adaptations with Alnus since it includes both temperate zone trees and arctic and montane shrubs, but Betula contributes many more important upland trees to the deciduous forests of eastern North America than Alnus , which is more important as a source of dominant trees in western riparian forests than Betula .

California has two species of Betula : B . occidentalis (B . fontinalis ) and B . glandulosa , but only the former reaches tree size. B . occidentalis (water birch) is a large shrub or small tree of riparian sites which is widespread in the cordilleran region of western North America (Little 1976) but is restricted to just a few parts of California. It is relatively frequent in the Klamath Mountains and on the east slope of the southern Sierra Nevada, but much less so in the Warner, White, and Panamint Mountains (fig. 3). The Klamath and Warner Mountains have an abbreviated summer drought because of their northern locations, and the southern Sierra Nevada's east slope and the White and Panamint Mountains all regularly receive summer thunderstorms of tropical origin. As a result, all California populations of B . occidentalis receive quantities of summer rain which are unusual for that state and which approach the greater amounts received by the much larger populations in states to the east and north. Consequently, lack of summer rain must be suspected as an ecological factor limiting the range of this species despite its adaptation to riparian zones. Non-riparian Pinus balfouriana and other taxa have similar distributions for similar reasons (Raven and Axelrod 1978). Seedlings can be much more sensitive than mature

figure

Figure 3.
Range of Betula  occidentalis  (BO) (after Little 1976).


6

plants to environmental stresses like summer drought (Grime 1979).

B . occidentalis is in series Albae within Betula (Rehder 1940) and is thus a close relatie of the white briches such as B . papyrifera , B . pendula , and B . pubescens , which are very important early successional trees throughout the upland boreal forests of North America and Eurasia.

Cephalanthus (Button Bush or Button Willow)

Cephalanthusoccidentalis , an obligately riaprian small tree or shrub, is the single California representative of this genus of 17 species which is widespread in the warm regions of the world and is one of only three California genera in the very large (500 genera and 7,000 species) family Rubiaceae, best known in temperate regions for the large and usually herbaceous genus Galium . Most of the Rubiaceae, however, are understory trees and shrubs in tropical forests. The family is clearly of tropical derivation and its placement in the Gentianales by Dahlgren (1975) and Thorne (1976) and in the related Rubiales by Cronquist (1968) reflects considerable consensus concerning its evolutionary relationships. Cephalanthus is in the subfamily Cinchonoideae, which is largely woody and tropical, rather than in the Rubioideae, which includes most of the family's temperate herbs and its other California genera.

C . occidentalis is primarily a deciduous shrub and only rarely reaches tree size in California. Its flowers are small but corollate and probably entomophilous like those of most Rubiaceae, and the fruit is a dry schizocarpic mericarp which lacks obvious adaptations for dispersal.

Like A . negundo , C . occidentalis is found naturally in both Atlantic and Pacific coast states (fig. 4). It is widespread in the East and ranges south through Mexico to Honduras, but it is restricted to a few Arizona stations and to the floor and adjacent watershed of California's Central Valley in the West (Little 1976). In California and in most of the rest of its range it is limited to areas with mean July temperatures above 20 C where most of the root zone is reliably saturated with water throughout the year. Relatively poor dispersal has made it an inefficient colonizer of the banks of artificial ditches and canals, but it is still common along many permanent natural streams. In backwaters where still, poorly oxygenated water stands throughout the year, C . occidentalis is best developed and can be dominant (Conard etal . 1977), but such habitats in California have been almost entirely destroyed by water resource and agricultural development. Their Button Bush Swamp Forest vegetation type is thus among the rarest and most endangered in the state. A particularly fine example of this vegetation is still extant along the Cosumnes River in southern Sacramento County west of Galt, and its continued preservation should receive high priority from California's conservation community.

figure

Figure 4.
Range of Cephalanthus  occidentalis   (CO) (after Little 1976).

It is clear that C . occidentalis in California is a relict which has survived the loss of a warmer and wetter climate because of the fortuitous juxtaposition of the hot Central Valley and the high mountains which surround it and keep it continuously supplied with abundant water.

Fraxinus (Ash)

This genus has a range which matches almost exactly that of the Arcto-Tertiary Geoflora, and it shows a range of adaptations including deciduousness, anemophilous catkins, and wind-dispersed samaras which is typical of the flowering trees in the modern forests derived from it. Fraxinus clearly evolved these characters by convergence, however, since its probable ancestors had few if any of them.

It is a member of the Oleaceae, whose placement in the Oleales by Dahlgren (1975) and Thorne (1976) and in the Scrophulariales by Cronquist (1968) only hints at the lack of consensus among plant evolutionists about its origin. Most other members of the family have entomophilous flowers with well-developed corollas, and many are tropical species with evergreen leaves and fleshy fruits adapted to internal dispersal by birds. Fraxinus itself includes a floral reduction series which suggests the mode of evolution of its apetalous, wind pollinated catkins since several species along the southern periphery of its range, including F . cuspidata in the southwestern United States and northern Mexico and F . ornus in southeastern Europe, have


7

fragrant entomophilous flowers with conspicuous corollas. Evergreen leaves are less common, but they occur in F . gooddingii of southern Arizona and northern Sonora (Elias 1980).

Most ash species like F . cuspidata and F . ornus which have primitive characters typical of the Oleaceae are included in section Ornus . Section Fraxinaster , however, includes many species of upland (F . americana , F . excelsior , F . quadrangulata ) and riparian (F . nigra , F . pennsylvanica ) trees which are important in north temperate deciduous forests and share many characters with the trees most highly adapted to that ecosystem in other families (Rehder 1940).

California is usually considered to have four Fraxinus species (F . dipetala , F . anomala , F . latifolia , and F . velutina ) (Munz 1959). F . dipetala is interesting among these as a Fraxinaster species with a corolla (Rehder 1940) and F . anomala for its frequently simple leaves, but only F . latifolia and F . velutina are important riparian trees in California (F . anomala is a riparian species of the Colorado Plateau with a few relict populations in the mountains of the eastern Mojave Desert). These are only nominally species, however, since the riparian ashes of California (fig. 5) are part of an attenuated but essentially continuous cine between more important ash populations in Arizona (F . velutina ) and in Oregon and Washington (F . latifolia ) along which species can be separated only artificially and arbitrarily (Griffin and Critchfield 1972).

The Pacific Northwest has a relatively short summer drought because of its northerly latitude, and Arizona regularly receives heavy summer thunderstorms of tropical origin, so both areas have much more summer rain than California. There ashes must rely almost entirely on riparian water during the growing season, and probably as a result, they are a very subordinate component of the state's riparian forests except near its northern border, where F . latifolia becomes more important as the climate becomes more like that of Oregon. In the rest of California F . latifolia /F . velutina occurs sparsely as a non-dominant riparian tree in the northern Coast Ranges, the Central Valley, the west slope of the Sierra Nevada, and in southern California, but it is rare or absent in the southern Coast Ranges, where summer drought is especially strongly developed and very few streams are naturally permanent. The Tehachapi Mountains and the western Transverse Range are conventionally used to separate these "species" in California (Griffin and Critchfield 1972).

The biology and distribution of California's riparian ashes suggest that they are declining relicts like Acer negundo var. californicum which are probably somewhat more tolerant of heat and low humidity but less tolerant of summer soil moisture deficits than that taxon. On a larger scale, Arizona and the Pacific Northwest appear to be relict nodes where populations of a once more widespread (Robichaux 1977) and probably continuously transcontinental riparian ash have successfully survived Quaternary climatic perturbations that eliminated it in much of the West and greatly reduced it in California. F . velutina and F . latifolia are, in fact, both similar enough to riparian F . pennsylvanica of the eastern United States (fig. 5) to be considered its subspecies (Miller 1955).

figure

Figure 5.
Ranges of Fraxinus  latifolia  (FL), F. velutina  (FV),
and  Fpennsylvanica  (FP) (after Little 1971, 1976).

Juglans (Walnut)

This genus of deciduous trees has a largely Arcto-Tertiary distribution like many of the other important California riparian genera, but its distribution within the Arcto-Tertiary zone is incomplete because of its absence from large areas, including much of Europe. It is best developed along the southern margins of this zone and extends far south of it to Argentina along the Andes.

Juglans and Carya are the only genera in their family, the Juglandaceae, which still include widespread and important north temperate forest trees. Both have distributions which suggest reductions from formerly more complete Arcto-Tertiary ranges. The other genera of the family, Pterocarya , Engelhardtia , Oreomunnea , Platycarya , and Alfaroa , are all restricted to much smaller warm temperate to tropical Arcto-Tertiary refuges in Middle America or Asia.

The Juglandaceae have often been treated as a distinctive order, the Juglandales, and associated (in the subclass Hamamelidae or Amentiferae)


8

with other families of temperate trees which share their characters of large-seeded woody fruits and anemophilous catkins (Cronquist 1968), but much current opinion (Dahlgren 1975; Thorne 1976) interprets these similarities as convergence and places the Juglandales close to or in the Sapindales/Rutales, the order of compound-leaved tropical trees from which the Aceraceae were also derived through a separate lineage.

The United States has six of the world's 15 species of Juglans , but J . cinerea is the only strongly distinctive species among these six. The other five include J . nigra , an important upland to weakly riparian forest tree of the eastern deciduous forest (Fowells 1965), and four species of various refuge areas in the West (fig. 6). The western species closely resemble J . nigra and suggest the same pattern of Late Tertiary to Quaternary reduction in the range of a formerly transcontinental species which we have seen in Fraxinus . These four include the two California species of Juglans , J . californica and J . hindsii , both of which are endemic to the state.

J . californica is a mostly non-riparian tree of southern California which is depauperate relative to J . nigra and J . hindsii but is not greatly different from them morphologically. It is restricted to deep, friable Tertiary marine shales with high water-holding capacity which permit it to survive as a local dominant on upland sites since the warm spring temperatures of southern California allow summerwet conditions to be simulated earlier in the year wherever soil storage capacity is adequate to hold surplus water from winter rains.

figure

Figure 6.
Ranges of Juglans  hindsii  (JH), J . californica  (JC),
 J . major  (JMA), J . microcarpa  (JMI), and
J . nigra  (JN) (after Little 1971, 1976).

J . hindsii was apparently restricted to a very few sites in central California when European settlement began there, and at least some of these sites were riparian (Griffin and Critchfield 1972). Since this species was probably derived from ancestors which were adapted to a summer-wet climate and were only weakly riparian, it is likely that J . hindsii was escaping a mediterranean-type climate to which it was completely unadapted in a riparian zone to which it was poorly adapted. Its large, nutrient-rich seeds in heavy nuts with little obvious capacity for dispersal are a more appropriate adaptation for reproduction in a stable forest (Grime 1979) than in the highly unstable, frequently floodprone riparian environment that existed in California before most of its streams were dammed.

J . hindsii was clearly on the verge of natural extinction when California was first settled by Europeans and was at the midpoint on a continuum between those taxa with similar histories such as Nyssa and Ulmus which are now known only from California's fossil record (Axelrod 1973) and those such as Acernegundo and Fraxinuslatifolia which survived until the settlement period with greater but still declining ranges and abundances (Robichaux 1977). Ironically, since European settlement, J . hindsii has been widely planted and subsequently commonly naturalized in California's now largely stabilized riparian systems at a time when its once much more abundant congener J . californica is declining rapidly because of the urban expansion of Los Angeles.

Platanus (Sycamore)

Platanus , even more than Juglans , is an example of an old, declining Arcto-Tertiary genus, since it is now largely restricted to warm temperate to tropical refuges along the southern periphery of the Arcto-Tertiary zone despite an extensive and diverse fossil record from as far north as Greenland (Engler and Melchior 1964). Only P . occidentalis of the eastern United States is still an important forest tree in a major north temperate forest biome.

Platanus is traditionally placed in the monotypic family Platanaceae, which is widely agreed to belong in the order Hamamelidales (Cronquist 1968; Dahlgren 1975; Thorne 1976), a relationship which links it to several other old families of Arcto-Tertiary trees and shrubs. The Hamamelidales show ancient tendencies toward the deciduous tree habit, unisexual wind pollinated flowers, and wind dispersed fruits, characters which are typical of the modern dominants of north temperate forests and of all 10 living species of Platanus , a taxon which culminates one of probably several floral reduction series within the order and its relatives (Thorne 1976).


9

Platanus in the United States includes P . occidentalis and two closely related species of the Southwest, P . wrightii of Arizona, New Mexico, and northwestern Mexico, and P . racemosa of California (fig. 7). All three species are strongly riparian, but the two southwestern species are more similar to P . orientalis , a riparian tree native from southeastern Europe to the Himalayas, than to the geographically closer P . occidentalis (Hsiao 1973). This may reflect ancient relationships and patterns of extinction within Platanus , but the very close relationship between P . racemosa and P . wrightii suggests they were separated relatively recently when expanding deserts separated woodlands that were continuous between Arizona and California in the Miocene (Axelrod 1975; Raven and Axelrod 1978).

figure

Figure 7.
Ranges of Platanus  racemosa  (PR) and
P . wrightii  (PW) (after Little 1976).

P . racemosa is a common riparian tree in northwestern Baja California, southern California, the southern Coast Ranges, the southern Sierra Nevada foothills, and the Sacramento Valley, but it is scarce in the San Joaquin Valley and absent from the northern Coast Ranges, where much seemingly suitable habitat occurs (Griffin and Critchfield 1972). P . racemosa is an important secondary component of the mixed riparian forests of the Sacramento Valley, where it is often associated with sites higher and drier than those where dominant Populusfremontii is found (Conard et al . 1977), but it is particularly conspicuous as frequently the single dominant tree along the intermittent streams of the southern Coast Ranges and southern California. Very large sycamores form an open woodland along such streams, and fine examples of this distinctive vegetation-type can be seen along Pacheco Creek in southern Santa Clara County and along Orestimba Creek in Stanislaus County.

Intermittent streams are general in southern California and the southern Coast Ranges because of their mediterranean-type climate and lack of extensive highland snowfields to provide summer runoff, and sycamore woodlands are particularly characteristic of those with beds of coarse, porous sand and gravel. Such substrates are common in the region where sycamore woodlands occur because it has been subjected to very rapid and recent Plio-Pleistocene uplift which may still be continuing and to massive erosion which has inevitably followed (Page 1981). The small, comose achenes of P . racemosa are easily carried long distances by wind, enabling the rapid reestablishment of these woodlands after the flood damage which was frequent before California streams were dammed.

The obligate restriction of P . racemosa to riparian zones indicates a need for access to groundwater within its root zone, but its preference for dry, porous sites within riparian zones suggests that for a riparian species it also has a rather high requirement for aeration of at least part of its root zone. The reasons for its complete absence from the northern Coast Ranges are not obvious since seemingly suitable intermittent streams with coarse beds are fairly common there. Along some of these streams on the dry east slope of the northern Coast Ranges native riparian trees are replaced by halophytic graminoids and an introduced Tamarix species, probably because their flows are made brackish by salts leached from the Cretaceous marine sediments which dominate their watersheds,[3] but many other northern Coast Ranges streams have fine riparian gallery forests along their banks. The clay-rich Franciscan Formation dominates the northern Coast Ranges, but the same formation yields enough sand and gravel to support major stands of sycamore woodland in parts of the southern Coast Ranges. Temperature does not provide a simple explanation for the absence of sycamores from the northern Coast Ranges because summers there are not necessarily hotter or cooler nor winters colder or milder than those at places well within the range of P . racemosa .

A possibly significant factor limiting the capacity of sycamores to invade the northern Coast Ranges is that region's cool, wet spring. The collective mean precipitation for May is 43 mm. among the climatic stations of both the northern Coast Ranges and the Sacramento Valley, but that month is 1ºC warmer at the Valley sta-

[3] A high Mg/Ca ratio may be important in these streams as well since many have much serpentinite in their watersheds. This ratio is 1.6 in Cache Creek, which has many tributaries which have always lacked riparian trees. The Mg/Ca ratio, electrical conductivity, and dissolved Na are, respectively, 87%, 628%, and 975% greater in Cache Creek than in the Sacramento River into which it flows.


10

tions. In the southern Coast Ranges the collective May mean temperature is also 1°C warmer than in the northern Coast Ranges, but the collective mean precipitation for that month is 28 mm. less (US Department of Commerce 1970). Anthracnose (Gnomoniaplatani ) is a very serious and prevalent disease which can cause complete spring defoliation of Platanus species including P . racemosa , and it is known to be promoted by cool and wet spring weather (Fowells 1965; Collingwood etal . 1974; Pirone 1970). This fungus is currently severely stressing wild populations of P . racemosa in Alameda and Contra Costa Counties at the northwestern limit of the range of that species, and it must be suspected of limiting the further expansion of sycamores northwestward in California.

Populus (Cottonwood)

Populus is the most important riparian genus in California, and one of the two major genera of the Salicaceae, probably the most important riparian family in the world. This family was traditionally placed close to the Hamamelidales and Fagales in the artificial taxon Amentiferae because of its unisexual catkins, but it is now recognized to be misplaced there. Its characters, which include capsular fruit with many seeds, suggest a much closer relationship to the small, largely halophytic Tamaricales and to the large and diverse assemblage of plants variously known as the Violales or Cistales. It is distinctive enough, however, to be retained in its own monotypic order, the Salicales (Cronquist 1968; Dahlgren 1975; Thorne 1976).

The Salicaceae, which include the large and widespread genus Salix and the monotypic East Asian Chosenia in addition to Populus , are deciduous woody plants which are dioecious and have very light and easily wind dispersed comose seeds. They share the pattern seen in the Betulaceae of adaptation to riparian zones in temperate climates (as well as tropical in the case of Salix ), with much wider extension into upland habitats in boreal, montane, and arctic climates where late snowmelt saturates the soil during part or all of the growing season. Unlike Alnus , Betula , and Salix , however, Populus consists entirely of trees. Unlike Salix , which is secondarily entomophilous (Thorne 1976), it is entirely wind pollinated.

Populus consists of 35 species and ranges throughout the North Temperate Zone into parts of the Arctic. Four species (P . tremuloides , P . trichocarpa , P . fremontii , and P . angustifolia ) are native to California. P . tremuloides (aspen) is a largely upland species which is widespread in the boreal and montane parts of North Amnerica, and extends south to some of the higher California mountains. P . angustifolia is a riparian species of the Rocky Mountains, which occurs in a few colonies in the area east of the southern Sierra Nevada crest where summer thunderstorms of tropical origin also permit larger but still relict populations of Betulaoccidentalis to survive.

P . tremuloides is the most taxonomically distinctive Populus species in California, and is set off from the others in section Leuce . P . trichocarpa and P . angustifolia are close enough to share placement in section Tacamahaca , but even though P . fremontii is set off from these species in section Aegeiros (Rehder 1940), it can hybridize with P . trichocarpa (Little 1953). Such hybrids seem to be rare in California, but hybrids between P . angustifolia of Tacamahaca and P . sargentii of Aegeiros are abundant in the Great Plains (Elias 1980).

P . fremontii (Fremont cottonwood) and P . trichocarpa (black cottonwood) are the two principal riparian species of Populus in California, and P . fremontii is the single most important riparian species in the state since it dominates the great riparian forests of the Central Valley (Conard etal . 1977) as well as many of those elsewhere in cismontane and transmontane California (Roberts etal . 1977). Most of these magnificent forests have been destroyed (Thompson 1977), but small good examples have been preserved by the Nature Conservancy on the Kern River, by the California Department of Parks and Recreation at Caswell State Park, and by a few other groups and agencies elsewhere. Because of their great ecological significance (Sands 1977; Hehnke and Stone 1978) every effort should be made to preserve what remains of these rapidly vanishing natural communities. Particular attention should be given to those in the Sacramento and lower San Joaquin Valleys, where preservation opportunities are greatest, and to what remains of those along the Colorado River, where destruction has been most complete.

P . trichocarpa is one of the largest broad-leaved trees in North America, but it is a less conspicuous riparian tree than P . fremontii in California because it is most common in the cooler, wetter parts of the state, where it frequently associates with highly competitive riparian species such as Alnusrhombifolia , and often grows near upland forests dominated by giant conifers. Magnificent riparian forests dominated by P . trichocarpa do occur in coastal and montane California, however, and a fine example remains along the Carmel River in Monterey County.

The California ranges of P . trichocarpa and P . fremontii overlap (Griffin and Critchfield 1972), and individuals of the two species frequently grow sympatrically without hybridization. P . trichocarpa is essentially limited to those parts of California with July mean temperatures cooler than 25°C, while California populations of P . fremontii grow at sites with a range of July means approximately between 17°C and 36°C. The cooler P . fremontii sites are limited to coastal areas around San Francisco Bay and from San Luis Obispo County south where winters are mild and the growing season long.


11

The total ranges of these species and their closest relatives outside California (fig. 8 and 9) reflect a pattern similar to that of their ecological relationships in the state. P . trichocarpa is common throughout the cool, wet Pacific Northwest north to southern Alaska and east to the northern Rocky Mountains (Little 1971), and its closest North American relatives are P . angustifolia of the Rocky Mountains and P . balsamifera , a frequently upland species which is widespread in the continent's boreal regions (Rehder 1940). P . trichocarpa is considered conspecific with the latter by Eckenwalder (1980).

figure

Figure 8.
Ranges of P . trichocarpa  (PT) and
P . balsamifera  (PB) (after Little 1971).

figure

Figure 9.
Ranges of Populus  fremontii  (PF), Pdeltoides
(PD), and Psargentii  (PS) (after Little 1971).

P . fremontii , in contrast, is found east to Trans-Pecos Texas in riparian sites throughout the Southwest, and it is most closely related to the riparian species P . arizonica of the Southwest, P . deltoides and P . sargentii of warm temperate eastern North America, and P . nigra of warm temperate Europe (Axelrod 1975). Macrofossils intermediate between P . fremontii and P . deltoides are known from the then warmer and wetter Miocene Ellensburg Flora of Washington, where neither species occurs today (Robichaux 1977).

These relationships suggest that both P . trichocarpa and P . fremontii are western derivatives of formerly transcontinental ArctoTertiary entities within Populus . P . trichocarpa and its relatives within section Tacamahaca are derivatives of a cool temperate to boreal species complex, and P . fremontii and the other species of section Aegeiros are of warm temperate ancestry.

Quercus (Oak)

This huge genus of 450 species dominates the upland deciduous forests of the North Temperate Zone, but it also includes many riparian, shrubby, and evergreen species, and extends south through the American tropics as far as the Colombian Andes. Quercus is in the Fagaceae, which it shares with several other major tree genera, and thus in the Fagales, which it shares with the Betulaceae, Corylaceae, and Carpinaceae (Willis and Airy Shaw 1973).

Quercus and other Fagaceae are wind pollinated and frequently deciduous like the Betulaceae, but their heavy, nutrient-rich fruits, like those of Juglans , are poorly dispersable and better adapted to germination in mature forests than in the regularly disturbed riparian zones to which the light, easily wind dispersed fruits of Alnus and Betula are well adapted (Grime 1979).

The 16 California species of Quercus include most of the range of morphological diversity in the genus, and all of its three subgenera (Quercus , Erythrobalanus , and Protobalanus ), but Q . lobata (valley oak) is the state's only major riparian oak. The other species are primarily or exclusively upland trees and shrubs, and even Q . lobata is somewhat more common in upland than in riparian zones. In the upland oak woodlands of the Coast Ranges it is common in sites which have heavy, poorly aerated soils with high water-holding capacity. Such ecological conditions are similar to those of the riparian sites where it occurs since these tend to be both drier and less well aerated than sites dominated by the other principal riparian trees.


12

In addition to its occasional dominance of upland oak woodland in the Coast Ranges when ecological conditions are suitable, Q . lobata can dominate two kinds of riparian communities: 1) riparian forest adjacent to streams when aeration is too poor for Populusfremontii , the typical riparian forest dominant. Q . lobata can form gallery forests in a matrix of treeless grassland in such situations, which were once common in the area of excessively heavy soil in the Sacramento Valley where rice is now extensively grown. The grasslands have almost entirely been converted to rice fields in this area, and many gallery forests of Q . lobata lost as well, but a fine example is still extant along Honcut Creek in northern Yuba County; 2) forest, woodland, and savanna on alluvial plains and terraces, usually above and toward the upland edge of typical riparian forest dominated by Populus fremontii (Conard etal . 1977). In these communities oaks must have access to water throughout the growing season, and their field relationships suggest that the accessibility of their water supply determines their density. Closed forests overwhelmingly dominated by Q . lobata can occur where water is abundant at relatively shallow depths, but progressively more open woodland and savanna communities in which oaks are scattered in a matrix of grassland are found as water apparently becomes more limiting. One of the very few field studies of the water relations of California oaks was done at such a Q . lobata community in Monterey County. It suggested that while Q . lobata had access to a reliable water table, Q . douglasii of adjacent uplands probably did not (Griffin 1973). However, since Q . lobata can also occur on upland sites similar to those of Q . douglasii (Griffin 1977), it should not be assumed that all its populations have the ready access to groundwater of its alluvial communities.

California's alluvial Q . lobata communities were once fairly common in parts of the Central Valley and in many Coast Ranges valleys as well, but since they were indicators of some of the world's best agricultural soils, most have long since been converted to farmland (Rossi 1980). A very few small but good examples of California's alluvial Q . lobata forests are still extant in Mendocino, Butte, Yolo, and Sacramento Counties, and perhaps elsewhere. Every effort should be made to permanently preserve them while the opportunity still exists.

All oaks need water, and several other upland species share some of Q . lobata's tolerance of poor soil aeration, so it is not surprising that they occasionally dominate riparian communities as well. Riparian Q . douglasii occurs along Mitchell Creek in Contra Costa County; riparian Q . engelmannii is found along Pala and other similar creeks in San Diego County; and Q . agrifolia forms a fine but very unusual riparian forest along the lower Mokelumne River on the floor of the Central Valley. Since the latter species is ordinarily restricted to the Coast Ranges and southern California, it must be assumed that marine airflow through the Carquinez Straits permits its survival in this part of the lower San Joaquin Valley. It is hoped that this rare and unstudied natural community will also soon receive adequate protection.

Q . lobata is a distinctive species endemic to California (fig. 10) of subgenus Quercus , the only one which extends to Eurasia (Tucker 1980). This subgenus is quite diverse and includes many large deciduous and evergreen trees as well as a number of evergreen shrubs in the Southwest and northern Mexico, but Q . lobata does not seem to be particularly closely related to any of these. As a large deciduous tree it is superficially similar to Q . garryana , but it stands somewhat apart from the series of increasingly drought-adapted species which Q . garryana forms with Q . douglasii and Q . engelmannii . It can occasionally hybridize with each of these, however. Surprisingly, it naturally hybridizes most abundantly with the shrub Q . dumosa (ibid .), and it is interesting but perhaps not significant that several other small white oaks of the Southwest have similarly elongated acorns with shallow cups. Since it is not particularly close to any of the eastern North American white oaks either, it is perhaps best to view Q . lobata as a distinctive derivative of subgenus Quercus which shares a complex pattern of interrelationships with other species of that taxon, and which has been a recognizable entity at least since the Miocene, when it was more widespread in western North America (Robichaux 1977).

figure

Figure 10.
Range of Quercus  lobata  (QL) (after Little 1971).


13

Salix (Willow)

Salix , the second major genus of the Salicaceae and Salicales, consists of about 500 species of trees and shrubs. The trees are very important components of riparian communities of the North Temperate Zone, and have invaded similar habitats in the tropics and South Temperate Zone as well, but the shrubs are largely restricted to the Northern Hemisphere and tend to be smaller and more associated with upland zones as high latitudes and altitudes are approached, a pattern of adaptation similar to but more welldeveloped than that seen in Alnus and Betula . Willows are typically deciduous and share the dioecious catkins and easily dispersed comose seeds of other Salicaceae, but they are usually secondarily entomophilous (Thorne 1976), and can be almost evergreen in the tropics (e.g., S . bonplandiana ).

California has about 32 Salix species (Munz 1959, 1968); the exact number is uncertain because of the difficult and controversial taxonomy of the genus. Which of these species should be considered trees is almost as controversial since the state's willow species are a continuum between large trees and dwarf shrubs, and several of the species which are usually shrubs can develop into small trees when conditions are favorable. The California willows which most frequently reach tree size are S . exigua , gooddingii , hindsiana , hookeriana , laevigata , lasiandra , lasiolepis , rigida (mackenziana ), scouleriana , sitchensis (coulteri ), and tracyi . All of these are riparian, but S . hookeriana , rigida , scouleriana , and tracyi are small local or northern species largely limited to riparian zones within montane or northwest coast coniferous forests, and are of little importance in the riparian communities of the rest of California.

Salixgooddingii is the most important willow of the great riparian forests of California's Central Valley, and it frequently shares dominance there with Populus fremontii , particularly at intermediate successional stages. It is a better pioneer than P . fremontii , if not as good as S . hindsiana , and it usually dominates the new riparian forests which often form in the Valley along neglected ditches and canals. Since it is generally more weedy and tolerant of stress than P . fremontii as long as water is abundantly available, it is particulaly important in the depauperate riparian forests along the lower San Joaquin River, where high salinity and poor development of natural levees have probably long limited maximal riparian community development (Kahrl 1979). S . gooddingii is limited to riparian zones of the Central Valley, southern California, and the desert Southwest (Little 1976; Elias 1980), a distribution which suggests a need for long, hot growing seasons as well as abundant groundwater (fig. 11). The relationships of this species are not in doubt since it is so similar to S . nigra , the most important large willow of eastern North America, that it is still some-times included within it as S . nigra var. vallicola (Little 1953, 1976).

figure

Figure 11.
Ranges of Salix  gooddingii  (SG) and
S. nigra  (SN) (after Little 1971, 1976).

S . lasiandra and S . laevigata are similar enough to one another that Hoover (1970) doubted their distinctness. Their ecological niche seems similar as well since both are large riparian willows which grow along streams in the Coast Ranges and the lower foothills of the Sierra Nevada. S . laevigata is reported to prefer well-aerated, rapidly flowing streams (Elias 1980), and it has been mapped as absent from most of the Central Valley by Little (1976), who also excludes S . lasiandra from most of the San Joaquin Valley. Conard etal . (1977) and Roberts etal . (1977) report both species to be common components of Central Valley riparian forests, however. What is clear about these two species at this time is: 1) they are more common along streams in the highlands surrounding the Valley than along the Valley floor; 2) they occur on the Valley floor; and 3) the details of their distribution and ecological relationships in California need to be much better understood. S . lasiandra may have less tolerance for habitats along intermittent streams than S . laevigata and thus may have a greater need for permanent water, but this observation needs verification.

The total ranges of these species do suggest that S . laevigata may be the more drought-adapted of the two since S . lasiandra extends down the mountains and coast of California from a wide range in the cool and wet parts of the Pacific Northwest, the northern Rocky Mountains, western Canada, and central Alaska while S . laevigata is restricted to mediterranean Cali-


14

fornia and a few relict stations in Arizona, Nevada, and Utah (fig 12 and 13) (Little 1976). S . lasiandra is reported to be closely related to S . lucida of the boreal forests of eastern North America (Rehder 1940), and S . laevigata is similarly reported to be related to S . bonplandiana , a semi-evergreen species of southern Arizona and tropical western Mexico (Elias 1980), but a critical reexamination of their relationships to each other and to other species which they resemble would be desirable.

figure

Figure 12.
Ranges of Salix  lasiandra  (SL) and
Slucida  (SLU) (after Little 1976).

figure

Figure 13.
Ranges of Salix  laevigata  (SLV) and
S. bonplandiana  (SB) (after Little 1976).

S . hindsiana and S . exigua (fig. 14) are largely shrubs, but they are both major components of California riparian vegetation because they are usually the first woody plants to colonize sandbars and other newly-formed riparian habitats when these are relatively fine-grained and shallow to groundwater. The dominance of such sites by these willows produces a distinctive and common riparian shrub community (Conard etal . 1977), but Baccharisviminea and B . glutinosa can become more important when alluvium is coarser and the water table deeper.

S . hindsiana is largely cismontane and endemic to the California Floristic Province while S . exigua is mostly transmontane in California and widespread in the rest of North America (fig. 14) (Little 1976). Both are ecologically and morphologically similar, however, and difficult to distinguish when sympatric (Hoover 1970; Smith 1970). They are part of a complex of closely related and ecologically similar western willows which also includes S . fluviatilis , S . sessilifolia , and S . melanopsis .

S . lasiolepis is a common small willow of much of the California Floristic Province, and it also occurs at scattered, possibly relict stations throughout the West (fig. 15) (Little 1976). It becomes an important vegetation component in the fog belt of the California coast, however, because there it dominates a distinctive forest community on alluvial bottomlands and in dune slacks. Myricacalifornica is an important associate in these forests, and a rare thistle, Cirsium loncholepis , is entirely restricted to them. Most of this apparently previously undescribed community was lost early

figure

Figure 14.
Ranges of Salix  hindsiana  (SH)
and Sexigua  (SE) (after Little 1976).


15

figure

Figure 15.
Range of Salix  lasiolepis  (SLL) (after Little 1976).

to agriculture since it frequently dominated wide coastal plains in the Arroyo Grande, Oso Flaco, and Santa Maria Valleys, which are now rich vegetable districts. A small remnant of it is now protected at Pismo State Beach in San Luis Obispo County, and a larger stand, which includes critical habitat of the endangered Unarmored Threespine Stickleback (Gasterosteusaculeatus williamsoni ), could be saved along San Antonio Creek in Santa Barbara County.

S . lasiolepis is closely related to S . hookeriana and S . tracyi (Elias 1980), two small trees of north coastal riparian communities, and probably to a number of northern and montane shrubs as well. It is less close to S . sitchensis , a small tree which also grows along fog belt streams as far south as Santa Barbara County (Smith 1976) but seldom forms extensive forests.

Riparian Origins

When the Arcto-Tertiary Geoflora was decimated throughout western North America in the Late Tertiary and Quaternary by spreading drought and cold, it is clear that some of its elements which were already strongly adapted to riparian conditions were able to survive along California's permanent and intermittent streams (Axelrod 1977). Their descendents dominate the state's riparian forests today. Some Arcto-Tertiary elements which were weakly adapted to riparian conditions such as Juglans hindsii were also able to precariously survive to the present in riparian refuges. Riparian forests are not among California's major refuges for Arcto-Tertiary and other relicts, however (Stebbins and Major 1965). This is partly because most riparian taxa are still too successful to be considered relictual but primarily because riparian environments are too competitive and frequently disturbed to promote high plant species richness and thus the survival of many marginal, relict species. Grime (1979) has shown that plant species density is highest in environments of intermediate productivity in which neither competition nor stress are excessive.

Before California streams were dammed, floods periodically disturbed riparian communities, renewing nutrients and understory light in an environment where warmth and soil moisture were already ideal for maximal productivity. Such conditions of regular but relatively infrequent disturbance when resources are not limiting are conducive to maximum plant competition and thus low species richness (ibid .). In contrast, California's concentrations of relictual species are in areas of intermediate productivity where plant species density is not limited by extremes of either stress or competition.

Riparian Dominance and Environment

Populusfremontii is the most common dominant of central California's riparian forests, but as discussed previously, environmental factors can shift dominance to other species. The most obvious of these factors are frequency of disturbance, air temperature, root zone aeration, and depth to groundwater, but others are probably important as well. It has been shown that when disturbance is high, dominance is shifted to Salix hindsiana and when somewhat less severe to S . gooddingii . Cool growing seasons favor P . trichocarpa , and hot environments sites with ahigh water table and low root aeration promote Cephalanthus occidentalis , but when turbulent, well-aerated water is close to the surface, Alnusrhombifolia can become dominant. When water tables are relatively deep, Platanusracemosa is the usual dominant when aeration of the intervening soil is high and Quercuslobata when it is low.

Q . lobata , the only major California riparian tree which is probably not of riparian origin, is most frequently dominant in riparian systems when two stressing factors, deep groundwater and low soil oxygen, are both present. This suggests that it is a relatively more stress-tolerant competitor than other riparian dominants. It is interesting that this species is probably derived from drought-stressed upland climax forests and woodlands, where trees with the stress-tolerant competitor adaptive strategy would be expected to dominate, rather than from riparian communities, which are more frequently dominated by trees with a simply competitive strategy (Grime 1979).


16

Deciduousness and Productivity

Mediterranean-type climates, with their mild, wet winters and dry summers, are well known for their sclerophyllous evergreen vegetation (Mooney etal . 1977; Cody and Mooney 1978; Walter 1979), but the presence of seemingly anomalous winter-deciduous riparian vegetation well within such a climate in California has generated relatively little comment. Air temperature obviously does not exclude evergreens from the Central Valley since they are common there in non-riparian zones. This led Stebbins (1974) to suggest that winter-deciduousness is favored when a highly productive growing season alternates with a cool season which is much less favorable but not necessarily extremely cold. He further postulated that it arose in riparian zones because wet roots aggravate winter cold stress and thus deciduousness.

The first hypothesis is undoubtedly correct, but the second is unlikely since evergreen woody angiosperms are more common in riparian than in upland zones on the Atlantic Coastal Plain in South Carolina, where summers are hot, wet, and highly productive, and winters are about as cold as those of the Central Valley. Evergreen angiosperm trees common in some riparian zones on the South Carolina Coastal Plain include Gordonia lasianthus , Ilexcassine , I . coriacea , I . myrtifolia , I . opaca , I . vomitoria , Magnolia virginiana , Myricacerifera , M . heterophylla , Perseaborbonia , P . palustris , and Quercuslaurifolia (Elias 1980).

In January Columbia, South Carolina, at the inner edge of the coastal plain, has a mean temperature of 7°C and a mean minimum temperature of 1°C. Sacramento in January has the same mean temperature and a mean minimum of 3°C. Despite the similarity of these temperatures, however, Sacramento has a mean frost-free growing season of 307 days and Columbia of only 248. Charleston, on the coast at the outer edge of the coastal plain, has milder winters than Columbia or Sacramento since it has a January mean of 9°C and mean minimum of 3°C, but even here the mean frost-free growing season is only 285 days, fully 22 days shorter than at Sacramento (US Department of Agriculture 1941).

The shorter growing season and greater spread between winter mean and mean minimum temperatures of these South Carolina cities relative to Sacramento are caused by the much more frequent penetration of outbreaks of cold arctic air to the coastal plain than to the Central Valley, which is usually protected from them by the Rocky Mountains and the Sierra Nevada and Cascade Ranges. The riparian evergreens of South Carolina must cope with these regular cold outbreaks as well as with their mean winter climate, so it is unlikely that the winter-deciduousness of the California riparian community is a general phenomenon which occurs wherever winter cold and wet soil interact.

Rundel (1980), in a comparative study of the adaptive strategies of mediterranean-climate oaks, supported Stebbins' view that winter-deciduousness is favored when highly productive summers alternate with winters which are much less productive but not necessarily highly stressful. Rundel assembled evidence which showed that deciduous oak leaves are considerably more photosynthetically efficient than those of evergreen oak species. For this extra efficiency to be profitable, however, a growing season which is sufficiently long, warm, and stress-free must be predictably present to compensate for the energetic cost of producing a new crop of leaves each year.

There is every reason to believe that Rundel's generalizations about the adaptive strategies of oaks apply equally well to those of other taxa. Deciduousness is clearly an example of the ability to rapidly respond to environmental change, a characteristic which Grime (1979) considered central to the competitive adaptive strategy. As discussed above, riparian environments, with their high productivity, minimal stress, and regular but infrequent disturbance, provide just the conditions which Grime predicted would most favor this strategy.

Major (1963) has shown that the activity of upland plant communities can be estimated from readily obtainable climatic data by using Thornthwaite's water balance concept (Thornthwaite 1948; Thornthwaite and Mather 1955). Thornthwaite's potential evapotranspiration (PE) is a function of temperature and day length and thus of warmth and light. His actual evapotranspiration (AE) predicts the evapotranspiration which can take place at a site if no more water is available to it than that received from precipitation. Since AE is a function of warmth, light, and precipitation (as well as soil water storage) and these are three of the most essential ingredients of plant productivity, Rosenzweig (1968) pointed out that AE can provide a reasonably good estimate of this as well.

In mediterranean-type climates AE is depressed far below PE because lack of summer rain causes severe drought stress and suppresses plant productivity just at the time when warmth and light are maximal. At Sacramento, for example, in the heart of California's mediterranean-type climate, annual PE is 815 mm. but annual AE is only 458 mm. (Mather etal . 1964). AE and PE are both 15 mm. in January, but while PE climbs as high as 140 mm. in July, AE peaks at 72 mm. in May and then declines because of summer drought. If less soil moisture storage were assumed than the 300 mm. used to calculate these figures, AE would peak even earlier and its annual sum would be even less.

Grassland is the dominant upland vegetation type at Sacramento. Upland broad-leaved trees are sparse and consist almost entirely of two species, evergreen sclerophyllous Quercus wislizenii and deciduous but semi-sclerophyllous Q . douglasii .


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At Columbia, South Carolina, however, summer rain is abundant, and the annual AE of 915 mm. almost matches the annual PE of 952 mm. Both AE and PE are 13 mm. in January, and both rise to similar peaks in July, when PE is 172 mm. and AE is 162 mm. Columbia is surrounded by a rich upland forest which can be dominated by pines or by several species of deciduous broad-leaved trees.

When rivers flowing from distant mountains import far more water to an area than would be available from local precipitation, keeping soil saturated at shallow depths throughout the year, AE, in effect, becomes equal to PE. This is exactly what happens in the riparian forests of California's Central Valley. As a result their defacto AE, their activity cycle, their productivity, and even their physiognomy are all very similar to those of the upland deciduous forests of South Carolina's coastal plain.

It can be seen that a gigantic natural experiment has confirmed Stebbins' and Rundel's hypothesis. Deciduousness is promoted wherever a long, very productive growing season is paired with a minimally productive but not necessarily very stressful cool or cold season. Like human beings with high incomes and low expenditures, deciduous trees can afford to rest during the season when their income would otherwise be lowest. The poorer evergreens do not have this luxury.

Quercuskelloggii (black oak) is found from San Diego County to central Oregon and is one of California's most abundant broad-leaved trees (Bolsinger 1980). Since Q . kelloggii is a non-riparian tree with deciduous, nonsclerophyllous leaves, theory predicts that it should occur where the local climate promotes maximal productivity during a well-defined growing season. Table 1 validates this prediction. Maximum monthly AE, and thus seasonal productivity, is considerably higher within the black oak's California range than in those parts of the state where it does not occur.

 

Table l.—Maximum monthly actual evapotranspiration (AE) in mm. (water balance data from Mather etal . 1964; Q . kelloggii range from Griffin and Critchfield 1972).

California climatic stations (N)

X + SE

Outside Q . kelloggii range (43)

47.9 + 3.66

Inside Q . kelloggii range (14)

83.1 + 1.66

AE is high within the range of Q . kelloggii because this species is limited to mountain slopes too low and too far inland to have cool summers but of relief sufficient for high orographic precipitation. Summers are dry, but where soil storage is good, surplus water from winter and early spring rains can promote high productivity during the warm days of late spring and early summer and thus favor this upland tree's deciduous habit.

Mineral Nutrition

Monk (1966) found that forests in north-central Florida are much more likely to be dominated by evergreen than deciduous trees when mineral nutrients and pH are low, and he generalized that relative soil sterility promotes evergreenness. Rundel (1980) also noted that evergreen leaves are more nutrient-use efficient. It is clear that nutrient losses from the regular shedding of deciduous leaves represent a cost which can only be made up during a long and productive growing season in a reasonably fertile environment. Since nutrient deficiencies lower productivity (Kramer and Kozlowski 1979) they, in effect, lower AE and promote evergreenness indirectly as well as directly.

California riparian forests receive imported nutrients as well as water from their rivers and streams (or did before dams stopped floods and became nutrient traps). Thus their productivity and deciduousness are doubly promoted. It is interesting that the Sacramento and the Stanislaus, the two Central Valley rivers with the most limestone in their watersheds and thus the most calcium, are also those with the best developed riparian forests along the banks of their lower reaches.

It was noted earlier, however, that some riparian communities on the Atlantic Coastal Plain are evergreen while surrounding upland communities are deciduous. These riparian communities occur because the low relief of the Coastal Plain does not permit rapid drainage of the heavy precipitation which it receives. They are nutrient-poor because their water is of local, meteorological origin, and can only leach and carry away mineral nutrients, not deposit them (Wharton and Brinson 1979). In this climate, where abundant summer rain makes AE maximal, the water available to riparian communities can not raise their productivity much above that of adjacent upland vegetation. It can only lower it through leaching. The result is evergreen vegetation in riparian communities on the Coastal Plain when the water is of local origin, but deciduous riparian forests dominated by species of Salix , Populus , Quercus , Platanus , and Fraxinus similar to those of California occur along the major rivers. These flow out of the Appalachians and import nutrients to the Coastal Plain to replace those lost by local leaching (Braun 1950; Hosner 1962; Wharton and Brinson 1979).

Productivity and Community Ecology

California's riparian communities are its most productive because they receive abundant water during hot, cloudless summers which are


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ideal for maximum photosynthesis. Their high PE thus becomes a high AE. Everywhere else in California except on the highest mountain summits summer drought suppresses AE below PE and plant productivity below its potential. Outside of alpine areas AE approaches PE most closely among California's upland communities in the coastal redwood belt of Del Norte and northwestern Humboldt Counties, but summers are too cool and cloudy there for productivity and either AE or PE to be extremely high. Crescent City, in the center of this area, has an AE of 597 mm. and a PE of 650 mm. while Davis, in the Central Valley, has an upland AE of 420 mm. and a PE and thus riparian AE of 810 mm. (300 mm. soil storage assumed).[4]

The riparian systems of California are clearly far more productive than any of that state's communities which are dependent on their local climate can be. Maximal riparian productivity more closely approaches that of eastern deciduous forests in summer and of tropical rain forests throughout the year. It is not surprising, then, that California's riparian forests share some features with exotic ecosystems which are absent, rare, or poorly developed elsewhere in the state.

Herbs with tropical affinities, such as Hibiscus californicus and Fimbristylisvahlii , occur in California riparian communities, and riparian Vitis californica is a well-developed liana, a growth form 90% confined to tropical forests (Walter 1979) and very poorly developed in upland California. Abundant warmth and water are apparently essential to large lianas, and the inability to tolerate even a brief winter rest period is probably what confines most taxa to the tropics. Notoriously high root pressures have undoubtedly helped Vitis cope with this problem and survive in seasonally highly productive temperate habitats like California riparian zones (Kramer and Kozlowski 1979).

Despite their small overall area California's riparian forests are especially well known for the abundance and diversity of their bird fauna (Small 1974; Gaines 1977). Their breeding avifauna is particularly important because it includes many species which occur in virtually no other California habitat. Gaines (ibid .) has shown that these birds are very frequently insectivorous foliage gleaners which winter in tropical forests and have vicariant populations in eastern deciduous forests, two habitats which share the high productivity of western riparian communities.

Insects, as poikilotherms which are largely primary consumers, are expected to increase in abundance with increasing warmth and primary productivity, and in California upland vegetation insect biomass does, in fact, peak in spring and closely fluctuate with primary productivity throughout the year (Cody etal . 1977). Comparable data do not seem to be available for any California riparian community, but the extremely high summer productivity of such communities undoubtedly induces similarly high summer peaks of insect biomass. These in turn act as magnets for insectivorous migratory birds. Gaines (1977) was ambivalent about this since at more than one point he noted the connection between riparian insect and insectivorous bird abundance but also yielded to Willson's (1974) view that bird density is not dependent on habitat productivity. Willson reached this conclusion after field work in what were apparently mostly various successional stages of upland forest and woodland vegetation within a single local climate in east central Illinois. Her studies showed that avian biomass was similar at all these successional stages and bird density greatest at intermediate ones. Willson concluded that her data showed these parameters of bird populations are unrelated to either plant or insect productivity since she assumed plant productivity is highest in early successional stages and insect productivity highest in late stages. Her first assumption ignored the very important stem and root components of primary productivity, however, and the second was the result of a literature review which, in effect, assumed that vegetation in different climates—and thus productivity regimes—can represent stages of and thus show the ecological effects of a single successional sequence. Her data do not support her conclusion that bird populations are unrelated to community productivity, but they do suggest that bird density may be highest at intermediate successional stages. These are just the successional stages when primary productivity is greatest (Larcher 1975).

Bird abundance does appear to be positively related to community productivity, and riparian bird populations can be expected to be augmented most relative to those of upland habitats when contrasts between upland and riparian productitivity are greatest. Such contrasts occur whenever perennial streams reliably bring water to arid or semiarid lands. In deserts with summer rainy seasons, however, vegetation along ephemeral streams which merely carry away the floodwaters of rare storms may actually be less productive of plants and animals than nearby uplands which are less disturbed and no drier (Wauer 1978). The biotic effects of riparian environments are much less conspicuous in areas such as the Atlantic Coastal Plain where upland vegetation is highly productive, but even here the variety of drainage conditions typical of riparian zones produces edaphic diversity and resultant habitat and species diversity. (Hosner 1962; Hair etal . 1974).

Bird populations are not simply a function of primary productivity, however, since highly productive irrigated cropland supports bird populations which are less diverse and frequently less abundant than those of natural riparian

[4] Major, J. No date. Water balances for California climatic stations. Unpublished manuscript.


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communities within the same local climate (Hehnke and Stone 1978). MacArthur and MacArthur (1961) demonstrated that bird species diversity is greatest in tall, highly stratified vegetation, and this can only occur when community phytomass is high. High phytomass is not universal in productive environments, but it is limited to them (Walter 1978).

It is tragic that the rich bird fauna of California's riparian communities has declined drastically within just the last few decades. Gaines (1977) cited reports which attribute this decline to brood parasitism by the recently introduced Brown-headed Cowbird, but he also noted that its introduction to Arizona occurred long before a similar decline in the riparian avifauna there. The cowbird has been especially frequently linked to the virtual extirpation of the riparian and insectivorous Bell's Vireo from California and Arizona, and yet these two species coexist in abundance in the less agricultural Rio Grande Valley of Texas (Wauer 1977). The riparian communities of Califorina and Arizona are frequently surrounded by agricultural areas where massive quantities of insecticides are used, but there seems to have been little comment about or investigation of their potential impact on a largely insectivorous riparian avifauna.

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Wauer, R. 1977. Significance of Rio Grande riparian systems upon the avifauna. p. 165–174. In : R.R. Johnson and D.A. Jones (tech. coord.). Importance, preservation, and management of riparian habitat: a symposium. [Tuscon, Ariz., July 9, 1977]. USDA Forest Service GTR-RM-43. 217 p. USDA Forest Service Range and Experiment Station, Fort Collins, Colorado.

Wauer, R. 1978. The breeding avifauna of Isla Tiburon, Sonora, Mexico. Unpublished manuscript. 75 p. USDA Fish and Wildlife Service, Washington, D.C.

Wharton, C, and M. Brinson. 1979. Characteristics of southeastern river systems. p. 3240. In : R.R. Johnson and J.F. McCormack (tech. coord.). Strategies for protection and management of floodplain wetlands and other riparian ecosystems. [Callaway Gardens, Georgia, December 11–13, 1978]. USDA Forest Service GTR-WO-12. 410 p. Washington, D.C.

Willis, J., and H. Airy Shaw. 1973. A dictionary of the flowering plants and ferns. Eighth edition. 1245 p. Cambridge University Press, London.

Willson, M. 1974. Avian community organization and habitat structure. Ecology 55:1017–1029.


23

A Brief History of Riparian Forests in the Central Valley of California[1]

Edwin F. Katibah[2]

Abstract.—Riparian forests once occupied substantially greater areas in the Central Valley of California than they do today. This paper explores the hydrologic influences which allowed the original riparian forests to establish themselves, the extent and reasons for the decline of the pre-settlement forests, as well as an estimate of the extent of today's remaining forests.

Introduction

One hundred and fifty years ago, California's Central Valley was endowed with a natural environment the scope and magnitude of which it is difficult, if not impossible, to fully comprehend today. Two major river systems, the Sacramento and the San Joaquin, drained the Valley. Flooding in the winter and spring, these rivers and their tributaries formed vast flood basins and huge, shallow seasonal lakes. Marsh vegetation (primarily Scirpus spp. and Typha spp.) occupied these wetter sites. Extensive perennial grassland (Stipa spp.) and scattered valley oak (Quercuslobata ) woodlands were found on the drier uplands, while the southern end of the Valley had large areas of saltbush (Atriplex spp.) desert. Through all of these vegetation communities, along the major river and stream systems, were strips of dense forest. These riverine, or riparian, forests developed on the natural levees of river-deposited silt, lining most of the Valley's drainages.

Riparian forests are structurally and floristically complex vegetation communities. These forests are difficult to characterize, for they occur in many different forms throughout the Valley. Under ideal conditions, these forests consist of several layers with dense undergrowth, similar in some cases to tropical jungles (Holmes etal . 1915). Fremont cottonwood (Populusfremontii ), California sycamore (Platanusracemosa ), willow (Salix spp.), and valley oak are common upper canopy species found throughout the Valley. Such species as box elder (Acernegundo subsp. californicum ), Oregon ash (Fraxinus latifolia ), and various species of willow generally occur in intermediate layers. Vines (lianas) are characteristic of many riparian forests, with wild grape (Vitiscalifornica ), poison oak (Rhus diversiloba ), Dutchman's pipe vine (Aristolochiacalifornica ), and wild clematis (Clematis spp.) growing through the various layers. Riparian forest undergrowth has a very diverse flora which varies widely throughout the Valley. Too many characteristic undergrowth plant species occur to mention but a few: mugwort (Artemisia douglasiana ), mulefat (Baccharisviminea ), wild rose (Rosacalifornica ), and blackberry (Rubus spp.).

Riparian forests have been greatly reduced or eliminated throughout much of the Valley. Ecologically they continue to play an important role with many plant and animal species dependent on them. Riparian forests are popular recreation sites, providing a wide range of beneficial values for the Valley's populace. These facts, among others, have recently aroused an interest in riparian forest ecology and management by both the general public and various Federal, State, and local agencies. This new interest has prompted questions as to why these forests occurred more along some river systems than others; how extensive the pre-settlement forests were; what caused their decline; and how many of these forests remain today. This paper attempts to provide a brief, informative look into these questions.

Hydrology of the Central Valley

There is significant hydrologic diversity throughout the Central Valley, and it was this diversity which was in part responsible for differences between individual riparian forests. For example, the Valley has two major riverine hydrologic systems: that of the Sacramento Valley component in the north and of the San Joaquin Valley component in the south. The influences of these major hydrologic systems on the nature of

[1] Paper presented at the California Riparian Systems Conference. [University of California, Davis, September 17–19, 1981].

[2] Edwin F. Katibah is an Associate Specialist, Department of Forestry and Resource Management, University of California, Berkeley.


24

the riparian forests associated with them were profound. Figure 1 depicts the Central Valley and its major surface hydrology as it may have appeared under pre-settlement conditions.

figure

Figure l.
Surface hydrology of the Central Valley as it may have appeared
around 1850. Areas in black within the Tulare Subbasin represent
seasonal lakes. Shaded areas, shown throughout the Valley,
indicate flood basins and freshwater marshes.

Hydrology of the Sacramento Valley

The Sacramento Valley is bordered by the mountains of the Coast Ranges to the west, the Klamath and Cascade Ranges to the north, and the Sierra Nevada to the east. To the south, the Sacramento Valley joins the San Joaquin Valley at the Sacramento/San Joaquin River Delta. The comparatively dry interior Coast Range mountains have no large rivers draining into the Valley, only streams, some of the larger being Stony, Cache, and Putah Creeks. The Sacramento River originates in the Klamath Mountains and is joined by two rivers, the McCloud and the Pit, in what is now Shasta Lake. The Sierra Nevada mountains to the east provide the greatest number of rivers and major streams draining into the Sacramento Valley—the Feather, Yuba, Bear, and American Rivers, and Butte and Big Chico Creeks.

Numerous other streams also flowed into the Sacramento Valley from the surrounding mountains. Not all of these streams actually reached the Sacramento River. Historically, natural levees and naturally occurring flood basins prevented some streams from reaching the main rivers. Instead, these streams spread out "through a welter of distributaries" (Thompson 1961) on the Valley floor. These distributaries typically ended in "sinks" of tule marsh. Putah, Cache, and Butte Creeks are among those streams which never joined the main river network in the Sacramento Valley.

The Sacramento Valley and its surrounding foothills, unlike the San Joaquin Valley region, receive substantial rainfall in the winter and early spring. This resulted in Sacramento Valley rivers experiencing maximum flows from December through March instead of May and June as is characteristic of most western rivers, including those in the San Joaquin Valley (Fortier 1909). Snowmelt fortified the river flow in the Sacramento Valley through the late spring. Annual summer drought brought the low flow rates found in these rivers through late fall.

During the peak flows of the Sacramento Valley rivers, the flood basins were filled by sediment-carrying waters. The natural levees dividing the flood basins from the major rivers were initially developed and then augmented by this annual flood cycle. Impressive natural levees along the Sacramento River, ". . . from 5 to 20 feet above the flood basins . . ." and 1.6–16 km. (1–10 mi.) in width, averaging 4.8 km. (3 mi.), ". . . formed corridors of generally dry land during times of flooding . . ." (Thompson 1961). The other major Sacramento Valley rivers and streams also formed well-developed natural levees.

Hydrology of the San Joaquin Valley

The San Joaquin Valley is bounded by the flat relief of the Sacramento/San Joaquin River Delta to the north, the mountains of the Sierra Nevada to the east, the Coast Ranges to the west, and the Tehachapi Mountains to the south.

The Coast Ranges and the Tehachapi Mountains bordering the San Joaquin Valley are very arid. Thus, the streams which originate from these mountains were characteristically intermittent in flow. Probably the most notable of these intermittent streams was Los Gatos Creek, whose alluvial fan helped form the Tulare Subbasin, a major influence in the hydrology of the San Joaquin Valley.

Numerous Sierra Nevada rivers and streams flowed into the San Joaquin Valley, including the Cosumnes, Mokelumne, Calaveras, Stanislaus, Tuolumne, Merced, Chowchilla, Fresno, San Joaquin, Kings, Kaweah, Tule, White and Kern Rivers.


25

The San Joaquin Valley is itself divided into two distinct hydrologic subbasins: the San Joaquin and the Tulare. The San Joaquin Subbasin is drained by the San Joaquin River; the Tulare Subbasin has no perennial surface outlet.

The Tulare Subbasin was formed at the south end of the San Joaquin Valley by the merging of alluvial fans from the Kings River to the east and Los Gatos Creek to the west (Cone 1911). Water originating from the major Tulare Subbasin rivers—the Kings, Kaweah, Tule, White, and Kern—flowed into this subbasin and found no normal outlet to the sea. Instead, large inland lakes formed—the Tulare, Buena Vista, Kern, and Goose. These largely temporary lakes, extremely shallow as they flooded the nearly flat landscape, rose dramatically as winter and spring runoff filled them. As the seasonal lakes filled beyond capacity they flowed into one another, finally rising above the natural alluvial barriers which divided the Tulare and San Joaquin Subbasins, sending tremendous quantities of water down the Fresno Slough into the San Joaquin River.

Later in the season, after the overland flow of water had ceased, substantial quantities of water were still drained from the Tulare Subbasin into the San Joaquin River via subsurface flow. This underground accession may have doubled the San Joaquin River's volume (Irrigation in California 1873). This undoubtedly helped to maintain the flow of the San Joaquin River in its southern reaches during the long, dry California summers.

The San Joaquin Valley rivers, whose waters were primarily snowmelt, tended to reach maximum flow in May and June. In contrast, peak flow of the Sacramento was usually in March, although some of the major peak flow rainfloods have occurred much earlier in the winter (1955–56 flood—December and January; 1964–65 flood—December and January; 1970 flood—January). In addition, the San Joaquin River's flow into the Delta in its peak flow period was less than onehalf the discharge rate of the Sacramento River during its usual peak flow period in March. Despite this difference in peak flow timing, the two rivers discharged approximately equal amounts of water into the Delta.

San Joaquin Valley rivers and streams in some instances did not produce the large, natural levees characteristic of the Sacramento Valley. Peak water flows in San Joaquin Valley rivers and streams were typically less than those in the Sacramento Valley, thus limiting their ability to pick up and carry sediment for great distances. Natural levees did form along the major northern San Joaquin Valley rivers—the Tuolumne, Stanislaus, Merced, Mokelumne, Cosumnes, and northern San Joaquin.

The southern (upper) reaches of the San Joaquin River developed natural levees only poorly, and only as the river entered the Valley floor. Never a particularly big river, it ranked third in peak flow after the Tuolumne and Kings Rivers (Cone 1911). Relatively low-energy peak flows resulted in suspended sediment deposition and natural levee formation only where it first entered the Valley. From there until it reached Fresno Slough, the San Joaquin River received no surface tributaries. At that point it received the surface floodwater flows through the Fresno Slough from the Tulare Subbasin and the underground flow through the extensive Tulare Subbasin aquifer.

Both of these flows were substantial, but both lacked significant sediment content. The overland flow through Fresno Slough had already deposited its sediment load in the shallow Tulare Subbasin lakes. The subsurface waters had been filtered of any sediment long before they joined the San Joaquin River. Thus while the southern San Joaquin River gained a large water accession, especially during the peak spring flood, it was unable to build any significant natural levees because of the low sediment load. With no natural levees to contain its waters, the San Joaquin River spread out over the flat Valley floor, sustaining the large freshwater marshes still found there today. The first major sediment-carrying waters to reach the San Joaquin River for many miles occurred at its confluence with the Merced River. From here to the Delta, substantial natural levees were built along the San Joaquin River.

The Tulare Subbasin rivers developed natural levees where these rivers first entered the Valley. The shifting courses of these rivers undoubtedly allowed many miles of levees to be formed, though they were quite narrow and confined compared to the levees of the Sacramento Valley rivers.

Extent of Pre-Settlement Riparian Forests

While the largest and most diverse riparian forests occurred on rivers having natural levees, well-developed riparian systems were found along virtually all watercourses in the Central Valley. Most riverine floodplains supported riparian vegetation to about the 100-year flood line. Virtually all watercourses supported dense vegetation from the water's edge to the outer edge of the riparian (moist soil) zone, whether or not natural levees were present. The overall presettlement riparian vegetation pattern was one of stringers or corridors of dense, mesic, broadleaf vegetation of varying widths bounding the watercourses, the widths being determined by local hydrologic and landform characteristics.

According to various accounts, the Sacramento Valley had approximately 324,000 ha. (800,000 ac.) of riparian forest remaining after 1848 (Smith 1977; Roberts etal . 1977). No comparable estimate for riparian forests is available for the San Joaquin Valley. However, based on a map compiled by J. Greg Howe (ibid .) showing presumptive original riparian forest distribution, and estimates by this author, it is


26

conservatively estimated that the Central Valley had greater than 373,000 ha. (921,000 ac.) of riparian forest under pre-settlement conditions.

Howe's map is based on early soil maps and covers an area in the Central Valley from the Sacramento River at Redding in the north to the Merced River in the south. I measured for areal extent the presumptive riparian forests shown on Howe's map. This estimate, presented in table 1, yields a value of 312,400 ha. (771,600 ac.) of pre-settlement riparian forest. This value must be considered conservative for that area, as Howe's map depicts only the large, contiguous riparian forests. The many smaller areas of riparian-indicator soil-types were below the mapping level of the historic soil maps used in the presumptive-riparian-forest map preparation.

In addition, Howe's map excluded the southern rivers of the San Joaquin Valley—the San Joaquin below its confluence with the Merced; and the Kings, Kaweah, Tule, and Kern. The above figure reflects that exclusion. I judged the riparian systems associated with those rivers to have totalled an estimated 20,200 ha. (50,000 ac.) (table 1). Furthermore, I estimated approximately 40,500 ha. (100,000 ac.) to account for the riparian forest vegetation present along the small streams, sloughs, lakes, ponds, and marsh borders throughout the entire Central Valley (table 1). These estimates are undoubtedly quite conservative and subject to considerable refinement.

 

Table 1.—Estimates of areal extent of pre-settlement riparian forests in the Central Valley of California.1

Forest name

Description

Estimated size
ha.
(ac.)

Central Valley Riparian Forest Area Estimated From Howe Map

Upper Sacramento River

Sacramento River from Table Mountain to near Redding (includes forests along Cottonwood, Stillwater, and Cow Creeks).

    17,500
   (43,200)

Big Bend

Sacramento River in the vicinity of Big Bend.

         800
     (2,000)

Antelope Creek

Antelope Creek east of Red Bluff.

         300
        (700)

Sacramento River

Sacramento River from below Sacramento to above Red Bluff (includes Elder, Mill, Thomes, Deer, Rice, Stony, Pine, Rock, Big Chico, Little Chico, Butte, Honcut, and Cache Creeks;  Feather, Yuba, Bear, and American Rivers).

  206,000
(508,800)

(Near) Knight's Landing

An area near Knight's Landing

         500
     (1,300)

Putah Creek

Putah Creek from above Winters to the Putah Creek Sinks.

                8,900
             (22,000)

Dixon

An area in the vicinity of Dixon.

      2,200
     (5,400)

Lower Sacramento River

Sacramento River below Courtland.

      1,100
     (2,600)

Cosumnes/Mokelumne Rivers

Upper reaches of Cosumnes and Mokelumne Rivers to below their confluence.

     23,400
    (57,800)

Calaveras River

Calaveras River north of Stockton.

      9,500
   (23,500)

Upper San Joaquin River

San Joaquin River west of Stockton.

         300
        (700)

San Joaquin River

San Joaquin River from its confluence with Merced River to just outside Stockton (includes Merced River, parts of Stanislaus and Tuolumne Rivers).

    36,700
   (90,600)

Middle Tuolumne River

Middle Tuolumne River near Modesto.

      3,100
     (7,700)

Upper Tuolumne River

Upper Tuolumne River from where it enters the Valley downstream.

      2,100
     (5,300)

Total

 

   312,400
(771,600)


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Table 1.—Estimates of areal extent of pre-settlement riparian forests in the Central Valley of California.

Forest name

Description

Estimated size
ha.
(ac.)

Additional Riparian Forest Area Based On Estimates By Katibah

South San Joaquin Valley

Series of forests along major southern San Joaquin Valley rivers (includes upper San Joaquin, Chowchilla, Fresno, Kings, Kern, and Tule); and the alluvial floodplains from these rivers.

    20,200
   (50,000)

Miscellaneous

Riparian forest present along small streams and sloughs; and lake, pond, and marsh borders throughout the entire Central Valley.

    40,500
(100,000)

Total

 

    60,700
(150,000)

Total Estimated Pre-Settlement Central Valley Riparian Forest Area

  373,100
(921,600)

1 Based on a map by J. Greg Howe (Roberts etal . 1977) and estimates by E. Katibah.

Decline of Central Valley Riparian Forests

"No natural landscapes of California have been so altered by man as its bottomlands" (Bakker 1972). The once-lush riparian forests, forming natural vegetation corridors along many of the Central Valley's watercourses, are mostly gone today. These forests were, in Thompson's words, ". . . modified with a rapidity and completeness matched in few parts of the United States" (Thompson 1961).

The reasons for the rapid decline of this once extensive ecosystem are not hard to find; one needs only to review the cultural history of the Central Valley for the last 150 years.

Prior to 1822 the land known as California was claimed and ruled by Spain. Little development occurred during this period, and at the cessation of Spanish rule in 1822 only about 30 ranches or farms had been granted in California (Fortier 1909). Mexico assumed control of California until 1848. By ". . . 1846 no less than eight hundred large tracts containing some of the best land in the State had been given away" (ibid .). The character and size of the large Mexican land grants had a profound influence on the social, commercial, and agricultural development of the Central Valley (ibid .), development which would ultimately and adversely affect riparian vegetation.

With the annexation of California to the United States in 1848, rapid development of the Central Valley began. The Gold Rush, beginning in 1849, exerted enormous land use pressures and led to rapid and often unplanned development of the Valley.

Riparian vegetation removal was one of the first significant losses in the natural environment. The large number of immigrants seeking their fortunes in the gold-bearing Mother Lode rivers and streams soon found that agriculture provided a much more stable and practical existence. The riparian forests, often the only significant woody vegetation on the Valley floor, were utilized by the growing agricultural community for fencing, lumber, and fuel (Thompson 1961). Steamships using the Sacramento River were also heavy users of local wood fuel. Knight's Landing on the Sacramento River was a site where cordwood was loaded onto these ships. It has been speculated that this wood came from the Cache Creek and Sacramento River riparian forests because Knight's Landing is adjacent to the treeless Yolo flood basin (ibid .). This supplying of fuel wood to the numerous woodburning vessels on the Sacramento River must have made a significant contribution to the early destruction of the local riparian forests (ibid .).

As early as 1868 the general scarcity of woody vegetation was noted in the Valley by some of its inhabitants (ibid .). The pressures on riparian forest vegetation continued as farmers found that the soil on the natural levees was highly fertile, easily managed, and not subject to the seasonal flooding of nearby lower-lying ground (ibid .). As agriculture expanded in the Central Valley, water demand began to exceed water supply. Farmers also found that the Valley had too much water in the winter and spring and not enough in the summer. Water development and reclamation projects were started, primarily for agriculture and community flood protection, and rapidly eliminated many of the Valley's native wetland systems.

With agricultural expansion, cities grew to support the new industry. Many Valley towns and cities were built in flood basins and upon active floodplains, and were subject to seasonal flooding. The city of Sacramento suffered a tremendous flood in 1850, and its response, the buil-


28

ing of levees around the town, ". . . set the course for Valley development over the next several generations" (Karhl 1979). To promote the reclamation of the tule marsh and floodplain lands, the Arkansas Act of 1850 was applied in California. This act gave the State of California millions of acres of federally owned floodplains, provided that the State drain and reclaim these lands. The Arkansas Act of 1850 stipulated that all manmade levees were to be constructed along natural drainage systems. The Green Act of 1868, passed by the California Legislature, however, freed the reclamation process of most controls. The effects of the Green Act were devastating to riparian forests. Levees were built for the convenience of landowners with little or no regard for the natural hydrologic systems. Remaining riparian forests, occupying natural levees along river courses, were destroyed in the quest to protect lands from flooding.

As in the Sacramento Valley, artificial levees were built along major San Joaquin Valley rivers. San Joaquin Valley agriculture faced different water-related problems. Winter and spring rainfall there is substantially less than in the Sacramento Valley, thus San Joaquin Valley land needed to be irrigated if it was to reliably produce crops. With the Green Act as guiding legislation, more than 1,600 km. (1,000 mi.) of irrigation canals were developed by 1878 in Fresno County alone (ibid .).

In the following years, and continuing up to the present time, numerous and controversial water projects have been the hallmark of Central Valley development. The demand for water, so tied to the agricultural, commercial, and urban development of the Valley, was, at least indirectly, responsible for the degradation of many of the remaining riparian forests. Artificial levees, river channelization, dam building, water diversion, and heavy groundwater pumping were among the factors which reduced the original riparian forest to the small, scattered remnant forests found today.

Present Extent of Remnant Riparian Forests

In 1979, the Geography Departments of California State University, Chico, and California State University, Fresno, under contract to the California Department of Fish and Game, compiled riparian vegetation distribution maps for the Central Valley (Nelson and Nelson 1983). This mapping effort provided an essentially complete inventory of all extant riparian vegetation (not just mature forest) in the Central Valley.[4]

Using these maps, the areas and lengths of riparian systems were calculated on an individual map and county basis.[5] Even though there is no explicit riparian forest category on these maps, applicable classifications were determined which should represent riparian forests. Using this approach, it was determined that approximately 41,300 ha. (102,000 ac.) of riparian forest remain in the Central Valley today (Katibah etal . 1983). Of the 41,300 ha. of forest, approximately 19,800 ha. (49,000 ac.) are in a disturbed and/or degraded condition based on the riparian mapping category code. Approximately 21,500 ha. (53,000 ac.) were identified as mature riparian forest, with no indication of condition. However, based on recent research findings (Katibah etal . in press), it can be surmised that the majority of these 21,500 ha. of mature riparian forest have been and are currently being heavily impacted by human activities.

Conclusions

The complex hydrologic systems found in the Central Valley of California under pristine conditions are gone. The original riparian forests, dependent on the diverse Valley hydrology, are likewise gone for the most part. Today's riparian forests are in a precarious position as the demand for greater land utilization by the agricultural industry and the spread of urbanization threaten the remaining forest tracts.

Offsetting this trend, however, is a greater apreciation of the values (economic and noneconomic) of riparian forests by Valley landowners and the general public. Riparian forests are present in some of the finest and most popular parks in the Central Valley. These forests provide habitat for many of the Valley's wildlife species. They also contain numerous and diverse native plant species.

These values, among others, must compete with the most complex and controversial issue of all: water. In California as in the rest of the West, water equals development, and California does not have adequate water to meet its anticipated future demands. How the remaining riparian forests will fare in the future is not known. As interest in and knowledge about this resource develops, and as hindsight provides an understanding of the past, it is hoped that a reasonable compromise can be achieved between this unique and valuable resoure and the needs of society.

[4] Central Valley riparian mapping project. 1979. Interpretation and mapping systems. Report prepared by the Riparian Mapping Team, Geography Department, California State University, Chico, with the Department of Geography, California State University, Fresno. Unpublished report to the Califronia Department of Fish and Game, Planning Branch, Sacramento. 24 p.

[5] Katibah, E.F., N.E. Nedeff, and K.J. Dummer. 1980. The areal and linear extent of riparian vegetation in the Central Valley of California. Final report to the California Department of Fish and Game, Planning Branch. Remote Sensing Research Program, Department of Forestry and Resource Management, University of California, Berkeley.


29

Literature Cited

Bakker, Elna S. 1972. An island called California. 357 p. University of California Press, Berkeley, California.

Cone, Victor M. 1911. Irrigation in the San Joaquin Valley, California. USDA Office of Experiment Stations, Bulletin 239. 62 p. Government Printing Office, Washington, D.C.

Fortier, Samuel. 1909. Irrigation in the Sacramento Valley, California. USDA Office of Experiment Stations, Bulletin 207. 99 p. Government Printing Office, Washington, D.C.

Holmes, L.C., J.W. Nelson, and party. 1915. Reconnaissance soil survey of the Sacramento Valley, California. USDA Publication. Government Printing Office, Washington, D.C.

Irrigation in California: the San Joaquin and Tulare Plains, a review of the whole field. 1873. 22 p. Record Steambook and Job Printing House, Sacramento, California.

Kahrl, William L. 1979. The California water atlas. Prepared by the Governor's Office of Planning and Research in cooperation with the California Department of Water Resources. 113 p. Sacramento, California.

Katibah, Edwin F., Nicole E. Nedeff, and Kevin J. Dummer. 1983. A summary of the riparian vegetation areal and linear extent measurements from the Central Valley riparian mapping project. In : R.E. Warner and K.M. Hendrix (ed.). California Riparian Systems. [University of California, Davis, September 17–19, 1981]. University of California Press, Berkeley.

Katibah, Edwin F., Kevin J. Dummer, and Nicole E. Nedeff. In press. Evaluation of the riparian vegetation resource in the Central Valley of California using remote sensing techniques. Proceedings of the ASP and ACSM fall technical meeting. [San Francisco, California, September 9-11, 1981].

Nelson, Charles W., and James R. Nelson. 1983. Central Valley riparian mapping project. In : R.E. Warner and K.M. Hendrix (ed.). California Riparian Systems. [University of California, Davis, September 17–19, 1981]. University of California Press, Berkeley.

Roberts, W.G., J.G. Howe, and J. Major. 1977. A survey of riparian forest flora and fauna in California. p. 3–19. In : A. Sands (ed.). Riparian forests in California: their ecology and conservation. Institute of Ecology Publication No. 15. 122 p. University of California, Davis.

Smith, F.E. 1977. A short reveiw of the status of riparian forests in California. p. 1–2. In : A. Sands (ed.). Riparian forests in California: their ecology and conservation. Institute of Ecology Publication No. 15. 122 p. University of California, Davis.

Thompson, K. 1961. Riparian forests of the Sacramento Valley, California. Annals Assoc. of Amer. Geog. 51:294–315.


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The Importance of Riparian Systems to Amphibians and Reptiles[1]

John M. Brode and R. Bruce Bury[2]

Abstract.—California has a rich herpetofauna, including about 120 native species. Riparian systems provide habitat for 83% of the amphibian and 40% of the reptile species. Amphibians and reptiles utilize these systems to varying degrees and can be classified according to the type of use. Riparian systems provide corridors for dispersal and also allow certain species to use otherwise unsuitable environments. Amphibians and reptiles may be abundant in riparian systems where they may outnumber other taxa. Harvesting timber and creating reservoirs are detrimental to amphibians and reptiles in the zone of influence of such activities. These activities have their greatest effects upon reptiles and amphibians whose entire life histories occur in the riparian zone.

Introduction

California has a rich herpetofauna, including about 120 native species. Amphibians and reptiles represent important ecological components of riparian communities, where they may reach high densities. In California, we estimate riparian systems provide habitat for 83% of the amphibians and 40% of the reptiles. Many species are permanent residents of the riparian zone, while others are transient or temporal visitors.

In many (if not most) natural communities, nongame species constitute the greatest portion of vertebrate species, individuals, and biomass; and they are energetically critical elements in the functioning of ecosystems (Bury etal . 1980). Based on figures compiled by Bury etal . (ibid .) 88% of the vertebrate species (fish excluded) in California are nongame.

Much emphasis has been placed on the loss of California's Central Valley riparian forests (Sands 1977). However, there are many other riparian systems in California that have suffered substantial degradation. Logging has proved detrimental to certain animal species that depend on cool, shaded streams. Reservoirs have been created on many streams in California, eliminating the original riparian environment and much of the herpetofauna, while providing habitat for nonnative species which are usually managed more intensely than the original fauna. Many of the species lost, especially the amphibians and reptiles, are endemic to California.

In this paper, we present background information on species diversity and abundance, review the habitat requirements of California amphibians and reptiles, and suggest use classifications for species using riparian systems. Lastly, we review the effects of logging on selected species and discuss the effects of reservoirs on amphibians and reptiles, presenting preliminary data from two preimpoundment studies.

Species Diversity and Abundance

Species diversity and abundance of amphibians and reptiles may be dramatic in riparian systems. For example, the riparian system of Corral Hollow Creek, San Joaquin County (fig. 1), supports 7 species of amphibians and 21 species of reptiles, including 13 species of snakes (Stebbins 1966; Sullivan 1981). Burton and Likens (1975) estimated there were 2,950 salamanders per ha. within the Hubbard Brook Experimental Forest, New Hampshire, and concluded there were more salamanders than either birds or small mammals. In biomass, salamanders were 2.6 times greater than birds and approximately equal to mammals. Burton and Likens were surprised at this result as most ecologists have ignored amphibians in ecosystem energy flow and nutrient cycling studies while considering birds and mammals in detail.

[1] Paper presented at the California Riparian Systems Conference. [University of California, Davis, September 17–19, 1981].

[2] John M. Brode is a Herpetologist, Endangered Species Program, California Department of Fish and Game, Rancho Cordova, Calif. R. Bruce Bury is a Research Zoologist, Ecology Section, Denver Wildlife Research Center, USDI Fish and Wildlife Service, Fort Collins, Colo.


31

figure

Figure 1.
Corral Hollow Creek, San Joaquin County, California. This riparian system supports
7 species of amphibians and 21 species of reptiles. Photo by John E. Hummel.

Other workers have obtained similar results regarding amphibian abundance. Nussbaum[3] estimated the density of the Siskiyou Mountain salamander (Plethodon stormi ) to be 0.27 per m2 (2,700 per ha.) in optimal habitat. Murphy and Hall (1981) reported in certain streams, Pacific giant salamander (Dicamptodonensatus ) was the dominant vertebrate in both biomass and frequency of occurrence and made up as much as 99% of the total predator biomass in some sites. The population density of an eastern stream salamander (Desmognathusfuscus ) was estimated at 0.4 to 1.4 per m2 (400 to 1,400 per ha.) (Spight 1976); in certain areas, male D . ochrophaeus occur at densities of 4.4 per m2 (Tilley 1974). Western pond turtle (Clemmysmarmorata ) may reach densities of 425 per ha. in California ponds and streams (Bury 1979). Fitch (1975) estimated densities of 1,000 to 1,500 ringneck snakes (Diadophispunctatus ) per ha. Sullivan (1981) reported a density of 22.4 snakes per km. along an 11-km. road transect in Corral Hollow.

Use of Riparian Systems by Amphibians and Reptiles in California

Amphibians that utilize riparian systems in California can be placed in one of three classifications, according to their dependency upon

[3] Nussbaum, R.A. 1974. The distributional ecology and life history of the Siskiyou Mountain salamander, Plethodon stormi , in relation to the potential impact of the proposed Applegate Reservoir on this species. 52 p. Report submitted to the US Army Corps of Engineers, Portland, Ore.


32

aquatic environments and the extent to which they utilize terrestrial riparian systems (table 1). All amphibians in California, except lungless salamanders of the family Plethodontidae, require aquatic environments to complete their life cycle. Certain frogs (Rana , Ascaphus ) and salamanders (Rhyacotriton , some Batrachoseps ) frequent the riparian zone throughout their lives. Other salamanders and newts (Ambystoma , Taricha ) and some toads (Bufo ) utilize riparian systems primarily for breeding, spending most of their adult life in upland areas. Lungless salamanders are more generalized in their habitat requirements, but many species utilize

 

Table 1.—Use classification of amphibians occurring in California riparian systems.

Type of use

Constant1

Breeding2

General3

Northwestern salamander
Ambystomagracile

Long-toed salamander
Ambystomamacrodactylum

Del Norte salamander
Plethodonelongatus

Pacific giant salamander
Dicamptodonensatus

Rough-skinned newt
Tarichagranulosa

Siskiyou Mountain salamander
Plethodonstormi

Olympic salamander
Rhyacotritonolympicus

California newt
Tarichatorosa

Ensatina
Ensatinaeschscholtzi

Dunn's salamander
Plethodondunni

Red-bellied newt
Taricharivularis

Pacific slender salamander
Batrachosepspacificus

Desert slender salamander
Batrachosepsaridus

Colorado River toad
Bufoalvarius

California slender salamander
Batrachosepsattenuatus

Inyo Mountains salamander
Batrachosepscampi

Western toad
Bufoboreas

Black salamander
Aneidesflavipunctatus

Tailed frog
Ascaphustruei

Yosemite toad
Bufocanorus

Clouded salamander
Aneidesferreus

Red-spotted toad
Bufopunctatus

Woodhouse's toad
Bufowoodhousei

Arboreal salamander
Aneideslugubris

Black toad
Bufoexsul

Southwestern toad
Bufomicroscaphus

Limestone salamander
Hydromantesbrunus

California treefrog
Hylacadaverina

Great Plains toad
Bufocognatus

Shasta salamander
Hydromantesshastae

Red-legged frog
Ranaaurora

Pacific treefrog
Hylaregilla

Mount Lyell salamander
Hydromantesplatycephalus

Spotted frog
Ranapretiosa

   

Cascades frog
Ranacascadae

   

Foothill yellow-legged frog
Ranaboylei

   

Mountain yellow-legged frog
Ranamuscosa

   

Leopard frog
Ranapipiens

   

1 Species that occur in the riparian zone throughout their lives.
2 Species that utilize riparian systems primarily for breeding, but may leave the riparian zone as adults.
3 Species that utilize riparian systems as well as other systems throughout their range.


33

riparian systems. Wide-ranging plethodontid salamanders (Ensatina ) have generalized habitat requirements in the mesic environments of northern California, but tend to associate with riparian systems in xeric environments.

Reptiles that utilize riparian systems in California can also be placed in one of three categories (table 2). Turtles (Clemmys ) and most garter snakes (Thamnophis ) depend on aquatic environments and occur primarily in the riparian zone throughout their lives. Some lizards (Gerrhonotus ) and snakes (Contia ) have rather general habitat requirements but become riparian obligates in arid portions of their range. The remaining reptiles that occur in riparian systems (Cnemidophorous , Pituophis , Lampropeltis ) are more generalized in their habitat requirements, but they frequent ecotones and water bodies associated with riparian areas.

The riparian zone also provides corridors of dispersal and islands of habitat for many species of amphibians and reptiles, especially in arid climates. The Gilbert's skink (Eumecesgilberti ) and ringneck snake (Diadophis punctatus ) are foothill species that extend their ranges into the Central Valley along the American River and other riparian corridors. The desert slender salamander (Batrachoseps aridus ) and Inyo Mountains salamander (B . campi ) are restricted to the narrow riparian zones of desert seeps and springs.

Historically, riparian corridors probably facilitated the maintenance of genetic continuity between populations. Now, due to habitat disruption, certain populations are isolated. The wide-ranging California slender salamander (Batrachoseps attenuatus ) was probably once common in the southern Sacramento Valley. Now, in the Valley this species is restricted to a few isolated remnants of valley oak woodland while still common elsewhere. Ultimate consequences of habitat disruption include local extinctions, reduction in species diversity, and loss of population heterogeneity.

Examples of Activities Detrimental to Amphibians and Reptiles in Riparian Systems

Timber Harvest

The tailed frog (Ascaphustruei ), the most primitive frog in North America, is highly specialized for life in cool, fast-flowing waters. The southern terminus of the species in the United States is in small streams along the north coast and in the North Coast Range of California (Bury 1968). Larval Ascaphus prefer temperatures at or below 15°C., and avoid waters over 22°C. (deVlaming and Bury 1970); such behavior is unlike any other native frog, and underscores the dependence of Ascaphus on a cool, shaded habitat. Removal of timber by lumbering or fire results in the disappearance of tailed frogs, apparently due to increased temperatures of the exposed stream-bed (Noble and Putnam 1931; Bury 1968).

Similarly the Olympic salamander (Rhyacotriton olympicus ) frequents cool ravines and rivulets in northwestern California. This species is absent in open (postlogging) habitat; logging apparently eliminates populations even in wet, coastal redwoods (Bury in prep.).

The Siskiyou Mountain salamander (Plethodonstormi ) inhabits shaded talus slopes in canyons and along stream courses above the floodplain. Nussbaum3 considered the gradual elimination of the overstory vegetation by clearcutting to be a serious threat to this species.

Reservoirs

Barrett and Cordone (1980) counted 1,272 reservoirs in California. Out of these, 926 (73%) are "mixed" or "warm water" types, those most commonly found on foothill and mid-elevation streams and rivers. Reservoirs have adverse effects on amphibians and reptiles by flooding their habitats. They often result in bodies of water with fluctuating levels, which prevents reestablishment of natural riparian communities. In addition, reservoirs are usually managed for human activities.

Specific examples of the effects of reservoirs on amphibians and reptiles are few. Nussbaum3 estimated that the Applegate Reservoir in Oregon and California would cover 1.06% of the total known range and 2.1% of the estimated total population of the Siskiyou Mountain salamander. He further stated that although the construction of Applegate Reservoir in itself will pose no threats to the continued existence of P . stormi , the effects of Applegate Reservoir added to numerous other man-caused effects could seriously threaten the existence of the species.

We do not have data regarding the numbers of individual amphibians and reptiles that may have been affected by previous reservoir construction in California, but information on two proposed reservoir projects will serve as examples of what may be lost.

Los Vaqueros Reservoir

The primary effect of the proposed Los Vaqueros Reservoir will be on Kellogg Creek, Contra Costa County. Preliminary investigations by the Department of Fish and Game (DFG) indicate that the Kellogg Creek area supports at least 6 species of amphibians and 12 species of reptiles. The reservoir, as proposed, would inundate 12 km. of tributaries. An additional 6.4 km. of Kellogg Creek would be affected below the dam due to changes in streamflow.

A species of special concern that occurs in Kellogg Creek is the red-legged frog (Rana aurora —fig. 2), which is well adapted for living in arid environments with intermittent or temporary aquatic habitat. However, it has


34
 

Table 2.—Use classification of reptiles occurring in California riparian systems.

Type of use

Constant1

Arid2

General3

Western pond turtle
Clemmysmarmorata

Western skink
Eumecesskiltonianus

Western fence lizard
Sceloporusoccidentalis

Sonoran mud turtle
Kinosternonsonoriense

Gilberts skink
Eumecesgilberti

Sagebrush lizard
Sceloporusgraciosus

Common garter snake
Thamnophissirtalis

Panamint alligator lizard
Gerrhonotuspanamintinus

Long-tailed brush lizard
Urosaurusgraciosus

Western aquatic garter snake
Thamnophiscouchi

Northern alligator lizard
Gerrhonotuscoeruleus

Western whiptail lizard
Cnemidophorustigris

Checkered garter snake
Thamnophismarcianus

Ringneck snake
Diadophispunctatus

Southern alligator lizard
Gerrhonotusmulticarinatus

 

Sharp-tailed snake
Contiatenuis

California legless lizard
Anniellapulchra

 

Western terrestrial garter snake
Thamnophiselegans

Western blind snake
Leptotyphlopshumilis

   

Rubber boa
Charinabottae

   

Racer
Coluberconstrictor

   

Striped racer
Masticophislateralis

   

Gopher snake
Pituophismelanoleucus

   

Common kingsnake
Lampropeltisgetulus

   

California mountain kingsnake
Lampropeltiszonata

   

Northwestern garter snake
Thamnophisordinoides

   

Western black-headed snake
Tantillaplaniceps

   

Night snake
Hypsiglenaplaniceps

   

Western rattlesnake
Crotalusviridis

1 Species that occur primarily in the riparian zone throughout their lives.
2 Species that depend on riparian systems in the arid parts of their range.
3 Species that utilize riparian systems as well as other systems throughout their range.


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little tolerance for habitat disturbances or competition from exotic species. Approximately 18 km. of red-legged frog habitat, virtually the entire Kellogg Creek population, could be adversely affected if Los Vaqueros Reservoir impoundment project is built.

Thomes-Newville Reservoir

The primary effect of the proposed Thomes-Newville Reservoir will be on the North Fork Stony Creek, Glenn and Tehama Counties. Preliminary investigations by DFG indicate that the North Fork Stony Creek area supports at least 4 species of amphibians amd 14 species of reptiles. The proposed reservoir will inundate about 14 km. of perennial stream and about 40 km. of intermittent stream. In addition, about 13 km. of Thomes Creek may be affected by water diversion. Another species of special concern, the foothill yellow-legged frog (Ranaboylei ) occurs in North Fork Stony Creek and its tributaries. These frogs are adapted to rocky foothill streams. Salt Creek, on the project site, supports an excellent population of yellow-legged frogs. The majority of the yellow-legged frog population will be affected adversely if this project is completed.

Conclusions

Amphibians and reptiles represent important ecological components of riparian communities. Many species are permanent residents of the riparian zone, while others are transient or temporal visitors.

Amphibians and reptiles may be abundant in riparian systems where they can outnumber other taxa. Riparian systems provide important corridors of dispersal for many species. Disruption of these corridors can cause isolation and may lead to local extinctions.

figure

Figure 2.
Adult red-legged frog (Rana   aurora ). Photo by Robert L. Livezey.

Activities which affect riparian systems adversely have their greatest effects on those amphibians and reptiles that occur in the riparian zone throughout their life. There is critical need for more quantified studies on how these activities directly affect riparian herpetofaunas; and a need for research on the relation of amphibians and reptiles to structural diversity of riparian vegetation.

Acknowledgements

We thank Kimberly A. Nicol and David P. Muth for assistance in preparing the tables. Stephen J. Nicola and Larry L. Eng reviewed an early draft.

Literature Cited

Barrett, John G., and Almo J. Cordone. 1980. The lakes of California. Inland Fish. Admin. Rep,. 80–5. 10 p. California Department of Fish and Game.

Burton, Thomas M., and Gene E. Likens. 1975. Salamander population and biomass in the Hubbard Brook experimental forest, New Hampshire. Copeia 1975:541–546.

Bury, R. Bruce. 1968. The distribution of Ascaphustruei in California. Herpetologica 24:39–46.

Bury, R. Bruce. 1979. Population ecology of freshwater turtles. In : Marion Harless and Henry Morlock (ed.). Turtles: perspectives and research. 695 p. John Wiley and Sons, Inc., New York, N.Y.

Bury, R. Bruce, Howard W. Campbell, and Norman J. Scott, Jr. 1980. Role and importance of nongame wildlife. Trans. 45th North Amer. Wildl. Nat. Res. Conf. 1980:197–207.

deVlaming, Victor L., and R. Bruce Bury. 1970. Thermal selection in tadpoles of the tailed frog, Ascaphustruei . J. Herpetol. 4: 179–189.

Fitch, Henry S. 1975. A demographic study of the ringneck snake (Diadophispunctatus ) in Kansas. Univ. Kansas Mus. Nat. Hist. Publ. 62. 53 p.

Murphy, Michael L., and James D. Hall. 1981. Varied effects of clear-cut logging on predators and their habitat in small streams of the Cascade Mountains, Oregon. Can. J. Fish Aquat. Sci. 38:137–145.

Noble, G.K., and P.G. Putnam. 1931. Observation on the life history of Ascaphustruei Stejneger. Copeia 1931:97–101.


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Sands, Anne (ed.). 1977. Riparian forests in California: their ecology and conservation. Institute of Ecology Pub. 15. 122 p. University of California, Davis.

Spight, T.M. 1967. Population structure and biomass production by a stream salamander. Amer. Midl. Nat. 78:437–447.

Stebbins, Robert C. 1966. A field guide to western reptiles and amphibians. 279 p. Houghton Mifflin Co., Boston, Mass.

Sullivan, Brian K. 1981. Distribution and relative abundance of snakes along a transect in California. J. of Herp. 15:247–248.

Tilley, S.G. 1974. Structure and dynamics of populations of the salamander Desmognathus ochrophaeus Cope in different habitats. Ecology 55:808–817.


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Some Implications of Population Growth to California's Renewable Resources[1]

Judith Kunofsky[2]

Abstract.—Efforts at better management of riparian systems will ultimately fail unless zero population growth is achieved. The increasing population in the United States, often overlooked as a causal factor, has contributed to the significant deterioration of riparian resources in this country. Advocates of riparian protection can be a vital link between proponents of population stabilization and the public and political leaders capable of effecting reversal of present population trends.

Introduction

This paper is a presentation that is not of original research. Nor am I a researcher. Rather, its perspective is that of advocate, and I hope it will be regarded as welcome diversity to other technical presentations, rather than as an aberration.

The organization I represent, Zero Population Growth (and, in particular, its California arm), is a political and educational non-profit membership organization founded in 1969 to advocate a rapid end to human population growth in this country and around the world. We have active programs in Washington, D.C; in Sacramento; and in communities around the state and the country. In addition, my position as director of the Population and Growth Policy Program of the national Sierra Club enables me to represent that organization on this issue as well.

The case I will make is that efforts at better management of riparian resources will ultimately fail unless the population stops increasing—unless we achieve zero population growth.

For those unfamiliar with the concept, zero population growth (zpg) occurs globally if the number of births each year equals the number of deaths. In a limited geographical area such as the United States or California or this room, population change is more complicated. Population change equals the number of births plus the number of people moving in (immigrants), minus the number of deaths and the number of people moving out (emigrants). If these balance, if the population remains roughly constant from year to year, we achieve a state of zero population growth, also known as population stabilization.

Most people now believe that the population of the United States has stopped growing or is well under way toward stabilization. This is not true. The country's population is increasing by two and a half million people per year, the result of roughly 3.6 million births, 2.0 million deaths, and 800,000 net immigration (immigrants minus emigrants). While the goal is much closer than it was a decade ago in terms of the birth rate, zpg is neither here nor is it assured. Despite the decrease in the number of births per woman, continued population growth is resulting from the combination of an "echo" of the post-war baby boom and immigration to this country. Growth could continue for several decades or perhaps far into the distant future. The US population could increase from today's 228 million to 260 million in 50 years and stop increasing, or it could reach 350 million or more by the year 2030, depending on the future course of fertility in and migration to the United States. Here in California, the state's population of 24 million is increasing by almost half a million people per year (more precisely, 479,000). We are far from achieving zero population growth.

Current Status of Riparian Systems

It is useful to briefly review the status of this country's riparian systems, i.e.: ". . . the vegetation and associated animal life found in close proximity to streams and other watercourses, around lakes, and adjacent to springs, seeps, and desert oases" (Warner 1979). According to Dr. Warner, riparian systems are:

[1] Paper presented at the California Riparian Systems Conference. [University of California, Davis, September 17–19, 1981].

[2] Judith Kunofsky is past National President of Zero Population Growth (1977–1980) and continues to serve on its board of directors. She also heads the Population Growth Policy Program of the Sierra Club.


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". . . perhaps the most important of all ecosystems to fish and wildlife," determining the health of associated aquatic environments, enhancing erosion control, and improving water quality (ibid .). They constitute important agricultural lands and sources of timber. Riparian vegetation is the source of nutrients for streams, of diverse recreational opportunities, of clean water, fuel, and shade.

However, America has in the last 150 years destroyed between 70% and 90% of her indigenous riparian resources and badly damaged much of the rest (US Council on Environmental Quality 1978). Examples of that destruction:

1) In 1977 the USDI Bureau of Land Management concluded that 83% of the riparian systems under its control were ". . . in unsatisfactory condition and in need of improved management, largely because of the destruction caused by excessive livestock grazing, road construction, and other damaging human activities" (Almand and Krohn 1979).

2) "On the 2.3 million acres of riparian lands and wetlands within the National Forest System, livestock grazing . . . timber harvest and associated road construction and silvicultural practices, recreation, public highway construction, and mining . . . all . . . continue to exert destructive pressures requiring prompt and concerted corrective measures (USDA Forest Service 1979).

3) In California: ". . . riparian systems are now so decimated as to be in jeopardy as a productive ecological resource" (Warner 1979).

What Is the Source of the Problem?

Our riparian resources are in such terrible shape because of human impact. This impact is increasing because of continued conversion of riparian lands to other uses—agriculture, forestry, livestock grazing, water control, highways, recreation, and housing. Directly or indirectly: ". . . all the dominant impacts are human ones" (ibid .).

ZPG maintains that the role of sheer humannumbers cannot be ignored, and an end to population growth, the achievement of zpg, is an integral part of any serious, long-term plan for rehabilitating and sustaining riparian systems. To the extent that researchers, planners, regulators, and concerned Americans ignore this issue, they are dooming their work to ultimate failure.

This appraisal of the effect of population growth is applicable to any ecosystem or natural feature. This is part of the difficulty of the population concept; the impact of the size and growth of the human population is relevant to all resources, exclusive to none, and therefore, unfortunately, too often overlooked or considered such a general problem as not to be worth mentioning in any specific context.

Protection of Riparian Systems

Returning to the discussion of riparian systems, since the source of the problems is human impact, we clearly need to change human activity. What does this mean?

First, we need specific management protections for riparian systems. However, even the best management will eventually be overwhelmed by continued population growth. When the pressure of human demands is great enough, any scheme of resource management or protection will go out the window. This is not a law of biology, but one of politics. When short-term human needs conflict with the long-term maintenance of the carrying capacity of an ecosystem, unfortunately we, as a society, as a world, seem to always sacrifice the long-term goal for the short-term need.

Resource management alone, however well-done, is simply not enough to protect riparian systems. These specific protections must be coupled with a reduction in demand for those services provided by riparian systems. This reduction requires a change in patterns of consumption (e.g., conservation and adoption of more environmentally sound technologies). It also necessitates a change in the quantity of consumption, which means, for example, fewer people directly enjoying the benefits of recreation along rivers, or fewer people relying on the products of riparian environments.

A decade ago, the Science and Technology Advisory Council of the California Assembly held a forum at the University of California, Davis, to analyze the nature and consequences of population change in the state. At that conference, demographers Kingsley Davis and Frederick G. Styles observed:

If any state in the United States epitomizes the dilemmas of advanced technology, it is California; and if any one of its problems embodies the dilemmas, it is rapid population growth . . . The productivity of its economy makes it a prime target for interstate and international migration, causing it to be . . . the most populous state in the union . . . Although it has been subject to temporary lulls in growth . . . its population increase has been remarkably persistent . . . The resulting environmental damage is greater than that found almost anywhere else in the United States. . . .

If advanced societies are to solve their environmental problems, not to mention other questions concerned with the quality of life, they cannot in-


39

dulge in continued rapid population growth. No sensible planning, no satisfactory management of land use, no long-run solution to urban problems is possible in the State of California if it continues to add half a million to its population each year (Davis and Styles 1971).

Zero population growth will be reached eventually. I have no doubt of this, nor do I think it is a matter of opinion. In the long run, the population of the earth will be no greater than its carrying capacity, that being a function of the level and style of consumption of humans, the quality of natural systems at the time, and the population size.

We still have a long way to go in convincing some people of this. Last year I was being interviewed by a member of the press for a story on California's population growth. "Tell me," he said, "does California have a carrying capacity?" "Of course," I responded, "but that is not a matter of my opinion, that is a biological fact." I pointed out to him that people might disagree about what California's carrying capacity for humans actually was, but I had no doubt at all that there certainly was one! I suspect he remained skeptical.

It is my opinion that the earth is probably well beyond its carrying capacity now. One device for generating a sense of the earth's carrying capacity is to list the countries one thinks could support populations twice their current numbers for the next 1,000 years. Assume, for the purpose of this exercise, that those population levels are reached within 100 years. If your sense of the world is anything like mine, your list will be very short. If it is, you believe the world is close to or beyond its carrying capacity.

Are any of these statements new? Not really. A decade ago, these same observations could have been made about the effect of population growth on riparian systems. Scientifically, little remains to be done except to document the degradation of natural resources that has occurred in the past ten years. This relative lack of "new" scientific research is another reason it is sometimes difficult to focus attention on population growth.

California might try to manage its riparian resources despite increasing population in a number of ways. Here are some theoretical examples. We could encourage a smaller fraction of the population to utilize the systems. Each person could, on the average, visit them less often. Californians could decide to visit other ecosystems (or use timber from other ecosystems). Or we could expand the number of riparian systems open for human recreation—or for timber production. However, this merely postpones the inevitable day of reckoning with growth. Already more than one million people are turned away annually from over-booked state campgrounds, whether riparian or not.

No, this will not be enough. A concerted effort over time to limit California's numbers must be part of all of our efforts to protect riparian systems.

This is not to assert that any particular resource "runs out" or becomes totally degraded overnight. To the contrary, change is most often gradual, as the choices and our future options become ever more limited.

Of course, achievement of zero population growth alone will not solve our problems. It will not by itself protect any ecosystem, preserve the quality of human life or the wellbeing of the economy. It is not a substitute for wise management and stewardship of resources, but it is an essential complement to and component of such management.

Analyzing Population's Effect on Riparian Systems

Before I tell you what has been done and what needs to be done, let me point out some dilemmas in analyzing the problem and developing solutions.

First, the local population in and around a riparian system is not self-regulating with respect to the carrying capacity of that system, because resources to sustain the population are imported from outside the system. For example, the number of people living near a riverbank is not related to the carrying capacity of that riverbank, because the population can bring in outside resources to satisfy its needs.

Second, the demands on a riparian system are not limited to the demands of the people living near it because resources produced by riparian systems are exported from the system. For example, agriculture responds to demands for goods from outside that system where the goods originate. According to the National Agricultural Lands Study, the harvest of one-third of the cropland in the United States is exported from the country (US Department of Agriculture and Council on Environmental Quality 1981).

Another example of this phenomenon is the National Forest Management Act, which calls for the Executive Branch to establish national targets for timber, wildlife, recreation, and wilderness. These are then apportioned to particular national forests and finally to particular ecosystems or parcels of land. This is not the kind of approach likely to match resource demands with the carrying capacities of natural systems.

Third, population growth comes from two sources, fertility and immigration. Fertility is only indirectly influenced by the public will, through social pressure and some government actions. Immigration is influenced directly only


40

at certain geographic levels, specifically, by national governments, and only very indirectly at lower levels such as states or communities. Regions wanting to slow or end their population increases have few strong legal foundations on which to do so.

Fourth, those most motivated to be aware of the problems of population growth in its biological diminsions are not the ones best situated to affect policy. It is not surprising that the political leader in California most sensitive to the problems of population growth is Huey Johnson, Secretary of the Resources Agency for the State—someone who has no jurisdiction whatsoever over those factors influencing fertility and migration.

Fifth, the effects of population are gradual and cumulative, just as the degradation of riparian systems is gradual. The expression "population bomb" is an inappropriate metaphor. In a particular crisis, population growth is never seen as the proximate cause and therefore is often ignored completely.

A fine discussion of this problem—population being overlooked as a causal factor—was contained in a recent editorial in "Science" by demographer Kingsley Davis (Davis 1981).

Seldom are public policies constrained only by scientific and engineering limitations; they are also limited, consciously and unconsciously, by social norms. Solutions to the energy problem, for example, usually take one of two forms: to conserve energy, or to increase or at least maintain the total supply . . . A third approach—stopping or reversing population growth—is seldom treated as a part of energy policy . . .

(S)topping or reversing population growth could play a major role in solving the energy problem. When we take into account the environmental problems that heroic efforts to increase the total energy supply will entail, or the human problems that reducing average per capita consumption throughout the world will bring, we conclude that population control is not only a desirable but also a necessary part of any effective energy policy. To "solve" the energy problem otherwise is like fixing a leaky roof by putting more containers on the floor . . .

(W)e still construe energy policy as producing or saving energy for however many people there are, not as producing fewer people so as to give each one as much energy as he or she needs . . .

Yet it is people who use energy. With fewer people, less energy is needed. This may seem obvious, but so far we have tragically postponed acting on it. . . .

My sixth, and final observation, is that the decisions which cause population growth, namely fertility and migration decisions, whether of individuals or governments, are virtually never seen as environmental decisions at all.

Fertility zxdecisions are matters of individual choice. Public policy aspects are the protection of those rights, ensuring (theoretically) that every child is a wanted child, and protecting the health of women and children.

Immigration decisions are made because the individual believes, in most cases correctly, that his or her life will be bettered by the move. Immigration policies are seen as labor policies, components of international relations, fulfillment of commitments to family reunification, and service to refugees.

Still further, migration within the country is seen as a response to economic growth or economic stagnation. Many cities in the Northeast or Midwest see their current population stability or decrease not as a welcome sign of balance but rather as a symptom of serious economic problems.

Response to These Dilemmas

One response to the problems posed by population growth, and a common one, is to try to "buy time". Journalist Hall Gilliam addressed the problem of "Finding Space for All the People".[4] He considered tradeoffs among population growth, urban open space (within cities and as farmland at the fringes), and density, and concluded that those concerned about environmental protection must endorse higher densities of housing. He then broadened his observations with a conclusion paralleling some of my own. To make it more relevant to this discussion, read "riparian system protection" where he uses "open space protection."

. . . (G)reater urban density is no guarantee that regional open-space lands will remain open, even with legal protection. Open-space laws can be changed, and if population pressure becomes intolerable, they will be.

That brings us to the unanswered question: How can unlimited population growth be accommodated in a limited area?

Probably the best we can do now is to buy time to find an answer. Meanwhile, we can house more people in existing urban areas, keep the farmlands intact

[4] Earthwatch column, San Francisco Sunday Examiner/Chronicle, August 30, 1981.


41

to feed the cities, and pray for insight.

I do not believe that "buying time" is all we can do. The evidence of the last decade is that much can be done to slow population growth, as indicated by these gains:

1) the establishment of Federal and state programs to fund family planning services;

2) the conclusion of the 1972 Commission on Population and the American Future that the nation should welcome and plan for an end to population growth (Commission on Population and the American Future 1972);

3) the 1973 Supreme Court decisions legalizing abortion throughout the country;

4) the rapid and continuing proliferation of movements to control growth in individual communities (whose motives range from the very best to the very worst);

5) the decrease in the number of children born to American couples and the decrease in the number of children they desire;

6) the turnaround in public attitudes towards population as evidenced by a 1977 Gallup poll that found 87% of those polled would rather that the US population not increase any more;

7) the increase in attention given to immigration as a source of half of our country's population growth.

In early 1981, a Governmental task force prepared recommendations for the (Carter) Administration on how to respond to the Global 2000 Report (US Council on Environmental Quality and Department of State 1980). The task force's findings included this recommendation (US Council on Environmental Quality and Department of State 1981):

Population growth in richer countries, though much slower (than in less developed countries), is of concern because consumption of resources per capita . . . is very much higher . . . The United States should develop a national population policy.

In fact, in 1974 then-Governor Reagan stated:

Our country . . . has a special obligation to work toward the stabilization of our own population so as to credibly lead other parts of the world toward population stabilization.

Recommendations

What is needed now is a way to articulate goals linking policies on fertility and immigration with the overall need to end population growth. We need a national population policy.

H.R. 907, introduced into the House of Representatives by Richard Ottinger of New York, declares a policy of comprehensive and coordinated planning for demographic change and establishes the goal of eventual stabilization of the population of the United States by voluntary means. The bill has been co-sponsored by more than two dozen representatives.[5]

Researchers, scientists, and managers of government programs to protect riparian systems do not have direct or indirect control of programs influencing the numbers of people in the country. They can, however, serve as a vital link between those who best understand why we need population stabilization, and those political leaders who can articulate such policies and bring zpg about. I offer as a model the policy statement issued by the Society of American Foresters:[6]

If human populations continue to increase substantially, insatiable demands on forestland resources will occur. The United States has the capacity to provide leadership in this global population challenge—as it has done in the conservation movement. Our legislative measures . . . have established a world standard. Yet these measures treat only the symptoms of uncontrolled population growth. This primary conservation issue has yet to be seriously addressed by the nation . . .

The best science and technology we can devise will not extricate us from the absolute limitations of the carrying capacity of our environment.

Therefore the Society of American Foresters supports a national policy of population stabilization and establishment of an office to coordinate its implementation. While recognizing that

[5] More recently, in October 1981, Senator Mark O. Hatfield of Oregon introduced S.B. 1771, the Global Resource, Environment, and Population Act of 1981. That bill, co-sponsored by Senators Alan Cranston (California), Charles Mathias (Maryland), Slade Gorton (Washington), and Spark Matsunaga (Hawaii), is a stronger version of H.R. 907.

[6] Excerpted from "Statement of the Society of American Foresters" submitted to the Subcommittee on Census and Population, Committee on Post Office and Civil Service, US House of Representatives, May 12, 1981, re: HR 907, to establish a national population policy and Office of Population Policy.


42

the technical aspects of such a policy are peripheral to the expertise of professional land managers, we also recognize that the long-term effectiveness of our management and conservation efforts depends on the resolution of this major domestic and global challenge.

In this context I wish to offer several recommendations. As scientists, managers, administrators, planners, and concerned public, you are in an advantageous position to define population problems and provide guidance in their solution.

First, professional organizations to which you belong should pass resolutions supporting population stabilization for the United States, endorsing the Ottinger and Hatfield bills or, if the latter is prohibited by your organization's tax status, calling for hearings on the two bills.

Second, you must continue to teach each new generation of Americans about the need to end population growth, because what is obvious to one generation may be forgotten by the next. Population education is not sex education, just as learning how to build, control, and put out a campfire is not the same as learning about the (positive and negative) effects of fire on forest ecosystems.

Third, you must expand research on the carrying capacity of particular ecosystems and on the concept of carrying capacity in general. It is important that you continually stress that "proper management" cannot possibly be enough; stabilization of the demands on a system must accompany management.

Fourth, use the language of goals. You need to say "when we reach zpg . . ." or "the ultimate population of this area will . . ." You must stress the tradeoffs between numbers of people and their consumption or lifestyles.

Fifth, in your professional lives, make recommendations for population stabilization. Raise this theme of the need for zpg in government service, on committees to which you belong, in reports you write to or for government agencies, and in testimony you prepare. Every time there is developed a set of recommendations for action, make sure action on population is among them. Remember that acknowledgment of the need for rapid achievement of zpg will come because those who think about resources point it out.

Sixth, take a public stand endorsing an end to population growth for the country and for the state. The latter is important because we experience the impacts of growth primarily at state and local levels. The former is important because immigration policy, critical in controling growth, is a national concern. Population policy therefore must be established at the national level.

And last, request that the State conduct an analysis of California's long-term carrying capacity, as has been suggested by Secretary of Resources Huey Johnson. You should also examine what the optimum population for California might be. The Resources Agency's report, "Investing for Prosperity" (California Resources Agency 1981), is an excellent model, having specific goals for enhancing California's resources by the year 2000. If only it had had a section on population goals for the state!

Overall, we must all use our commitment the protection of natural systems to be public leaders in making the link between our concerns and the need for population stabilization.

Conclusion

The problem of controlling California's growth, or that of any state, is a difficult because the state does not directly control migration across its borders. We in California much more than our share of foreign immigration to the country and our currently healthy economy attracts migrants from other states. To some extent we still need to take Hal Gilliam's advice to accommodate growth as best we can, thereby buying time to find a real solution.

In welcoming participants to the previously-mentioned conference on California's growth held in 1971, Bob Moretti, Speaker of the Assembly, stated that the Assembly was interested in developing:

. . . some aproaches to legislation which will influence state population growth and distribution. Even though the personal decisions of individuals will always govern where they live . . . I do not agree that we are powerless to influence them through legislation. . . . (F)ederal and state legislation in this field . . . has contributed significantly to changed attitudes and population distribution.

We can no longer accept the proposition that all growth is good. In fact the quality of our life and our economic well-being may in the future depend to a great extent on more effective management of growth. What we need to seek is a balance between our resources of air, water, and open space and our population growth.

These are tough problems, and we are not so naive as to believe that there are any simple answers. I believe, however, that unless we deal with them, our efforts to control smog, clean up our waters, and open spaces [and here one might add 'protect and enhance the


43

state's riparian systems'] will become mere stopgaps.

Mr. Moretti's comments are as true today as they were ten years ago when he said them.

Literature Cited

Almand, J.D., and W.B. Krohn. 1979. Position paper: the position of the Bureau of Land Management on the protection and management of riparian ecosystems. p. 359–361. In : R.R. Johnson and J.F. McCormack (tech. coord.). Strategies for protection and management of floodplain wetlands and other riparian ecosystems. [Callaway Gardens, Georgia, December 11–13, 1978]. 410 p. USDA Forest Service GTR-WO-12, Washington, D.C.

California Resources Agency. 1981. Investing for prosperity: enhancing California's resources to meet human and economic needs. California Resources Agency, Sacramento.

Commission on Population and the American Future. 1972. Population and the American future. Report of the Commission on Population Growth and the American Future. US Government Printing Office.

Davis, Kingsley. 1981. It is people who use energy. Science 211(4481):439.

Davis, K., and F.G. Styles (ed.). 1971. California's twenty million: research contributions to population policy. Population Monograph Series, No. 10. 349 p. Institute of International Studies, University of California, Berkeley.

US Council on Environmental Quality. 1978. The Ninth Annual Report of the Council on Environmental Quality. 599 p. US Government Printing Office, Washington, D.C.

US Council on Environmental Quality and the Department of State. 1980. The global 2000 report to the President: entering the Twenty-first Century. US Government Printing Office.

US Council on Environmental Quality and the Department of State. 1981. Global future: time to act. Report to the President on global resources, environment and population. US Government Printing Office.

US Department of Agriculture and Council on Environmental Quality. 1981. National agricultural lands study. US Government Printing Office.

USDA Forest Service. 1979. Report of a USDA Forest Service riparian study task force on riparian policies and practices in the National Forest system. 15 p. Unpublished manuscript.

Warner, R.E. 1979. California riparian study program. 177 p. California Department of Fish and Game, Planning Branch, Sacramento, Calif.


45

2—
STRUCTURE, STATUS, AND TRENDS IN THE CONDITION OF CALIFORNIA RIPARIAN SYSTEMS

figure


46

Summary of Riparian Vegetation Areal and Linear Extent Measurements from the Central Valley Riparian Mapping Project[1]

Edwin F. Katibah, Nicole E. Nedeff, and Kevin J. Dummer[2]

Abstract.—This paper summarizes the areal and linear extent measurements of riparian vegetation on the floor of the Central Valley of California, based on the maps produced by the Central Valley Riparian Mapping Project. Results are presented by riparian vegetation category for the applicable counties, and for the depositional bottomland or floor of the Central Valley as a whole.

Introduction

In 1978, the California Legislature, responding to the need for information on riparian resources in the state, appropriated $150,000 to the Department of Fish and Game (DFG) for a study of riparian resources in the Central Valley and California Desert (AB 3147, Fazio). A portion of this money was allocated for the mapping of riparian vegetation in the Central Valley.

In June, 1979, riparian mapping teams from the Geography Departments of California State University, Chico, and California State University, Fresno, completed mapping of the riparian vegetation on the floor of the Central Valley. The Department of Water Resources (DWR) made available 35mm. color slides of aerial photographs of those parts of the Central Valley (principally the irrigated and non-irrigated agricultural zones) for which it had photocoverage. Surrounding foothills and higher slopes were not included in the mapping project. The teams transferred riparian vegetation distributional data onto standard USDI Geological Survey (GS) 1:24,000 topographic quadrangle maps (quads). Riparian vegetation was mapped on fade-out blue copies or mylar overlays for each quad. A total of 465 individual map sheets, covering 388 unique quads, were compiled.

Area and Limits of Mapping Coverage

While the enabling legislation called for the study of Central Valley riparian resources up to the upper edge of the blue oak/digger pine zone (about 760 m. (2,500 ft.) elevation in the mountains surrounding the floor of the Central Valley) (Küchler 1977), only the depositional bottomlands of the Central Valley were mapped in this project. This was because the available DWR aerial photography was limited to those portions of the Central Valley where patterns of water use (principally agricultural) were being monitored.

Thus, the data on areal and linear extent reported here must not be construed either as the total amount of riparian vegetation for the entire Central Valley, which includes upland slopes as well as depositional bottomlands, or for the listed counties. As indicated in figure 1, only the depositional bottomland portions of the listed counties were mapped. As a result, summaries for Central Valley counties having only small amounts of depositional bottomlands (e.g., Nevada, Amador, Napa, Shasta) reflect only a small portion of these counties' total riparian resources.

Figure 1 indicates the actual mapping coverage by quad, within the relevant counties. Quads are identified by an index numbering system commonly used by California state agencies. A complete list of 388 individual quads, mapped for riparian vegetation, and the respective length and area measurements derived for each quad, are presented in the final report to DFG (Katibah, Nedeff, and Dummer 1980).

[1] Paper presented at the California Riparian Systems Conference. [University of California, Davis, September 17–19, 1981].

[2] Edwin F. Katibah is Associate Specialist, Remote Sensing Research Program, Department of Forestry and Resource Management, University of California, Berkeley. Nicole E. Nedeff is a Graduate Student, Department of Geography, and affiliated with the Remote Sensing Research Program, Department of Forestry and Resource Management, University of California, Berkeley. Kevin J. Dummer is Staff Research Associate, Remote Sensing Research Program, Department of Forestry and Resource Management, University of California, Berkeley.


47

figure

Figure l.
Locations of 1:24,000 quads in which riparian vegetation
was mapped. Quads only partially mapped are included.

Mapping Procedures

For the actual mapping of riparian vegetation, the teams used a physiognomic mapping category system, with vegetative life-form as the basic criterion: trees, shrubs, and herbaceous cover. These three basic lifeform categories were further refined by certain "modifiers", and by hybridizing the primary categories. Table 1 is a summary of the riparian mapping category codes developed by the mapping teams. The table does not include hybridized vegetation categories (i.e., R1/R2, R1/R3) developed and used by the teams. A more complete description of the riparian mapping project methodology may be found in Nelson and Nelson (1983).

 

Table l.—Summary of riparian vegetation mapping category codes (adapted from Central Valley Riparian Mapping Project 1979).

Code

Category and description

Rl—

Large woody vegetation.
Tall mature forests with significant woody understory.

Rlv*—

Valley oak woodland.
Mature, well-spaced stands of valley oaks (Quercus lobata ) without woody understory.

R2—

Low woody vegetation.
Low dense stands of young trees and shrubs.

R3—

Herbaceous vegetation.
Low herbaceous growth occurring along stream channels or in natural clearings among other riparian vegetation categories.

R3p*—

Perennial seeps.
Herbaceous vegetation occurring near perennial springs and seeps.

M—

Marsh.
Herbaceous emergent vegetation of perennially moist areas.

S—

Sandbars and gravelbars.
Exposed sand, gravel, or rock areas.

W—

Open water.
Standing or moving waters.

A—

Agricultural land.
Cultivated lands completely or nearly surrounded by riparian vegetation.

U—

Urban land.
Built-up areas nearly or completely surrounded by riparian vegetation.

c**—

Channelized.
Irrigation canals and highly channelized streamcourses so altered as to no longer show natural stream characteristics.

d**—

Disturbed.
Areas readily identified as severely altered by human activities.

i**—

Intermittent.
Used to designate spottiness or non-consistent occurrence of any given vegetation category.

* Subcategory
** Modifier

Central Valley Riparian Vegetation

Table 2 is presented to give the reader some idea of the actual plant species found within Central Valley riparian systems. Typical riparian trees and shrubs are listed, along with an indication of their relationship to the mapping category codes used in the project.


48
 

Table 2.—Riparian vegetation of the Central Valley, California (adapted from Roberts etal . 1977).

1. Typical native riparian trees (potential R1 when mature, R2 when young.

Acernegundo subsp.
      californicum

box elder

Aesculuscalifornica *

California buckeye

Alnusrhombifolia *

Sierra alder

Fraxinuslatifolia

Oregon ash

Juglanshindsii

black walnut

Platanusracemosa

California sycamore

Populusfremontii

Fremont cottonwood

Quercusagrifolia *

coast live oak

Quercuslobata

valley oak

Quercuswislizenii *

interior live oak

Salixgoodingii var. goodingii *

Gooding willow

Salixlaevigata

red willow

Salixlasiandra

Pacific willow

2. Typical riparian shrubs (potential R2).

Artemisiadouglasiana

mugwort

Atriplexlentiformis *

quail-bush

Baccharisdouglasii *

false-willow

Baccharisglutinosa *

seep-willow

Baccharisviminea

mulefat

Cephalanthusoccidentalis

button willow

Cornusglabrata *

brown dogwood

Cornusoccidentalis *

red osier dogwood

Heteromelesarbutifolia *

toyon

Hibiscuscalifornicus *

wild hibiscus

Lonicerainvolucrata *

twinberry honeysuckle

Nicotianaglauca ***

tree tobacco

Phylostachosbambosoides **

bamboo

Pteleacrenulata *

hop tree

Rosacalifornia

wild rose

Salixhindsiana

sandbar willow

Salixlasiolepis

arroyo willow

Salixmelanopsis

willow

Sambucusmexicana

elderberry

Symphoricarposrivularis

snowberry

Tamarixparviflora

tamarisk

3. Typical riparian vines (potential R2).

Aristolochiacalifornia

Dutchman's pipe vine

Clematislasiantha

wild clematis

Clematisligusticifolia

western clematis

Lonicerahispidula var.
      vacillans *

wild honeysuckle

Rhusdiversiloba

poison oak

Rubusdiscolor *

Himalayan blackberry

Rubusursinus

wild blackberry

Rubusvitifolius

wild blackberry

Similaxcalifornica

greenbrier

Vitiscalifornica

wild grape

* Uncommon
** Exotic

Measurement Methods

Upon completion of the Central Valley Riparian Mapping Project, the DFG contracted with the Remote Sensing Research Program, Department of Forestry and Resource Management, University of California, Berkeley, to calculate the lengths and areas of each category of riparian vegetation by individual quad and by county.

Riparian vegetation on each overlay for each quad, comprising a network of polygons and linear features (with representative mapping category codes), was measured using a flat bed digititizer.[3] The digitizer has a resolution of 1,000 points per inch and 1,000,000 points per square inch. Areas and lengths of riparian vegetation were calculated in digitizing units and converted to acres and miles, as appropriate. At a map scale of 1:24,000, the digitizer conversion factors were:

lines:

figure

areas:

figure

Results

The riparian length and area results were tabulated by county and by quad overlay. An example of the county riparian vgetation tabulations is presented in figure 2. The complete set can be found in Katibah etal . (1980). In virtually all cases, the applicable counties did not have complete mapping coverage (see figure 1).

Table 3 gives an aggregated summary of the riparian vegetation mapping category measurements for the entire mapped portion of the Central Valley study area. Mapping categories were consolidated by combining all hybridized categories by their principal components (e.g., R1/R2 and R1/R3 would be included in the aggregated category R1 hybrid). Also included in the hybridized categories were categories where the modifiers "c", "d", and "i" were combined with a major riparian vegetation category (e.g., R3d would be included in R3 hybrid). The "miscellaneous" category refers to categories where the principal component in a hybridized category does not represent riparian vegetation (e.g., M/R3, where M designates marsh). Additionally, categories for valley oak are given under the codes R1v and R1v hybrid, even though this is a subcategory.

[3] Talos Series 6000 high resolution digitizer.


49
 

Table 3.—Aggregated summary, by category, of area and length measurements for Central Valley depositional bottomland riparian vegetation.

Code

  ha. (ac.)

       km. (mi.)

R1

  20,725

   773

 

(51,191)

       (480)

R1 hybrid

18,157

1,248

 

(44,849)

          (775)

Rlv

9,204

   151

 

(22,734)

           (94)

Rlv hybrid

1,294

   227

 

(3,195)

       (141)

R2

5,341

  683

 

(13,193)

       (424)

R2 hybrid

10,256

1,315

 

(25,332)

       (817)

R3

14,737

   369

 

(36,400)

       (229)

R3 hybrid

8,168

  214

 

(20,174)

       (133)

Miscellaneous

5,882

    55

 

(14,528)

         (34)

Total

 

5,035

 

(231,596)

    (3,127)

figure

Figure 2.
Example of a county summary tabulation for
bottomland floodplain, riparian and aquatic wetlands.

Authors' Note

The results presented in this paper are based on a report submitted to the DFG (Katibah, Nedeff, and Dummer 1980). This report, containing more detailed information than is presented here, is filed with the original riparian vegetation maps (compiled by the Central Valley Riparian Mapping Project) at the California Natural Diversity Data Base, DFG, Sacramento.

Literature Cited

Central Valley Riparian Mapping Project. 1979. Interpretation and mapping systems. Report prepared by the Riparian Mapping Team, Geography Department, California State University, Chico, in cooperation with the Department of Geography, California State University, Fresno. 24 p. California Department of Fish and Game, Planning Branch. Unpublished manuscript.

Katibah, Edwin F., Nicole E. Nedeff, and Kevin J. Dummer. 1980. Areal and linear extent of riparian vegetation in the Central Valley of California. Final report to the California Department of Fish and Game, Planning Branch. Remote Sensing Research Program, Department of Forestry and Resource Management, University of California, Berkeley.


50

Küchler, A.W. 1977. Map of the natural vegetation of California. 1:1,000,000 + 31 p. A.W. Küchler. Department of Geography, University of Kansas, Lawrence.

Nelson, C.W., and J.R. Nelson. 1983. The Central Valley riparian mapping project. In : R.E. Warner and K.M. Hendrix (ed.). California Riparian Systems. [University of California, Davis, September 17–19, 1981]. University of California Press, Berkeley.

Roberts, W.G., J.G. Howe, and J. Major. 1977. A survey of riparian forest flora and fauna in California. p. 3–19. In : A. Sands (ed.). Riparian forests of California: their ecology and conservation. Institute of Ecology Pub. No. 15. 121 p. University of California, Davis.


51

An Historical Overview of the Sacramento River[1]

Lauren B. Scott and Sandra K. Marquiss[2]

Abstract.—This paper summarizes an analysis of two aspects of the history of the Sacramento River: the fluvial process; and man's development of the floodplain over the last 130 years. The analysis was made to trace the origins of problems—seepage, loss of riparian vegetation, and limited public access—occurring in the riparian zone, and to establish a perspective from which to study these problems. Significant historical aspects of these problems must be considered in a comprehensive study of the river.

Introduction

This paper presents an historical overview of the Sacramento River, shown in figure 1, to trace the origins of some of the problems occurring in its riparian zone, and to provide a perspective from which these problems can best be studied. The overview focuses on: 1) the fluvial process of the river itself, and 2) the principal activities of man over the last 130 years which have affected the river.

The Sacramento River has played a significant role in the history of the Central Valley and the State. The first humans occupying northern California chose to live along the banks of the Sacramento River as did later settlers who populated the floodplain, reclaiming the river's lands and diverting its waters. Today the river continues to provide a means of sustenance to the people of the Valley and the State.

Except for the lower reaches of the Mississippi River and certain reaches of the Columbia and Ohio Rivers, the floodwaters of the Sacramento River are greater than those of any other river in the United States. The river system, when combined with the runoff from the north and coastal areas, accounts for 70% of the State's total water production (US Army Corps of Engineers 1978). The water is used for irrigation, power, and municipal and industrial needs. The river itself is a navigation route, an increasingly important recreation resource, particularly near heavily urbanized areas, and a haven for numerous species of fish and wildlife which depend on its waters and the riparian system along its banks to survive.

Long before man came in contact with the river, natural processes that develop and shape rivers were creating the Sacramento River man would have to live with when he entered the Valley. The problems that we struggle with today have their roots in the early, pre-settlement development of the river.

Over the last 130 years, dams, dikes, levees, drainage works, bypasses and bank protection systems have been built to control the river and to protect people living in the floodplain. These facilities, often built years apart, to varying standards, and for different purposes, have greatly altered the river system. Built to solve a variety of problems, they created other problems. Among these problems are seepage of river water into adjacent agricultural lands, loss of riparian vegetation to urban and agricultural encroachment, and restriction of public access to the river. The many uses of the river have also resulted in diverse and sometimes conflicting views on how and by whom these problems should be resolved and how future development of the river should or should not proceed.

The overview presented here identifies significant historical aspects of these problems showing how the changes inherent in the fluvial process itself, together with the changes caused by man, have resulted in the river as we know it today.

Fluvial Morphology

Fluvial morphology can be defined as the science of the forms created by the action of flowing water (Lane 1955). The relationships among the many factors operating in this process are complicated and not completely understood. Two concepts from fluvial morphology—equilibrium and evolutionary development of rivers—have been chosen to show the importance of the fluvial process in understanding some of the problems of the Sacramento River.

[1] Paper presented at the California Riparian Systems Conference. [University of California, Davis, September 17–19, 1981].

[2] Lauren B. Scott is a Civil Engineer, and Sandra K. Marquiss is a Technical Writer-Editor, USDI Bureau of Reclamation, Sacramento, Calif.


52

figure

Figure l.
Location map.

Equilibrium

Alluvial rivers are among the most dynamic of all geomorphic forms. All changes in the river, however, whether occurring over geologic eons, or within a human lifetime, are governed by the principle of equilibrium; that is, although the river continually changes, only those changes leading to equilibrium, or stability, persist (Maddock 1976).

The principle of equilibrium is based on the assumption that all variables influencing the form of a river are interrelated in such a way as to represent a predictable system (Leopold and Maddock 1953). Since morphology and form of a river are primarily determined by the nature and quantity of sediment and water moving through the channel, the river's configuration is the result of a relationship among four variables: quantity of sediments, size of sediments, water discharge, and channel slope. The relationship among these variables is expressed as

figure
. By the theory of equilibrium, changes in any one of these variables will be compensated for by corresponding changes in the other three, thus tending to change toward stability. For example, a decrease in sediment load is compensated for by a decrease in water discharge or slope, or by an increase in the sediment diameter.

A result of the dynamic properties of the fluvial process operating on a portion of the Sacramento River is illustrated in figure 2, which shows the configuration of the Sacramento River in 1874 and again in 1974. Some of the changes are notable: for example, the creation of a slough.

Evolutionary Development of Rivers

The variables of the fluvial process working to create a river valley have been characterized by some geomorphologists as an evolutionary process, a progression from youth to old age. There is no sharp division between the ages and no general agreement as to when one age ends and another begins (Johnson 1932).

By the time a river is old, as is the Sacramento River, the features of its valley are well developed and distinct. In the case of the Sacramento, floodplains are wide with low relief, and the river follows a broad, meandering course. Its channel is graded; that is, its energy and slope are just sufficient to carry away the material delivered to it from the uplands. Natural levees occur along its banks, with low-lying poorly drained swamp areas or flood basins on either side (Simmons and Senturk 1977). Two of these features—natural levees and meandering—are keys to not only understanding problems along the river but formulating their solutions.

Natural levees are the result of repeated overflows of sediment-laden river water onto adjacent lands, and occur where the valley slope is lowest and the duration of overbank flow is highest. The coarse, sandy material deposited close to the channel gradually builds up forming broad slopes which fall gently away from the river. Because they are comprised of coarse sediment, these levees are extremely porous and transmit water readily.

Natural levees along the Sacramento River occur discontinuously from Red Bluff downstream, and are most extensively developed in the river's middle reach from Ord Ferry to Sacramento. This is the same reach where the most extensive seepage problems occur. Here the river has adjusted to the lower slope of the Valley floor by annually overflowing its banks and emptying its water into the adjacent lateral flood basins. Near the city of Sacramento, levee heights range from 3.0–4.6 m. (10–15 ft.) above the adjacent low basin lands. Levee widths range from 3.2–4.8 km. (2–3 mi.).

Another important feature of the Sacramento River is its meandering. Meandering results from the constant and sometimes rapid changes in the form of a river and is the configuration taken by most alluvial rivers.

Meandering is thought to be caused by the direction of currents in the channel. These currents, in essence, cause a constant process of erosion of the riverbank and deposition of this


53

figure

Figure 2.
Sacramento River, 1874 and 1974 (from Brice 1977).

material at a point farther downstream. The material deposited downstream accumulates as a point bar which builds out from the bank, constricting the channel and subsequently forcing the channel to move in a lateral direction. In such a way meander loops are thought to form and "move," or migrate down the valley (Simmons and Senturk 1977). The loops move unequally however, and may occasionally be cut off and abandoned as the river changes its course.

When acutoff occurs, the part of the river bypassed forms an oxbow lake, which gradually begins to fill in with sediment. The lower end of the oxbow, receiving the relatively impermeable finer silts and clays, eventually forms what is, in effect, a clay plug between the old meander loop and the main channel. Because of its impermeability this plug is essentially a semipermanent geologic control which can affect river geometry. Natural levees deposited from overflow and point bar, oxbow, and alluvial deposits laid down in meandering create complex soil structures along the river. It is through these soils that groundwater flows between the mountains and the river. Some deposits are very permeable and transmit water readily; others are impermeable, but influence the possible directions, horizontal and vertical, that water can travel.

A major factor in the fluvial process is the interrelation of all reaches of an alluvial river. Although specific changes in a river may originally be local, the effects of the changes can extend to all parts of the river (Burkham 1981). This characteristic is important when assessing the impact of man's activities on a river basin. Since the effects of a development on the river cannot be isolated to the reach in which it occurs, the net result of any change can be a greater departure, along the whole river, from equilibrium than that which was originally present.

Development of the Sacramento River by Man

Beginning with the discovery of gold at Coloma on the American River in 1848, man became another variable in the fluvial process. Principal activities of man affecting the river were urban settlement and agricultural development on the floodplain, and hydraulic mining of the surrounding foothills. The combined effect of these activities on the regime of the river was profound and far-reaching; the problemns of seepage, loss of riparian vegetation, and restricted public fishing access may be cited as consequences. The effects of hydraulic mining were so immediate and so drastic as to influence the course of all other development on the floodplain.

Hydraulic Mining

Hydraulic mining began in 1852 with the discovery that water under pressure could easily and economically remove the layers of lava and sediment covering the gold deposited in the ancient stream channels of the Sierra Nevada. Eventually, giant machines operated from considerable distances could tear apart a bank several hundred feet high in a very short time.


54

The machines that removed gold from the hills deposited millions of tons of silt and gravel in the nearby streams. Erosion that would have occurred naturally over hundreds of years occurred literally overnight. In one analysis of the amount of sediment in the rivers resulting from hydraulic mining, it was concluded that the 35 years of hydraulic mining tripled for about 100 years the average annual amount of sediment passed from the Sacramento Basin into San Francisco Bay under natural condititons. Over 1,000,000 acre-feet of debris has been deposited throughout the valley or passed into the Bay.[3]

The effect on the valley below was enormous. As river channels filled with more and more debris, the rivers rose. It is estimated that in some reaches the elevations of the Sacramento, Feather, Yuba, Bear, and American Rivers, the rivers most affected by sediment deposition, rose as much as 6 m. (20 ft.) (State of California 1978). With higher streambeds, capacities to carry water were greatly diminished. During a series of floods in 1861–62, 1875, and 1878, the debris washed out of the mountains and into the streams. The rivers overflowed their banks, inundating farms and homes with muddy polluted water.

By 1880, fertile land lost to hydraulic mining totaled more than 17,400 ha. (43,000 ac.).[4] The State Engineer, speaking to the State Legislature in 1880, described the effect of debris on farmland adjacent to the Yuba and Bear Rivers:

. . . the bottom lands were submerged . . . with sand and clay sediment, to such depths that in places orchards, gardens fields, and dwellings were buried from sight . . . and the course of the devastating flood was marked out by broad commons of slimes and sands.[3]

Antagonism between farmers and miners grew, culminating in a series of suits filed against the mining companies, in which the farmers at first sought damages, and eventually sought the complete abolition of hydraulic mining. In 1884, the State Supreme Court in the case of Woodruff v. North Bloomfield etal . prohibited the discharge of any mining debris into the streams. This decision, known as the Sawyer Decision, ended hydraulic mining.

The most adverse effects of hydraulic mining were on the rivers. Debris had choked and clogged some channels and completely obliterated others. With their equilibria destroyed, the rivers readjusted by overtopping their banks, depositing large quantities of debris in the valleys and carrying the remainder to San Francisco Bay.

Transport of the debris from hydraulic mining downstream took many years. Fluctuations in the low water levels, or streambed elevations, for the mouth of the Yuba River at Marysville and for the Sacramento River at Sacramento, shown in figure 3, indicate the length of time, depth of deposition of mining debris in riverbeds, and rate of erosion back to original stream elevations. The changes illustrated for the Yuba and Sacramento Rivers would occur in a similar manner in other streams in the Sacramento River system which experienced hydraulic mining.

Although the bed of the Sacramento River returned to its original elevation, the plan view of the river was permanently altered. Before the river established a new pattern of stability, dams and levees were built to control floods.

Development of the Floodplain

One of the most important impacts of hydraulic mining on the Valley came when mining was stopped. By the late 1800's development of the Valley's resources had come to an impasse. The interests of farming and mining appeared incompatible; one could continue only at the expense of the other. The Sawyer Decision in 1884, which ended the hydraulic mining era, signaled the beginning of the agricultural era, and also determined the course of future development of the Sacramento River. With the growth of agriculture and commerce as the Valley's principal economic activities, the Sacramento River system would be extensively developed for irrigation supplies and for flood control.

Urban settlement of the floodplain began with the Gold Rush and was concentrated around the city of Sacramento. The city's population of about 150 in 1848 exploded to 12,000 by 1852 (Sacramento Magazine 1976). With its favorable location at the juncture of the American and Sacramento Rivers, the city was an important port and supply center, linking the coast and the city of San Francisco with the goldfields. Upstream, the city of Marysville, also at the juncture of two rivers—the Feather and the Yuba—was another population center in the Valley.

In the decade following the Gold Rush many settlers turned to farming, and within a few years agriculture had become the principal use of land in the Valley. Agricultural development began on the natural levees, called rimlands

[3] Jones, G.H. January, 1967. Alteration of the regimen of the Sacramento River and tributary streams attributable to engineering activities during the past 116 years. Prepared for the Historical Records of Sacramento Sector, American Society of Civil Engineers.

[4] Hagwood, J.J. 1970. From North Bloomfield to North Fork: attempts to comply with the Sawyer Decision. Unpublished draft thesis for completion of Master of Arts degree, California State University, Sacramento.


55

figure

Figure 3.
Changes in bed elevation for portions of the Yuba and Sacramento Rivers, 1850–1950 (from G.H. Jones4  ).

because of their higher locations, which supported dense stands of riparian forests. It is estimated that in 1842, nearly 324,000 ha. (800,000 ac.) along the Sacramento River were forested, sometimes extending 8 km. (5 mi.) from the river.[5]

After the rimlands, the overflow, or tule. lands, comprising approximately 200,000 ha. (500,000 ac.) were developed (State of California 1976). Impetus for large-scale reclamation of the tule lands came in 1850 when the passage of the Arkansas Act transferred ownership of all such swamp and overflow lands from the Federal Government to the State on the condition that the lands be drained. The State in turn made these lands available for private ownership on the same condition of reclamation. This conditional transfer of ownership is significant because it determined that much of the land along the river would be used for agriculture and that ownership would be private, which has resulted in the problem of restricted public access to the river.

Levee Construction

As tule lands were reclaimed, the number of towns and farms increased, as did the need for flood protection. During very large storms the volume of water delivered to the river could be from four to eight times greater than the capacity of the channel, depending on the section of the river. The Sacramento River, particularly in its middle reaches over the flat valley floor, could not contain the volumes of water resulting from winter storms and spring runoff, and overflowed its banks almost annually. In the lower portion of the river the severity of these floods was amplified during the hydraulic mining period. For much of the year the floodplain was an inland sea, as vast quantities of water moved slowly down the valley through the flood basins to reenter the river in its lower reaches.[4]

At first, levees were constructd piecemeal by individuals or small groups with little or no consideration given to the effects on other areas along the river or the natural tendency of the river to meander. Natural drainage boundaries were ignored, with the result that some natural drains were closed off and marshes created in places which had previously been welldrained. Levee wars began as landowners on one side of the river raised their levees to force the floodwaters onto the opposite side of the river.

[5] Michny, F. 1980. Causes for the loss of riparian forest along the Sacramento River. Unpublished report. USDI Fish and Wildlife Service.


56

The configuration of the river changed rapidly and radically. Some levees eventually measured 7.6 m. (25 ft.) high and 61 m. (200 ft.) wide at the base. As levees were built higher, the water levels rose higher, and water that had previously overflowed into natural flood basins was now confined to a channel between the levees. As a result, during floods, the surface of the river water was often well above the level of the surrounding land.

Levee construction was accelerated when debris from hydraulic mining raised the riverbeds, decreasing the capacities of the river channels, including the Sacramento, which even under natural conditions could not contain its floodwaters. By the 1870's the beds of the Yuba and the Feather Rivers, tributaries to the Sacramento River, were higher than the town of Marysville, whose citizens responded by building better and even higher levees to protect the city. The city of Sacramento, inundated by a series of floods during the 1850's and 1860's, had by 1870 literally been raised by as much as 3.8 m. (12 ft.) to prevent future flooding of the city (Sacramento Magazine 1976).

Ultimately, efforts by individuals and small reclamation districts to prevent extensive flooding were ineffective. As the century closed, the complications from mining debris, a series of floods, and the inefficient and, in some cases, even detrimental levee system amply demonstrated the need for a Valley-wide flood control system.

Flood Control

The first centralized flood control plan was the Sacramento River Flood Control Project, formulated by the California Debris Commission. This project in essence rearranged the landscape to allow the river to revert to its natural regime during floods. The changes in regime enabled floodwaters overflowing into the adjacent flood basins to be conveyed slowly down the valley and returned back into the river in its lower reaches.

Authorized in 1914, the project was essentially in place in 1944 and is now about 90% complete. From the Sacramento River, water flows east into Butte Basin, thence to Sutter Bypass where it flows across the river into Yolo Basin, then through Yolo Bypass back into the river.

Foundation and composition of the man-made levees are part of the seepage problem. Man-made levees were built on top of the natural levees which were extremely porous. For economic reasons, the levees were often constructed from soils adjacent to or within the channel. These coarse, silty soils, which were deposited on the natural levees, were also extremely porous.

Levee construction and reclamation of levee lands destroyed large amounts of riparian vegetation and began the conversion of riparian lands to croplands which continues today. Levee systems often evolve into bank protection systems. This results in further loss of vegetation because the use of riprap and rock revetment to control erosion requires stripping the land of vegetation.

The Central Valley and State Water Projects

The Central Valley Project, begun in the 1940's, and the State Water Project, begun in 1960, were also constructed as part of the Valley-wide flood control system. Their purpose was in part to alleviate the imbalance in water supply between the northern and southern parts of the State. Both projects store and transfer water from the north to the central and southern parts of the State for irrigation and domestic use. The Sacramento River and its tributaries are the principal conveyors of this water to collection points in the Delta, where it is distributed south by a series of canals and holding reservoirs.

Key features of the Central Valley Project are Shasta Dam and Reservoir, which are operated for flood control and which modify the flow of the entire river downstream from the dam. Overall, this development has resulted in substantially higher summer flows, and intensified problems of erosion and sediment deposition. Because of the high flows, the streambanks never dry out and are more susceptible to erosion. Substantial amounts of sediment formerly deposited in flood basins are now deposited in the downstream overflow and bypass areas adjacent to the river and in the navigation and flood control channels.

Conclusions

This historical overview of the river points up two conditions as the basis for seepage, loss of riparian vegetation, and limited public access along the river. These conditions are: a) the location, composition, and foundation of flood control levees, resulting both from fluvial morphology and the activities of man; and b) the nature of land ownership and control along the river, laid out by the Arkansas Act.

Seepage problems were an inevitable consequence of agricultural development of levee lands and construction of man-made levees on top of the natural ones. Permeable complex soils deposited along the river are a major part of the problem. And although the impermeable deposits do not transmit water, they do influence the direction the seepage water can flow.

Construction of levees began and then accelerated the conversion of riparian lands to croplands. The riparian vegetation which remains today is essentially limited to thin strands along the river.


57

Land ownership patterns are directly related to both the loss and preservation of riparian vegetation, and directly affect the most popular recreational use of the river—fishing. Public access for recreation in general and fishing in particular is very limited and in some reaches almost nonexistent, a problem which will become more acute in the future.

A final value of an historical overview is the awareness of a continuing theme in the river's development—that of perspective. The levee building of the late 1800's was the result of piecemeal solutions to what was a Valley-wide problem of flooding. The broad and unified planning approach ultimately required to solve the flooding problem, is required again today to study the problems existing in the riparian zone. The fragmentary nature of land use and ownership patterns along the river has resulted in the creation of several publics, each competing to control some aspect of the river. Agreement on a common perspective of the river is difficult to achieve.

An overview suggests that an agreement on such a perspective could begin with the recognition that the river at any given time is the result of a continuing process among interrelated variables, of which the activities of man is but one. Planning from this point of view would seek to reinforce the natural tendency of the river toward equilibrium, and hence offer more satisfactory solutions to problems existing in the riparian zone.

Literature Cited

Brice, James. 1977. Lateral migration of the middle Sacramento River, California. USDI Geological Survey, Water Resources Investigations 77–43. Menlo Park, Calif.

Burkham, D.E. 1981. Uncertainties resulting from changes in river form. J. Hydraulics Division, Proceedings of American Society of Civil Engineers 107(HY5):593–610

California Department of Water Resources. 1955. Report to the Water Project Authority on seepage conditions in the Sacramento Valley.

California Resources Agency. 1978. Sacramento River Environmental Atlas. Prepared by the Upper Sacramento River Task Force for the California Resources Agency. Sacramento, Calif.

Johnson, Douglas. 1932. Streams and their significance. p. 78–96. In : S.A. Schumm (ed.). Benchmark papers in geology: river morphology. Dowden, Hutchinson, and Ross, Inc., Pennsylvania.

Lane, E.W. 1955. The importance of fluvial morphology in hydraulic engineering. p. 180–201. In : S.A. Schumm (ed.). Benchmark papers in geology: river morphology. Dowden, Hutchinson, and Ross, Inc., Pennsylvania.

Leopold, L.B., and T. Maddock, Jr. 1955. The hydraulic geometry of stream channels and some physiographic implications. USDI Geological Survey Professional Paper 252.

Maddock, T., Jr. 1976. A primer on floodplain dynamics and water conservation. J. Soil and Water Conservation 31(2):44–47.

Sacramento Magazine. 1976. Special Bicentennial issue. p. 21–25. July–August, 1976.

Simmons, D.B., and Fuat Senturk. 1977. Sediment transport technology. Water Resources Publication, Fort Collins, Colorado.

U.S. Army Corps of Engineers. 1978. Reconnaissance report on Sacramento River and tributaries bank protection and erosion control investigation, California. U.S. Army Corps of Engineers, Sacramento District, Sacramento, Calif.


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Regeneration of Riparian Forests of the Central Valley[1]

Jan Strahan[2]

Abstract.—Riparian forests of the Sacramento River have an overstory and a regeneration pattern corresponding to the successional stage and fluvial landform associated with the forest stands. Cottonwood/willow forests form initially on gravelbars. With development of the floodplain and maturation of the forest, other species enter. Floodplain forest regeneration is primarily box elder, black walnut, and valley oak with few sycamore and ash. Riverside floodplain forests differ from oxbow lake forests in species diversity, density, and reproduction. Land use and water development projects alter fluvial landforms and fluvial events to create changes in forest composition and regeneration.

Introduction

Riparian systems provide an excellent opportunity to study the effects of landform and fluvial processes on vegetation distribution and forest regeneration. Erosion, deposition, and lateral channel migration regulate both the distribution and development of vegetation in the riparian zone. With continual changes in landforms as a result of seasonal and catastrophic fluvial events, vegetation dynamics remain in a state of "perpetual succession" (Campbell and Green 1968).

The generalized patterns of vegetation zonation resulting from fluvial processes have been described and illustrated by Conard etal . (1977) for the Sacramento Valley region. The Sacramento River Atlas (Upper Sacramento River Task Force 1978) illustrates the pattern of zonation as well as the successional stages found in riparian forests. McGill (1975, 1979) has also correlated the existing riparian vegetation with fluvial landforms. Gaines (1974) has noted that the more extensive remaining riparian forests occur on islands, along bends in the river, and adjacent to oxbow lakes and other areas subject to flooding. As such, the remaining forests are a result of the most dynamic interplay between the fluvial system and riparian vegetation.

Objectives

The primary objective of this study was to develop regeneration data for the dominant tree species in the riparian forests of the Sacramento River. The information compiled can be used to assess present conditions and future trends of the forests. Work by Conard etal . (1977) and Michny etal . (1975) illustrates the variety of plant community structure and composition encountered in the riparian zone. Recognizing this, information was gathered at two levels to gain a more comprehensive picture of the structure and composition than previously developed. A detailed quantitative study was undertaken at three sites near Princeton, Glenn County, where disturbance to the fluvial system and vegetation is relatively minimal. At these sites, regeneration was examined relative to landform in different successional stages: a young forest (less than 30 years) associated with a gravelbar; an established forest (less than 70 years) located on the floodplain along the current river channel; and a mature forest (greater than 85 years) adjacent to an oxbow lake. To understand the larger patterns occurring along the length of the river, a broad survey of the river as a fluvial system was undertaken. This survey relates the effects of land use and water resource development projects to regeneration potential and stand development. The survey included a review of the geomorphic and ecological literature as well as air and ground reconnaissance.

Methods

Floodplain vegetation was sampled using the point-centered quarter method of Cottam and Curtis (1956). Transects were located perpendicular to the water course at 50-m. intervals.

[1] Paper presented at the California Riparian Systems Conference. [University of California, Davis, September 17–19, 1981].

[2] Jan Strahan is a Graduate Student, Wildland Resource Science, Department of Forestry and Resource Management, University of California, Berkeley.


59

Points were centered at 10-m. intervals. At each point-center a 1-m. circular plot was used to tally the number of tree seedlings by species and a 10-m2 circular plot was used for saplings. Seedlings were defined as having become established this season, and saplings were classed as other size-classes less than 10-cm. diameter-at-breast-height (DBH). Saplings were further classified into seven size-classes: (1) less than 0.3-cm.; (2) 0.3- to 1-cm.; (3) 1- to 1.5-cm.; (4) 1.6- to 2.4-cm.; (5) 2.5- to 5-cm.; (6) 5- to 7.5-cm.; and (7) 7.5- to 10-cm. Vegetative reproduction was not distinguished from seed reproduction as part of this tabulation, but was recorded wherever observed. Composition and cover of the shrubs and groundcover were also recorded. On gravelbars, seedling establishment was sampled through the use of 1-m2 plots. Five-m. by 20-m. belt transects were used in the young forests on gravelbars and for levee sampling.

Physiography

Fluvial processes result in a number of characteristic landforms. Floods contribute to overbank deposition and aid in the building of floodplains. Lateral channel migration results in progressively building point bars which account for much of the existing natural topography of the Sacramento River riparian zone (Leopold 1973; Brice 1977). A cross-section through the riparian zone may have the following landforms: cut bank, point bar, natural levee, floodplain, oxbow lakes, meander scars, and islands. Variable surface features occur on these landforms, depending on the type of aggradation and frequency of flooding. The microtopography of the floodplain, consisting of ridges and swales, was formed by flows of old channels and is periodically altered by flood channel flows (Nanson and Beach 1977). These slight variations in elevation lead to considerable differences in soils and drainage conditions which provide the opportunity for tree species with different flood tolerances to occupy different elevations of the floodplains (Hosner and Minckler 1960). Vegetation, once established, also plays an active role in the depositional environment by acting as a sediment collector. Erosional bowls frequently form around trees and shrubs in the active channel.

Distinct landform changes occur in the downvalley progression of the Sacramento River. Brice (1977) describes the following features which change in the reach between Chico Landing and Colusa. As with most rivers, there is a downward progression in gravel size as one moves downvalley. The Sacramento River is classified as a gravel-bed stream from Red Bluff to Glenn. Below Glenn, it is a sand-bed stream. (Note: This shift was noted by Bryan in 1923, prior to the construction of Shasta Dam.)

Natural levees are composed of coarser materials deposited as floods flowed over the top of channel banks. Beginning at Hamilton City, the levees form a strip 4.8 to 8 km. (3 to 5 mi.) wide between Hamilton City and Colusa. Levees are discontinuous for several miles south of Stony Creek and continuous from near Butte City southward.

Brice (1977) also reviews the changes in the river which have occurred since white settlement, using the "natural" river of 1870 as a baseline. According to Brice, channel sinuosity has decreased while channel width has increased. Morphologic changes have been attributed to both clearing of riparian vegetation and the effect of levees in reducing overflow areas. These changes have caused the main river channel to be scoured deeper and wider and water velocities to increase. Meander loops from Butte City to Colusa are confined by artificial levees and tend to be distorted and unstable. Flow regulation by Shasta Dam has resulted in an increase in mean monthly flows at Red Bluff for June, July, and August from 6,190 ft3 /sec. (1889 to 1944) to 10,520 ft3 /sec. (1945 to 1970). Maximum observed flood peaks at Red Bluff before regulation attained about 250,000 ft3 /sec. with subsequent peaks of 140,000 ft3 /sec.

The California State Department of Water Resources (McGill 1979) identified 29,352 ha. of riparian zone from Butte Creek to Keswick Dam in 1977. This includes 3,828 ha. high terrace riparian vegetation (rarely flooded), 3,395 ha. low terrace (frequently flooded), 2,096 ha. gravelbars, 162 ha. oxbow lakes, and 3,942 ha. water surface, for a total of 13,423 ha. undeveloped lands. Agricultural lands comprise 14,852 ha. of the zone and 1,097 ha. are in other developed uses. Of particular significance in this study is the reduction of high terrace lands by 15% in the five years between 1972 and 1977, mostly through agricultural conversion. Erosional losses from bank undercutting are not concurrently offset by building processes.

These variations in physiography have major ecological significance in the riparian zone. Lindsey etal . (1961) attributed the different plant communities to the differences in soil-water relationships resulting from physiographic variation. The amount of floodplain activity and influence of the river on landforms results in different degrees of community stability. Wilson (1970) found stabilized forest communities developed along the Missouri River floodplain after the river had been stabilized by a series of dams and reservoirs. Campbell and Green (1968) link "perpetual succession" to rivers which actively meander over their floodplains. They found the frequent shifting of landforms and channels resulted in early successional stages occupying the majority of the floodplain. Everitt (1968) and Fonda (1974) attributed spatial distribution of the riparian plant communities primarily to the meandering pattern of the river.

Along the Sacramento River, physiographic variation was sampled through the use of transects perpendicular to the river. The three main


60

landform categories sampled were: gravelbar, floodplain adjacent to the riverside, and floodplain adjacent to oxbow lakes. These three categories are representative of a sequence of landform and soil development which led to progressively older forests with distance away from the channel.

Forest Establishment and Composition

Establishment and distribution of species in riparian forests is controlled by the interaction between fluvial events and ecological requirements of the species.

Fluvial Processes

The water regime of the river influences distribution through both seasonal fluctuations and catastrophic occurrences (Sigafoos 1964; Bell and Johnson 1974). Both the low-flow regime and high flows or floods causing inundation influence distribution. The low-flow regime, which provides freshly exposed surfaces, is the most important factor for successful seedling establishment and is critical for survival of young trees.

Whether the result of flooding is an adverse or beneficial effect on the plant is dependent on the frequency, duration, and depth of inundation (Teskey and Hinckley 1978). Susceptibility to flooding affects species location on the floodplain relative to the height of the water table. Tolerance to flooding may also vary between young and old trees of the same species (Lindsey etal . 1961). Inundation may result in the death of young or established plants through mechanical abrasion or through lack of sufficient soil oxygen. For established dormant plants, floods deposit soil nutrients necessary to maintain high productivity rates (Johnson etal . 1976). Time between major disturbances determines the amount of forest stands that will be in early, middle, or late successional stages throughout the floodplain. Both scour and fill processes, resulting from high flows, determine vegetation patterns: a flood may eliminate a portion of a mature forest through bank undercutting with the undercut material forming new depositional surfaces for seedling establishment further downstream. Aside from being the agent of plant mortality, flooding can also cause topping or "flood-training" (Sigafoos 1964) of both young and mature trees, resulting in the formation of sprout groups.

Ecological Characteristics

Ecological characteristics of the dominant tree species are important determinants of successional events in the riparian zone. Of particular importance are the light-weight seeds of the pioneer species dispersed by wind or water. Seed disperal at the time of a falling water level is essential for successful establishment of the pioneer species. These characteristics result in the initial colonization of a site by the pioneer species cottonwood (Populusfremontii ) and willow (Salix spp .). Shade intolerance of cottonwood and willow has been noted to be the limiting factor in preventing their establishment in mature forests as well as the need for a mineral seedbed for germination (Sigafoos 1964; Johnson etal . 1976; Lindsey etal . 1961). Mid-successional stages have species with both light-weight seeds (box elder, ash) and heavy seeds (black walnut, oak). However, they all are able to germinate through litter and under the canopy of a cottonwood/willow forest.

Results

The interaction of fluvial events, landforms, and autecological requirements has led to the development of heterogeneous forest stands along the Sacramento River. The following tree species were encountered frequently in the floodplain forests: box elder (Acer negundo ssp. californicum ), Fremont cottonwood (Populusfremontii ), willow (Salix spp., including S . hindsiana , S . laevigata , S . gooddingii , S . lasiandra , and S . lasiolepis ), and black walnut (Juglanshindsii ). Sycamore (Platanusracemosa ), valley oak (Quercuslobata ) and ash (Fraxinuslatifolia ) occurred less frequently.

Overstory composition associated with each landform in the intensive survey is shown in table 1. This mixed riparian forest (of the species listed above) is found in different successional stages along the majority of the floodplain. As shown by the table, early stages are usually pure cottonwood/willow. Mid- and late-successional stages frequently have a cottonwood/willow overstory and oak and sycamore ocasionally. Box elder, black walnut, and ash comprise the second canopy layer in these later stands. The broad survey also revealed different types of forest stands than encountered in the intensive survey of the river. There are several older groves of pure oak or oak/sycamore on high terraces. Within the later stages of the mixed forest, small stands of pure box elder or box elder/black walnut, approximately 200/m2 or less, were encountered in several locations. In the pure box elder stands average densities were 100 stems per 100 m2 . In these stands, saplings from 2.5 to 7.5 cm. were most frequent with no stems greater than 15 cm. found. Several standing dead stems and many small stems on the ground were evidence of an even higher density at one time. Shade was sufficient to prevent groundcover but a few Prunus sp . and valley oak seedlings were in the stand.

Regeneration

Establishment and survival of riparian species are related to landforms and a sequence of fluvial events (table 2). Most seedling establishment occurs along the newly exposed surfaces of gravelbars and is significantly


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Table 1.—Riverside and oxbow lake riparian forests:  overstory density and composition. (n = 178)

RIVERSIDE FORESTS

 

Density
(trees/ha)

Relative
density

Basal
area
(m2 /ha)

Acernegundo

1.04

1%

0.03

Ficuscarica

Fraxinuslatifolia

Juglanshindsii

1.04

1%

0.01

Platanusracemosa

Populus fremontii

53.8

52%

6.52

Quercuslobata

Sambucusmexicana

Salixlasiolepis

Salixspp . (tree)

48.6

47%

2.83

Total

104.4

100%

9.38

OXBOW LAKE FORESTS

 

Density
(trees/ha)

Relative
density

Basal
area
(m2 /ha)

Acernegundo

42.1

13%

0.83

Ficuscarica

16.2

4.8%

0.17

Fraxinuslatifolia

6.4

1.9%

0.39

Juglanshindsii

40.4

  12%

3.07

Platanusracemosa

16.2

4.8%

8.63

Populusfremontii

57.2

17%

38.99

Quercuslobata

74.1

22%

10.56

Sambucusmexicana

9.8

3%

0.22

Salixlasiolepis

3.4

1%

0.03

Salixspp . (tree)

70.7

21%

13.07

Total

336.5

100%

75.96

different in species composition than regeneration in the established forests.

Gravelbar Regeneration

Seasonal variation in flow regimes greatly influences establishment and survival of the pioneer species on gravelbars. During the winter, streamflows must remove humus and freshly fallen leaf litter from the surface so that the seeds land on mineral soil. A receding water level in late spring and early summer must coincide with cottonwood and willow seed dispersal. As establishment is directly related to the low-flow line (McBride and Strahan 1983), a 1-m. wide band of seedlings and saplings is often found along the river's edge. Prior to further flooding, seedlings must achieve sufficient size to withstand mechanical injury. The subsurface of bars must remain moist throughout the summer in order for the seedlings to withstand late summer drought. Late summer desiccation results in the death of many seedlings (McBride and Strahan ibid .). Winter floods often wash away or bury many seedlings. While density in the initial stages of establishment on bars is extremely high (table 3), the latter two factors account for significant mortality.

Floodplain Regeneration

Within the mature riparian forests of the floodplain, the link between regeneration and the flow regime of the river is not as direct. The most influential flows here are the floods which may remove seedlings established for a season or longer and at the same time prepare seedbeds. While low flows have less direct influence on these species than on those of pioneer species, McGill (1979) attributed some losses on high terraces of riparian vegetation to the lack of occasional flooding during the drought of 1976 and 1977.

In the mature forest, young cottonwoods and willows are rare while box elder and black walnut are common (table 2). The latter two species enter at a later successional stage, establishing through litter and under the shade of a cottonwood/willow canopy. While regeneration in the floodplain is currently occurring primarily in swales or on the banks of swales, young trees are much more scattered throughout the forest and much less dense (table 2), than on gravelbars. Some riverside forests 30–40 years old have little reproduction. Thus, distinct compositional differences exist between reproduction in the riverside floodplain forests and the oxbow lake forests with an increase in seedling density occurring in the oxbow lake forests. Factors limiting successful seedling establishment in the floodplain forests appear to be associated primarily with extremely dense groundcover. Grape vines were noted entwined around many dead saplings.

Succession

The successional progression of forest stands in the riparian zone begins with seedling establishment on gravelbars. The amount of available soil moisture may be an important factor governing these zonal sequences, with the younger land surfaces significantly drier than the older ones. Vegetation establishes on fresh surfaces of the point bar when sufficient sediment accumulates above summer low-water levels. Young cottonwood and willow stands do not form a continuous protective cover on the gravelbar because of the river cutting across point bars during floods. Providing floods do not alter the bar significantly, plant colonization creates additional deposits. Several inches of soil may be deposited by a single flood. As the bar builds higher, it is less frequently flooded. This deposition, in combination with channel migration, results in a stabilized floodplain developing from a shifting gravelbar.

If bars remain relatively undisturbed for a number of years, deposition gradually occurs until the floodplain supports mature cottonwood/willow forests. Eventually an understory of shade tolerant species enters the forests. Should the forests be missed by flood scouring


62
 

Table 2.—Riverside and oxbow lake riparian forests: reproduction density. (stems/ha)

Oxbow Lake Forests

 

Seedlings

Saplings (stem diameter classes in cm.)

Species

 

0.3

0.4–1

1.1–1.5

1.6–2.4

2.5–5

5.1–7.5

7.5–10

Acer
         negundo

385

10

154

144

29

19

Ficus
         carica

289

58

135

29

39

Fraxinus
         latifolia

10

Juglans
         hindsii

29

29

154

39

29

Platanus
         racemosa

77

10

10

Quercus
         lobata

866

19

29

10

19

Sambucus
         mexicana

10

10

Salix
         lasiolepis

10

10

Prunus
         sp .

19

19

Riverside Forests

 

Seedlings

Saplings (stem diameter classes in cm.)

Species

 

0.3

0.4–1

1.1–1.5

1.6–2.4

2.5–5

5.1–7.5

7.5–10

Acer
         negundo

96

Juglans
         hindsii

29

29

19

for many years, the cottonwood/willow may be replaced by these understory species. In places where the river has moved progressively across the floodplain in a uniform direction, a sequence of stand ages is produced, chronologically arranged in the direction of bend migration with the youngest stands nearest the river.

A broad perspective of Sacramento River successional stages is available through aerial reconnaissance. Bands of vegetation of successive ages can be found to occupy the floodplain (Murray etal . 1978). Channel lateral migration studies (Brice 1977) show the maximum ages of the forests in the intensive survey to be 32 years for the developing forest, 73 years for the riverside forest, and >85 years for the oxbow lake forest. Everitt (1968) noted similar findings for the Little Missouri River with germination and growth of cottonwood intricately related to the discharge of the river, movement of the channel, and development of the floodplain. Tree age increases both upvalley and away from the channel according to Everitt (ibid .) and is the result of the rise of sapling thickets along gravelbars.

Physiognomy

The forest structure and physiognomy differ considerably according to the age of forests and landforms on which they develop. Young cottonwood/willow forests are dense with many small trees, but have few other woody species. These gravelbar forests develop in progressive bands, each associated with a rise in elevation of the ridge-swale topography. In the older cottonwood/willow forests, the trees are tall and widely spaced, allowing sufficient light for shrub and herb development. Lianas are prominent in some stands and non-existent in others. Older forests have a two-layer tree canopy and are denser than


63
 

Table 3.—Characteristics of progressive bands of cottonwood on gravelbars.

Type

Species

Density
(/m2 )

Age Range
(yrs)

Aver. Dia.
(cm)

Max. Dia.
(cm)

Aver. Ht.
(m)

Aver. Stand Width (m)

Seedlings at stream edge

cottonwood

124.0

0.3

1

sandbar willow

32.0

tree willow

28.0

1st Sapling Band: beginning of ridge-swale topography

cottonwood

23.6

1–3

0.9

2.5

2.1

2

sandbar willow

17.2

0.5

1

tree willow

4.0

2nd Sapling Band: swale

cottonwood

64.0

1–3

1.3

5.5

3.6

3

sandbar willow

72.0

tree willow

4.0

3rd Sapling Band: swale banks

cottonwood

76.0

1–4

4

8

6

4

sandbar willow

20.4

1.6

3.1

tree willow

14.4

1.8

3.5

4th Sapling Band: ridge

cottonwood

10.4

2–4

1;7.5

12

8

13

sandbar willow

4.0

1.8

3.5

tree willow

2.0

2.5

4

5th Sapling Band: ridge and banks of swales

cottonwood

2.0

2–11

8

15

10+

20

sandbar willow

3.4

2

5

tree willow

1.0

7

11

the mid-successional stage forests. Forests adjacent to cut banks are more frequently composed of alder, oak, or sycamore than are the forest edges that develop behind bars. Young oaks and sycamores were only found in mixed species stands, while old oaks and sycamores are found in groves without the associates. Diameter-classes (table 4) of the oxbow lake and riverside forests show the difference in species composition and structure of the two forests.

Reproductive Strategies

The most common method of reproduction is by seed. However, throughout the floodplain vegetative reproduction is also common. Sandbar willow (Salixhindsiana ) was frequently observed sprouting on higher portions of the gravelbars. This was explained by Wilson (1970) who noted an adaptive value of vegetative reproduction on sandy soils where seedling establishment is limited by surface soil moisture availability. Sprouting was also recorded on the floodplain in areas infrequently flooded: older sycamore trees frequently had basal sprouts. In areas which undergo severe mechanical abrasion from flows (banks downstream from reservoir flow releases or banks receiving a high degree of wave action from boats), vegetative reproduction was as common as seedling establishment.

Survival

In the developing cottonwood/willow forests, survival is reduced by both drought and winter flooding as well as shade and competition from groundcover. Significant attrition occurs for different stages of cottonwood development (compare tables 2 and 3). Floodplain forests had many dead trees, probably a result of the 1976–1977 drought (McGill 1979).

Discussion

Initial Establishment

The study indicates that the initial establishment of riparian forests is along point bars. Cottonwood and willow can be regarded as classic pioneer species; within this region, their seeds germinate almost exclusively on fully exposed alluvium recently deposited by the river. Not a single seedling of these species was found in any of the floodplain samples (table 3). This indicates that neither functions as a gap-phase species (Watt 1947) by establishing seedlings in forest openings following disturbance. Smaller stems of cottonwood/willow in the floodplain forests (table 4) appear to result from suppression or sprouting (Note: the two size-classes in table 3, plot 4 had all established at the same time). In areas with sufficient light, flood deposits of fresh alluvium may provide areas for a younger age class to develop. Other dominant tree species, such as box elder and black walnut, all have the ability to germinate and grow under the cottonwood/willow overstory. Without disturbance, they in time could replace the cottonwood/willow overstory.


64
 

Table 4.—Riverside and oxbow lake forests: diameter size-classes of dominant species.(Stems/ha; all size-classes in cm.).

Riverside Forests

Species

Seed-
ling

Sap-
ling

10–
20

21–
30

31–
40

41–
50

51–
60

61–
70

71–
80

81–
90

91–
100

101–
110

111
+

Acer
negundo

96

1.5

Juglans
hindsii

77

1.5

Populus
fremontii

10.4

11.8

14.8

5.9

8.8

5.9

Salix
spp
. (tree)

19.4

20.7

5.9

1.5

3.0

Oxbow Lake Forests

Acer
negundo

385

356

35.6

3.2

Juglans
hindsii

280

22.7

3.2

6.5

6.5

3.2

Platanus
racemosa

97

3.2

3.2

3.2

6.4

Populus
fremontii

3.2

3.2

3.2

9.7

3.2

3.2

6.4

6.4

3.2

16.4

Quercus
lobata

866

77

22.6

9.7

22.6

3.2

9.7

3.2

3.2

3.2

Salix
spp
. (tree)

20

3.2

12.9

16.2

12.9

13.0

3.2

9.7

Structure and Composition

The data also show that the structure and composition of the overstory are strongly related to stand age and horizontal and vertical position of the floodplain. For example, cottonwood and willow predominate in young stands on low terraces near the river. Ash, box elder, and black walnut enter cottonwood/willow stands over time and predominate in stands away from the river. Oak and sycamore are found in old stands on high terraces with the other dominants and along banks high above the river. Reproduction in these stands is very limited (table 5). Thus, species diversity initially increases as stands age, reaches a maximum in stands with mixtures of both pioneer and later successional species, and may decline slightly in oldest stands.

The high frequency of sapling box elder and black walnut in cottonwood/willow forests suggsts that the next successional stage will consist predominantly of these two species. However, although box elder was found in small pure patches, there is no evidence available at this time that large scale replacement of the cottonwood/willow type along the Sacramento River by these two species is occurring. Despite the establishment of cottonwood only on point bars, mature cottonwoods remain throughout the floodplain. Lateral channel migration occurs frequently enough to retain cottonwoods and willows in most stands except the few high terraces where only oak and sycamore remain.

Cultural Impacts on Regeneration

The Sacramento River riparian system is much altered both in its natural flow regime and floodplain characteristics. Land use and water resource development projects may have a significant effect on the current regeneration situation and on the future regeneration potential. While further research into these areas is necessary to provide quantitative data for the Sacramento River, correlation with other major rivers provides us with clues to changes caused by alteration of the riparian zone. Historical research, although qualitative, provides a picture of the riparian forests of the past upon which we may also draw.


65
 

Table 5.—Riparian oak woodland: stem diameter-classes.
(Stems/ha; diameter-classes in cm.)

Species

Seed. Sapl.

10– 20

21– 30

31–
40

41–
50

51–
60

61–
70

71–
80

81–
90

91–
100

101–
110

Acer

3.6

negundo

                     

Platanus

3.6

racemosa

                     

Populus

3.6

fremontii

                     

Quercus

7.3

14.6

14.6

21.8

7.3

10.9

14.5

10.9

lobata

                     

Salix

3.6

spp .

                     

Land Clearing

Removal of all but the frequently flooded areas of the riparian forests has had obvious impacts on the reduction of certain species such as oak and sycamore in the Sacramento Valley. Thompson (1961) cites several descriptions of the riparian forests prior to extensive clearing which speak of forests of oak, cottonwood, and sycamore. While the oak is found in large groves in several areas along the upper river, individual sycamores are scattered very infrequently throughout the forests. Ongoing reduction of the high terrace lands (McGill 1979) will contribute to a further reduction of these two magnificent species.

Introduced Species

The introduction of exotic species in the area has also changed species composition. For example, figs (Ficuscarica ) in patches in the forest create such a dense shade that reproduction under them is limited to sprouting figs. While these patches are fairly small in extent (100 m2 ), they have created a major change in the localities in which they are found by their high reproduction (table 2). Prune seedlings (Prunus sp.), and tree of heaven (Ailanthusaltissima ) are also found in many areas along the river.

The native black walnut (Juglanshindsii ), now so common in the riparian forests, appears to have become widespread in the forest through the use of its rootstock for commercial propagation of the English walnut (Juglansregia ). The only population noted along the Sacramento River prior to the arrival of European man was between Freeport and Rio Vista (Fuller 1978). This was discovered by Richard Brindsley Hinds of the Sulphur Expedition in 1837 (Thomsen 1963).

Grazing

Grazing of the forest may lower reproduction densities in floodplain areas. When grazed, forests are kept clear of groundcover and young trees. When grazing is excluded, the regrowth of a thick understory which may prevent seedlings from establishing has occurred in the riparian forests. Thus, grazing could be responsible for the lack of establishment of certain age-classes in the flood-induced age structure through seedling elimination. Further work is necessary to substantiate the degree to which this has affected the Central Valley riparian forests. Carothers (1977) had shown it to be a major cause of reduction in reproduction in the Southwest riparian forests.

Water Resource Development

Levees : Aerial photography of the river reveals a large-scale change resulting from the artificial levees. Above Colusa, artificial levees are either non-existent or are far away from the channel. This allows lateral migration to form point bars at most bends and provides new surfaces for cottonwood and willow establishment. Below Colusa, the levees are adjacent to the river channel preventing point bar formation. Aerial photography (Murray etal . 1978) depicts 18 bars forming in a 20-river-mile (RM) reach above Colusa and only four bars forming in a 20-RM reach below Colusa. Bars below Colusa are much smaller in size than those above Colusa. Without the initial landform on which to colonize, riparian forest formation and regeneration will not continue in the same pattern.

NewLandforms : Development of man-made levees has caused a disruption of gravelbar formation thereby limiting reproduction. However, the levees themselves could provide new habitats for the development of new forests, providing current management practices were discontinued. The following species were common on levees: alder, ash, fig, cottonwood, valley


66

oak, sandbar willow, and tree willow. Densities for saplings ranged from 3/100 m2 for most species up to 85/100m2 for willows and cottonwood <2.5 cm. stem diameter. Regeneration density was partially dependent on levee management. Survival in burned areas was mainly in swales with sandbar willow and a few sapling oaks near the top of the levee. Species zonation is very noticeable with oaks often lining the tops of the levees; alder, ash, and cottonwood near the water level; and willows in swales. Weirs also provide a place where seasonal water flows and abundant light have created an oak phase of riparian forests along their levees.

FlowRegulation : The impacts of controlled flows on seedling establishment and survival have two effects. On certain rivers, willow encroachment on the streambanks has occurred as a result of controlled flows (Pelzman 1973). Pelzman (ibid .) attributed this to a prolonged soil moisture which allowed greater establishment and survival. McGill (1979) and Brice (1977) have also noted an increase in vegetated bar surfaces for the Sacramento River. They both attributed this to the moderating effect of Shasta Dam which has resulted in the lack of scour. The data for seedling establishment for the Sacramento River as a controlled stream reveals a lower density of seedlings (table 3) than similar data collected for a non-controlled stream (McBride and Strahan 1983). This suggests that the annual falling of the water level that coincided with seed dispersal and allowed abundant germination on the non-controlled stream did not occur on the Sacramento River. Daily flow data (USDI Geological Survey 1978, 1979; 1980 and 1981 data not available) for the Butte City gauging station reveal a wide fluctuation of streamflow with high flows following low flows frequently during the months of May-September. Thus, the absence of a continual lowering of the water level could have resulted in a limited amount of seedling establishment this year. However, the controlled flows may result in a higher survival percentage through lack of scouring. Also, a continual provision of moisture throughout the summer would reduce losses from desiccation for those seedlings which do become established.

LandandWaterEffects : Forest composition for the entire Sacramento River riparian zone must differ from the earlier forests because only frequently flooded areas remain to be sampled. Thus our results probably show a more flood-tolerant community dominating the area than we once had. With the decrease in bank stability of the river (Brice 1877), bank erosion has caused the loss of high terrace lands resulting in further decrease of sycamore and oak forests. Infrequent flooding and higher stands due to controlled flows and levees has probably resulted in the development of a greater proportion of older trees, since flooding of the areas does not clear out the undergrowth and provide bare areas for establishment to occur. As the rate of meandering is a major factor in determining the proportion of the floodplain in pioneer, transitional, and later successional stages, changes in meandering noted by Brice (1977) would suggest different proportions of forest stands in these stages may occur in the future than we had in the past.

Summary

Existing riparian forests have been shown to have an overstory and regeneration that corresponds to landforms and fluvial processes as well as successional stages. Establishment, growth, maturation, and death of floodplain trees are merged with the complete flow regime of the river and the erosion and deposition of sediment. The heterogeneity of forests is an indicator of a dynamic fluvial system. Establishment of the forests begins on gravelbars with the development of a cottonwood/willow type, making bars a critical landform in forest development. With deposition and time, the forests develop and mature, with understory species of box elder and black walnut becoming frequent. While regeneration on the bars is almost totally cottonwood and willow, regeneration on the floodplain is predominantly box elder and black walnut, especially on the low terraces. High terraces have minor amounts of oak, sycamore, and ash establishing. Forests surrounding oxbow lakes are older and have higher densities of reproduction than riverside floodplain forests. Water resource development projects and land uses have significant impacts on regeneration potential of riparian forests.

Literature Cited

Bell, D.T., and F.L. Johnson. 1974. Floodcaused mortality around Illinois reservoirs. Trans. Ill. State Acad. Sci. 67(1):28–37.

Brice, James. 1977. Lateral migration of the Middle Sacramento River, California. USDI Geological Survey Water-Res. Investigations 77–43. 51 p.

Bryan, Kirk. 1923. Geology and ground-water resources of Sacramento Valley, California. USDI Geological Survey Water-Supply Paper 495. 285 p.

Campbell, C.J., and Win Green. 1968. Perpetual succession of stream-channel vegetation in a semiarid region. J. Ariz. Acad. Sci. 5:86–98.

Carothers, S.W. 1977. Importance, preservation, and management of riparian habitat: an overview. p. 2–4. In : R.R. Johnson and D.A. Jones (tech. coord.). Importance, preservation, and management of riparian habitat. USDA Forest Service General Technical Report RM-43. Fort Collins, Colo.


67

Conard, S.G., R.L. MacDonald, and R.F. Holland. 1977. Riparian vegetation and flora of the Sacramento Valley. In : A. Sands (ed.). Riparian forests in California: their ecology and conservation. Institute of Ecology Pub. 15. 122 p. University of California, Davis.

Cottam, Grant, and J.T. Curtis. 1956. The use of distance measures in phytosociological sampling. Ecology 37(3):451–460.

Dietz, R.A. 1952. The evolution of a gravel bar. Missouri Bot. Garden Annals 39:249–254.

Everitt, B.L. 1968. Use of the cottonwood in an investigation of the recent history of a flood plain. American J. of Sci. 266:417–439.

Fonda, R.W. 1974. Forest succession in relation to river terrace development in Olympic National Park, Washington. Ecology 55: 927–942.

Fuller, T.C. 1978. Juglans hindsii Jepson ex. R.E. Smith. Northern California black walnut. Rare plant status report. California Native Plant Society.

Gaines, D. 1974. Review of the status of the Yellow-billed Cuckoo in California: Sacramento Valley populations. Condor 76:204–209.

Hosner, J.F., and L.S. Minckler. 1960. Bottom-land hardwood forests of southern Illinois—regeneration and succession. Ecology 44(1):29–41.

Johnson, W.C., R.L. Burgess, and W.R. Keammerer. 1976. Forest overstory vegetation and environment on the Missouri River floodplain in North Dakota. Ecol. Mono. 46:59–84.

Leopold, L.B. 1973. River channel change with time: an example. Geol. Soc. Amer. Bull. 84(6):1845–1860.

Lindsey, A.A., R.O. Petty, D.K. Sterling, and W. Van Asdall. 1961. Vegetation and environment along the Wabash and Tippecanoe Rivers. Ecol. Mono. 31(2):105–156.

McBride, J.R., and Jan Strahan. 1983. Influence of fluvial processes on patterns of woodland succession along Dry Creek, Sonoma County, California. In : R.E. Warner and K.M. Hendrix (ed.). California Riparian Systems. [University of California, Davis, September 17–19, 1981.] University of California Press, Berkeley.

McGill, R.R., Jr. 1975. Land use changes in the Sacramento River riparian zone, Redding to Colusa. California Dept. of Water Resources, Northern Dist. Report. 23 p.

McGill, R.R., Jr. 1979. Land use change in the Sacramento River riparian zone, Redding to Colusa. An update—1972 to 1977. 34 p. California Department of of Water Resources, Sacramento.

Michny, F.J., D. Boos, and F. Wernette. 1975. Riparian habitat and avian densities along the Sacramento River. California Dept. of Fish and Game Adm. Report 75–1.

Murray, Burns, and Kienlen. 1978. Retention of riparian vegetation. Sacramento River, Tisdale Weir to Hamilton City. California Dept. of Water Resources, The Reclamation Board.

Nanson, G.C., and H.F. Beach. 1977. Forest succession and sedimentation on a meandering-river floodplain, northeast British Columbia, Canada. J. Biogeog. 4:229–251.

Pelzman, R.J. 1973. Causes and possible prevention of riparian plant encroachment on anadromous fish habitat. California Dept. of Fish and Game. Adm. Report 73–1.

Sigafoos, R.S. 1964. Botanical evidence of floods and floodplain deposition. USDI Geological Survey Prof. Paper 485-A. 35 p.

Sudworth, G.B. 1908. Forests trees of the Pacific slope. USDA Forest Service. 441 p.

Teskey, R.O., and T.M. Hinckley. 1978. Impact of water level changes on woody riparian and wetland communities. Vol. 1: Plant and soil responses to flooding. USDI Fish and Wildlife Service. 30 p.

Thompson, Kenneth. 1961. Riparian forests of the Sacramento Valley, California. Ann. Assoc. Amer. Geog. 51(3):294–315.

Thomsen, H.H. 1963. Juglans hindsii . The Central California black walnut, native or introduced? Madrono 19(1):1–10.

USDI Geological Survey, 1978, 1979. Water resources data for California. Vol. 4: Northern Central Valley basins and the Great Basin from Honey Lake to Oregon state line.

Upper Sacramento River Task Force. 1978. Sacramento River environmental atlas. California Dept. of Water Resources.

Watt, A.S. 1947. Pattern and process in the plant community. J. Ecol. 35(1&2):1–22.

Wilson, R.E. 1970. Succession in stands of Populusdeltoides along the Missouri River in southeastern South Dakota. Amer. Midl. Nat. 83(2):330–342.


68

Plant Succession on Merced River Dredge Spoils[1]

Thomas H. Whitlow and Conrad J. Bahre[2]

Abstract.—One hundred and nine species of vascular plants were collected from 22 stands at six sites in the 2,800 ha. (7,000 ac.) of dredge spoils along the Merced River near Snelling, California. Five sites were dredged, one per year, in 1910, 1928, 1938, 1941, and 1950; one was not dredged. Association analysis of the stand data identified four species groups closely related to dredge-spoil topography and moisture availability. In addition, the program ordinated stand data according to floristic affinities. The ordination showed no age-dependent patterns.

Introduction

Nearly 24,000 ha. (60,000 ac.) of floodplains and terraces in the northeastern part of California's Central Valley were mined by huge gold dredges from 1898 to 1968 (fig. 1). In all, 12 major gold fields were dredged between Butte Creek and the Merced River (Clark 1970; Wagner 1970). The dredge spoils consist of wormlike ridges of unsorted boulders and cobbles with intervening swales of fine-textured soils and standing water (fig. 2). Except for a few areas of limited extent leveled for housing or used as a source of aggregate, the spoils now serve as little more than poor grazing lands and wildlife habitat. Nevertheless, they offer plant ecologists a novel means of studying plant succession because the spoils are of similar structure and can be dated to the week of deposition as far back as 70 years. Summarized here is a preliminary investigation of successional patterns in the Snelling dredge field (fig. 3).

The Snelling dredge field, mined between 1907 and 1951 (Aubury 1910; Davis and Carlson 1952; Clark 1970), consists of 2,800 ha. (7,000 ac.) of spoils paralleling the Merced River near the town of Snelling (fig. 4). Snelling (79 m. [259 ft.] above sea level) has an average annual precipitation of 840 mm. (33.2 in.), most of which falls between November and April (California Department of Water Resources 1980). Local vegetation is valley oak woodland (sensu Griffin 1977), grassland (sensu Heady 1977),

figure

Figure l.
Yuba Dredge No. 2. This dredge, once owned by Yuba
Goldfields, was brought to Snelling from Montana in 1935.
Only 23 m. (75 ft.) long, it was one of the smallest dredges
ever used at Snelling. It was dismantled in 1939 and
taken to Chico.

figure

Figure 2.
Dredge spoil mound tops. Note cobbles and boulders
as well as sparse vegetation cover. Trees in the swales
are Salix  spp. and Populus  fremontii . and riparian forest
(sensu  Conard et  al . 1977).

[1] Paper presented at the California Riparian Systems Conference. [University of California, Davis, September 17–19, 1981].

[2] Thomas H. Whitlow is Research Associate, Urban Horticulture Institute, Cornell University, Ithaca, N.Y. Conrad J. Bahre is Assistant Professor, Department of Geography, University of California, Davis.


69

figure

Figure 3.
Map of east-central California. Note the Snelling field.

The gold is mostly flour gold derived from the pocket belt of the Mother Lode in Mariposa Country, which is traversed by the upper course of the Merced River. It is found in the Quaternary gravel deposits of the modern river which range in depth from 5.4 to 11 m. (18 to 36 ft.)

Bucket-line gold dredges, constructed chiefly of steel, were so heavy and cumbersome they had to be assembled in a dry pit. Water from a canal was turned into the pit, allowing the dredge to float (Aubruy 1910). The dredges were only capable of digging 7.6 to 9.1 m. (25 to 30 ft.) below the surface of the dredge pond. Their earth-moving capacity, depending on their size, ranged from 153,000 to 260,000 cu. m. (200,000 to 340,000 cu. yd.) per month.

Individual dredge piles usually differ in slope and elevation. Fines may or may not be found on the surfaces. Whereas some dredge piles are in neat rows. most are rather haphazard. Differences in spoil topography reflect dredging depths, the particulars ways in which the tailing

figure

Figure 4.
Vertical aerial photograph of part of the Snelling dredge field. Note tree-lined swales and sparsely
vegetated spoil tops. The oldest spoils do not necessarily have tree-lined swales. In some cases, the
spoils were stacked so that no swales were left for trees to colonize (photograph taken in 1959).


70

stackers were operated, and whether overburden was sent directly to the stacker without sorting.

Methodology

Five study-sites in the Snelling dredge field were selected and dated using USDI Geological Survey 1:24,000 topographic maps, large-scale aerial photographs, mining progress maps, interviews with local residents, and records in the Merced County Recorder's Office (table 1). These sites were dredged, one per year, in 1910, 1928, 1938, 1941, and 1950. One undredged site was selected as a control.

Stands on mound tops, high swales, and low swales at each dredge site were subjectively chosen to conduct a complete floristic inventory. This inventory was needed to detect floristic distinctions between sites of different ages. The sharp gradients and irregular depositional patterns of the spoils made random and systematic sampling techniques impractical and highly sensitive to artifacts of sample location. Edge effects were minimized by placing the stands no closer than 100 m. (300 ft.) from the edges of the spoils. The stands, which varied in size and shape, were inventoried using the Braun-Blanquet relevé method (Mueller-Dombois and Ellenberg 1974). High swales were inventoried intoto , while mound tops and low swales were inventoried along belt transects whose lengths were designed to include all species in a particular habitat. The sampling method was designed to eliminate minimum area problems arising from the use of discrete sample sizes, to represent the total flora, and to establish within-stand homogeneity while maximizing the possibility of between-stand differences.

The stand data were analyzed using the association analysis program of Ceska and Roemer (1971). This program, which identifies associational relationships between species using pre-established phyto-sociological criteria, arranges species into groups of co-occurrence and ordinates stands according to floristic similarities. Of the program's five different "inside-outside" rules, the 50%-inside: 20%-outside rule was chosen because it included the highest percentage of the entire flora and hence accounted for more variations than the other rules. According to this rule, a species belongs to a species group if it occurs in 50% of the stands in its group and does not occur in more than 20% of the stands outside of its group. A stand belongs to a species group when it contains 50% of the species in the group. Field work was carried out between March and May 1980, during the peak bloom of the annual flora.

Results and Discussion

One hundred and nine species of vascular plants were collected from 22 stands at the six study-sites in the dredge field. The association

 

Table l.—Age and location of sites and topography of stands in the Snelling dredge field.

A. Site age—1928

 

Location—SNESE Sec. 6,

 

T. 5 S., R. 15 E.

 

Stand number

Topography

1

Low swale

2

High swale

3

Mound top

4

High swale

5

High swale

B. Site age—Undredged site

 

    Location—SENWSE Sec. 5,

 

T. 5 S., R. 15 E.

 

Stand number

Topography

6

River terrace top

C. Site age—1950

 

     Location—ESWSW Sec. 6,

 

T. 5 S., R. 15 E.

 

Stand number

Topography

7

Mound top

8

High swale

9

Mound top

10

High swale

11

High swale

D. Site age—1941

 

     Location—NWSWSE Sec. 7,

 

T. 5 S., R. 14 E.

 

Stand number

Topography

12

High swale

13

Mound top

14

High swale

15

Low swale

16

Mound top

E. Site age—1938

 

    Location—NESWSE Sec. 9,

 

T. 5 S., R. 14 E.

 

Stand number

Topography

17

Mound top

18

High swale

19

Low swale

F. Site age—1910

 

    Location—WNENE Sec. 9,

 

T. 5 S., R. 14 E.

 

Stand number

Topography

20

Mound top

21

High swale

22

Low swale

analysis program organized the stand data into four species groups (table 2). Only 36 of the 109 species were sufficiently well associated to be included in these groups. From left to right in table 2, the stands range from dry mound tops with sparse annual grass and herbaceous cover, to high dry swales dominated by thickets of Salix spp., to low mesic swales with forests of Salix spp. and Populusfremontii surrounding


71
 

Table 2.—Stand ordination and species groups on the Snelling dredge field summarized in a species-by-stand matrix using the association analysis program of Ceska and Roemer (1971). Cover values are: – = not present; R = single individual; + = <1%; 1 = 1–5%; 2 = 6–25%; 3 = 26–50%; 4 = 51–75%; and 5 = 76–100% (Mueller-Dombois and Ellenberg 1974). Date of deposition: A—1928; B—undredged site; C—1950; D—1941; E—1938; F—1910.

figure

 

72

shallow ponds. The four high-swale stands at the far right of the table do not fit within the topographic-moisture gradient of the rest of the ordination or within any single species group. This fact, plus their affinities to Groups 1, 2, and 4, are due to small-scale habitat variation. Stand 2, a high swale covered by grass, also falls within the xeric mount tops, whereas Stand 10, another high swale, contains two species groups.

The nesting of the species groups according to moisture availability and topography is readily apparent in table 2. Group 1, composed primarily of introduced annual species, grows exclusively on mound tops and corresponds floristically and physiognomically to the "California annual type", a climax annual grassland described by Heady (1956, 1958, 1977). Heady's climax annual grassland depends on the development of organic mulch; here it has developed on largely unweathered dredge spoil and completely lacks a litter layer.

Group 2, made up entirely of native tree species, occupies the bottom of nearly every swale with fine-textured soils. It overlaps little with Group 1; only Stand 10 includes extensive representation from both groups. Group 2 species are common pioneers in disturbed riparian zones in the Central Valley, and except for Quercuslobata all have wind-dispersed seeds (Munz and Keck 1959; Thompson 1961; Conard et al . 1977). Except for two large individuals at the 1910 site, the oaks are seedlings growing in the shade of willows. Since no parent oaks grow nearby, the oaks probably germinated from acorns dispersed by animals.

Group 3, consisting of woody perennials and emergent aquatics, occupies the edges of forested sites and shares most of the low mesic swales with Group 2. Group 3 reflects the greater habitat diversity of the low swales because of the presence of perennial ponds and a forest canopy. Vitiscalifornica and Rubusprocerus occupy the landward margins, whereas Typhalatifolia and Juncuseffusus occupy the pond margins.

Group 4 is made up largely of herbaceous annuals growing in semi-shaded, moist places in the swales containing standing water. The species in this group range from emergent and floating aquatics (Cyperusalternifolius , Alisma sp., and Marsileavestita ) to plants usually found in open, droughty habitats (Centaureamelitensis , Brizaminor , and Cynodondactylon ). Group 4, like Group 3, is also associated with a forest canopy.

Sixty-two percent of the species collected in the dredge field are native, 38% are introduced. According to Heady (1977), the percentage of native plants in species lists for individual stands in California's annual grassland ranges between 71% at Hastings Reservation (White 1967) and slightly less than 20% at Hopland (Heady 1956). Our findings indicate that the Snelling dredge field has a relatively high proportion of native species.

In addition to identifying associational groups, the Ceska and Roemer program ordinated the stand data according to floristic affinities (table 2). However, the ordination shows no age-dependent patterns. In some cases, closer affinities occur between stands of the oldest and youngest sites than between stands of the same age.

Seventy-three species were not included in any of the four species groups because they were too frequent (>66% is the threshold value of the program) or non-faithful. Although we lack the quantitative data to fully interpret the significance of these rare species, two conclusions are drawn. First, our sampling was adequate because it included so many rare species. Large stands usually include a high proportion of rare species (Preston 1948). Secondly, rare species are continually being added to the flora for at least 50 years after spoil deposition.

Table 3 summarizes the percentage of rare species in proportion to the total flora of the six study sites. Vicia benghalensis was excluded because its occurence exceeded the 66% threshold of the program. The other species had frequency values of 18% or less. Note that the rare species made up 55% or more of the total species in the undredged and 1910 sites, and only 30–39% of the species in the other sites. A similar trend has been documented by Bazzaz (1975) in his study of old field succession in Illinois. There, he found that species diversity increased most rapidly during the first 15 years after field abandonment and that the species colonization curve maintained a positive slope for at least 40 years. Since the youngest spoils at Snelling are 30 years old, we have probably missed the rapid colonization phase that occurred shortly after dredging. White (1966) in his studies of abandoned fields at Hastings Reservation noted that only 18 to 28 years were needed after initial disturbance for the dominant species of the climax grassland to re-establish themselves.

Changes in species diversity were not quantifiable because the stands were of different sizes. Nevertheless, the 1910 and 1928 sites were floristically richer than the other sites (table 3). Of particular interest is the fact that Chlorogalum grandiflorum , Brodiaeacalifornica , and B . multiflora , all native perennials, were only found at the 1910 site. The occurrence of these perennials and greater species diversity at this site may not be entirely age-dependent. The site, which is periodically flooded by the Merced River, has some alluvium and is exposed to flood-borne propagules. The undredged grassland site contained most of the Group 1 species plus three native perennials: Stipapulchra , Brodiaeahyacinthina , and Calochortus luteus . In general, species


73
 

Table 3.—Percent of rare species for each age-class.

 

Undredged control

1910

1928

1938

1941

1950

Total number of species

12

56

57

29

41

54

Total number of outliers

7

31

17

9

13

21

Percent outliers

58

55

30

31

32

39

diversity was highest in the forests of the mesic swales and lowest in the grasslands of the mound tops.

Conclusions

Only small changes in species composition were noted in the dredge-spoil sequence investigated at Snelling. The dominant species probably colonized rapidly after spoil deposition. The four species groups identified by the Ceska and Roemer (1971) program occur on all sites regardless of age. The groups correlate most closely with dredge-spoil topography and moisture availability. In general, the slow weathering of the dredge spoil has not resulted in enough soil development to affect the vegetation. Only in a few swales with moist, shallow soils and standing water is the vegetation very diverse or structurally complex. Several immature Quercuslobata in the swales and a Quercus wislizenii at the 1910 site are the only evidence of direct species replacement in the study-sites. The data suggest that species richness increases with successional age and that 50 years or more are required for the accumulation of well-developed flora. Structural changes will be much slower, correlating with the slow development of soil.

Acknowledgments

Financial support was provided by a Faculty Research Grant from the University of California, Davis. We thank the following residents of Snelling for their assistance and information: Robert Peirce, H.G. Kelsey, Ed Romero, and Kermit Robinson. Thanks must be extended also to Jack Major and Marlyn Shelton who read and commented on the manuscript.

Literature Cited

Aubury, L.E. 1910. Gold dredging in California. California State Mining Bureau, Bull. 57. 312 p. California State Printing Office, Sacramento, Calif.

Bazzaz, F.A. 1975. Plant species in old-field successional ecosystems in southern Illinois. Ecology 56:485–488.

California Department of Water Resources. 1980. California rainfall summary: monthly total precipitation 1849–1979. Various pages. California Department of Water Resources, Sacramento, Calif.

Ceska, A., and H. Roemer. 1971. A computer program for identifying species-relevé groups in vegetation studies. Vegetatio 23:255–277.

Clark, W.B. 1970. Gold districts of California. 180 p. California Division of Mines and Geology, San Francisco, Calif.

Conard, S.G., R.L. MacDonald, and R.F. Holland. 1977. Riparian vegetation and flora of the Sacramento Valley. p. 47–55. In : A. Sands (ed.). Riparian forests in California: their ecology and conservation. Institute of Ecology Pub. 15, University of California, Davis. 122 p.

Davis, F.F., and D.W. Carlson. 1952. Mines and mineral resources of Merced County. Calif. J. Mines Geol. 48:207–251.

Griffin, J.R. 1977. Oak woodland. p. 383–415. In : M.G. Barbour and J. Major (ed.). Terrestrial vegetation of California. 1002 p. John Wiley and Sons, New York, N.Y.

Heady, H.F. 1956. Changes in a California annual plant community induced by manipulation of natural mulch. Ecology 37:798–812.

Heady, H.F. 1958. Vegetational changes in the California annual type. Ecology 39:402–416.

Heady, H.F. 1977. Valley grassland. p. 491–514. In : M.G. Barbour and J. Major (ed.). Terrestrial vegetation of California. 1002 p. John Wiley and Sons, New York, N.Y.

Mueller-Dombois, D., and H. Ellenberg. 1974. Aims and methods of vegetation ecology. 547 p. John Wiley and Sons, New York, N.Y.

Munz, P.A., and D.D. Keck. 1959. A California flora. 1689 p. University of California Press, Berkeley, Calif.


74

Preston, F.W. 1948. The commonness, and rarity of species. Ecology 29:254–283.

Thompson, K. 1961. The riparian forests of the upper Sacramento Valley. Ann. Assoc. Am. Geogr. 51:294–315.

Wagner, J.R. 1970. Gold mines of California. 259 p. Howell-North Books, Berkeley, Calif.

White, K.L. 1966. Old-field succession on Hastings Reservation, California. Ecology 47:865–868.

White, K.L. 1967. Native bunchgrass (Stipapulchra ) on Hastings Reservation, California. Ecology 48:949–955.


75

Historical Vegetation Change in the Owens River Riparian Woodland[1]

Timothy S. Brothers[2]

Abstract.—This study evaluates human-caused vegetation change in the riparian woodland of Owens River (Inyo Co., Calif.). The greatest change has occurred below the intake of the Los Angeles Aqueduct, where drying of the channel has eliminated most native riparian cover and allowed invasion by salt cedar (Tamarixramosissima ) and Russian olive (Elaeagnusangustifolia ). Fire, water management, and other factors may have reduced tree cover above the aqueduct intake and encouraged proliferation of weedy native shrubs. The present scarcity of tree seedlings suggests that one or more of these factors continues to inhibit tree regeneration.

Introduction

Owens River has long been an important source of water for an otherwise arid region. Since settlement of Owens Valley by Europeans in the 1860's it has supported a mix of farming, mining, stock raising, and other economic activities common in the West. Its waters have been diverted for agriculture within Owens Valley and for export to Los Angeles. This study examines how these activities have changed the character and extent of the riparian woodland bordering Owens River.

Physical Setting

Owens River runs from just south of Mono Lake through Owens River Gorge to the head of Owens Valley, and from there the length of Owens Valley to Owens Lake. This study was limited to Owens Valley.

Below Owens River Gorge, Owens River is a meandering, low-gradient stream (fig. 1), winding over a floodplain whose width varies from less than 100 m. to more than 1 km. The floodplain lies at a lower elevation than the rest of the valley floor and is bounded by abrupt bluffs along much of the river. The floodplain surface is crisscrossed in many places by abandoned river meanders, but is otherwise fairly level. The river channel is relatively deep and narrow, bordered in many places by steep banks composed of fine-textured, cohesive alluvium.

The Owens River system is fed almost entirely by runoff from the Sierra Nevada, but even before man altered the hydrologic regime only about a third of its Sierra tributaries maintained perennial flow to the river. The rest normally disappeared short of the river channel as a result of percolation and evaporation. Much Sierra runoff thus reaches the river as subsurface flow. South of the Poverty Hills, however, the 1872 earthquake fault (fig. 1) restricts eastward groundwater movement (Los Angeles Department of Water and Power 1966). No groundwater reaches the river channel where it lies well east of the fault, but seepage increases gradually above the intersection of river and fault near Manzanar Road. From there south to Lone Pine many small springs occur in and along the channel, probably the combined result of channel entrenchment, proximity of the earthquake fault, and inflow from the alluvial fan of Lone Pine Creek.

Under natural conditions, maximum monthly discharge of Owens River normally occurred in June or July with melting of the Sierra snowpack; minimum discharge usually came in August or September. River flow was comparatively regular: the ratio of maximum to minimum monthly discharge at Pleasant Valley from 1919 through 1940 was 2.8 to 1[3] —much lower than, for example, the Kings River at Piedra (46.4 to 1); the Kern at Bakersfield (13.4 to 1); and the Kaweah at Three Rivers (53.6 to 1) (USDI Geological Survey 1959). Factors responsible for this low variation may

[1] Paper presented at the California Riparian Systems Conference. [University of California, Davis, September 17–19, 1981].

[2] Timothy S. Brothers is a Graduate Student in the Department of Geography, University of California, Los Angeles, Calif.

[3] Unpublished streamflow records, Los Angeles Department of Water and Power (LADWP).


76

figure

Figure 1.
Owens Valley.

have included the gentle gradient of the river channel; low precipitation east of the Sierra crest and regulation of the discharge by the Sierra snowpack and groundwater. River regime and channel morphology suggest that most floods were relatively mild events, causing little disturbance of the floodplain surface.

Present Vegetation

Sampling Methods

Field sampling of the present riparian woodland was carried out in August, 1979, and in April, May, and June, 1980. (Only data from 1980 are included here.) At each of 20 systemically spaced sites, three parallel l-m.-wide belt transects were extended 20 m. apart at right angles to the river channel. Presence of woody perennial species was noted in each meter of the transect. At sites below the aqueduct intake, transects extended across the channel and 35 m. outward from the bank top on each side. Above the intake, water in the channel limited sites to one side of the river; transects at these sites extended 35 m. from the bank top.

Trees were counted at each site within a plot 50 m. wide, ending 50 m. from the bank on each side of the river (one side only at sites 1–10). Plots thus measured 50 m. by 50 m. above the bank on each side, but area of the channel section at sites 11–20 varied with channel width. Trees less than 2 m. tall were counted as a subset of the total tree population at each site to provide a rough measure of recent reproduction from seed.

Species Composition and Patterning

The Owens River riparian woodland is somewhat species-poor compared to many other riparian areas in California (Roberts, Howe, and Major 1977). Of the 17 woody perennials observed in 1980 (tables 1 and 2), only 10 are primarily members of the riparian woodland: valley willow (Salixgooddingii ), black willow (S . laevigata ), and cottonwood (Populusfremontii ), which make up the tree stratum; and the shrubs narrowleaf willow (Salixexigua ), Rosawoodsii , rabbitbrush (Chrysothamnus nauseosus ), Nevada saltbush (Atriplextorreyi ), salt cedar (Tamarixramosissima ), Russian olive (Elaeagnusangustifolia ), and desert olive (Forestieraneomexicana ). The remaining species are found more often as members of desert scrub communities bordering the floodplain. Of these ten, all except rabbitbrush and Nevada saltbush grow mostly near the present river channel. The latter two also grow down to the water's edge, but they are more abundant on higher ground and are the only woody species present on much of the floodplain outside the immediate vicinity of the river.

Herbaceous species form an understory throughout the riparian woodland. Areas that remain wet most of the year support marsh vegeta-


77
 

Table 1.—Percentage frequency of riparian woodland species above channel banks.1

Site

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

20

Bank

W

W

E

E

W

E

E

W

W

E

W/E

W/E

W/E

W/E

W/E

W/E

W/E

W/E

W/E

W/E

Artemisia
     spinescens

7

Atriplex
     canescens

3/

Atriplex
     confertifolia

14

/31

Atriplex
     parryi

26

/3

Atriplex
    torreyi

44

11

13

19

+

38/9

18/11

28/41

17/38

30/16

11/44

47/43

15/27

15/

+/

Chrysothamnus
     nauseosus

27

46

53

18

44

31

11

5/10

/3

56/21

11/18

8/

23/15

15/

+/

Populus
    fremontii

1

Rosa
     woodsii

11

22

+

6

2

1

16

Salix
     exigua

22

93

8

2

1

2

19

2/2

Salix
     gooddingii

21

5

85

+

44

/2

1/1

2/9

1/1

1/13

31/6

Salix
    laevigata

5

16

Sarcobatus
     vermiculatus

2

7

14

37

/+

/+

1/38

Tamarix
     ramosissima *

+

+

/6

14/

5/

/+

/3

Tetradymia
    axillaris

/2

1 Frequency is expressed as percentage of meters transected (105 m. per bank) in which species is present.
* Introduced species.
+ Present on site but not on transect.

 

Table 2.—Percentage frequency of riparian woodland species in channel.1

Site

11

12

13

14

15

16

17

18

19

20

No. of m. transected

76

90

79

168

115

174

97

119

115

83

Artemisiatridentata

+

Atriplexcanescens

2

Atriplexconfertifolia

1

1

Atriplextorreyi

4

10

30

8

2

5

5

6

10

Chrysothamnusnauseosus

5

5

4

2

9

Elaeagnusangustifolia *

+

Forestieraneomexicana

2

+

+

Rosawoodsii

+

+

Salixexigua

2

Salixgooddingii

13

7

42

24

25

42

26

61

Tamarixramosissima

14

18

4

17

3

1 Frequency is expressed as percentage of meters transected in which species is present.
* Introduced species.
+ Present on site but not on transect.


78

tion dominated by Typha , Scirpus , Carex , and Juncus . On much of the floodplain, however, the herb layer is a dense perennial sod of Distichlisspicata , Sporobolusairoides , and Juncus balticus .

At the boundary between floodplain and valley floor, vegetation on both sides of the river changes in most areas to a desert scrub dominated by Sarcobatusvermiculatus , Atriplexconfertifolia , and A . parryi . Less frequently encountered are Artemisiaspinescens , A . tridentata , Atriplexcanescens , A . polycarpa , Daleafremontii , D . polyadenia , Tetradymiaglabrata , and T . axillaris .

Species turnover along Owens River is low: eight of the ten most common riparian woodland species occur at least sporadically throughout the study area. The exceptions are desert olive, not observed north of Manzanar Road, and Russian olive, encountered only between the aqueduct intake and Mazourka Canyon Road. Nevertheless, the character of the woodland varies greatly from one end of Owens Valley to the other because of differences in the abundance of the few species present, as shown in tables 1 and 2. (Sites 11–20 are separated into above-bank and channel sections to allow better comparison with sites 1–10, where transects did not extend into the channel.)

North of Bishop, the woodland consists mostly of dense stands of Rosawoodsii , narrowleaf willow, and rabbitbrush that extend well back from the river on low ground (fig. 2). Tree cover (mostly valley willow) increases below Bishop, and the frequency of R . woodsii and narrowleaf willow declines, though both remain common to the aqueduct intake. Rabbitbrush and Nevada saltbush are abundant everywhere; both were observed at or near all sites north of the intake.

Below the intake an immediate change occurs. Few trees grow on the floodplain surface south to Mazourka Canyon Road; woody vegetation above the

figure

Figure 2.
Owens River north of Bishop.

banks consists almost entirely of Nevada saltbush and rabbitbrush, with salt cedar scattered along dry washes (fig. 3). The dry channel bottom is lined with Atriplex and Tamarix , though trees become more frequent southward. Russian olive grows sparsely on the floor of the channel for several kilometers north of Mazourka Canyon Road. Narrowleaf willow and R . woodsii were observed only in the channel, at places where damp soil indicated a shallow groundwater table.

Below Mazourka Canyon Road, tree cover continues to increase both in the channel and along the banks (fig. 4). Salt cedar becomes less frequent and rabbitbrush more so; Rosa woodsii and narrowleaf willow are also more common, but for the most part do not occur in the large stands found in the Bishop region.

Like the woody overstory, most herbaceous species become less abundant along the dry channel. In contrast to the thick sod present in other areas, much of the floodplain surface in this section is bare except for Salsola iberica , Bassiahyssopifolia , and other weedy annuals.

Few tree seedlings were seen north of the aqueduct intake except at site 8 (table 3). Seedlings are also absent in most of the dry section below the intake, but become more common from site 14 south in the channel bottom.

Human Impact

Early Descriptions of the Riparian Woodland

Descriptions of the riparian woodland as it appeared before European settlement are few and somewhat contradictory. Expeditions escorted by Joseph Walker passed through Owens Valley in 1834, 1843, and 1845 (Goetzmann 1966; Davidson 1976), but apparently none left a first-hand account of vegetation along the river. The 1845 expedition was directed, but not accompanied, by

figure

Figure 3.
Salt cedar lining dry bed of Owens River near Independence.


79
 

Table 3.—Riparian tree density.1

                     

Above banks

             

Site

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

20

Bank

W

W

E

E

W

E

E

W

W

E

W/E

W/E

W/E

W/E

W/E

W/E

W/E

W/E

W/E

W/E

Salix
     gooddingii

                                       

Taller than 2 m.

29

2

71

1

9

1/1

2/13

/1

4/38

10/4

Less than 2 m.

2

44

Salix
     Laevigata

                                       

Taller than 2 m.

9

Populus
     Fremontii

                                       

Less than 2m.

2

                     

In channel

Site

                   

11

12

13

14

15

16

17

18

19

20

Salix
     gooddingii

                                       

Taller than 2 m.

                   

1

19

24

26

7

48

4

8

Less than 2 m.

                   

2

2

9

4

3

1

1 Area sampled above bank at each site is 2500 m2 (0.25 ha.) per bank. Area sampled in channel varies between 1200 and 2900 m2 .

John C. Fremont, who later described Owens River as "wooded with willow and cottonwood" (Fremont 1849), perhaps on the basis of descriptions furnished him by members of the expedition. Much of Owens Valley was surveyed by A.W. von Schmidt in 1855, but his field notes only mention riparian vegetation near Lone Pine, where von Schmidt encountered willows along the river.[4] A cor-

figure

Figure 4.
Owens River near Keeler Road.

respondent accompanying a military expedition through Owens Valley in 1859 described it as untimbered except for a few small cottonwoods (Davidson 1976). William Brewer, of the California Geological Survey, encountered no trees at all in the valley in 1864 (Brewer 1930). An 1886 settler's tract states that before settlement there was "no timber of any kind" in Owens Valley; the river was bordered by "grassy plains" dotted with occasional shrubs (Anon. 1886). An early inhabitant of the valley, however, recalled large willows lining the river east of Independence (Earl 1976).

These accounts suggest that tree cover has always been sparse along Owens River, though it seems unlikely that trees were ever entirely absent. Early explorers may have kept mostly to the west side of the valley, where travel is easier but the river is often hidden from view. Although no clear picture of the presettlement riparian woodland emerges from these descriptions, examination of the history of land use and water management in Owens Valley provides indirect evidence of the changes that may have occurred since settlement.

Mining

Between 1860 and 1864 numerous claims were located in the Inyo and White Mountains, and four mining towns were established near Owens River (Chalfant 1922). Reduction works were built at five sites near the river, at least two of them

[4] USDI Bureau of Land Management. Surveyor General of California. 1855. Unpublished surveyor's field notes, books 115, 203, 296. On file at Bureau of Land Management, Sacramento, Calif.


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requiring wood or charcoal for operation (Raymond 1869). Although additional discoveries were made in the valley after 1864, the early excitement died out rapidly. By 1870, three and perhaps all four of the small mining towns were deserted, and most of the mills were idle (California State Mining Bureau 1888). The impact of this short-lived mining boom on the riparian vegetation of Owens River was probably small. Canals were dug from the river to at least two mills, but their construction entailed little disturbance of the riparian zone. Trees may have been cut near the river to supply the mills, but most wood no doubt came from the mountain slopes flanking Owens Valley.

Browsing

Livestock

Livestock were driven through the valley as early as 1859; by 1861 permanent ranches were established near present-day Bishop (Chalfant 1922; Davidson 1976). Local stock were wintered on the meadows of the Owens River floodplain and other shallow-groundwater areas on the valley floor, then moved to mountain pastures in summer (Earl 1976). In addition, large herds of sheep were driven through Owens Valley to mountain ranges each spring (Anon. 1886), and in dry years cattle and sheep were driven into the valley to take advantage of its subirrigated grasslands (California State Mining Bureau 1888).

Stock raising suffered along with the rest of the valley economy as Los Angeles bought up land for the Los Angeles Aqueduct. The greatest decline took place after 1923, when the city began to buy land in the Bishop-Big Pine region. Collapse of the industry was averted by Los Angeles' decision to lease some land back to ranchers. Expansion of the lease program was encouraged by a series of wet years beginning in 1936 and by completion of the aqueduct extension to Mono Lake in 1940 (Los Angeles Department of Water and Power 1966). Most of the valley floor, including the floodplain of Owens River, is now occupied by large grazing leases devoted almost entirely to cattle production. Animals are still moved seasonally to mountain range, but some ranchers keep stock in the valley year-round. In general, stock graze the river lands from October or November to March or April, and are absent the rest of the year.

Without detailed historical records, the impact of livestock on the riparian woodland must largely be surmised. The river grasslands provide a perennial water supply and abundant forage, and have probably always been used more heavily than the surrounding desert range. Grazing pressure may have become severe in dry years before institution of the present lease program, but if overgrazing occurred it seems not to have been recorded. Creation of large leases reduced fluctuations in the size of the valley's livestock population, and probably also reduced summer grazing intensity near the river. Determination of range carrying capacity has been left to leaseholders, however, and some overstocking may have occurred since leasing began.

Regardless of past stocking levels, livestock have probably exercised selective pressure on the composition of the riparian woodland. All of the shrub species in the woodland are browsed, but some are of low palatability or have weedy characters that enable them to persist despite browsing. Narrowleaf willow spreads by means of root suckers, in some areas forming dense stands that appear to exclude livestock. Rabbitbrush is well known as an invader of overgrazed rangeland and other disturbed areas in the West. Presence of livestock in the riparian zone may have favored these shrubs at the expense of other species. Livestock browse mature willow trees very lightly, according to local ranchers—perhaps partly because most animals are removed from bottomland pastures when the trees are in leaf. Browsing does not appear to injure mature trees greatly, though some have browse lines. Damage to seedlings may be greater: many of those observed during field work appeared to have been cropped by browsing animals.

Tule Elk

An initial herd of 54 tule elk (Cervuselaphus nannodes Merriam) was released north of Independence in 1933 and 1934. The herd multiplied to 189 head by 1943, but has since fluctuated between 150 and 500 because of hunts held to control population size (McCullough 1969). At least four herds of elk now browse near Owens River. Although seasonal movements vary from one herd to the next, elk may use most of the bottomland from Owens Lake to the bend north of Bishop in the course of a year (Curtis etal . 1977).

The elk subsist on browse plants, particularly on willows, to a much greater degree than do livestock (McCullough 1969). They may have contributed to development of browse lines on some trees, but like livestock are more likely to have damaged seedlings than mature trees. Nevertheless, the elk population is small in relation to the livestock population, and its effect on the riparian woodland is probably small by comparison.

Beaver

Beaver were introduced to Owens Valley by the California Department of Fish and Game at Baker Creek in 1948.[5] They have since spread to Owens River, both above the aqueduct intake and in the spring-fed section below it.

Beaver feed on cottonwood and on both willow tree species. They often gnaw willows completely through, but the willows are able to stump-sprout if not further disturbed. Large cottonwoods are often girdled and completely killed. Beaver are

[5] Unpublished records, California Department of Fish and Game.


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found the entire length of the upper river, but their activity is localized. In some areas almost all trees have been affected; in others they remain untouched. Approximately 24% of the trees at sites 1–10 showed signs of gnawing by beaver. Despite the presence of beaver in the lower river, none of the trees at sites 16–20 appeared to have been damaged.

Crop Cultivation

Cultivation of crops began in the 1860's, largely as an adjunct to the livestock industry. Farms were at first clustered along creeks on the west side of the valley, but later spread onto the valley floor following construction of large irrigation canals from Owens River. Expansion of irrigated cropland was greatest near Bishop and Big Pine, where approximately 17 canals began operation between 1872 and 1890.[6]

Los Angeles' acquisition of valley lands halted irrigation of cropland from Owens River by about 1930.[7] Although Los Angeles began to make water available again in the late thirties for irrigation of pasture and fodder crops on grazing leases, local irrigation allotment has depended on annual runoff and cultivated acreage has remained small (Los Angeles Department of Water and Power 1979).

Land-use maps compiled for most of the valley floor early in this century[8] suggest that, despite the extensive canal system, little land was ever farmed near Owens River. A few fields were cultivated on the floodplain at Big Pine and Bishop, but there as elsewhere most of the bottomland was left in native pasture, probably because of its shallow water table and salt-affected soils.

Agricultural land clearing thus caused no wholesale reduction of the riparian woodland in Owens Valley. Cultivation and abandonment of the few fields on the floodplain may have encouraged the growth of rabbitbrush—a frequent invader of abandoned fields in the Bishop area—but the maps cited above show vegetation patterns approximating those of today: the floodplain largely covered by herbaceous growth, with willows confined to the river and other runoff channels.

Fire

Intentional burning has been practiced at one time or another along most of Owens River. Ranchers probably burned the bottomland pastures occasionally in pre-aqueduct days, and present leaseholders say that intentional burning occurred on many leases from shortly after institution of the lease system until about 1970. During the sixties, for example, the floodplain was burned between Lone Pine Station Road and Mazourka Canyon Road, and between Pleasant Valley Reservoir and Five Bridges (north of Bishop). The latter area has been burned several times, and part of it sprayed with herbicides, to improve livestock access to the river.

The incidence of wildfires has probably increased along the upper river with greater use of the riparian zone by campers and fishermen in the last 30 years. Local residents recalled several recent wildfires on the floodplain, including a large one northeast of Bishop in about 1968. I found evidence of burning at 12 of the 20 sites sampled in 1980 (sites 1–3, 6, 12, and 14–20).

The riparian woodland may have been affected most by fire north of Bishop. Repeated burns there could have eliminated willow and cottonwood trees and favored faster-maturing shrubby species like rabbitbrush and narrowleaf willow, which resprout readily after fire. The impact of burning is difficult to assess, however, without better information about the post-fire responses of the other woodland species.

Plant Introductions

Two Eurasian shrubs, Russian olive and salt cedar, have become established in the riparian woodland as an indirect result of human dispersal. Both were probably introduced to the Southwest as ornamental plants in the nineteenth century, but have since become naturalized along many southwestern watercourses (Christensen 1963; Robinson 1965). Earliest evidence I have found of Russian olive in Owens Valley is a 1942 collection from naturalized plants growing along Lone Pine Creek,[9] but it had probably been introduced in cultivation long before then. Russian olive appears to have become established on Owens River only in the Independence region, where it is scattered along the bottom and sides of the dry channel. Salt cedar reached Owens Valley at least by 1944, when aerial photographs show it growing along the 1872 earthquake fault near Mazourka Canyon Road.[10] It too may first have been introduced as an ornamental, but has now become naturalized throughout Owens Valley and is a notable element of the riparian woodland

[6] Los Angeles Department of Water and Power [n.d.]. History Owens Valley irrigation ditches. Unpublished report by J.L. Graham.

[7] Unpublished canal discharge records, LA DWP.

[8] Los Angeles Department of Water and Power. Map of Bishop region in Owens Valley [unpublished]. Prepared under the direction of C.H. Lee. 6 sheets. Scale 1:12,000.

Los Angeles Bureau of Water Works and Supply [n.d.]. Detail map of a portion of Owens Valley near Lone Pine, California [unpublished]. 2 sheets. Scale 1:6000. On file at LADWP.

[9] Constance, Lincoln. 1980. Personal communication.

[10] Los Angeles Department of Water and Power. 1974. Vegetational resource inventory and potential change assessment, Owens Valley, Calif. Unpublished report by Earth Satellite Corporation.


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south of the aqueduct intake. Establishment of salt cedar and Russian olive along Owens River appears related to alteration of the river's natural regime by the Los Angeles Aqueduct system (discussed below).

Water Management

Irrigation

Most irrigation diversions in Owens Valley began before 1890; by 1904 it was estimated that over 75% of the annual runoff in the valley was diverted for irrigation.[11] These diversions reduced the total discharge of Owens River and altered its natural regime: maximum and minimum flows were both reduced downstream by large summer irrigation diversions, but winter flow was almost doubled by agricultural drainage.[12] Flood frequency and magnitude doubtless diminished as well.

These changes may have affected regeneration of willows and cottonwoods, whose reproduction is tied to the natural runoff regime. Reduction of maximum and minimum flows could have decreased the area of freshly exposed alluvium available for colonization during the growing season or shifted the zone of seedling establishment downward in the channel, where young plants would be more susceptible to damage by the increased winter discharge. Consumptive use of water by agriculture would also have decreased the total water supply to riparian vegetation downstream. The effects of irrigation have since been obscured, however, by changes associated with more recent water management practices.

The Los Angeles Aqueduct System

Operation of the Los Angeles Aqueduct system began with completion of the aqueduct in 1913. The aqueduct had little effect on Owens River above the intake until 1929, when Tinemaha Dam began to regulate flow to the aqueduct at the Poverty Hills. The rest of the upper river remained unregulated until 1941, when Long Valley Dam was completed at the head of Owens River Gorge. Pleasant Valley Dam was added in 1957 to smooth out fluctuations caused by powerplants below Long Valley Dam.

Natural river discharge has been increased above the intake by interbasin transfers and groundwater pumping. The Mono Basin extension of the aqueduct system began diverting water to Owens River at Long Valley in 1941, and diversions increased following construction of the Second Los Angeles Aqueduct (located outside the study area) in 1970. These increases can be seen in the record of annual river discharge at Pleasant Valley (fig. 5).

figure

Figure 5.
Annual discharge of Owens River at
Pleasant Valley and Keeler Bridge.
Source: unpublished streamflow records, LADWP.

During a prolonged dry period in the twenties and thirties, Los Angeles drilled approximately 170 wells in Owens Valley to increase supply to the aqueduct (Los Angeles Department of Water and Power 1966). Many of these wells were located north of the intake and discharged water into the river channel rather than the aqueduct. Pumping occurred from 1919 through 1935, then halted until the dry years 1960–62 (Los Angeles Department of Water and Power 1979). More wells were drilled after completion of the Second Aqueduct, and pumping now occurs every year.

South of the aqueduct intake, Owens River and most other streams have been diverted by the aqueduct since 1913, though some water continued to flow down the lower channel past the intake in most years until Tinemaha Dam provided a means of storing high flows. Since then water has been shunted downstream on just a few occasions, mostly when runoff has exceeded system capacity: in 1936–39 (before completion of Long Valley Dam), then again in 1967, 1969, and 1975.[13] The 1938 and 1969 flows were exceptionally large, as can be seen from the record at Keeler Bridge east of Lone Pine (fig. 5).

Groundwater seepage has maintained some surface flow in the lower channel south of its intersection with the 1872 earthquake fault. This discharge has been quite small, often dropping to almost nothing from July through September, but relatively constant from year to year when no water is released past the intake.

Vegetation change associated with operation of the aqueduct system should be greatest in the section of channel between the aqueduct intake and the river-fault junction, which has remained dry since 1929 except for scattered seeps and irregular flood discharges. Field data (tables 1

[11] U.S. Reclamation Service. 1904. Report on the Owens Valley, California. Unpublished report by J.C. Clausen. On file at the Los Angeles Public Library, Water and Power Branch.

[12] Unpublished streamflow records, LADWP.

[13] Unpublished streamflow records, LADWP.


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and 2) support this conclusion: diversion of surface flow appears to have eliminated most of the native riparian woodland from this area, except for the species least closely associated with riparian zones. Riparian taxa persist mainly in the channel bottom just north of the fault, where groundwater is most readily available. South of the fault, the small surface flow provided by spring discharge has evidently been sufficient to maintain much of the original riparian cover.

Establishment of salt cedar and Russian olive in the woodland is also best explained as a consequence of aqueduct system operation. Although salt cedar was perhaps naturalized near the river by 1944, local residents say that it became common only after flooding of the lower river in 1967 and 1969. The shrub spread rapidly into flooded areas, becoming especially dense in the dry section below the intake. Salt cedar is similar to the native willows and cottonwoods in being adapted for establishment after such fluvial disturbances, but here as elsewhere in the Southwest it has been better able than the native flora to colonize a habitat created by alteration of the natural runoff regime. Its success may be partly attributable to such inherent ecological advantages as more prolonged annual seed production and lower moisture requirement than the native riparian species (Horton 1977), Water was released down the old channel during the entire summer of both 1967 and 1969, perhaps delaying most seedling establishment until only salt cedar was still dispersing seed. On the other hand, willow and cottonwood seedlings may have been present initially but failed to survive without a permanent water supply.

When Russian olive reached the river is not certain, but the small size of all individuals observed during field work suggests that it too may have become established since 1969. It has not become as widespread as salt cedar, perhaps because its olive-like fruits are not wind dispersed.

Above the aqueduct intake, operation of the aqueduct system has changed the natural regime of Owens River (fig. 6): instead of cresting early in summer and falling rapidly to a late-summer minimum, the river now remains high from spring through fall, and maximum monthly discharge often occurs at the time of former low water. Flood magnitide and frequency have decreased, because flood discharge can be diverted or stored upstream. Similar changes in natural river regime have been found to hinder reproduction of riparian species elsewhere by eliminating the substrate necessary for seedling establishment (Johnson etal . 1976), and may partly account for the scarcity of young cottonwood and tree willow seedlings along the upper river channel. (The single exception, at site 8, is difficult to explain since other, apparently similar sites are devoid of young trees, but it does show the potential for seed reproduction where favorable conditions exist.) Seed reproduction appears more active in the channel itself below the earthquake fault, the only area in which river discharge still rises and falls more or less naturally.

Since 1970, tree regeneration along the upper river may also have been reduced by erosion associated with increased import for the Second Aqueduct. Bank slumping has in many areas produced vertical, unstable channel sides on which seedlings are unable to take root.

figure

Figure 6.
Mean monthly discharge of Owens River at Pleasant Valley.
Source: unpublished streamflow records, LADWP.

Conclusions

The most obvious human-caused changes in the Owens River riparian woodland have stemmed from diversion of the river by the Los Angeles Aqueduct. Elimination of much of the native riparian vegetation between the intake and the earthquake fault has created an open niche that has been partly filled by salt cedar and Russian olive with recent flooding of the old channel. Both species will probably continue to spread in the future because of the need to waste water from the aqueduct system in very wet years.

Below the fault, native riparian vegetation has been maintained by spring flow, and has in fact spread into the channel with reduction of river discharge. The riparian woodland may be as dense now in some parts of the lower river as it was before completion of the aqueduct.

North of the intake, the combined effects of browsing, burning, clearing, and water management may have caused a reduction in the tree cover and an increase in such weedy shrubs as rabbitbrush and narrowleaf willow—especially near Bishop, where human impact has been most concentrated. Lack of seed regeneration by native tree species along the upper river may be due to browsing or the disruption of the natural river regime. Nevertheless, sexual regeneration of riparian species could be naturally uncommon along Owens


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River. Historical records suggest that the river's unusually small annual discharge range, together with a shallow groundwater table and relatively erosion-resistant floodplain material, allowed development of a dense growth of herbaceous perennials that covered much of the floodplain and often extended, as at present, right to the water margin. Competition from this herbaceous cover could have limited most seedling establishment to areas of intense fluvial disturbance, perhaps present only after infrequent major floods. In this regard the dynamics of the riparian zone along Owens River may have differed from those of many other western streams, which annually rework a much wider expanse of alluvium because of their greater discharge range and might provide greater opportunity for seed regeneration. Comparison of the relative success of vegetative and seed reproduction in relation to discharge regime in other riparian systems might clarify processes in the Owens River woodland.

Regardless of whether tree regeneration is being artificially suppressed or is naturally uncommon, the present scarcity of young trees along the upper river may portend further decline of the tree cover. Management of the river discharge for aqueduct operations will no doubt continue to prevent most flooding, and tree establishment may be increasingly confined to the immediate river channel, which is now near bankful stage much of the time.

Literature Cited

Anon. 1886. Inyo County, its resources and attractions for settlers. Inyo Independent Printers, Independence, Calif.

Brewer, W.H. 1930. Up and down in California in 1860–1864. F.P. Farquhar (ed.). Yale University Press, New Haven, Conn.

Chalfant, W.A. 1922. The story of Inyo. Published by the author.

Christensen, E.M. 1963. Naturalization of Russian olive (Elaeagnusangustifolia L.) in Utah. American Midland Naturalist 70:133–137.

Curtis, B. etal . 1977. Owens Valley tule elk habitat management plan. 2 sections.

Davidson, J.W. 1976. The expedition of Capt. J.W. Davidson from Fort Tejon to the Owens Valley in 1859. In : P.J. Wilke and H.W. Lawton (ed.). Publications in archaeology, ethnology, and history, No. 8. Ballena Press, Soccorro, N.M.

Earl, G.C. 1976. The enchanted valley and other sketches. Arthur H. Clark Co., Glendale, Calif.

Fremont, J.C. 1849. Notes of travel in California. James M'Glashan, Dublin, Ireland.

Goetzmann, W.H. 1966. Exploration and empire: The explorer and the scientist in the winning of the American West. Alfred A. Knopf, New York, N.Y.

Goodyear, W.A. 1888. Inyo County. p. 224–288. In : Eighth annual report of the state mineralogist. California State Mining Bureau.

Horton, J.S. 1977. The development and perpetuation of the permanent tamarisk type in the phreatophyte zone of the Southwest. p. 124–127. In : R.R. Johnson and D.A. Jones (ed.). Importance, preservation and management of riparian habitat. USDA Forest Service General Technical Report RM-43.

Johnson, W.C., R.L. Burgess, and W.R. Keammerer. 1976. Forest overstory vegetation and environment of the Missouri River floodplain in North Dakota. Ecological Monographs 46:59–84.

Los Angeles Department of Water and Power. 1966. Report on water supply management in Inyo and Mono Counties. Prepared by R.V. Phillips etal .

Los Angeles Department of Water and Power. 1979. Final environmental impact report: Increased pumping of the Owens Valley groundwater basin. 2 volumes.

McCullough, D.R. 1969. The tule elk: Its history, behavior, and ecology. University of California publications in zoology, Vol. 88. University of California Press, Berkeley, Calif.

Raymond, R. 1869. Statistics of mines and mining in the states and territories west of the Rocky Mountains. First annual report of the U.S. commissioner of mining statistics. Government Printing Office, Washington, D.C.

Roberts, W.G., J.G. Howe, and J. Major. 1977. A survey of riparian forest flora and fauna in California. p. 3–21. In : A. Sands (ed.). Riparian forests in California: Their ecology and conservation. Institute of Ecology Pub. 15. 122 P. University of California, Davis, Calif.

Robinson, T.W. 1965. Introduction, spread and areal extent of salt cedar (Tamarix ) in the western states. U.S. Geological Survey Professional Paper 491-A.

USDI Geological Survey. 1959. Compilation of records of surface waters of the United States through September, 1950. Part 11-B. Pacific slope basins in California, Central Valley. Water-Supply Paper 1315-A.


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The Transitional Nature of Northwestern California Riparian Systems[1]

R. Chad Roberts[2]

Abstract.—Within the region between the Sacramento Valley and the northwestern California coast, riparian vegetation undergoes a change in species composition apparently related to floristic history, climate, and local conditions. While forest areas appear structurally convergent, there may be significant regional taxonomic differences. Each plant species shows an individualistic response. Broad-niched nonriparian species may constitute the riparian forest in some sites. The vegetation type is used by many bird species distributed throughout the area; northcoast forests appear to have more resident species, but lack oak tree specialists.

Introduction

This paper presents a first look at biogeographic patterns in northwestern California riparian systems. Sacramento Valley riparian studies were just being planned a decade ago, motivated by the imminent demise of the native forests. To many northwestern California residents, riparian forests are a nuisance, an income source from logging, or a hindrance to agriculture. At best, the riparian strips are known to provide flood protection, and may be considered picturesque. Given these local viewpoints, it is not surprising that no studies similar to those of the last decade in the Sacramento River system have been done.

The 1980's should see such studies; northwestern California riparian systems are both different from those in the Sacramento Valley, and are subject to similar conversion pressures. These attributes raise a plea for attention from academic scientists, conservation biologists, and agency personnel. This paper is motivated to extend the concern that has developed for riparian systems elsewhere to include northwestern California. I show here how the biogeographic face of riparian forest changes within this region, and suggest preliminary explanations for the changes.

Interested readers are encouraged to investigate the area for themselves.

Methodology

Because this was a preliminary survey, no attempt was made to be quantitative or to rigorously test alternative hypotheses. These actions are logically deferrable to more detailed secondlevel studies. Information used herein was derived from field sampling and literature descriptions. Field sampling involved recording tree species, most shrub species, and common herbaceous species at sample sites within the study area. In most cases, notes were made of adjacent nonriparian vegetation. Additionally, (given my training and long-standing predilection) I recorded all bird species encountered.

Sample site choice was decidedly nonrandom. The coastal areas in Humboldt and Del Norte Counties are better covered than interior areas, and these counties are better sampled than inland counties. The Eel River's South Fork, the lower Mad River, and the Trinity River drainage are better sampled than are other basins.

The area covered by this survey extends from the lower Sacramento Valley (Yolo County; see figure 1) north to western Siskiyou County. West of that transect, the study area includes Del Norte, Humboldt, Trinity, northern Mendocino, Lake, and eastern Napa Counties. The area from southern Mendocino County to San Pablo Bay and nearby areas is specifically excluded.

Numerous literature sources proved useful, including descriptions accompanying mapping, planning documents and agency descriptions, published papers, and textbook descriptions. Some of these are cited below; others will be cited in subsequent papers.

[1] Paper presented at the California Riparian Systems Conference. [University of California, Davis, September 17–19, 1981].

[2] R. Chad Roberts is a Staff Environmental Analyst with Oscar Larson & Associates, P.O. Box 3806, Eureka, Calif.


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figure

Figure 1.
County outline map of northern California, showing study area and its
relationship to other areas. Adapted from Griffin and Critchfield (1972).

Results

Plant Biogeography

Species

Certain tree and shrub species are often considered characteristic of riparian systems, due either to requirements for high soil water content or to a tolerance of it. In this paper I assume that this requirement and/or tolerance is the criterion of riparian species in general. Other factors (light intensity, flood-scour potential, seed-source proximity, history, and competition) are likely to affect species distribution as well. Two distinct species groups comprise riparian forests in the study area. The following summaries deal only with tree species, but shrubs and herbaceous plants show similar (or even greater) regional differentiation.

SouthernGroup .—The study area includes parts of the Central Valley Riparian Forest region and most of the North Coast Riparian Forest region of Roberts etal . (1980). The entire west side of the Sacramento River Valley below elevations of 914 to 1218 m. (3000 to 4000 ft.) contains Foothill Woodland (Munz and Keck 1959), the riparian face of which includes species such as valley oak (Quercuslobata ), interior live oak (Q . wislizenii ), blue oak (Q . douglasii ), California buckeye (Aesculuscalifornica ), Fremont cottonwood (Populus fremontii ), and digger pine (Pinussabiniana ). In the study area's southern end, Hind's walnut (Juglans hindsii ) is a conspicuous element, and larger creeks may have Oregon ash (Fraxinuslatifolia ) and box elder (Acernegundo ).

The small creeks draining the inner Coast Ranges largely lack the extensive and diverse flora found beside major rivers (Conard etal . 1980). Larger creeks (Putah Creek, for example) have riparian forests containing many typical riparian species, but these disappear from riparian systems to the northwest. Cache Creek resembles the smaller creeks in its riparian borders. Figure 2 shows a typical riparian section from a southern creek.

NorthernGroup .—As a useful generalization, the opposite extreme of southern group creeks is the small coastal streams of Del Norte and Humboldt Counties. Elk Creek in Del Norte County has a relatively undisturbed, secondgrowth riparian forest, with red alder (Alnusrubra ), Pacific wax-myrtle (Myricacalifornica ), California bay (Umbellulariacalifornica ), and madrone (Arbutusmenziesii ) the most abundant hardwoods. North coast riparian forests contain a significant conifer element; Elk Creek includes Sitka spruce (Piceasitchensis ), Douglas-fir (Pseudotsugamenziesii ), redwood (Sequoiasempervirens ), and several other conifer species (Del Norte County Planning Dept. 1979). The same species are characteristic of small, coastal streamchannel forests from southern Oregon as far south as Ft. Bragg in Mendocino County. Since most coastal streams have been logged at least once, however, the conifer element is often less conspicuous, or is missing entirely.

figure

Figure 2.
Riparian vegetation bordering Chickahominy Slough, Yolo
Co. Blue oak, interior live oak, and digger pine are evident.


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North coastal riparian forests also contain diverse shrub and understory floras, including several willow (Salix ) species, several berry (Rubus ) species, two huckleberry (Vaccinium ) species, Pacific red elder (Sambucus callicarpa ), cascara (Rhamnuspurshiana ), and a number of others (Del Norte County Planning Dept. 1979; Roberts etal . 1980; McLaughlin and Harradine 1965). Most of these species are equally characteristic of other nonriparian zones near the streams, suggesting that they may not be obligate riparian species. This appears to be true of most riparian tree species listed above, though the species appear to achieve their best growth in riparian situations.

South or inland of coastal Del Norte County, additional species occur which are characteristic of the northern species group. Bigleaf maple (Acermacrophyllum ) is an important redwood forest understory component, reaching maximum growth as a riparian species. Bigleaf maple occurs from the coast to the Sierra Nevada foothills (Griffin and Critchfield 1972); in eastern Shasta County it is often a shrub restricted to stream vicinities. Figure 3 shows a typical north coastal riparian forest.

Inland from the coast, additional riparian species are encountered that appear to be part of the northern species group. Oregon ash is a major riparian component in the Klamath River region of eastern Humboldt County, as well as in the upper Eel basin in northern Mendocino County. It occurs throughout the Trinity River basin and is still prominent in the Cottonwood Creek basin southwest of Redding. Oregon ash is present, but not prominent, in the North Fork, Cache Creek drainage, Lake County.

White alder (Alnusrhombifolia ) replaces red alder away from the coast, assuming the riparian alder role. It is present in the upper Eel River basin of southern Humboldt, where its range overlaps the red alder (A . rubra ), and is common throughout the Klamath, Trinity, and

figure

Figure 3.
Riparian forest, Mad River, Humboldt Co.; including
red alder, bigleaf maple, and Pacific elderberry.

upper Sacramento River basins. I have noted it in the upper Russian River drainage in eastern Mendocino County, but am uncertain of its abundance south and east of Clear Lake.

A major northern group species is the black cottonwood (Populustrichocarpa ). It is largely restricted to riparian zones, and forms the dominant structural component in floodplain forests in the lower Eel, Klamath, and upper Trinity River systems. It is not common in coastal areas, per se , reaching the Pacific only in the Eel, Mad, and Klamath River floodplains (fig. 4). The same gallery forests in the Eel (and probably the Klamath) River valley contain large willow trees, up to 24 m. (80 ft.) tall. At least Pacific willow (Salixlasiandra ) is present as a tree, along with black cottonwood and red alder. These riparian gallery forests are impressive for their luxuriance and structural diversity (fig. 4).

A third group of species exists which is technically related to the northern group. Generally part of the mixed evergreen association, it is composed of species found in the Klamath and Siskiyou Mountains and the interior Coast Ranges. Several species in this group occupy the riparian zone along creeks or rivers throughout much of the study area, in much the same way foothill woodland species do in the southern group. The most prominent facultative

figure

Figure 4.
Riparian gallery forest, Eel River, Humboldt Co.
Red alder, Oregon ash, black cottonwood, and
willow constitute the dominant vegetation.


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riparian species appear to be canyon live oak (Quercuschrysolepis ), tanoak (Lithocarpusdensiflorus ), and to a lesser extent black oak (Q . kelloggii ) and garry or Oregon white oak (Q . garryana ). Riparian species such as white alder, bigleaf maple, and dogwood may or may not be present, as is true for Douglas-fir, redwood, madrone, and other facultative riparian species noted above. Figure 5 shows a typical area where these ecologically eurytopic species occupy riparian zones.

Physiography

The words "riparian forest" usually evoke an image of a floristically and structurally diverse community growing by a large river. It is immediately clear that most northwestern riparian forests do not fit that mold. The following three community types appear to reflect on-the-ground conditions.

HeadwatersAreas .—Throughout the study area, the uppermost stream reaches have a border mostly comprised of the common species in the region. Southeastward in the region, chaparral species are prominent in this role; northward and westward, mixed-conifer forest species fill the role. In the Sacramento, Trinity, and Eel River headwater reaches, white alder, bigleaf maple, and various riparian shrubs are usually present.

The small headwaters streams are often actively eroding their channels at or close to bedrock. It appears that a significant physical parameter affecting the plants is the ability to find a foothold and nourishment in the thin alluvial soils of these mountain canyons. In most cases, the streamflow regime provides adequate year-round water.

MidlevelAreas .—As the stream grade flattens, most north coast rivers show gravelbars and sand flats supporting riparian vegetation. Often these are narrow strips squeezed between the river and bedrock hillslopes (fig. 5). Fluctuating water levels and flood scour may

figure

Figure 5.
Midlevel riparian zone, upper Eel River, Mendocino Co. Canyon
live oak, white alder, and Douglas-fir are the major riparian species.

leave relatively little riparian vegetation in these areas. Where a valley is wide enough terraces form, which often support riparian groves.

Community composition on the terraces appears to result from a dynamic process of elimination, colonization, and exploitive competition. There communities typically have "nonriparian" canyon live oaks, tanoaks, or madrones growing in the riparian corridors, with or without alders, Oregon ashes, and other species. Apparently, individuals are eliminated from the community through bank scour or competitive death. Recolonization depends on seed source proximity and dispersal factors. In the midlevel Eel and Trinity River drainages, the result is a mosaic of riparian community types. Throughout much of northwestern California, the characteristic riparian species are white alder, canyon live oak, and Douglas-fir. The same process apparently leads to dominance of foothill woodland species in the Sacramento Valley area riparian communities.

Broad-ValleyFloodplainAreas .—Deposition of a thick sediment layer near abundant water leads to the formation of riparian gallery forests. In the Sacramento River drainage, this is the community primarily addressed in Sands (1980), which is present in this study area only in a few major, interior Coast Range channels. In the westward drainages, the broad floodplains are largely confined to the lower reaches (except in the Weaverville and Scott Valley areas where they are in large part due to gold dredging). Apparently, these areas once supported mixed conifer/deciduous redwood communities such as that on Elk Creek. Those riparian plant communities still present for the most part lack conifers, and consequently resemble deciduous gallery forests in interior river basins (fig. 6).

figure

Figure 6.
Floodplain gallery forest, Eel River near Miranda, Humboldt
Co. Black cottonwood and willow have reached large sizes
on terrace probably dating from 1964 flood.


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Colonization processes on the major floodplains appear to occur very rapidly. However, these floodplain areas are the primary agricultural areas in the north coast, and barring effective land use regulation, many of the gallery forests are likely to be cleared for agricultural purposes or in flood-control projects.

Bird Biogeography

Several Sacramento Valley studies have catalogued riparian bird use (Gaines 1980, and included references; Motroni 1979; Hehnke and Stone 1979). No studies have been done to date specifically on riparian birds in northwestern California. Gaines (1980) noted 69 species during the breeding season and 66 wintering species in Central Valley riparian forests. Motroni (1979) observed 71 species. Hehnke and Stone (1979) apparently recorded 90 species. By contrast, Harris (1974) listed 142 species for mid-Humboldt County riparian systems, and (1979) 157 species for this type of system in the "North Coast/Cascade Zone" that includes this study area. Taken as a whole, northwestern riparian forests are apparently used by more species than are Central Valley riparian forests.

Gaines (1980) recorded 26 migrant species in the 69-species breeding avifauna (38%), and 30 migratory or sporadic visitors among the 66 wintering species (45%). Harris' (1974) list contains 36 summer visitors and 27 wintering species of the 142 total species, the remainder being residents. After the appropriate adjustments, 31% of the 115 summer species are visitors and 25% of the 106 wintering species are not permanent residents. As initial hypotheses, north coastal riparian forests appear to support more total bird species and more resident bird species than do the Sacramento River forests.

In comparing Harris' (1979) listing with Gaines (1980) the Falconidae, Rallidae, Hirundinidae, Strigidae, and Charadriidae are better represented in northwestern forests. Very likely, recent habitat simplification in the Central Valley is the basis for the difference. However, one ecological (but not taxonomic) group, namely oak woodland birds, appears to be under-represented in the north. Throughout the Sacramento River basin, the Plain Titmouse (Parusinornatus ), White-breasted Nuthatch (Sittacarolinensis ), Scrub Jay (Aphelocomacoerulescens ), Nuttall's Woodpecker (Picoides nuttallii ), and Acorn Woodpecker (Melanerpes formicivorus ) are common resident riparian species. Of these only the Scrub Jay and Acorn Woodpecker regularly occur in Humboldt County, and use systems other than riparian forests (Harris 1974, 1979; personal observation). A likely hypothesis to account for this is the lack of riparian valley oaks north of northern Mendocino County.

Discussion

Geofloristic History

When Axelrod (1958, 1959) postulated the Arcto-Tertiary and Madro-Tertiary Geofloras, he separated northwestern California from the Central Valley and its fringes. The former was called the Border-Redwood Forest (Axelrod 1959: 7); this association apparently dates to Pliocene age and represents a combination of floristic elements from Arcto- and Madro-Tertiary backgrounds.

As Robichaux (1980) showed, elements in the present riparian flora can be linked to fossils within both these geofloristic associations. Oregon ash and Pacific willow appear to be Arcto-Tertiary in origin and California sycamore (Platanusracemosa ) and arroyo willow (S . lasiolepis ) are more likely to have come from the southeast. Nonetheless, since the several species are all adapted to conditions near streams, they can be found intermixed to greater or lesser degree. For example, Fremont cottonwood is a Madro-Tertiary species now found along Central Valley watercourses, including those in the southeastern part of the sample area. Black cottonwood is an Arcto-Tertiary species; in the sample area, it is both coastal and higher elevation. Nonetheless, the two species overlap in the Trinity River basin at least from Douglas City to west of Weaverville. This site is in a drainage where black cottonwood are expected. Even if the present overlap were an artifact, there are dense stands of Fremont cottonwood along Cottonwood Creek, less than 33 air km. (20 air mi.) from the Trinity River stands, over a low ridge.

Axelrod (1977) discussed the range alterations induced in California vegetation by climatic change. In northwestern California there is little to impede north-south range shifts induced by changing temperature and rainfall regimes. The Franciscan Formation, the major geological substrate for the region, is faulted in a northwestward-trending direction; the north coastal rivers have followed the faultblock alignment (fig. 7). It appears that this alignment would be conducive to riparian species mixing, if species showed differential climatic responses along this north-south transect.

Substrate availability within the river channel should modify the pattern induced by climate. Narrow, rocky canyons could prove an obstacle to species requiring thick sediment deposits. Extreme channel scouring through high runoff during winter rainy periods could prevent seedling establishment and remove parent trees. Conversely, high erosion levels (typical of north coast rivers) could provide alluvial sediment deposits favoring riparian growth.

Present Communities

Given the origins shown in geological records, combined with other factors affecting


90

figure

Figure 7.
Raised relief map of northern California.
Note northwest-trending mountain blocks.
Modified from Griffin and Critchfield (1972).

plant evolution in California (Raven 1977), it follows that present riparian communities reflect species' tolerances of recent geoclimatic conditions. As an hypothesis, communities along a southeast-to-northwest transect show decreasing cold (or wetness) tolerance toward the southeast end.

Riparian plant associations at opposite ends of the transect appear quite different in species composition, though there are great structural similarities. However, the changes along the transect appear gradual; species composition changes by percentages, rather than in sharp discontinuities. Both the lower Sacramento and lower Eel Rivers have forests dominated by broad-leaved deciduous trees; the forests are structurally similar but taxonomically different. Between those endpoints, tree taxa respond to local ecological conditions, and one finds conifers mixed with broad-leaved riparian species (both evergreen and deciduous). The forest composition at a particular site within the sample area depends on ecofloristic factors reflecting species ranges, and on physical conditions at the site. Hence, one expects to find an isolated Fremont cottonwood among the white alder, Oregon ash and canyon live oak in the upper Eel River drainage in Mendocino County; or sparse-foliaged Oregon ash among the oak and digger pine in Chickahominy Slough in Yolo County; or California buckeye within three kilometers of the Pacific Ocean in the lower Mattole River in Humboldt County.

It is time that biologists and conservationists interested in riparian forests investigated these northwestern sites. This holds for zoologists as well as botanists. The absence of oak forest birds from Humboldt County riparian forests suggests it may be profitable to consider the evolutionary association of birds such as Nuttall's Woodpecker and Plain Titmouse with such California endemics as the blue oak (Quercusdouglasii ) and valley oak. I am unaware of California studies of riparian small mammal communities, such as that by Geier and Best (1980) in Iowa, or those of the Lower Colorado River Project. Comparisons between the structurally similar but taxonomically distinct forests in the Sacramento Valley and the lower Eel or Klamath River basins could serve to test biogeographic habitat-diversity models. These studies should be initiated soon, however, for the north coast riparian forests, like those elsewhere, are under duress, and the situation will likely get worse rather than better.

Literature Cited

Axelrod, D.I. 1958. Evolution of the Madro-Tertiary Geoflora. Bot. Rev. 24:433–509.

Axelrod, D.I. 1959. Geological history. p. 5–9. In : P.A. Munz and D.D. Keck, A California Flora. 1681 p. University of California Press, Berkeley, Calif.

Axelrod, D.I. 1977. Outline history of California vegetation. p. 139–193. In : M.G. Barbour and J. Major (ed.). Terrestrial vegetation of California. John Wiley & Sons, New York, N.Y.

Conard, S.G., R.L. MacDonald, and R.F. Holland. 1980. Riparian vegetation and flora of the Sacramento Valley. p. 47–55. In : A. Sands (ed.). Riparian forests in California—their ecology and conservation. Institute of Ecology Pub. 15. 122 p. University of California, Davis, Calif.

Del Norte County Planning Department. 1979. Elk Creek wetland special study; Del Norte County Local Coastal Program. 51 p.

Gaines, D.A. 1980. The valley riparian forests of California; their importance to bird populations. p. 57–85. In : A. Sands (ed.). Riparian forests in California—their ecology and conservation. Institute of Ecology Pub. 15. 122 p. University of California, Davis, Calif.

Geier, A.R., and L.B. Best. 1980. Habitat selection by small mammals of riparian communities: evaluating effects of habitat alterations. J. Wildl. Manage. 44:16–24.

Griffin, J.R., and W.B. Critchfield. 1972. The distribution of forest trees in California. USDA Forest Service Research Paper PSW-82. 114 p. Pacific Southwest Forest and Range Experiment Station, Berkeley, Calif.


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Harris, S.W. 1974. No title. p. II-94– II-105. In : Eureka-Arcata Regional Sewage Facility Project Environmental Impact Report. Environmental Research Consultants, Inc.

Harris, S.W. 1979. Bird narratives. In : B. Marcot (ed.), California Wildlife/Habitat Relationships Program—North Coast/Cascades Zone, Vol. 2. USDA Forest Service. Washington, D.C.

Hehnke, M., and C.P. Stone. 1979. Value of riparian vegetation to avian populations along the Sacramento River system. p. 228–235. In : R.R. Johnson and J.F. McCormick (ed.). Strategies for protection and management of floodplain wetlands and other riparian ecosystems. USDA Forest Service GTR-WO-12. Washington, D.C.

McLaughlin, J., and F. Harradine. 1965. Soils of western Humboldt County, California. 85 p. Department of Soils and Plant Nutrition, University of California, Davis, with Humboldt County, Calif.

Motroni, R.S. 1979. Avian density and composition of a riparian forest—Sacramento Valley, California. 172 p. M.S. Thesis, Sacramento State University.

Munz, P.A., and D.D. Keck. 1959. A California Flora. 1681 p. University of California Press, Berkeley, Calif.

Raven, P.H. 1977. The California flora. p. 109–137. In : M.G. Barbour and J. Major (ed.). Terrestrial vegetation of California. John Wiley & Sons, New York, N.Y.

Roberts, W.G., J.G. Howe, and J. Major. 1980. A survey of riparian forest flora and fauna in California. p. 3–19. In : A. Sands (ed.). Riparian forests in California—their ecology and conservation. Institute of Ecology Pub. 15. 122 p. University of California, Davis, Calif.

Robichaux, R. 1980. Geological history of the riparian forests of California. p. 21–34. In : A. Sands (ed.). Riparian forests in California—their ecology and conservation. Institute of Ecology Pub. 15. 122 p. University of California, Davis, Calif.

Sands, A.(ed.) 1980. Riparian forests in California—their ecology and conservation. 122 p. Institute of Ecology Pub. 15. University of California, Davis, Calif.


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Classification and Dynamics of Subalpine Meadow Ecosystems in the Southern Sierra Nevada[1]

Nathan B. Benedict[2]

Abstract.—Subalpine meadow ecosystems are an important high elevation riparian vegetation type in the Sierra Nevada. The study of meadows has proceeded in two directions: classification; and studies of meadow dynamics. This paper reviews current research on these two topics in the southern Sierra Nevada.

Introduction

At high elevations in the southern Sierra Nevada, California, one of the most frequently referred to riparian systems is meadow ecosystems. Although there are other high elevation riparian systems, meadows are often chosen for study due to their visual attractiveness and importance for grazing and camping. High elevation meadows, though, are not exclusively riparian in that they can occur in any area with a sufficient amount of moisture, e.g. spring-fed meadows. This correlation between meadow ecosystems and moisture suggests that meadows play an important role in the hydrology of high elevation watersheds. As a result, a discussion of meadow classification and dynamics is vital to a thorough understanding of Sierran high elevation watersheds and riparian systems. This paper reviews current research on the classification and dynamics of southern Sierran meadow ecosystems.

Classification

Until recently, the classification of Sierran meadows was based on a simplistic scheme first suggested by Sumner[3] and subsequently followed and modified by Sharsmith[4] , Benedict (1965), and Strand (1972). The classification consists of three basic meadow types: 1) wet; 2) short-hair; and 3) woodland. Harkin and Schultz[5] proposed a topographic classification of meadows in the Rock Creek drainage, Sequoia National Park which consists of three meadow types: 1) level meadows; 2) hanging meadows; and 3) elongated stringers. More recently three meadow classifications have been presented for the southern Sierra Nevada (Benedict 1981; Benedict and Major 1980, 1981; Ratliff 1979). These three recent classifications look at meadows from three different and complementary points of view. Vegetation studies in other parts of the Sierra contain scattered descriptions of additional meadow communities and those described in the southern Sierra are discussed by Benedict (1981).

Ratliff (1979) presents a classification of meadow sites based on floristic composition. A meadow site is an area of meadow homogenous within itself and having a general species composition which is visually different from that of the adjacent areas (Ratliff ibid .). The classification was derived using various cluster analysis procedures until a final optimum classification was developed. Fourteen "site-classes" were described (table 1). Ratliff (ibid .) notes several problems with the classification. He states that the current site-classes are at least two levels above the individual meadow site. This increases the variability between sites within one site-class making it difficult to assign sites in the field to a given site-class. Another problem is that the actual number of sites in the classes is small in most cases. A total of 82 meadow sites were sampled for the classification and only 71 of over 200 species present were selected for use in the analysis proceedures.

[1] Paper presented at the California Riparian Systems Conference. [University of California, September 17–19, 1981].

[2] Nathan B. Benedict is with the Biology Department, University of Nevada, Reno, Nevada.

[3] Sumner, E.L. 1941. Special report on range management and wildlife protection in Kings Canyon National Park. Unpublished report. Sequoia National Park, Three Rivers, Calif.

[4] Sharsmith, C.W. 1959. A report on the status, changes, and ecology of back country meadows in Sequoia and Kings Canyon National Parks. Unpublished report. Sequoia National Park, Three Rivers, Calif.

[5] Harkin, D.W., and A.M. Schultz. 1967. Ecological study of meadows in Lower Rock Creek, Sequoia National Park. Unpublished report. Sequoia National Park, Three Rivers, Calif.


93
 

Table 1.—Site-classes of Sierran meadows (Ratliff 1979).

Association

Series (Site-class)

Dry Meadow

B—

Kentucky bluegrass

 

F—

tufted hairgrass

 

Moist Meadow

B—

Kentucky bluegrass

 

E—

longstalk clover

 

F—

tufted hairgrass

 

G—

Nebraska sedge

 

I—

pullup muhly

 

J—

bentgrass

 

K—

carpet clover

 

Wet Meadow

A—

beaked sedge

 

C—

ephemeral lake

 

D—

hillside bog

 

H—

fewflowered spikerush

 

Subalpine/Alpine Dry Meadow

 

N—

short-hair sedge

Subalpine/Alpine

L—

short-hair

Moist to Wet Meadow

M—

gentian/aster

Benedict (1981) presents a classification of meadow plant communities based on floristic composition of stands. Stands are defined as homogenous units of vegetation of variable size. Sampling was done using the Braun-Blanquet releve technique (Mueller-Dombois and Ellenberg 1974). The classification was derived using tabular association analysis of the 134 stands sampled. All species present (141) were used in the analysis procedure (Benedict 1981). Three main meadow types were described on the basis of floristic composition: 1) hydric; 2) mesic; and 3) xeric (table 2). Within each of these larger units, 19 plant associations were described with more narrowly defined species composition (table 2). The plant associations are at the stand or "site" (Ratliff 1979) level thus making them readily useable in the field. The geographic distribution of these plant associations is not known at present, but is thought to include most of the southern Sierra. Other meadow plant associations remain to be described (Benedict 1981).

 

Table 2.—Meadow plant associations. Sequoia National Park (Benedict 1981).

Meadow Type

Associations

Hydric

Carexrostrata

 

Eleocharispauciflora

 

Eleocharispauciflora /
     Mimulusprimuloides

 

Carex rostrata /
     Mimulusprimuloides

 

Calamagrostiscanadensis /
     Dodecatheonredolens

 

Deschampsiacaespitosa /
     Cardaminebreweri

 

Mesic

Calamagrostisbreweri /
     Asteralpigenus

 

Calamagrostisbreweri /
     Vacciniumnivictum

 

Calamagrostisbreweri /
     Oryzopsiskingii

 

Calamagrostisbreweri /
     Trisetumspicatum

 

Deschampsiacaespitosa /
      Senecio scorzonella

 

Deschampsiacaespitosa /
     Senecioscorzonella /
     Achillealanulosa

 

Juncusorthophyllus

 

Penstemonheterodoxus /
     Achillealanulosa

 

Carexheteroneura /
     Achillialanulosa

 

Xeric

Artemisiarothrockii

 

Carexexserta

 

Muhlenbergiarichardsonis

 

Eriogonum / Oreonana clementis

Benedict and Major (1980, 1981) present a classification of whole meadows on the basis of physiographic characteristics (table 3). Two major physiographic meadow types are described: Type I meadows with predominately vegetated margins (fig. 1), and Type II meadows with predominately sandy margins (fig. 2). Type I meadows occur in areas glaciated relatively recently and are usually surrounded by forests composed mainly of Pinus contorta subsp. murrayana . Type II meadows typically occur in areas of relatively more ancient glaciation or in areas that have not been glaciated, and are surrounded by forests composed of either pure Pinus balfouriana or a mixture of P . balfouriana and P . contorta subsp. murrayana . Both major types have a variety of subtypes distinguished by topographic position and rock type (Benedict and Major 1980, 1981; table 3). The geographic distribution of the different physiographic types is not completely

figure

Figure l.
Rock Creek Meadow #3, Sequoia National Park. Example
of physiographic Type I subalpine meadow.


94

known. Type II meadows, though, are correlated with the southern boundary of mountain glaciation in the Sierra Nevada (Benedict and Major 1980, 1981).

Meadow Dynamics

The dynamic description of meadows until recently was based largely on inferences from spatial patterns and on the presence or absence of decreasers, increasers, and invaders (Sharsmith4 ). Recently Wood (1975) has described long-term changes in seven montane meadows based on the soil stratigraphy revealed in deep erosion gullies. DeBenedetti (1980) and DeBenedetti and Parsons (1979a) have been following meadow recovery after a natural wildfire in 1977. Benedict (1981) has initiated a study of the long-term development of subalpine meadows as revealed in the stratigraphy of soil cores collected in the Rock Creek drainage, Sequoia National Park, which will be directly comparable with Wood (1975).

 

Table 3.—Physiographic meadow types, Sequoia National Park (Benedict 1981, Benedict and Major 1980, 1981).

Code

Type Description

Example

Elev.

I

Predominately vegetated margins

   

A

Topographic basin

   

  1

Bedrock

Lower Crabtree Meadow

3148

   

Rock Creek Meadow #1

3185

   

Rock Creek Meadow #2

3145

  2

Moraine

Upper Crabtree Meadow

3184

   

Rock Creek Meadow #3

3048

   

Wright Creek Meadows

3292– 3353

B

Slope

   

  1

Lateral moraine

Rock Creek Meadow #4

2426

   

Lower Rock Creek

2804–
2126

  2

Bedrock

Trail Crew Stringer, Rock Creek

3195

C

Stream

Army Pass Creek Meadows

3292– 3414

II

Predominately sandy margins

   

A

Basin

Siberian Outpost

3292

   

Big Whitney Meadow

2450

   

Guyot Flat

3243

B

Stream

Sandy Meadow

3200–
3231

figure

Figure 2.
Siberian Outpost, Sequoia National Park. Example
of physiographic Type II subalpine meadow.

Classically meadows have been viewed as a seral stage in the hydrosere of a lake developing into a forest (Oosting 1956, and many others). Recent evidence suggests that this interpretation of meadow dynamics may be too restrictive (Benedict 1981). Two other possible hypotheses are: 1) meadow ecosystems, like any ecosystem, have changed through time as the climatic factors influencing meadows have changed; and 2) meadow ecosystems have changed the same amount or less than the surrounding forest vegetation over a given period of time. These two hypotheses are not necessarily alternatives to each other (Benedict 1981).

Evidence in support of the first hypothesis comes from three sources. Wood (1975) describes a generalized montane meadow stratigraphic sequence as: 1) a basal layer of alluvium deposited by pre-Holocene streams; 2) a paleosol dated at between 8,705 and 10,185 years B.P. developed under a mesic montane forest; 3) stratified sandy deposits dated at between 8,700 and 1,200–2,500 years B.P. and deposited under a fir, yellow pine, and lodgepole pine forest; and 4) stratified sedge peat, loams, and grus deposited since 2,500–3,000 years B.P. in a meadow environment. Based on this stratigraphic evidence, Wood (1975) suggests that meadow ecosystems can develop from, and develop to forest ecosystems, and that this is a result of climatic changes.

The second source of evidence for the first hypothesis comes from the widespread invasion of forest trees into meadows throughout the western United States (Dunwiddie 1977; Franklin etal . 1971; DeBenedetti and Parsons 1979b; Vale 1981 a,b). It has been suggested that this widespread tree invasion has resulted from excessive meadow grazing and climatic changes. It is only infrequently suggested that this is the result of successional processes. This implies that meadow ecosystems are in dynamic equilibrium with their total environment and that it is an oversimplification to view meadows only as stages in a hydrosere.


95

The third source of evidence that meadows are dynamically adjusted to their environment and climate comes from a man-induced experiment at Osgood Swamp near South Lake Tahoe, California (Benedict 1981). Osgood Swamp occupies a wet basin formed behind a morainal dam (Physiographic Type IA2, Adam 1967). When the morainal dam was artificially breached, the basin became drier simulating a dramatic change in climate. Subsequently, there was a massive invasion of Pinuscontorta subsp. murrayana into the meadow. This indicates that meadow vegetation changes not only as a result of successional processes but as a result of climatic and environmental changes. These changes can be either man-induced or natural.

Evidence for the second hypothesis that meadows are as stable as the surrounding forest has been discussed previously by Benedict (1981). Two sources of evidence support this hypothesis. Adam (1967) presents pollen diagrams from Osgood Swamp, and Soda Springs (near Tuolumne Meadows). These diagrams suggest that meadow vegetation is as stable or more stable than the surrounding forest vegetation. The second source of evidence comes from Wood (1975). From his stratigraphic work, seven of the meadows studied have been in existence since 1200–3000 years B.P., and two since 7700–9800 years B.P. This suggests that these meadows have been unstable over the past 10,000 radiocarbon years. In a similar manner, the forest vegetation at these same sites has also been unstable over the past 10,000 radiocarbon years (Wood 1975).

Conclusions

Meadows are variable in space and time. Spatial variation can be described from a static viewpoint and has resulted in both floristic and physiographic classifications. Temporal variation can be described from a dynamic viewpoint. Current evidence suggests that meadows have variable development patterns. The classic dynamic description of meadows as a seral stage in a hydrosere may apply to some meadows. Other meadows, though, may have developed in areas previously occupied by forest vegetation while still other meadows may be developing into forest as a result of climatic changes. Some meadows may have been in existence for the entire Holocene and are as stable or more stable than the surrounding forest vegetation. More studies are needed to determine if there are other as yet undescribed meadow development patterns.

Literature Cited

Adam, D.P. 1967. Late-Pleistocene and recent palynology in the Central Sierra Nevada, Calif. p. 275–301. In : Quaternary paleoecology. 433 p. Yale University Press, New Haven, Conn.

Beguin, C., and J. Major. 1975. Contribution a l'etude phytosociologique et ecologique des marais de la Sierra Nevada (Californie). Phytocoenologia 2:349–367.

Benedict, N.B. 1981. The vegetation and ecology of subalpine meadows of the southern Sierra Nevada, California. 128 p. Ph.D. Thesis, University of California, Davis.

Benedict, N.B., and J. Major. 1980. A physiographic classification of subalpine meadows of the Sierra Nevada, California. p. 323–336. In : Proceedings of the conference on scientific research in the national parks (2nd.). [San Francisco, Calif., November 26–30, 1979]. Volume 4: Resource analysis and mapping. 363 p. N.T.I.S., US Department of Commerce, Springfield, Va.

Benedict, N.B. and J. Major. 1981. A physiographic classification of subalpine meadows of the Sierra Nevada, California. Madrono [in press].

Bennett, P.S. 1965. An investigation of the impact of grazing on ten meadows in Sequoia and Kings Canyon National Parks. 164 p. M.S. Thesis, San Jose State College.

Burke, M. 1980. The flora and vegetation of the Rae Lakes Basin, southern Sierra Nevada: an ecological overview. 166 p. M.S. Thesis, University of California, Davis.

DeBenedetti, S.H. 1980. Establishment of vegetation following fire in a subalpine meadow of the southern Sierra Nevada: one year post-burn. p. 325–336. In : Proceedings of the conference on scientific research in the national parks (2nd). [San Francisco, Calif., November 26–30, 1979]. Volume 10: Fire ecology. 403 p. N.T.I.S., US Department of Commerce, Springfield, Va.

DeBenedetti, S.H., and D.J. Parsons. 1979a. Natural fire in subalpine meadows: a case description from the Sierra Nevada. Journal of Forestry 77:477–479.

DeBenedetti, S.H., and D.J. Parsons. 1979b. Mountain meadow management and research in Sequoia and Kings Canyon National Parks: a review and update. p. 1305–1311. In : Proceedings first conference on scientific research in the national parks. Volume 2. 1325 p. National Park Service Transactions and Proceedings. Series no. 5.

Dunwiddie, P.W. 1977. Recent tree invasion of subalpine meadows in the Wind River Mountains, Wo. Arctic and Alpine Research 9:393–399.


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Franklin, J.F., W.H. Moir, G.W. Douglas, and C. Winberg. 1971. Invasion of subalpine meadows by trees in the Cascade Range, Washington and Oregon. Artic and Alpine Research 3:215–224.

Klickoff, L.G. 1965. Microenvironmental influence on vegetational pattern near timberline in the central Sierra Nevada. Ecological Monographs 35:187–211.

Mueller-Dombois, D., and H. Ellenberg. 1974. Aims and methods of vegetation ecology. 547 p. John Wiley and Sons, New York, N.Y.

Oosting, H.J. 1956. The study of plant communities: an introduction to plant ecology. 440 p. W.H. Freeman and Co., San Francisco, Calif.

Pemble, R.H. 1970. Alpine vegetation in the Sierra Nevada of California as lithosequences and in relation to local site factors. 247 p. Ph.D. Thesis, University of California, Davis.

Ratliff, R.D. 1979. Meadow sites of the Sierra Nevada, California: classification and species relationships. 288 p. Ph.D. Thesis, New Mexico State University.

Strand, S. 1972. Investigation of the relationship of pack stock to some aspects of meadow ecology for seven meadows in Kings Canyon National Park. 125 p. M.S. Thesis, San Jose State University, California.

Taylor, D.W. 1976. Ecology of the timberline vegetation of Carson Pass, Alpine County, California. 124 p. Ph.D. Thesis, University of California, Davis.

Vale, T.R. 1981a. Tree invasion of montane meadows in Oregon. American Midland Naturalist 105:61–69.

Vale, T.R. 1981b. Ages of invasive trees in Dana Meadows, Yosemite National Park, California. Madrono 28:45–47.

Wood, S.H. 1975. Holocene stratigraphy and chronology of mountain meadows, Sierra Nevada, California. 180 p. Ph.D. Thesis, California Institute of Technology, Pasadena.


97

Composition and Trend of Riparian Vegetation on Five Perennial Streams in Southeastern Arizona[1]

Michael G. Rucks[2]

Abstract.—Composition and trend of 78 km. (49 mi.) of riparian vegetation on five watercourses was determined. Aravaipa Creek has been excluded from cattle since 1973 and was the only study area with a dominant broadleaf riparian community and a trend towards maintaining this community.

Introduction

There are only 1119 km2 (437 mi2 ) of riparian vegetation in Arizona of which 404 km2 (158 mi2 ) are within the Gila River drainage (Babcock 1968; Minckley and Sommerfeld[3] ). It is imperative we assess the composition and trend of these remaining riparian areas.

The Gila River, San Francisco River, Bonita Creek, Mescal Creek and Aravaipa Creek were chosen for study because they are the major riparian areas on public lands administered by the USDI Bureau of Land Management's Safford District. There are also numerous smaller riparian areas associated with short perennial stream reaches and springs not discussed in this paper.

The five riverine riparian systems were studied in the summer of 1980 to establish baseline data to be used for management decisions and future monitoring.

Methods

A point-sample pace-transect with 10- to 20-pace interval (approx. 18–36.5 m. (60–120 ft.)) was used to sample the selected riparian systems.

 

Riparian System

Pace Interval

Distance Sampled
km. (mi.)

Total Sample Points

Gila

20

20.6 (12.9)

570

San Francisco

20

14.0 (8.75)

370

Aravaipa

12

15.4 (9.6)

737

Mescal

10

  4.3 (2.7)

290

Bonita

20

23.8 (14.9)

624

A zig-zag pace route was followed to distribute sample points across the width of the riparian community from terrace to terrace. No sample points were established in the river itself.

Relative abundance of woody species for delineation of the riparian vegetation into mappable vegetation types was determined by recording the nearest woody species in a 180º -arc in front of each sample point. If the nearest woody species was not a broadleaf riparian species, the nearest broadleaf riparian species was recorded. This method maximized the amount of data collected on the broadleaf riparian species. Species recorded were designated as belonging to one of four plant communities: broadleaf riparian, riparian scrub, adjacent desert, and higher elevation. A 20-point running mean of the frequency of the members of each community was plotted to depict the mappable community at each point along the reach.

Relative abundance of herbaceous perennials was determined by recording the herbaceous perennial species closest to the sample point, expressed as a percent of the total points.

Population data on all tree species were obtained by recording the diameter-at-breast-height (DBH), or the diameter below the lowest branch of each tree recorded at each sample point. Diameters were estimated using a Biltmore scale and recorded to the nearest inch. Tree height was recorded for each tree under l-in. diameter.

Canopy coverage, density, and frequency of perennial species were determined using a line-

[1] Paper presented at the California Riparian Systems Conference. [University of California, Davis, September 17–19, 1981.]

[2] Michael G. Rucks is a Wildlife Biologist, Bureau of Land Management, Safford, Ariz.

[3] Minckley, W.L., and M.R. Sommerfeld. 1979. Resource inventory for the Gila River complex, eastern Arizona. Unpublished report to USDI Bureau of Land Management. Contract No. YA-512-CT6-2166. Arizona State University, Tempe, Ariz. XXV + 570 p.


98

plot method. From each 10th sample point on the pace transect, a 43.56-foot tape was stretched as close to the ground as possible in a predetermined direction roughly parallel to the channel. Canopy coverage of all woody species whose canopy intercepted a vertical plane above the tape was recorded by distance on the tape to the nearest 0.1-foot by species. Canopy coverage of a species is expressed as the percent of the total length of line.

The 43.56-foot tape also served as the center of rectangular 0.01-acre plot (435.6 ft2 ) in which species density was determined. Each plant with at least 50% of its basal area within 5 ft. of either side of the tape was tallied by species. Because of the difficulty of determining actual plant number of the sodforming Bermuda grass (Cynodon dactylon ), density of this species was recorded as one (1) when it was present in the plot.

Frequency of a species is expressed as the percent of 0.01-acre plots in which it occurs.

An importance value was determined for each woody species. This value incorporates three parameters of a species in relation to its community. Relative coverage (size or biomass), relative density (number), and relative frequency (ubiquitousness) of each species are combined in one value for comparative purposes. The importance value is determined as:

figure

The maximum importance value of a species would be 300 if it were the only species present.

Utilization of a plant species by browsing wildlife or domestic livestock was recorded at each sample point.

The following is a summary of the amount of line intercept and number of 0.01-acre plots recorded on each riverine riparian system.

 

Riparian
System

Line
Intercept
(ft.)

Number of
0.01-acre
plots

Gila

2482.92

57

San Francisco

1568.16

36

Aravaipa

3179.88

73

Mescal

1263.24

29

Bonita

2700.72

62

Results and Discussion

Table 1 lists perennial species recorded in the riparian inventory described in this paper. Plant common names are from the USDA Soil Conservation Service National Plant List (May 1980).

 

Table l.—Scientific and common names, occurrence of plants, and community classification of woody species.

 

BR: broadleaf riparian

AD: adjacent desert

   
 

RS: riparian scrub

HE: higher elevation

   

Scientific Name

Common Name

Aravaipa Creek

San Francisco River

Mescal Creek

Bonita Creek

Gila River

Community Classification

Acacia constricta

Whitethorn

X

 

X

   

AD

Acacia greggii

Catclaw acacia

X

   

X

 

AD

Acer negundo

Box elder

X

   

X

 

BR

Agave palmeri

Century plant

X

       

AD

Agrostis sp .

Bent grass

     

X

 

Allionia incarnata

Trailing allionia

     

X

 

Alnus oblongifolia

Arizona alder

X

       

HE

Artemisia ludoviciana

Wormwood

X

   

X

 

AD

Baccharis glutinosa

Seep willow

X

X

X

X

X

RS

Baccharis sarothroides

Desert broom

   

X

   

AD

Berberis haematocarpa

Red mahonia

   

X

   

HE

Brickellia spp .

Brickellia

X

 

X

X

 

AD

Celtis pallida

Desert hackberry

     

X

X

RS

Celtis reticulata

Netleaf hackberry

X

 

X

X

X

RS

Cercidium microphyllum

Yellow palo verde

     

X

 

AD

Chilopsis linearis

Desert willow

 

X

 

X

 

RS

Chrysothamnus nauseosus

Rubber rabbit-brush

   

X

   

RS

Condalia spp .

Greythorn

X

X

X

 

X

RS

Crossosoma bigelovii

Bigelow crossosoma

   

X

   

AD

Cynodon dactylon

Bermuda grass

X

X

X

X

X

Datura meteloides

Jimson weed

X

 

X

X

X

Dodonaea viscosa

Aalii

   

X

   

AD


99
 

Table l.—Scientific and common names, occurrence of plants, and community classification of woody species.

 

BR: broadleaf riparian

AD: adjacent desert

   
 

RS: riparian scrub

HE: higher elevation

   

Scientific Name

Common Name

Aravaipa Creek

San Francisco River

Mescal Creek

Bonita Creek

Gila River

Community Classification

Eriogonum fasciculatum

California buckwheat

   

X

   

AD

Fraxinus velutina

Velvet ash

X

 

X

X

X

BR

Gutierrezia spp .

Snakeweed

X

 

X

X

X

AD

Hymenoclea monogyra

Burro brush

X

X

X

X

X

RS

Juglans major

Arizona walnut

X

 

X

X

X

BR

Juniperus monosperma

Juniper

     

X

X

HE

Larrea divaricata

Creosote bush

   

X

X

X

AD

Lycium spp .

Wolfberry

 

X

X

X

X

AD

Marrubium vulgare

Horehound

     

X

 

Melilotus sp .

Sweet clover

     

X

 

Mentzelia sp .

Stickleaf

 

X

 

X

X

Mimosa biuncifera

Catclaw mimosa

   

X

 

X

RS

Mimulus guttatus

Common monkeyflower

   

X

   

Morus microphylla

Texas mulberry

     

X

 

RS

Nicotiana glauca

Tree tobacco

 

X

X

X

X

RS

Nicotiana trigonophylla

Desert tobacco

   

X

X

 

Nolina microcarpa

Bear grass

   

X

   

Opuntia spp .

Prickly pear/cholla

X

       

AD

Penstemon

Penstemon

     

X

 

Platanus wrightii

Arizona sycamore

X

 

X

X

X

BR

Populus fremontii

Fremont cottonwood

X

X

X

X

X

BR

Prunus serotina

Chokecherry.

X

       

HE

Prosopis juliflora

Mesquite

X

X

X

X

X

RS

Quercus arizonica

Arizona white oak

X

       

HE

Rhus radicans

Poison ivy

X

       

RS

Rumex spp .

Dock

X

X

X

X

 

Salix bonplandiana

Bonpland willow

X

 

X

X

 

BR

Salix gooddingii

Goodding willow

X

X

X

X

X

BR

Senecio longilobus

Threadleaf groundsel

     

X

 

Sphaeralcea spp .

Globe mallow

   

X

X

 

Stephanomeria pauciflora

Wire lettuce

   

X

X

 

Tamarix pentandra

Salt cedar

X

X

X

 

X

RS

Vitis arizonica

Arizona grape

X

   

X

 

RS

Community Classification of Woody Species

Occurrence on each system studied and the assignment of woody species to one of four plant communities (broadleaf riparian, riparian scrub, adjacent desert, higher elevation) is also shown in table 1.

Figures 1, 2, 3, 4, and 5 depict the relative abundance of the woody species communities in each

figure

Figure l.
Community classification of woody species and photograph of Mescal Creek.


100

figure

Figure 2.
Community classification of woody species and photograph of the Gila River.

figure

Figure 3.
Community classification of woody species and photograph of the San Francisco River.

figure

Figure 4.
Community classification of woody species and photograph of Bonita Creek.


101

figure

Figure 5.
Community classification of woody species and photograph of Aravaipa Creek.

riparian system, expressed as a running mean of the woody species per 20 sample points. Also included are photographs of the watercourses. A good distribution of mature broadleaf riparian trees without successful reproduction in the open areas made it more likely for riparian scrub, adjacent desert, or higher elevation species to be the nearest woody species to the sample point. Mescal Creek was found to be an example of fluctuation in community type caused by seedling absence. The Gila River and San Francisco River showed a very clear dominance of the riparian scrub community type. Bonita Creek also showed a riparian scrub community type with a slightly greater broadleaf riparian component.

Aravaipa and Mescal Creeks were the only systems with a dominant broadleaf riparian component. No apparent correlation appeared to exist between broadleaf riparian dominance and channel or terrace width. Broad areas on the watercourse might be expected to correspond to broadleaf riparian dominance, but this was not always the case.

Since no broadleaf riparian species was recorded if one was not present before the next sample point, the percent of sample points on each watercourse where broadleaf riparian species were recorded illustrates the ubiquity of these species. Broadleaf riparian species were recorded at the following percentages of sample points on the watercourses: Aravaipa Creek 99.5%; Mescal Creek 84.9%; Bonita Creek 73.1%; Gila River 22.5%; San Francisco River 21.1%.

Relative Abundance of Woody Species

Table 2 shows the relative abundance of woody species occurring at a frequency over 1.0%. Aravaipa Creek had a high percentage of broadleaf riparian species as would be expected from the community classification in figure 1. The San Francisco and Gila Rivers had a very high percentage of riparian scrub species. Salt cedar, burro brush, mesquite and seep willow account for 90% of the woody species recorded on the San Francisco River.

Relative Abundance of Herbaceous Perennials

Table 3 shows the relative abundance of the principal species of herbaceous perennials recorded. Bermuda grass is clearly the dominant herbaceous perennial on each of the watercourses. All the herbaceous perennials in table 3 are grazing-resistant with the exception of bent grass, a minor component of Bonita Creek.

After seven years of cattle exclusion on Aravaipa Creek, palatable grasses other than bermuda grass still occurred at negligible frequencies. Trend plot photos for Aravaipa Creek show bermuda grass in sparse clumps extending to form a solid mat after the cattle were removed. This extensive sod formation by bermuda grass has apparently limited establishment of other grasses.


102
 

Table 2.—Relative abundance of woody species.

Species

Occurrence (%)

Gila River

 

Burro brush

28.5

Seep willow

28.1

Mesquite

23.9

Salt cedar

6.0

Fremont cottonwood

3.7

Snakeweed

3.2

Desert broom

3.2

Mescal Creek

 

Fremont cottonwood

17.0

Burro brush

10.0

Velvet ash

9.0

Seep willow

9.0

Arizona sycamore

6.9

Willow (Salix)

5.9

Mesquite

5.5

Snakeweed

4.5

Red mahonia

4.5

Desert broom

4.2

Salt cedar

4.1

Netleaf hackberry

4.1

Tree tobacco

3.8

Wolfberry

2.1

Whitethorn

1.7

Arizona walnut

1.7

Juniper

1.1

San Francisco

 

Salt cedar

26.7

Burro brush

25.6

Mesquite

23.0

Seep willow

15.4

Tree tobacco

3.8

Fremont cottonwood

3.2

Aravaipa Creek

 

Fremont cottonwood

22.35

Seep willow

14.67

Velvet ash

12.34

Willow (Salix )

10.97

Burro brush

10.83

Mesquite

8.09

Arizona sycamore

4.66

Salt cedar

3.70

Snakeweed

2.74

Netleaf hackberry

1.78

Arizona walnut

1.64

Catclaw acacia

1.23

Box elder

1.09

Bonita Creek

 

Burro brush

34.5

Mesquite

23.5

Seep willow

12.9

Wolfberry

5.8

Greythorn

3.4

Desert hackberry

3.2

Sycamore

3.2

Netleaf hackberry

2.7

Willow

1.4

Fremont cottonwood

1.3

Arizona walnut

1.3

Creosote

1.3

Brickellia

1.1

 

Table 3.—Relative abundance of herbaceous perennials.

Species

Occurrence (%)

Aravaipa Creek

 

Bermuda grass

73.94

Dock

14.05

Jimson weed

7.77

Gila River

 

Bermuda grass

88.6

Tree tobacco

8.9

Threadleaf groundsel

7.1

Stickleaf

2.6

Jimson weed

1.9

Bonita Creek

 

Bermuda grass

55.0

Dock

8.3

Tree tobacco

7.3

Stickleaf

4.1

Desert tobacco

3.2

Globe mallow

2.6

Horehound

2.5

Trailing allionia

1.7

Penstemon

1.2

Brickellia

1.2

Bent grass

1.0

Jimson weed

1.0

Wire lettuce

1.0


103
 

Table 3.—Abundance of herbaceous perennials.

Species

Occurrence (%)

Mescal Creek

 

Bermuda grass

35.21

Tree tobacco

18.66

Desert tobacco

13.38

Jimson weed

11.26

Common monkeyflower

4.22

Globe-mallow

2.46

Wire lettuce

2.46

Brickellia

1.76

Bear grass

1.76

Dock

1.40

San Francisco River

 

Bermuda grass

85.1

Alfalfa

5.4

Tree tobacco

3.7

Stickleaf

2.7

Dock

1.6

Population Data

Figures 6–9 depict the size-class data for broadleaf riparian trees and mesquite on the five watercourses.

Aravaipa Creek

Aravaipa Creek (fig. 6) has been excluded from cattle since 1973 and shows a high percentage of seedlings in every species population. The survival of seedlings to the 1- to 3-inch size-class is good for the broadleaf trees with the exception of sycamore and walnut. Sycamore seed production and establishment is sporadic and sycamores often rely on sucker sprouts for reproduction. It would require a follow-up study to determine the number of sycamore seedlings surviving to the 1- to 3-inch size-class. The absence of walnuts in the 1- to 3-inch size-class may be due more to the small walnut sample (31 trees) than to ecological factors.

figure

Figure 6.
Size-class data for Aravaipa Creek (DBH size-classes in inches).

Gila and San Francisco Rivers

The Gila River and San Francisco River (fig. 7 and 8) show virtually no successful broadleaf riparian reproduction. The only trees in the 1-to 3-inch size-class are cottonwoods on the Gila River, and they comprise only 2% of the cottonwood sample. The low percentage or absence of 1-to 3-inch size-class trees indicates low seedling survival. On the San Francisco River, 82% of the cottonwood seedlings were browsed by cattle. On the Gila River, 62% of the cottonwood and willow seedlings were browsed, resulting in seedlings 6–10 in. tall with up to 0.6 in. diameters indicating the seedlings had been browsed for more than one growing season. Mesquite, however, is reproducing successfully on both of these rivers.

figure

Figure 7.
Size-class data for the San Francisco
River (DBH size-classes in inches).


104

figure

Figure 8.
Size-class data for the Gila River (DBH size-classes in inches).

Very poor broadleaf riparian tree establishment and successful mesquite establishment will eventually lead to the replacement of the broadleaf riparian community by mesquite and other riparian scrub species. This trend is already well established on the Gila and San Francisco Rivers (figs. 2, 3, 7, and 8).

Mescal Creek

All the broadleaf species on Mescal Creek (fig. 9) showed good representation in the seedling size-class. However, willows, sycamore, and walnut showed a total absence of 1- to 3-inch size-class trees. Cottonwood had 1.5% in this size-class and ash 5.5%. This strongly indicates seedlings were not surviving. Cottonwood seedlings were 70% browsed by cattle, willows 9%, sycamores 62%, ash 1%, and no walnut seedlings were recorded as browsed. Mesquite is reproducing successfully on Mescal Creek.

figure

Figure 9.
Size-class data for Mescal Creek
(DBH size-classes in inches).

Poor broadleaf riparian establishment and successful mesquite establishment will eventualy lead to the replacement of the broadleaf riparian community on Mescal Creek. A good distribution of mature broadleaf riparian trees on Mescal Creek results in a dominant broadleaf riparian community (fig. 1). However, poor reproduction will not maintain this broadleaf riparian community over time.

Bonita Creek

Data from Bonita Creek (fig. 9) indicated poor reproductive success of all broadleaf riparian species:

1) only 4% of the cottonwoods were in the seedling size-class and all of these seedlings were browsed by cattle. The 1- to 3-inch size-class represented only 2% of the sample;

2) only 1.5% of the willows were in the seedling size-class and 67% of these were browsed. No 1- to 3-inch size-class willows were recorded;

3) only 1.5% of the sycamores and no velvet ash were in the seedling or 1- to 3-inch sizeclass.

Grazing has occurred on Bonita Creek for over 100 years. The palatability of broadleaf riparian seedlings in descending order of


105

figure

Figure 10.
Size-class data for Bonita Creek
(DBH size-classes in inches).

preference is: cottonwood, willow, sycamore, ash, and walnut.[4] Prior to 1972, grazing pressure on Bonita Creek was perhaps severe enough to affect the most palatable species, but not severe enough to affect ash and walnut. Since 1972, grazing pressure has apparently increased sufficiently to affect the less palatable ash and walnut seedlings.

Sycamore, willow, and cottonwood populations indicate a size-class distribution the reverse of one needed to maintain these species in the community.

Arizona walnut and velvet ash are slow growing species. On Bonita Creek, size-classes for these trees show a normal size-class distribution from 4- to 16-in. and larger. This indicates successful seedling reproduction prior to about 8–10 years ago to establish the 4- to 16-in. trees. The grazing allotment history on Bonita Creek indicates a change in grazing allottees in 1972. The change in grazing allottees corresponds to the downward trend in successful reproduction of walnut and ash.

The trend on Bonita Creek is toward replacement of the broadleaf riparian community by mesquite and other riparian scrub species. This trend is already well established as illustrated in fig. 4 (community classification).

Summary

Aravaipa Creek is the only system where the trend is not toward replacement of the broadleaf riparian community by riparian scrub. Aravaipa is also the only system where cattle have been excluded.

Flooding

Flooding is another factor that influences reproductive success. In the winter of 1978–79, all five watercourses experienced severe floods. Mesquite is not damaged by cattle browsing, but is as susceptible to flooding as the broadleaf species. In each of the systems, mesquite indicated successful reproduction. Mesquite trees were recorded in all parts of the riparian systems from high on the upper banks to within feet of the water. Mesquite seedlings and 1- to 3-inch trees were found under mature broadleaf riparian species and in habitats suitable for broadleaf riparian reproduction.

Aravaipa Creek experienced severe flooding, yet did not indicate poor broadleaf riparian reproduction. Flooding does have adverse effects on tree seedlings, but is not, apparently, as detrimental to the broadleaf riparian communities as cattle browsing upon seedlings.

Importance Values

Table 4 shows the importance values for the major woody species on the five systems. An analysis of these data confirm the inferences drawn from the population analysis.

Aravaipa Creek

High coverage, density, and frequency of the cottonwoods indicate a mature population evenly distributed along the river with very successful reproduction. High coverage indicates large mature trees. High frequency indicates uniform distribution and high density indicates numerous seedlings and small trees. Walnut is the only broadleaf riparian tree with a low importance value, but Aravaipa Creek is the only system in the study where walnut is recorded in the 0.01-acre samples. High density relative to frequency of seep willow indicates clump-like concentrations. Nearly equal density and frequency of burro brush indicates a fairly uniform linear distribution.

[4] Steve Bingham. Personal communication.


106
 

Table 4.—Importance values.

Species

Relative Coverage

Relative Density

Relative Frequency

Importance Value

Aravaipa Creek

Fremont cottonwood

29.06

20.81

9.36

59.23

Seep willow

8.72

37.41

8.99

55.12

Velvet ash

14.42

5.37

6.74

26.53

Willows (Salix )

10.62

4.98

6.74

22.34

Mesquite

11.02

3.40

6.37

20.79

Arizona sycamore

14.68

2.54

3.37

20.59

Burro brush

1.72

7.14

5.62

14.48

Arizona walnut

6.28

1.10

1.87

9.25

Netleaf hackberry

2.17

1.82

3.37

7.36

San Francisco River

Mesquite

59.3

7.9

8.1

75.3

Salt cedar

15.1

42.4

11.1

68.6

Seep willow

5.8

17.6

13.2

36.6

Burro brush

2.0

6.2

9.1

17.3

Fremont cottonwood

9.1

2.4

3.0

14.5

Goodding willow

5.1

5.1

Desert willow

3.5

0.6

0.9

5.0

Gila River

Mesquite

58.1

8.4

9.0

75.5

Seep willow

12.8

37.2

17.0

67.0

Tree tobacco

7.8

17.6

7.0

32.4

Burro brush

0.4

17.8

14.0

32.2

Fremont cottonwood

18.7

2.1

2.0

22.8

Salt cedar

0.8

3.9

6.0

10.7

Mescal Creek

Velvet ash

32.48

0.79

1.87

35.14

Fremont cottonwood

10.69

9.71

5.61

26.01

Arizona sycamore

15.62

2.70

4.67

22.99

Seep willow

0.21

17.83

3.74

21.78

Netleaf hackberry

5.05

8.58

7.47

21.10

Tree tobacco

12.07

8.41

20.41

Mesquite

13.16

2.37

4.67

20.20

Willows (Salix )

8.05

5.08

1.87

15.00

Burro brush

0.43

8.13

5.61

14.17

Arizona walnut

11.42

11.42

Bonita Creek

Burro brush

11.8

48.27

13.3

73.37

Mesquite

27.0

5.15

13.3

45.45

Arizona sycamore

26.1

0.34

1.8

28.24

Seep willow

8.6

15.01

4.1

27.71

Netleaf hackberry

4.9

3.53

6.0

14.43

Willows (Salix )

4.6

0.30

0.9

5.8

Fremont cottonwood

4.7

0.09

0.5

5.29

Arizona walnut

3.4

3.4

Desert willow

1.0

0.85

0.9

2.75

Velvet ash

1.9

0.5

2.4

San Francisco River

The two broadleaf riparian species recorded on the San Francisco River have very low importance values compared to the riparian scrub species. High coverage and low but fairly equal density and frequency of the cottonwoods indicate large mature trees growing singly and sparsely along the river with very few seedlings. Low coverage of willows with none recorded in the


107

0.01-acre samples indicate very sparse distribution of mature trees with no successful reproduction. Very high coverage of mesquite and nearly equal, but high frequency and density indicate mature mesquite and successful reproduction. Extremely high density of salt cedar relative to its coverage indicates an abundance of young plants. The frequency is also high indicating uniform distribution and strongly suggesting salt cedar will become dominant.

Gila River

High coverage of cottonwood relative to its frequency indicates large mature trees sparsely distributed along the river. Low density of cottonwoods indicates few seedlings. Willow was recorded in only one of the 57 0.01-acre samples and this was a browsed seedling. Very high coverage of mesquite and nearly equal, but high frequency and density indicate mature mesquite and successful reproduction.

Mescal Creek

Data from Mescal Creek show a predominantly broadleaf riparian community (fig. 1). The very high coverage of ash relative to its density indicates large mature trees without successful reproduction. The low frequency value indicates these large trees are sparsely spread along the creek. The density of cottonwoods relative to frequency indicates good tree establishment. The coverage value for cottonwood is not disproportionately high indicating seedlings are fairly numerous. However, coverage, density, and frequency of cottonwoods on Mescal Creek are much lower than cottonwoods on Aravaipa Creek. Successful reproduction and establishment of the broadleaf riparian community on Mescal Creek is apparently less than on Aravaipa Creek.

Bonita Creek

Very high coverage of sycamore relative to its density and frequency indicates large mature trees distributed sparsely along the creek with very few seedlings. Sycamore was third in importance only because of its relatively high coverage. Riparian scrub species are clearly dominant. Willows, cottonwood, walnut, and ash all have low density compared to their coverage indicating a mature broadleaf riparian vegetation which is not successfully maintaining itself.

General Conclusions

Aravaipa Creek is the only system of the five studied with a dominant broadleaf riparian community and successful reproduction. Mescal Creek is also dominated by a broadleaf riparian community, but has poor reproductive success. The Gila River, San Francisco River, and Bonita Creek all show a well established trend toward replacement of the broadleaf riparian community by riparian scrub.

Cattle browsing appears to be the major contributing factor to the downward trend of broadleaf riparian communities. The only system in this study with an upward trend in the broadleaf riparian community is Aravaipa Creek, where cattle have been excluded since 1973.

Summary

Riparian vegetation along five perennial watercourses in the USDI Bureau of Land Management's Safford District was studied. Community classification of woody species, relative abundance of woody and herbaceous perennial species, and size-class data were recorded using a pace-transect. Coverage, density, and frequency were determined for each species.

These data were analyzed to determine condition and trend of the five riparian vegetation communities. Aravaipa Creek, where cattle have been excluded since 1973, was the only system with a dominant broadleaf riparian community and successful reproduction.

Acknowledgements

I appreciate the guidance of Steve Bingham, Botanist, Eastern Arizona College, Thatcher, Arizona, for the design of this study and identification of plant specimens. I would also like to thank Cindy French for her assistance with the field work.

Literature Cited

Babcock, H.M. 1978. The phreatophyte problem in Arizona. Arizona Watershed Symposium, Proceedings 12:34–36.

USDA Soil Conservation Service. 1980. National Plant List (May, 1980). USDA Soil Conservation Service. Washington, D.C.


109

3—
HYDROLOGIC AND HYDRAULIC CONSIDERATIONS IN THE STRUCTURE, FUNCTION, AND PROTECTION OF CALIFORNIA RIPARIAN SYSTEMS

figure


110

Fluvial Processes and Woodland Succession Along Dry Creek, Sonoma County, California[1]

Joe R. McBride and Jan Strahan[2]

Abstract.—Fluvial processes, as they relate to the formation of riffle bars and point bars, and banks, terraces, and swales of the floodplain terrace are examined in the context of Dry Creek, Sonoma County, California. These processes control seedling establishment and survival on riffle bars, point bars, and the banks of floodplain terraces. Autogenic forces were found to be more important in determining successional patterns on older, more stable portions of the floodplain terrace. Mule fat (Baccharisviminea ), sandbar willow (Salixhindsiana ), red willow (S . laevigata ), and Fremont cottonwood (Populusfremontii ) are dominant species in the pioneer stages on bars and at the base of the floodplain terrace. Hinds walnut (Juglanshindsii ), California box elder (Acernegundo ssp. californicum ), coast live oak (Quercusagrifolia ), and California bay (Umbellulariacalifornica ) dominate the climax woodlands of the undisturbed floodplain terrace.

Introduction

Dry Creek, a tributary of the Russian River, drains some 562 sq. km. (217 sq. mi.) along its 50-km. (31-mi.) course through the Coast Ranges in Sonoma and Mendocino counties of northern California. The lower 22.5 km. (14 mi.) of Dry Creek pass through a broad valley where fluvial geomorphic processes have created and destroyed environments for riparian woodland species. The purpose of this paper is to identify the influence of those processes upon the pattern of succession in the riparian zone.

Dry Creek is a fourth-order stream which forms with its tributaries a palmate, dendritic pattern. An overall channel gradient of 1.5% occurs from its headwaters to the Russian River. The lower reaches, in Dry Creek valley, follow a gradient of 0.2% and drop 1.9 m. per km. (10 ft. per mi.). Average annual precipitation over the Dry Creek watershed varies from 1,016 mm. (40 in.) near Healdsburg to 1,524 mm. (60 in.) in Mendocino County. Stream discharge ranges from average annual flood peaks of about 1,000 cubic feet per second (cfs) to 0 cfs when the stream dries up each year by late August. The maximum recorded flood occurred in December 1964 with a discharge of 32,400 cfs. The 100-year frequency flood is calculated to be 52,000 cfs. (US Army Corps of Engineers 1981).

The vegetation of the riparian zone along Dry Creek is typical of streams in the North Coast Ranges which drain eastward to the Eel and Russian rivers. A mosaic of woodland stands dominated by various mixtures of Fremont cottonwood (Populus fremontii ), Hinds walnut (Juglanshindsii ), red willow (Salixlaevigata ), white alder (Alnusrhombifolia ), California box elder (Acer negundo ssp. californicum ), and Oregon ash (Fraxinuslatifolia ) occur on the banks of these streams. Within the stream channels one finds patches of sandbar willow (Salixhindsiana ) and mule fat (Baccharisviminea ), as well as white alder, cottonwood, and red willow.

Fluvial Processes

Fluvial geomorphic processes, first described by Davis (1909), have recently been reviewed by Leopold etal . (1964) and Keller (1977). These processes determine the characteristics of a stream channel and its adjacent floodplain terrace(s). They also create substrates for the establishment of plants, as well as destroy areas of existing vegetation. As water moves across the land surface in response to gravity, it loses its potential energy as it loses elevation. This potential energy is dissi-

[1] Paper presented at the California Riparian Systems Conference. [University of California, Davis, September 17–19, 1981].

[2] Joe R. McBride is Associate Professor of Forestry and Landscape Architecture, Jan Strahan is Research Assistant in Forestry; both are at the University of California, Berkeley.


111

pated where the water is in contact with the ground surface or a streambed.

The amount of energy loss per unit area is referred to as the bed shear stress. Transportation of material by a stream occurs when the bed shear stress exceeds the gravitational forces acting upon materials in the streambed. Water velocity and particle size determine the threshold of shear stress required to transport material. Water velocity varies in different parts of a stream channel and, therefore, the potential for transporting materials also varies. In straight sections the greatest velocity occurs in the middle of the stream, just under the water surface. In bends of the channel the flow quickens, and the greatest velocity occurs near the outside of the bend.

Sediments are thus picked up on the concave sides of the stream and tend to be deposited on the convex sides. Along these convex sides the bank is gradually extended streamward by the deposition of a point bar. Along the concave sides the bank is eroded to form a cut bank. The result of these processes is a meandering of the stream, which causes the channel to move laterally. This lateral movement cuts back valley walls to form floodplain terraces. Once formed, the floodplain terrace will serve as a surface for the deposition of smaller particles carried by the stream when it overflows. Deposition on the floodplain terrace combined with scouring of the stream channel leads to an incision of the stream channel into the floodplain terrace. Deposition also occurs at the backs of the point bars. This deposition allows for the extension of the floodplain terrace as the stream moves laterally.

In relatively straight sections of a stream channel, the streambed will follow a somewhat sinuous path. Riffle bars tend to form in these straight sections on alternate sides of the channel. The pattern of riffles and pools tends to be maintained due to the greater bed shear stress in the pools during high flows. However, during peak flows the streambed may be shifted within the stream channel in these straight sections. Braiding of the streambed may also occur where the stream gradient is very low and the channel is wide.

Individual pieces of gravel are moved over the surfaces of both point and riffle bars when the bed shear stress overcomes the gravitational and frictional forces holding them in place. They are carried along the surface of the bar and redeposited as the potential energy of the water is dissipated. Smaller-diameter and lighter pieces are more easily lifted by the bed shear stresses and will be carried farther. Scouring of both the stream channel and the plants growing in the channel can occur during the movement of this material.

In addition to the fluvial processes which create and destroy surfaces for the establishment of riparian species, one must also consider streamflow characteristics which influence seedling establishment and survival in various substrates along the stream and across the stream channel. The fluctuation of water level in the channel both provides moisture to and excludes oxygen from seeds and roots of plants.

Previous Work

Publication of research into the dynamics of riparian vegetation in relation to fluvial processes in California has been limited. Conard etal . (1977) described the distribution of vegetation-types along the Sacramento River. They suggested idealized toposequences of riparian vegetation and indicated that the time interval between major disturbances was related to locations along the toposequence. Their work did not, however, specifically relate species establishment and replacement to fluvial processes.

Pelzman (1973) examined the causes of riparian plant encroachment into streambeds along streams below dams in northern California. Pelzman's field observations and laboratory experiments demonstrated the significance of fluctuations in stream height to successful establishment of common willows and mulefat. He concluded that their establishment was limited by declining spring and summer flows under natural streamflow regimes in California's Mediterranean climate. Pelzman's work is basic to an understanding of the initial stage of succession on newly created substrates in the riparian environment.

Outside of California a number of studies have investigated fluvial processes as they relate to riparian vegetation and succession. Some general concepts can be derived from this body of research; however, climatic differences and different floras limit the transfer of specific findings to the California situation. Swanson and Lienkaemper's (1979) research on the South Fork Hoh River in Washington is an outstanding study of the influence of fluvial processes upon the distribution of riparian and adjacent coniferous forest types. They were able to correlate the age of stands with the creation of various geomorphic surfaces in cross-sections of the South Fork Hoh River valley. They identified four distinctive floodplain terrace environments in the valley which were related to the geomorphic process and which described the character of the vegetation in each environment. They did not, however, examine successional trends on the various terraces.

Fonda (1974), working in the same area, did address the question of succession on the four floodplain terrace environments. He suggested a sequence of Alnusrubra to Piceasitchensis /Acer macrophyllum /Populus trichocarpa to Picea sitchensis /Tsuga heterophylla to Tsugaheterophylla . Soil profile development as it influenced moisture-holding capacity was proposed as a major factor controlling forest succession. Fonda demonstrated that an ability to tolerate soil moisture stress was a significant feature of plants in the early successional stages.


112

Nanson and Beach (1977) examined forest succession and sedimentation on a meandering-river floodplain in northwestern British Columbia. They used the changing age structure of dominant tree species to describe successional changes within the floodplain forest. The direction of channel migration and the earlier position of the channel's convex bank were accurately preserved in the form of ridges and swales on the floodplain terrace. This pattern allowed Nanson and Beach to establish a chronosequence of plots across the floodplain. The successional change from balsam poplar to white spruce occurred following the decline in overbank sedimentation on surfaces approximately 50 years old. Annual sedimentation during this initial 50 years destroyed any spruce seedlings beneath the balsam poplar crown canopy. The balsam poplar survived each increment of sediment by developing a new root crown near the surface of the deposition.

Research in the mid-western and eastern parts of the United States has identified successional patterns which could be linked to fluvial geomorphic processes (Hefley 1937; Ware and Penfound 1949; Shelford 1954; Wistendahl 1958; Lindsey etal . 1961; Everitt 1968; Wilson 1970; Johnson etal . 1976). Generalizations drawn from these papers suggest that sediment size on point bars controls the species composition of the pioneer stands. Willows are more commonly observed on finer-textured deposits, while cottonwoods develop on the more coarsely textured deposits. As floodplains extend over the back of point bars, the willows and cottonwoods are replaced by species adapted to mesic environments with somewhat reduced soil moisture, such as box elders, elms, ashes, and oaks. Major factors influencing species composition of the riparian forests on the floodplain are depth to water table and moisture-holding capacity of the soil. It would appear from a review of the previous research that initial patterns of succession on point bars are allogenic in character, while subsequent successional changes on the stabilized floodplain are autogenic.

Methods and Results

To study the influence of fluvial processes upon succession on Dry Creek, we selected three physiographic locations representative of the various consequences of fluvial geomorphic processes. These locations were: 1) riffle bars; 2) point bars; and 3) the hydrologically active, stream-adjacent floodplain terrace.

Stream Channel

Riffle Bars

Riffle bars in the relatively undisturbed portions of lower Dry Creek are characterized by low elevations. The highest elevations on these bars are seldom more than 2 m. above the lowest point in the channel cross section. The gradient across these bars, normal to streamflow, is generally very low, although some bars had slopes approaching 45° at the edge of the streambed.

Vegetation on these bars consists of occasional strips of basket sedge (Carexbarbarae ), mulefat, sandbar willow, or sandbar willow/cottonwood. At the back of some riffle bars, adjacent to the floodplain bank, we encountered a narrow secondary streambed which carried water only during higher flows. A lagoon was formed at both the upstream and downstream ends of this streambed. Red willow thickets were common on the floodplain side of these secondary stream banks, while mulefat, sandbar willow, and cottonwood were more commonly found on the riffle bar side.

To determine the pattern of seedling establishment and survival on riffle bars, we measured species density of seedlings and young saplings (plants less than 1 m. tall, assumed to be 1 year old in June 1981) in June and September, 1981. Twenty one-quarter-square-meter quadrats were established in strips of germinating seedlings near the stream edge during the last two weeks of June. Separate sets of 20 quadrats each were located in areas which appeared to be dominated by: 1) basket sedge; 2) mulefat; 3) sandbar willow; 4) cottonwood; and 5) red willow. A similar set of 20 quadrats was established in a zone of young saplings in which mulefat, sandbar willow, cottonwood, and red willow were present.

Results of these measurements suggest there are correlations between 1) species seedling establishment and gravel size; and 2) mortality during the first growing season and depth to groundwater. The transient viabilities of riparian species limit their germination to a moist zone adjacent to the receding stream in late spring. Floating seeds are concentrated on this moist zone. Successful establishment depends upon gravel size in the moist zone. Establishment of some species is limited by larger sizes of gravel. Our results indicate a close correlation between occurrence of particles less than 0.2 cm. and the establishment of sandbar willow (fig. 1.) Available moisture is present for a longer period of time in the fine-textured portions of riffle bars. The transient viability of sandbar willow prevents its establishment on the rockier and drier portions of the bars.

Seedling survival depends upon the availability of soil moisture through the summer months. Among tree species, mortality ranged from 65% to 100% on those plots adjacent to the section of the stream which dried out by September 1, 1981 (table 1). Weekly observations indicated mortality began during the third week in July. Mortality ranged from 6% to 88% for these same species on plots adjacent to water. The depth to water was about 20 cm. on these plots, while it exceeded 1 m. on the former plots by September 1, 1981.

In addition to drought-induced mortality, direct heat injury may kill seedlings during the summer months. Differences in survival among trees may be due to root growth capacity. Cottonwood roots for 1981 seedlings were three times


113

figure

Figure l.
Percentage occurrence of gravel sizes and seedlings
on riffle bar plots along lower Dry Creek.

 

Table 1.—Average density of seedlings (number/m2 ) on riffle bars in June and September, 1981 along lower Dry Creek.

Species

Average June

density Sept.

Mortality
(%)

Riffle bars adjacent to sections of stream which dried out by September1

Mulefat

50

33

34

Basket sedge

44

0

100

Fremont cottonwood

23

8

65

Sandbar willow

4

0

100

Red willow

41

0

100

Riffle bars adjacent to sections of stream which were not dried out by September1

Mulefat

81

74

9

Basket sedge

9

0

100

Fremont cottonwood

67

63

6

Sandbar willow

141

17

88

Red willow

8

3

62

as long as those of the willows. No mortality was recorded on the sapling plots. It is assumed that the seedlings on sapling plots produced sufficient root growth to remain in contact with a water supply during the summer of 1980. Furthermore, these plants survived the winter period of peak discharge. The absence of saplings from many areas on riffle bars suggests that winter scouring of the bars often removes seedlings which survive the first summer. Older saplings on point bars frequently have basal scars on the upstream side of their stems which are the result of scouring away of the bark, phloem, and cambium.

Examination of a series of aerial photographs of Dry Creek dating from the 1940s indicates a shifting of the locations of riffle bars. The streambed may move completely across the stream channel and obliterate a riffle bar with any seedlings and saplings growing upon it. The temporary nature of the riffle bar prevents the development of the riparian woodland beyond the pioneer stage.

Point Bars

The environment of the point bar shares certain characteristics with that of the riffle bar; however, since the point bar is built outward as the stream meanders, it is more stable over time and provides an environment for further development of the riparian woodland. Point bars along Dry Creek had a more significant increase in elevation as one moved away from the streambed than did riffle bars. They were also characterized by more vegetative cover. Seedling establishment at the margin of the streambed followed the same pattern as was observed on the riffle bars. Large numbers of seedlings became established in June only to succumb to heat and drought. Those which survived the rigors of summer, as well as winter scouring, produced linear stands ranging in length from a few to as many as 30 m. in length.

Plants in these strips reduced the velocity of water during high-flow periods and, therefore, caused gravels and smaller-sized particles to accumulate. As a result, point bars often had the appearance of ridges and swales as one moved from the streambed to the bank of the floodplain terrace. The pattern of sediment-trapping depended upon the density of the vegetation and the distance water travelled over the bar. Plant stems often trap larger-sized gravels at the upstream end of point bars and along the edge of the streambed. Finer sediments are deposited toward the downstream end of the bar and the floodplain terrace bank.

To study woodland succession on point bars we conducted a reconnaissance of several point bars along Dry Creek. Vegetative cover on these bars appeared to be closely tied to gravel size distribution and location relative to the streambed. Our reconnaissance indicated that point bars could be divided into five environments as follows: 1) point bar bank; 2) first ridge and swale; 3) interior ridges and swales; 4) lagoons; and 5) base of the floodplain terrace. Not all point bars exhibited all five of these environ-


114

ments along Dry Creek. Smaller point bars sometimes lacked areas of interior ridges and swales. Lagoons were also not found on all point bars.

A typical point bar exhibiting all five environments was chosen for a detailed analysis of its vegetation and gravel size distribution. The vegetation on the point bar was mapped and four transects were chosen to cut across the various environmental zones and vegetation-types. Along each transect ten adjacent one-quarter square meter plots were established parallel to the streambed in the point bar bank, first ridge and swale, and base of the floodplain terrace environments. In the area of interior ridges and swales, 10 similar plots were established at the top of each ridge and the bottom of each swale along the transect lines. Plants occurring on each plot were tallied as seedlings or, if they were older, their basal diameter and height were recorded. A point frame was also used to determine the distribution of gravel size on each plot.

The data collected along these transects suggested that an autogenic pattern of succession followed the establishment of seedlings along the point bar bank (table 2). Initial seedling establishment along these banks appeared to follow the pattern observed on the riffle bars. Numerous seedlings became established as water receded in the spring. Species success depended upon gravel size. The absence of any seedlings in the 1 cm. size-class suggested that none of last year's cohort survived. The occurrence of plants in the 1–5 cm. and >5 cm. size-classes indicated establishment had been successful in previous years.

On the first ridge and swale, current seedling establishment was dominated by cottonwood and red willow as evidenced by the 1981 seedlings and plants under 1 cm. in diameter. These ridges and swales were dominated by older sandbar willow and mulefat. It would appear that these pioneers established a footing on an earlier streambank and have trapped gravel to produce a ridge as the point bar advanced. The larger gravel sizes trapped by these plants, combined with the higher elevation of the seed beds, have not provided a suitable environment for the continued establishment of sandbar willow and mulefat. Cottonwood and red willow can become established here as evidenced by the data in table 2.

In the zone of interior ridges and swales, gravel size was associated with the distribution of the dominant species. Alder was found on areas of the smallest-sized particles, while sandbar willow and cottonwood occurred on sandy and gravelly sites. Many point bars along Dry Creek lacked extensive areas of smaller-sized particles and did not support alder. No current or recent seedling establishment was observed on any of the plots on the interior ridges and swales. Light intensities were reduced in this zone due to the crown canopy, which may have prevented successful establishment. More important, the elevation

 

Table 2.—Average density of plants (number/m2 ) by size-class (S—seedling; size-classes in cm.) and gravel size distribution on point bars along lower Dry Creek.

 

Bank

         
     

Density

   

Species

S

<1

1–5

>5

White alder

0

  0

0

0

Mulefat

85.9

  0

0.9

0.13

Fremont cottonwood

2.8

  0

1.6

0

Sandbar willow

38.4

  0

0.7

0.4

Red willow

12.7

  0

0.2

0

Arroyo willow

0

  0

0

0

Gravel size

<0.2
32%

0.2–1
20%

1–3
15%

3–6
20%

>6
13%

First Ridge and Swale

     

Density

   

Species

S

<1

1–5

>5

White alder

0

  0

0

0

Mulefat

0

  0.7

1.7

0.8

Fremont cottonwood

0.2

 

  2.7

2.2

0

Sandbar willow

0.3

  0.2

0.3

0.2

Red willow

3.7

  0.4

0.2

0

Arroyo willow

0

  0

0

0

Gravel size

<0.2
26%

0.2–1
5%

1–3
34%

3–6
22%

>6
13%

Interior Ridges and Swales—Alder

     

Density

   

Species

S

<1

1–5

>5

White alder

0

  0

1.2

2

Mulefat

0

  0

0

0

Fremont cottonwood

0

  0

0

1.8

Sandbar willow

0

  0

0

0

Red willow

0

  0.6

0

0

Arroyo willow

0

  0

0

0

Gravel size

<0.2
67%

0.2–1
20%

1–3
10%

3–6
3%

>6
0%

Interior Ridges and Swales—Cottonwood

     

Density

   

Species

S

<1

1–5

>5

White alder

0

  0

0

0

Mulefat

0

  0

0.7

0

Fremont cottonwood

0

  0

0.3

0.6

Sandbar willow

0

  0

0.6

0.4

Red willow

0

  0

0.2

0

Arroyo willow

0

  0

0

0

Gravel size

<0.2
11%

0.2–1
15%

1–3
35%

3–6
24%

>6
14%

Base of Floodplain Terrace

     

Density

   

Species

S

<1

1–5

>5

White alder

0

  0

0.2

0

Mulefat

0

  0

0

0

Fremont cottonwood

0

  0

0

1.8

Sandbar willow

0

  0

0

0

Red willow

0

  0.6

0

0

Arroyo willow

0

  0

2.4

0

Gravel size

<0.2
45%

0.2–1
30%

1–3
13%

3–6
5%

>6
7%


115

of this zone was above the elevation where the stream appeared to have deposited vast numbers of seeds during the spring. Seed beds in the interior ridges and swales zone may have been too dry for successful germination during this period of seed dispersal. Vegetative reproduction by layering may have been very important in this zone. Many alder sprouts were growing from buried trunks.

At the base of the floodplain terrace, a gulley occurred across the back of most of the point bars along Dry Creek. Bed shear stress is high at this location during periods of peak runoff. The larger percentage of smaller particle sizes reduces the bed shear stress necesssary to transport material. The gulleys were higher in elevation than the bank of the streambed and dried out much earlier. The more xeric character of these gulleys was responsible for the presence of arroyo willow (Salixlasiolepis ) and the absence of mulefat and sandbar willow. No seedling establishment was observed on the plots measured in these gulleys at the base of the floodplain terrace. Periodic establishment would be expected to occur in years of higher streamflow later in the spring. Winter scour may also be a factor in the dynamics of plants in this zone.

The lagoons supported a margin of mulefat or cattail (Typhalatifolia ) and basket sedge, depending upon the gravel size distribution. Mulefat occurred on coarser gravels, while the cattail and basket sedge grew on sediments less than 0.2 cm. Red willow also occurred above the lagoon margin on the finer sediments.

The conclusion drawn from investigation on point bars is that a type of autogenic succession is occurring in which the initial trapping of coarser sediments by mulefat, willows, and cottonwood produces a ridge of gravel along the outer edge of the point bar. This ridge is a more favorable environment for further cottonwood establishment. As the ridge is built up, finer sediments are deposited between it and the base of the floodplain terrace, toward the downstream end of the point bar. New ridges form adjacent to the stream as the point bar extends laterally. With the growth of cottonwood and willows in the interior ridges, more smaller-sized sediments are trapped, and the swales between ridges begin to fill in.

The increasing height of the bars also contributes to the trapping of smaller-sized particles. The decreased particle size of this substrate results in a more favorable soil-moisture regime for plant growth; however, seed bed conditions are less favorable for willows because of their transient viability. Alder becomes established on the finer sediments of these interior swales and grows up to form a dominant canopy. Shade-intolerant willows and cottonwood cannot survive beneath this canopy. With time, alder dominates the interior downstream portions of the point bars, reproducing primarily by layering. More gravelly areas remain dominated by cottonwood and willow. Floodplain terrace building during unusually high floods may eventually make the ground surface too high and therefore too dry for continued layering of the alder. As the point bar advances laterally, the distance from the streambed to the root systems of alders near the base of the floodplain terrace will become too great for effective water transport. Under these conditions alder will be replaced by species with better adaptations for the floodplain terrace environment.

Floodplain Terrace Environment

To investigate the structure and reproduction of woodlands occurring on the floodplain terrace, we first classified these woodlands into 10 types based on percent cover of dominant species (table 3). These types were mapped on aerial photographs, and their areal contributions to the total riparian woodland along lower Dry Creek were calculated. Types were considered to be dominated by a single species when over 80% of the crown canopy visible on aerial photographs was made up of that species. These types were given the name of the dominant species (e.g., cottonwood). In types where crown-cover dominance was shared by two species, the names of both species were applied using the name of the tallest species first (e.g., cottonwood/willow). Shared dominance was defined as two species making up 80% of the crown cover of an area, but neither species contributing less than 30% of the cover. The type name "mixed riparian woodland" was used for the commonly occurring stands in which several species occurred but none had a crown cover in excess of 30%.

In addition to the classification based on dominant species, the woodlands could also be divided into two broad categories on the basis of width. Narrow woodlands, seldom more than two crown diameters wide, occurred where channel erosion and land clearing had reduced the original riparian woodland. All woodland-types, based on dominant species, occurred in these narrow strips. Wider woodlands, up to 120 m. wide made up the second category. Only the mixed riparian type was observed to occur in this wider category. These wider woodlands were often situated behind point bars and were characterized by irregular surfaces. Distinct swales often cut 3–4 m. into the floodplain terrace surface, carrying water during periods of overbank flow. This characteristic may have prevented them from being cleared for agriculture.

Sampling for tree density, basal area, and regeneration was done in the mixed riparian woodland using the point quarter method with 10 square meter and one square meter plots at point centers for measuring saplings and seedlings. Nested rectangular plots (5 m. × 20 m. for trees; 2 m. × 20 m. for saplings; 1 m. × 20 m. for seedlings) were used in the narrow willow and cottonwood/willow types. Other woodland-types were not sampled because of their limited distribution.


116
 

Table 3.—Woodland-types occurring on the flood-plain along lower Dry Creek and their percent of the total riparian woodland.

Type

Dominant species

% of total

Mixed riparian

Hinds walnut
Coast live oak
Valley oak
Red willow
California box elder
Fremont cottonwood

40.2

Willow

Red willow

23.5

Cottonwood/
willow

Fremont cottonwood
Red willow

22.3

Oak

Coast live oak or
Valley oak

8.0

Cottonwood

Fremont cottonwood

2.3

Alder

White alder

2.0

Walnut/willow

Hinds walnut
Red willow

0.6

Walnut

Hinds walnut

0.5

Bay

California bay

0.4

Oak/bay

Coast live oak or
Valley oak
California bay

0.2

The mixed riparian woodlands were divided into three environments: 1) bank; 2) terrace; and 3) swale. Sample-points were located at 10-m. intervals along transects normal to the stream in each environment. Eleven transects with a total of 85 points were used in the sample. Eight rectangular plots were used to sample the narrow woodland-types.

Bank

Results from the survey of the mixed riparian woodland show a dominance of alder, cottonwood, and red willow in the bank environment (table 4). It should be noted that these two species were not uniformly distributed along the bank. Alder dominated at the upstream and downstream ends of the point bars where the streambed was adjacent to the bank. Cottonwood and red willow were dominant where the banks were in contact with point bars. Size distribution data (table 4) suggest that these dominant species were not regenerating by seed in this environment. Only current-year seedlings of box elder were observed. Stems under 2.5 cm. in diameter of alder and red willow may have been the products of layering or earlier seedling establishment. No cottonwood regeneration was observed.

 

Table 4.—Average density of plants (number/100 m2 ) by size-class (in cm.) in floodplain environment, mixed riparian woodland-type, along Dry Creek. S—seedling.

Bank

     

2.5–

5.0–

7.6–

Species

S

<2.5

5.0

7.6

10

California box elder

1.4

  0

0

0

0.1

Buckeye

0

  0

0

0

0

Red alder

0

  1.5

0.1

0.1

0

Oregon ash

0

  0.1

0

0

0

Hinds walnut

0

  0

0

0

0

Fremont cottonwood

0

  0

0

0

0

Coast live oak

0

  0

0

0

0

Valley oak

0

  0

0

0

0

Sandbar willow

0

  0

0

0

0

Red willow

0

  0.3

0

0.1

0

Arroyo willow

0

  0.4

0.3

0.1

0.1

Elderberry

0

  0

0

0

0

California bay

0

  0

0

0

0

Terrace

     

2.5–

5.0–

7.6–

Species

S

<2.5

5.0

7.6

10

California box elder

0

  1.8

0.9

0.1

0.3

Buckeye

0

  0

0.3

0.3

0

Red alder

0

  0

0

0

0

Oregon ash

1.4

  0

0

0

0

Hinds walnut

0

  0.5

0

0.3

0.1

Fremont cottonwood

0

  0

0

0

0

Coast live oak

0

  0

0

0

0

Valley oak

0

  0

0

0

0

Sandbar willow

0

  0

0

0

0

Red willow

0

  0

0

0

0

Arroyo willow

0

  0

0

0

0

Elderberry

0

  0.3

0.3

0.1

0.1

California bay

0

  0.2

0

0

0

Swale

     

2.5–

5.0–

7.6–

Species

S

<2.5

5.0

7.6

10

California box elder

0

  2.4

0.3

0.1

0.4

Buckeye

0

  0

0

0

0

Red alder

0

  0

0

0

0

Oregon ash

0

  0.7

0.1

0.3

0

Hinds walnut

0

  0.1

0.1

0

0.1

Fremont cottonwood

0

  0

0

0

0

Coast live oak

1.4

  0

0

0

0

Valley oak

0

  0

0

0

0

Sandbar willow

0

  0

0

0

0

Red willow

0

  0

0

0

0.1

Arroyo willow

0

  0

0

0

0

Elderberry

0

  0

0

0

0

California bay

0

  0

0

0

0

Terrace

On the floodplain terrace, the mixed riparian woodland exhibited a large basal area of both coast live oak and valley oak (table 5). However, the relative densities of these species were low compared to that of Hinds walnut and willow. Sandbar willow, alder, and cottonwood showed significantly reduced relative densities in


117

the floodplain terrace environment. The pattern of regeneration suggested Hinds walnut, bay, and Oregon ash were successfully establishing seedlings in this environment. Seedbeds in this environment were dominated by herbaceous cover (often Vincamajor ) or leaf litter. Following peak floods, deposits of silt may temporarily provide mineral seedbeds. The data collected in this portion of the study reflects establishment on nonmineral seedbeds where competition from herbaceous species may be intense.

Swale

The swale environment tended to be dominated by a mixture of Hinds walnut, box elder, coast live oak, and red willow (table 5). Hinds walnut exhibited the largest basal area, while box elder had the highest relative density. Coast live oak showed a large basal area but a much lower relative density than the other dominants; it was found at the upper edge of the swales, while the other species were more common on the lower portion of the swale slopes or in the swale bottoms. Reproduction in the swale environment was dominated by box elder, although regeneration of Hinds walnut, coast live oak, and Oregon ash was evident. Seed beds in the swales tended to be less dominated by herbaceous plants and leafy litter. The swales are more frequently flushed out by winter storms than are the higher surfaces of the floodplain terrace.

The densities of various stem diameter size-classes in the narrower willow and cottonwood/willow types suggests the invasion of more shade-tolerant Hinds walnut and box elder into these types (table 6). With time, stands of willow and cottonwood/willow occurring on the floodplain terrace can be expected to succeed to the mixed riparian woodland. Increment cores taken from larger cottonwood trees in the cottonwood/willow type suggest that these stands are of relatively recent origin (within the last 20 years). At some locations, these types had arisen on fresh deposits of silt following major floods. These deposits were laid down where the floodplain was extended into the stream channel behind newly formed point bars. The two types also appeared to arise at the base of the freshly eroded floodplain banks where gravel rather than the streambed was in contact with the bank. Although initial establishment occurred at the base of the bank, both cottonwood and red willow colonized the lower portions of the floodplain bank.

Conclusions

To summarize the pattern of succession in the environments of the floodplain, one must start with the deposition of silt at the back of the point bar or the exposure of silt on cut banks in the concave sections of streams. Initial colonization of these environments occurs by seedling establishment of red willow and cottonwood. In some cases, cottonwood which is partially buried by the silt deposit may be capable of developing new root systems in the deposit and continuing its growth. Alder may also become established at the base of banks in contact with the streambed. Sandbar willow does not become established in these situations because of the very fine texture of the floodplain silts. Subsequent seedling establishment of more shade-tolerant species occurs in willow and cottonwood/willow stands on the upper slope and top of the floodplain bank. Establishment of additional

 

Table 5.—Density, relative density, and basal area of tree species in floodplain environments along lower Dry Creek. D—density (number/100 m2 ); RD—relative density (%); BA—basal area (cm2 /100 m2 ).

 

Bank

Floodplain

Swale

Species

D

RD

BA

D

RD

BA

D

RD

BA

California box elder

0.32

3.8

27

0.26

12

112

0.76

28

281

Buckeye

0

0

0

0.11

5

13

0.05

2

8

Red alder

2.13

25

11.76

0.02

1

12

0.05

2

27

Oregon ash

0.15

1.8

34

0.06

3

17

0.08

3

12

Hinds walnut

0.64

7.6

337

0.53

25

650

0.70

25

630

Fremont cottonwood

1.45

17

2830

0.06

3

323

0.03

1

145

Coast live oak

0

0

0

0.26

12

864

0.16

6

519

Valley oak

0

0

0

0.11

5

904

0

0

0

Sandbar willow

1.02

12

200

0.04

2

7

0.05

2

12

Red willow

2.64

31

459

0.40

19

160

0.46

17

263

Arroyo willow

0

0

0

0.02

1

2

0.11

4

21

Elderberry

0.15

1.8

49

0.11

5

29

0.22

8

77

California bay

 

0

0

0

0.01

7

24

0.05

2

127

Total

8.50

100

5112

2.13

100

3117

2.70

100

2122


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Table 6.—Average density (number/100 m2 ) of tree species by size-class (in cm.) in narrow willow and cottonwood/willow floodplain woodlands along lower Dry Creek.

 

Willow woodland

Species

Seedling

Sapling

10– 15

16– 20

21– 25

26– 30

31– 35

36– 40

41– 50

90

California box elder

0

10.0

1.0

0

0

0

0

0

0

0

Red willow

0

  0

2.0

1.0

0

0

1.0

1.0

1.0

0

 

Cottonwood/Willow Woodland

Species

Seedling

Sapling

10– 15

16– 20

21– 25

26– 30

31– 35

36– 40

41– 50

90

California box elder

0

  9.2

0.3

0.3

0

0

0

0

0

0

White alder

0

  0

0.3

0

0

0

0

0

0

0

Oregon ash

0

  0

0.3

0

0

0

0

0

0

0

Hinds walnut

0

  5.8

1.3

0

0

0

0.3

0

0

0

Fremont cottonwood

0

  0.8

1.0

1.0

1.0

0.7

0.7

0.7

0

0

Red willow

0

  7.3

4.7

3.7

2.0

0.3

0

0

0

0

Elderberry

0

  4.2

1.0

0.3

0

0

0

0

0

0

species at the base of the bank is somewhat limited by the periodic inundation of this environment. Alder stands established here appear to be self-perpetuating as long as the streambed is in contact with the bank.

Left undisturbed by man, the cottonwood/willow floodplain woodland will undergo succession to a mixture of Hinds walnut, box elder, oak, and bay, with significant variations in basal area and relative density in relation to swales and floodplain terrace locations. As the floodplain terrace builds in height or extends into the stream channel, one can anticipate an increase in the importance of the more drought-tolerant species such as the oaks and bay. These species will dominate the higher elevations in portions of the floodplain woodland and those sites most removed from the stream channel. This steady state is achieved only for brief intervals because of the continuous migration of the stream channel. This migration either destroys the woodland or isolates it from the streambed and the groundwater it needs for the existence of its various species.

Literature Cited

Conard, S. G., R.L. MacDonald, and R.F. Holland. 1977. Riparian vegetation and flora of the Sacramento valley. p. 47–55. In : A. Sands (ed.). Riparian forests of California: their ecology and conservation. Institute of Ecology Pub. 15, University of California, Davis. 122 p.

Davis, W.M. 1909. Geographical essays (reprinted in 1954). 777 p. Dover Publications, New York, N.Y.

Everitt, B.L. 1968. Use of the cottonwood in an investigation of the recent history of a flood plain Amer. Jour. Science 266:417–439.

Fonda, R.W. 1974. Forest succession in relation to river terrace development in Olympic National Park, Washington. Ecol. 55:927–942.

Hefley, H.M. 1937. Ecological studies on the Canadian River floodplain in Cleveland County, Oklahoma. Ecol. Monog. 7(3): 345–484.

Johnson, W.C., R.L. Burgess, and W.R. Keammerer. 1976. Forest overstory vegetation and environment of the Missouri River floodplain in North Dakota. Ecol. Monog. 46:59–84.

Keller, E.A. 1977. The fluvial system: selected observations. p. 39–46. In : A. Sands (ed.). Riparian forests of California: their ecology and conservation. Institute of Ecology Pub. 15, University of California, Davis. 122 p.

Leopold, L.B., W.G. Wolman, and J.P. Miller. 1964. Fluvial processes in geomorphology. 522 p. W.H. Freeman and Company, San Francisco, Calif.

Lindsey, A.A., R.O. Petty, D.K. Sterling, and W.V. Asdall. 1961. Vegetation and environment along the Wabash and Tippecanoe rivers. Ecol. Monog. 31(2):105–156.

Nanson, G.C., and H.F. Beach. 1977. Forest succession and sedimentation on a meanderingriver floodplain, northeast British Columbia, Canada. Jour. Biogeography 4:229–259.

Pelzman, R.J. 1973. Causes and possible prevention of riparian plant encroachment on anadromous fish habitat. California Department of Fish and Game Environmental Services Branch, Administrative Report No. 73-1. Sacramento, Calif. 26 p.


119

Shelford, V.E. 1954. Some lower Mississippi Valley floodplain biotic communities: their age and elevation. Ecol. 35(2):126–142.

Swanson, F.J. nd G.W. Lienkaemper. 1979. Interactions among fluvial processes, forest vegetation, and aquatic ecosystems, South Fork Hoh River, Olympic National Park, Washington. Proceedings of the Second Conference on Scientific Research in the National Parks. [San Francisco, Calif., Nov. 26–30, 1979]. Vol. 7:23–34.

US Army Corps of Engineers. 1981. Channel improvements. Design Memorandum No. 18. Warm Springs Dam and Lake Sonoma Project. 25 p. US Army Corps of Engineers, San Francisco, Calif.

Ware, G.H., and W.T. Penfound. 1949. The vegetation of the lower levels of the floodplain of the South Canadian River in central Oklahoma. Ecol. 30(4):478–484.

Wilson R.E. 1970. Succession in stands of Populusdeltoides along the Missouri River. Am. Midl. Nat. 83:330–342.

Wistendahl, W.A. 1958. The flood plain of the Raritan River, New Jersey. Ecol. Mono. 28(2):129–153.


120

Riparian Vegetation Planting for Flood Control[1]

J. Fred Chaimson[2]

Abstract.—The area around Murphy Slough on the Sacramento River near Chico is critical in the operation of the Sacramento River Flood Control Project. Erosion at this location threatens the proper function of the area with potentially catastrophic results. This paper describes a planting plan intended to alleviate some of these problems.

Introduction

Usually flood control maintenance is much more involved in clearing riparian vegetation than in planting it. However, in some cases erosion and wave wash protection are of greater concern than channel capacity. This paper describes an instance of planting riparian vegetation on a site previously cleared for agriculture where erosion control and deposition of sediment is considered desirable.

Background

The area around Murphy Slough on the Sacramento River southwest of Chico, Butte County, is a key element in the Sacramento River Flood Control Project. It is the beginning of the overbank flow of excess water from the river to the Butte Sink and Sutter Bypass. It is also an area of considerable river dynamism, with areas of almost one section (259 hectares) each having changed sides of the river (and ultimately ownership) as late as 1921 (fig. 1).[3]

A review of the current USDI Geological Survey 7.5' quadrangle map dated 1949, and photorevised in 1969, shows a surprising amount of vitality; with the river continuing to erode laterally, narrowing the neck of the oxbow between river mile (RM) points 187.5 and 189.5 in that 20 years. Subsequent erosion has opened the mouth of Murphy Slough to the full force of the Sacramento River (reversing the direction in which it once flowed in this channel).

The problem with this is that when an excessive amount of water is directed into Murphy Slough, some of it returns to the river, across the narrow neck to RM 187 (fig. 2). With the energy of 4.8 km. (3 mi.) of river concentrated in .4 km. (.25 mi.) of cutoff, erosion is inevitable. If the river were to cut off almost 4.8 km. of channel at this location, the headward erosion of the river bottom would lower the water surface upstream of the cutoff, reducing or eliminating entirely the overbank flow at the Chico weir site and carrying the additional water down the channel with the streambed gravels and sands.

figure

Figure 1.
Centerline meanders of the Sacramento River near
Golden State Island, 1920 and 1969 (from Brice, 1977).

[1] Paper presented at the California Riparian Systems Conference [University of California, Davis, September 17–19, 1981].

[2] J. Fred Chaimson is Chief of the Flood Control Maintenance Branch for the State Department of Water Resources, Sacramento, California.

[3] George Carter, Manager of the M&T Ranch, Chico, California. Personal communication.


121

figure

Figure 2.
Bank lines, Sacramento River, 1980, RM 187 to RM 191
(from Sacramento River Aerial Atlas, September 1980,
Sacramento District, US Army Corps of Engineers).

There are three alternative scenarios to this.

1. The resulting increased flow and debris would stay in the river channel and overtax the levees downstream.

2. The increased velocity and flow, coupled with a rising river bottom (caused by the adjustment of the eroding river bottom upstream), would cause the river to complete eroding of its natural levees somewhere between Sidds Landing (RM 178) and Kimmelshew Bend (RM 186.5), diverting the Sacramento River into Butte Basin (Brice 1977). This would cause widespread flooding in Butte Basin, possible failure of the levees of the Sutter Bypass, and loss of usefulness of the levees of the Sacramento River from Ord Ferry to Verona.

3. The third alternative is similar to the second except that the breakout would be to the west, flooding the nearby towns of Colusa and Princeton. This alternative is considered much less likely, however.

To forestall these possibilities, in 1974–75 the US Army Corps of Engineers (CE), with the usual State participation, constructed two revetment areas on the narrow waist of the peninsula and built an embankment or plug at the cutoff on Murphy Slough. The embankment was outflanked in high water of 1978 with some damage and again in 1980 with considerable damage, including erosion of the unit three revetment at the return to the river. Using emergency funds, the CE repaired and extended the embankment at the cutoff in 1980.

Flood Control Vegetation Studies

Recognizing the value of riparian vegetation in preventing flood damage under some circumstances, the Reclamation Board commissioned the firm of Murray, Burns, and Kienlen to identify areas of riparian vegetation of value to the stability of the river. Of the 38 sites identified, three of them are in this area and two of these, sites 35 and 36 (fig. 3), are pertinent to the problems of the division of flows at Murphy Slough.

Flood Control Planting on Golden State Island

In 1980, the Department of Water Resources and the Reclamation Board entered into an agreement with the Department of Fish and Game and M&T Ranch (the landowners) to provide for revegetation of the riverside slope of Golden State Island. The landowner agreed to provide right-of-entry for the revegetation and agreed not to remove or cause the removal of any resulting vegetation. In addition, he provided irrigation for the first planting and has agreed to do so for the replanting this year.

The planting plan includes:

1. grading of the riverside slope of Golden State Island to a three-to-one or four-to-one slope to prevent rain-caused gullying,

2. planting a mixture of Bermuda grass and rye grass on the slope face, and,

3. planting willow and cottonwood cuttings in the lower part of the slope in the fall season


122

figure

Figure 3.
Proposed riparian vegetation retention sites in vicinity of
Murphy Slough (from Murray, Burns, and Kienlan 1978).

in accordance with the availability of moisture, and extending the cuttings up the slope in succeeding years as appears necessary or desirable.

In late summer/early fall of 1980, the initial planting of the Bermuda/rye grass mixture was made. Unfortunately, before it was sufficiently established, high water in the relatively mild winter of 1980–81 washed out most of the lower part of the slope (fig. 4). This year, with the promise of irrigation sprinkling being available after mid-August, we will get an earlier start and have better growth before winter (fig. 5). Also, when the California Conservation Corps crews are available, after the fire season in the fall of 1981, we will have the willow/cottonwood plantings made.

One purpose of these plantings, in addition to obvious ones of habitat replacement and erosion control, is to encourage deposition of river-borne materials. Figure 6 shows the deposition of sediments downstream of a willow clump.

The plan is to promote a growth of willows and cottonwoods along the slope of Golden State Island, so that deposition will eventually reclose the mouth of Murphy Slough, reducing the flow of water into it and the resulting pressure on the Murphy Slough Cutoff.

figure

Figure 4.
Eroded bank of Golden State Island.


123

figure

Figure 5.
Re-sloped bank of Golden State Island.

figure

Figure 6.
Depositions downstream of willow bush.

Conclusions

While flood control maintenance at times involves removal of riparian vegetation to maintain channel capacity, there are selected areas where vegetation is beneficial for wave wash control, erosion control, and in this case sediment deposition, velocity reduction, and the redirection of flows.

Literature Cited

Brice, James. 1977. Lateral migration of the Middle Sacramento River, California. U.S. Geological Survey, Water Resources Investigation 77–43. 51 p. Menlo Park, Calif.

Murray, Burns, and Kienlen. 1978. Report to the Reclamation Board, Sacramento, California, on retention of riparian vegetation. February, 1978.


124

The Role of Riparian Vegetation in Channel Bank Stability

Carmel River, California[1]

G. Mathias Kondolf and Robert R. Curry[2]

Abstract.—A narrow channel with well-vegetated banks developed on the lower 15 km. of the Carmel River by 1939, and by 1960 this condition had extended to the entire lower 24 km. of river channel. Noticeable die-off of riparian trees near water supply wells began in the 1960s and intensified during the 1976–1977 drought. Substantial bank erosion occurred during the winters of 1978 and 1980 along reaches which had suffered loss of bank-stabilizing riparian trees.

Setting

The Carmel River, Monterey County, drains a 660-sq. km. (255-sq. mi.) basin. Rising in the rugged Santa Lucia Mountains and passing through the 24-km. (15-mi.) long alluvial Carmel Valley, it ultimately discharges into the Pacific Ocean near Carmel, Monterey County (fig. 1 and 2). This alluvial reach is sub-divided by a bedrock constriction and narrowing of the valley (the "Narrows") into a lower 16-km. (10-mi.) reach (the "Lower Carmel"), and a middle 8-km. (5-mi.) reach (the "Middle Carmel"), with "Upper Carmel" indicating the segment above San Clemente Dam (fig. 3). Average annual rainfall ranges from 1,040 mm. (41 in.) in the mountainous headwaters to 430 mm. (17 in.) in the lower valley. While the upper river is perennial, the lower river is intermittent, with flows typically from December through June. Near the river mouth, average discharge is 2.7 cms (97 cfs), and the bankfull discharge (here, the 2.4-year flow) is 79.2 cms (2,800 cfs).

figure

Figure l.
Vicinity map of the Carmel River basin
(US Army Corps of Engineers 1967).

Two water supply dams, the Los Padres and San Clemente dams (fig. 2), together impound about 3,000 acre-feet (AF). The Carmel basin supplies most of the water for the Monterey Peninsula cities of Monterey, Pacific Grove, Seaside, and Carmel. As these areas have grown, demand for water has risen substantially. To meet demand over the past two decades, California-American Water Company (Cal-Am), a private utility, has drawn increasingly upon water supply wells in the alluvium along the Lower and Middle Carmel. Of the total 13,000 AF exported from the basin in 1980, 9,000 AF was diverted from reservoirs, and 4,100 AF was extracted from streamside wells.

In the late 1960s, residents began complaining that vegetation was dying off near the wells in the region near Robinson Canyon Road (Lee 1974). The Carmel Valley Property Owners Association hired a forestry consultant to study the vegetation problem; he concluded that lowered water tables near the wells had killed the vegeta-

[1] Paper presented at the California Riparian Systems Conference. [University of California, Davis, September 17–19, 1981].

[2] G. Mathias Kondolf is in the Department of Geography and Environmental Engineering, Johns Hopkins University, Baltimore, Maryland. Robert R. Curry is a member of the Board of Environmental Studies, University of California, Santa Cruz, Calif.


125

figure

Figure 2.
General map of the Carmel River basin (US Army Corps of Engineers 1967).

tion (Zinke 1971). Cal-Am hired another consultant; he acknowledged that lowered water tables near the wells affected vegetation, but stated that the effect was simply to accelerate the "natural succession" of plants (Stone 1971).

The drought of 1976–1977 imposed additional demand on streamside wells. The die-off of mesic riparian plants was significant between Schulte and Robinson Canyon roads and above the Narrows—two areas of substantial groundwater withdrawal. The high flows of 1978 and 1980 resulted in severe bank erosion, primarily in areas where bank-stabilizing vegetation had been affected.

River History

River course and pattern changes were documented by comparing maps of the Carmel River from 1858 to 1945 and aerial photos of the river from 1939 to 1980.

Changes in Course

Historical changes in the Carmel River from Garland Ranch to the mouth are plotted in figures 4 and 5. The 1858 and 1882 channels were determined from boundary surveys. The 1911 course appears on the Monterey 15' USDI Geological Survey topographic map (quad) of 1913 (based on surveys in 1911–12), and the 1945 course is taken


126

figure

Figure 3.
Location map, Middle and Lower Carmel River (base from Monterey, Seaside, and Carmel Valley 7.5' quads).

from the Monterey and Seaside 7.5' quads of 1947 (based on aerial photography in 1945). The 1947 maps were photorevised in 1968, but the only mapped revision in the river's course was downstream of Garland Ranch, where a northward bend of the river was eliminated by highway construction.

Comparison of these maps reveals nine localities where lateral channel migrations of 250–500 m. (820–1,640 ft.) occurred during the 87 years between 1858 and 1945. Except for the change near Garland Ranch Park, since the survey of 1911–1912, changes in course have been modest, generally less than 0.2 km. These migrations were gradual changes from 1911 to 1945, unlike the dramatic shifts that were wrought by floods in the preceding years. This is consistent with the observation that most major shifts take place during large floods. No floods comparable to the 1911 event occurred between that year and 1945, nor have they since.

Figures 4 and 5 show changes in the channel reach from San Clemente Dam downstream to Las Garzas Creek. The 1917 channel is plotted from the Jamesburg 15' quad of 1918 (from surveys in 1917). The 1954 course is from the Carmel Valley 7.5' quad of 1956 (compiled from 1954 aerial photography). The lack of dramatic changes comparable to those seen downvalley may be attributed to: 1) the lack of record prior to the 1860 and 1911 floods; and 2) bedrock confinement along much of this reach.

Flood History

The earliest flood on record along the Carmel River was the great statewide deluge of 1862. While no records exist to document the exact magnitude of this flood, it was severe enough to induce the few valley residents to move to higher ground.[3] Most of the great changes in channel course visible between the 1858 and 1882 channels in Rancho Canada de la Segunda probably occurred during this flood.

The next great flood occurred in 1911. An account in the "Monterey Cypress" of 11 March 1911 reported that Fannie Meadows and Roy Martin lost 10 acres and a pear orchard due to lateral migration of the river. Their adjacent properties extended downstream from the present Schulte Road to Meadows Road. The channel shift that consumed their land can be seen by comparing the river course of 1858 with that of 1911 (fig. 4).

[3] Roy Meadows. Personal communication of family history.


127

figure

Figure 4.
Course changes of the Carmel River, Garland Ranch to mouth.

figure

Figure 5.
Course changes of the Carmel River channel,
San Clemente Dam to Las Garzas Creek. Key:
dashed—1917 channel from 1918 edition
Jamesburg 15' quad; solid—1954 channel,
from 1956 edition Carmel Valley 7.5' quad.

The flood of 1911 was a big flood indeed. Before it was swept away, a staff gauge at the site of the San Clemente Dam indicated a discharge of 480 cms (17,000 cfs). The peak flow has been estimated at 708 cms (25,000 cfs). In 1914 another major flood occurred, but this one was far less destructive. It is not known whether this flood was significantly smaller than the 1911 event, or if it simply caused less disruption because it flowed through a channel pre-adjusted to the large 1911 flow.

No comparable floods occurred in the following decades. The absence of large floods, together with the drop in sediment load resulting from construction of the San Clemente Dam in 1921, served to permit channel narrowing, increased sinuosity, and bed degradation.

Changes in Sinuosity and Gradient

Sinuosity, defined as the ratio of stream channel length to valley length, was computed for several sequential channels. From 1911 to 1945, the reach of river from Garland Ranch to the mouth increased in sinuosity from 1.11 to 1.18. The reach from Sleepy Hollow to Las Garzas Creek experienced an overall increase in sinuosity of 1.05 to 1.09 from 1917 to 1954. Map slopes computed for the 1911 and 1945 channels from Garland Ranch to the mouth show a decrease from 0.0034 in 1911 to 0.0029 in 1945. The overall increase in sinuosity and decrease in gradient suggest that the Carmel River stabilized in the aftermath of the 1911 flood.

Changes in Channel Pattern and Form

Channel pattern (pattern in plan view, e.g., meandering, braided) and form (cross sectional shape, e.g., narrow, wide) of the Lower and Middle Carmel River have changed dramatically since the last major flood and construction of the dams. No doubt, the entire Lower and Middle Carmel were strongly modified by the 1911 and 1914 floods. The resulting channel is probably well represented by the historical photos (ca. 1918) from the Slevin Collection (University of California, Berkeley). These photos of the


128

river, at and downstream of the Narrows (fig. 6 and 7), show a wide, sandy channel, reflecting the recent passage of a major flood.

By 1939, the Lower Carmel had developed a narrower, more sinuous channel while the Middle Carmel retained much of its braided character, as evidenced by aerial photography of 1939. Figure 7 shows the area pictured in figure 6 as it subsequently appeared in the 1930s. By this time, a riparian forest had developed along virtually all of the Lower Carmel River, narrowing the channel. Aerial photographs taken in 1965 show further development of vegetation and narrowing of the channel.

This change in channel pattern occurred concurrently with the increase in sinuosity and decrease in gradient apparent by 1945. Together, they indicate that the Lower Carmel had adjusted to the absence of major floods and the cut-off of 60% of its previous sediment load (based on drainage area upstream of San Clemente Dam). These adjustments included channel narrowing with encroaching vegetation, an increase in sinuosity, and reduction of gradient through incision.

figure

Figure 6.
Carmel River channel, 1918, viewed from right bank
upstream from location of present Robinson Canyon
Road bridge, looking upstream. (Slevin Collection,
Bancroft Library, University of California, Berkeley.)

figure

Figure 7.
Carmel River channel, 1930s, viewed from right bank
upstream from location of present Robinson Canyon
Road bridge. View upstream. Contrast this with figure 6,
essentially the same view, taken in 1918. (Pat Hathaway
Photograph Collection, Pacific Grove, California.)

Similar adjustments have been documented in other rivers in response to the absence of floods or the construction of upstream dams (Leopold etal . 1964).

By 1939, the Lower Carmel had incised about 4 m. into deposits of the 1911 flood, leaving a 4 m. terrace. Some of this incision is visible when figures 6 and 7 are compared. The flat surface of sand and gravel to the right of the river in figure 6 is the 1911 channel floor. By 1918 (when figure 6 was taken), the channel had cut down about 2 m., and willows had begun to invade the low terrace. By the 1930s (when figure 7 was taken), the channel had incised about 4 m. The 1911 channel floor appears as the terrace in figure 7, with a farmed field and small building on it. This 1911 terrace can be confidently traced along much of the Lower Carmel on the basis of morphology and historic changes in course. Figure 8 shows the 1911 terrace (Qt1) and higher terraces. There is evidence that Qt2A may be the 1862 flood terrace, but otherwise the higher terraces are of unknown age.

Above the Narrows along the Middle Carmel, similar adjustments took place, but they occurred later. The aerial photos taken in 1939 show the scars of numerous anastamosing channels in the Middle Carmel. By 1971, most of these scars no longer appeared, as exemplified by the reach from Boronda Road to Robles del Rio (fig. 9). Accompanying this change in pattern was degradation of the bed. Sequential cross sections show 1.5 m. (5 ft.) of degradation under the Boronda Road bridge from 1946 to 1980.

By the 1960s, most of the Lower and Middle Carmel had developed a narrow, sinuous, well-vegetated course. It bears repeating that these


129

figure

Figure 8.
1911 flood terrace and other Quaternary deposits of the Carmel River, from the Narrows to Rancho San Carlos Road.
(Based on reconnaissance-level study of aerial photographs, historic ground photographs, and historic changes in course.)

figure

Figure 9.
Pattern changes, Middle Carmel River, from Boronda Road to Esquiline Road at Robles Del Rio.
 (Data from aerial photographs of 1939 and 1971, Map Library, University of California, Santa Cruz.)


130

conditions developed only in the absence of major floods and, further, may have depended upon a cut-off of upstream sediment by the dams.

Additionally, before their suppression by European settlers, fires occurred regularly in the upper Carmel basin, periodically leading to vastly greater sediment yields. The accumulation of sediment in the Los Padres Reservoir after the Marble-Cone fire of 1977 was dramatic. The capacity of this reservoir decreased from 3,200 AF upon closure in 1947 to 2,600 AF in 1977, a loss of storage of 600 AF in 20 years. Consequent to the Marble-Cone fire and the high flows in the ensuing winter, the reservoir's capacity decreased to 2,040 AF by the end of 1978. Thus, in one year the reservoir lost 560 AF of storage.[4] This post-fire sedimentation rate was nearly 20 times greater than the pre-fire rate.

Prior to dam construction, all this sediment passed through to the Middle and Lower Carmel. It is probable that a wide, sandy channel would have developed in order to transport these high sediment loads. However, it is notable that the sediment contributed by the recent bank erosion has passed through the lowermost reaches of the Carmel (Valley Greens Drive downstream) without destabilizing that narrow channel. The stability of this lowermost reach may be due, in part, to the automobile bodies and riprap emplaced within the banks or to the extensive irrigating of streamside golf courses. Without these stabilizing influences, the channel might have widened in response to the higher load. Alternatively, such a narrow channel in its natural state, protected only by bank vegetation, may be able to pass these high loads without disruption of its existing geometry. In this latter case, the observed changes in channel pattern, form, gradient, and sinuosity may best be ascribed to recovery from the major floods of 1911 and 1914.

Recent Bank Erosion

Peak discharges over the winters of 1978 and 1980 were 208 cms (7,360 cfs) and 168 cms (5,920 cfs) respectively. These flows resulted in massive bank erosion along parts of the Middle and Lower Carmel. Most severely affected was the region upstream of Schulte Road Bridge. Here the channel at bankfull discharge (defined as the flow with a recurrence interval of 2.4 years on an annual maximum series) increased in width from 13 m. (43 ft.) to 35 m. (115 ft.) in two years. This increased the width: depth ratio from 15 to 113. Aerial photographs show the changing aspect of this reach from 1939 to 1980. In 1939 and 1965, a narrow channel fringed by dense riparian vegetation is visible (fig. 10a and b). The 1977 photo indicates no obvious change in the channel, but does show a marked thinning of streamside trees (fig. 10c). The 1980 photo exhibits a major widening of the channel, most of which occurred during one storm in the winter of 1980 (fig. 10d).

Throughout the Middle and Lower Carmel, the river banks are composed of unconsolidated sands and gravels, which lack cohesive strength in the absence of binding vegetation. These banks offered no resistance to lateral erosion. A comparison of surveys and aerial photographs of 1965 and 1980 from Schulte Bridge upstream 0.6 km. (0.4 mi.) indicates that 100,000 cu. m. of bank material was consumed by the river, mostly during the winter of 1980. The resulting channel is wide and floored by sand and gravel (fig. 11).

The die-off of bank vegetation and consequent lateral erosion appear to be coincident with lowering of water tables below the root zone of trees. Downstream of Valley Greens Drive, where no producing wells were located, the riparian vegetation remained largely unaffected during the drought of 1976–77. The channel there remained stable during both the 1978 and 1980 winters. A plot of water table elevations for the drought, i.e., drawdown (October 1977), and post-drought, fully recharged conditions (April 1978) shows far less drawdown in this lowermost reach of the Carmel (fig. 12). Figure 12 shows that along much of the Middle and Lower Carmel the water table was drawn down about 10 m. This is generally considerd to be below the root zone of riparian willows (Zinke 1971). The depression of the water table upstream of Schulte Road is due to the drawdown created by wells in the highly permeable alluvium of the Carmel Valley. While the drought of 1976–1977 certainly exacerbated the drawdown problem, the drought alone cannot explain the fact that severe drawdown, vegetation die-off, and subsequent bank erosion affected certain areas only.

Erosion Mitigation

Individual efforts to control bank erosion along the Carmel range widely in cost and effectiveness. Riprap has been used with mixed results. Among the materials used for riprap on the Carmel are ornamental dolomite, concrete blocks, and rubble from Cannery Row. Gabions and pervious fences with rock fill have been used successfully. Some landowners are attempting to establish willows on their eroding banks, but many of these seedlings are not adequately irrigated and die. One of the most popular revetment strategies is emplacement of automobile bodies in the eroding banks (fig. 13). The individual bank protection efforts thus far are uncoordinated and may, in some cases, have deleterious downstream effects. The government agency charged with managing the area's water resources, the Monterey Peninsula Water Management District, is now considering an integrated management plan for the Carmel River.

[4] B. Buel. 1981. Monterey Peninsula Water Management District. Personal communication.


131

figure

Figure 10.
Aerial photographs of the Carmel River near Schulte Road bridge. Arrows point to bridge.
(Aerial photograph collection, Monterey County Flood Control, Salinas.)

figure

Figure 11.
Channel of the Carmel River upstream of Schulte Road bridge,
November 1980. View downstream from about 0.5 km (0.3 mi.)
upstream of bridge (photograph by the authors).

Redesigning the Carmel River

The "river-training" experience of New Zealand engineers provides a possible model for restoring unstable reaches of the Carmel (Nevins 1967). Their procedure is to determine "design geometries" from stable reaches of a river and to reengineer unstable reaches to these design geometries. Cross-sectional geometry, sinuosity, and gradient of the stable reaches are duplicated as closely as possible in the unstable reaches. Initially, bank protection works are used to stabilize the banks and willows are planted; once fully established, the willows are expected to become the principal bank-stabilizing agent. The reengineered channels in New Zealand have remained stable in all but very high flows. If large discharges disrupt the design channels, these reaches can be reengineered to design specifications at a lower cost than the initial work (ibid .).

For the Carmel River, the stable reaches downstream of the disturbed reaches can serve as design geometries. In figure 14, cross sections are plotted for an eroded reach upstream of


132

figure

Figure 12.
Water table elevations, drought and recharged conditions.
(Date from Monterey County Flood Control well level records.)

figure

Figure 13.
Automobile bodies used as bank revetment, downstream
of Meadows Road (photograph by the authors).

Schulte Road (section 37) and for a stable reach about 1.5 km. (1 mi.) downstream (section 45). No tributaries enter between these sections, so discharge remains essentially constant. Yet the present-day geometries are vastly different. Surveys by the US Army Corps of Engineers in 1965 (US Army Corps of Engineers 1967) indicate that the reach encompassing section 37 was characterized by a geometry closely resembling that of the present-day section 45. Thus, a design-stable geometry for section 37 could be drawn largely from the existing geometry at section 45. Certain corrections would have to be made for difference in gradient, sinuosity, and bed material size between these reaches. Fortunately, many of these parameters are well documented for the stable, pre-disturbance Carmel River.

The success of a river-training program depends, in part, on a favorable flow regime in the years following channel redesign. A major flood (e.g., a 20- to 30-year event) in the first few years following the redesign may take out the new banks before they have been stabilized by vegetation. A catastrophic flood (e.g., a 75- to 100-year event) will probably carve a new channel for itself regardless of how well vegetated the existing banks might be (Nevins 1967). Applying these concepts to the Carmel, we might expect that a flow comparable to the 1980 event within the first five-to-ten years following channel redesign could take out the design banks. A flow comparable to the 1911 flow could take out the design banks whether vegetated or not.

Summary

The lower 24-km. (15-mi.) reach of the Carmel River is alluviated and is divided by a bedrock constriction into a lower 16-km. (10-mi.) reach and a middle 8-km. (5-mi.) reach. This alluvial reach of the river has experienced major changes in channel course, pattern, and form over the past 130 years. Major floods in 1862 and 1911 changed the river's course by up to 500 m. (1,640 ft.). After 1914, the absence of severe floods, coupled with dam construction upstream, led to a change from a wide, braided channel to a narrow, more sinuous channel. Accompanying this change was a decrease in overall gradient in the lower reach from .0034 to .0029 between 1911 and 1945.

By 1939, the date of the first coverage by aerial photography, the lower reach had developed a narrow, sinuous channel with well-vegetated banks that remained stable for most of the next four decades. The middle reach of the river, however, displayed a predominantly wide, braided


133

figure

Figure 14.
Channel cross sections of the Carmel River near Schulte Road bridge. Section
37: 250 m. (820 ft.) upstream of bridge; section 45: 1,520 m. (5,000 ft.) downstream
of bridge. Discharge is essentially constant. (From field surveys by the authors).

pattern. Between 1939 and 1971, this middle reach developed a single thread channel and downcut up to 1.5 m. (5 ft).

As groundwater withdrawal from streamside wells increased in the 1960s, residents began complaining that riparian trees were dying near the wells. During the 1976–1977 drought, lowered water tables were associated with substantial die-off of riparian trees. The death of these bank-stabilizing trees is associated with significant lateral erosion that occurred during the winters of 1978 and 1980. Upstream of the Schulte Road bridge, the river's bankfull channel increased in width from 13 m. to 35 m., increasing the width:depth ratio from 15 to 113. Downstream, the channel remained stable despite passage of the sediment derived from the eroding reaches.

Individual efforts to control bank erosion have included planting of willows and emplacement in banks of automobile bodies and riprap. The mixed success of these efforts demonstrates that a coordinated program is needed to manage the river. Most promising as a model for the Carmel is the experience of New Zealand engineers in "river training." Their procedure is to determine design geometries from stable reaches and then redesign disturbed reaches to the design geometry. After initial stabilization using engineering works, planted willows are expected to serve as the primary stabilizing agents.

Acknowledgments

This study was supported by a contract with the Monterey Peninsula Water Management District. Our thanks to the District staff for generous assistance in every phase of the study. We are also grateful for the invaluable cooperation of Monterey County Flood Control, the California Department of Fish and Game, Monterey Office, and the US Army Corps of Engineers, San Francisco District. To the friends who helped with the field work, our thanks.

Literature Cited

Lee, E.B. 1974. A summary report of facts, analysis, and conclusions relating to the Monterey Peninsula water supply problems. Public Utilities Commission Case 9530. 23 p. Unpublished report.

Leopold, L.B., W.G. Wolman, and J.P. Miller. 1964. Fluvial processes in geomorphology. 522 p. W. Freeman and Company, San Francisco, Calif.

Nevins, T.H. 1967. River training—the single-thread channel. New Zealand Engineering 24 (Dec. 15, 1967):367–373.

Stone, E. 1971. The dynamics of vegetation change along the Carmel River. Unpublished report to the California-American Water Company, March, 1971. 54 p.

US Army Corps of Engineers. 1967. Flood plain information on Carmel River, Monterey County, California. 36 p. US Army Corps of Engineers, San Francisco District, San Francisco, Calif.

Zinke, P. 1971. The effect of water well drawdown on riparian and phreatophyte vegetation in the Middle Carmel Valley. Unpublished report to the Carmel Valley Property Owners Association, Carmel Valley, Calif. February, 1971. 27 p.


134

Sequential Changes in Bed Habitat Conditions in the Upper Carmel River Following the Marble-Cone Fire of August, 1977[1]

Barry Hecht[2]

Abstract.—Runoff following a major fire filled the upper Carmel River, Monterey County, California, with sediment. Repeated measurements of four habitat descriptors were made in riffles during three years following the fire. Habitat values were largely restored by the end of the first winter, with virtually complete recovery after three years.

Introduction

The importance of episodic or unusual events in the management of riparian systems in montane areas is increasingly being recognized. Wildfires are one of the major recurring disturbances affecting biologic and geomorphic processes in these watersheds. This is especially true in basins with significant areas of steep, chaparral-covered slopes.

Many resource managers consider the canyon bottoms—the channels, riparian zones, and valley flats—the most biologically significant zones in these watersheds. The bottomlands commonly remain unburned during fires which otherwise affect much of the drainage area. The primary physical changes in these corridors are frequently those associated with erosion, deposition, and channel instabilities induced by post-fire storm runoff. While numerous studies of fire-related increases in runoff and debris load have been made, relatively little is known of their effects on habitat values.

This report is a preliminary summary of an ongoing study addressing one aspect of the larger management problem—the indirect effects of fires on bed conditions affecting aquatic habitat values. The upper Carmel watershed in Los Padres National Forest, Monterey County, California was chosen for this study for three reasons. First, the drainage is used primarily for recreational, habitat, and watershed purposes; the alluvial corridor is central to all three uses. Second, direct human disruption of soil and vegetation in the basin is minimal, limited primarily to ridgetops far removed from the channels. Third, the watershed is in the size range of smaller basins capable of sustaining an anadromous fishery commonly considered to be from about 10–100 km2 (4–40 mi2 ).

There were two significant limitations on this study imposed by the choice of the upper Carmel watershed. First, there are no stream gauges in the basin. Synthesis of a flow-record for each site will be required to establish the relationship of the observed sequential changes to runoff. Data needed to develop the synthetic flow-record are presently not fully available. Secondly, access to the sites required a hike of about 8 km. (5 mi.) over damaged trails with backpacks and survey gear, limiting both the equipment which could be used and the number of sites which could be monitored during a given weekend.

Regional Setting

The Carmel River drains the northern slopes of the Santa Lucia Mountains (fig. 1). The upper portion of the basin is a rugged area of approximately 161 km2 (62 mi2 ) above Los Padres Dam, a municipal water-supply source for the Monterey Peninsula urban area about 50 km. (30 mi.) to the north.

The watershed is underlain by faulted crystalline rocks, primarily schists, gneisses, and metasomatic granitic rocks ranging in composition from granodiorite to gabbro (Wiebe 1970). Weathering of these rocks produces a large amount of medium-grained sand and a disproportionately small percentage of fine gravel. The courses of the main channels are structurally-controlled, primarily by faults and fractures. The channels are unusually steep for watersheds of comparable size in the region.

[1] Paper presented at the California Riparian Systems Conference. [University of California, Davis, September 17–19, 1981].

[2] Barry Hecht is Senior Hydrologist, HEA, a Division of J.H. Kleinfelder and Associates, Berkeley, California.


135

figure

Figure 1.
 Upper Carmel watershed and vicinity. Monitoring sites on the Carmel River are at Bluff Camp (1), Carmel
Camp (2), below Bruce Fork (3), at Sulphur Springs Camp (4), and on Miller Fork above its mouth (5).

Rainfall ranges from an average of 610 mm. (24 in.) per year at Los Padres Dam to an estimated 1150–1270 mm. (45–50 in.) at the drainage divide with the Big Sur watershed. This supports a vegetative mosaic with chamise/chaparral on steeper exposed slopes, oak/madrone woodland community on more protected slopes and terraces, and mixed hardwood/coniferous forest at the highest elevations.

The Marble-Cone Fire

The Marble-Cone Fire burned approximately 72,000 ha. (178,000 ac.) in the Santa Lucia Mountains during August, 1977 (fig. 1). Virtually all of the Carmel watershed above Los Padres Reservoir was affected by the fire. The USDA Forest Service staff estimated remaining canopy cover to be less than 10% in 42% of the upper Carmel basin; 11–50% over an additional 20% of the watershed; and more than 51% over the remaining 38% of the area.[3] No extensive fires had occurred in the watershed during the previous 50 years. Much of the basin had remained unburned for 76 years or more (Griffin 1978).

Two unusual occurrences contributed to the severity of the burn, and particularly to its impact on the canyon floor areas. Fuel levels were abnormally high due to an extreme amount of limb breakage sustained during a wet and sticky snowfall on January 3, 1974. The effect on fuel loadings was especially large in the riparian zone and on the terraces and lower slopes, areas seldom affected by snowfall. Secondly, conditions were also unusually dry following the severe drought of 1976 and 1977. Rainfall at Big Sur, the nearest long-term station, during each of these years was less than that measured for any of the previous 58 years.

Post-Fire Runoff

Rainfall during the 1977–78 and 1979–80 winter seasons was 40–50% above normal at many stations in the region; rainfall during 1978–79 was generally slightly below average. Runoff in the Carmel and nearby watersheds was markedly above normal during this 3-year period, reflecting both the above-average rainfall and the altered runoff characteristics (table 1). The duration of high flows was also much above normal. One measure of this duration is the number of days that flow exceeded bankfull conditions. In the Monterey Bay area (as in many other regions), this corresponds roughly to the flood with a recurrence of 1.5 years. The Big Sur River is the nearest gauged stream, and is consi-

[3] USDA Forest Service. Undated. MarbleCone fire: remaining vegetative cover. Unpublished staff report. Los Padres National Forest.


136

sidered most representative of the upper Carmel River. The 1.5-year flood discharge on the Big Sur River is approximately 1,600 cubic feet per second (cfs). Based on preliminary records, this discharge was exceeded for a total of about 10 days in 1978 and about 6 days in 1980, compared with an annual average of 1.1 days for the period prior to the fire.

 

Table l.—Post-fire runoff at gauges in the vicinity of the upper Carmel watershed.

USGS gage no.

11143000

11143200

11151870

Stream

Big Sur R.

Carmel R.

Arroyo Seco

Location

Big Sur

   Robles
del Rio

nr.
Greenfield

Period of record

1950-pres.

1957-pres.

1961-pres.

Drainage area
(sq. mi.)

46.5

193

113

Mean annual runoff

(cfs)

89.6

71.3

121

Runoff

       

1978

(cfs)

246

206

378

 

(% of mean1 )

275

289

312

1979

(cfs)

  97.9

63.5

163

 

(% of mean1 )

109

  89

135

1980

(cfs)

200

192

295

 

(% of mean1 )

223

269

243

1 Mean annual runoff through Sept. 30, 1977, excluding period of post-fire runoff.

More specific data are available on the effect of the fire on sediment yields of the upper Carmel watershed (table 2). Deposition in Los Padres Reservoir during the three years following the fire was about equal to that during the previous 30 years. In addition, a large but undetermined amount of debris has accumulated in the channels of the Carmel R ver and Danish Creek above the spillway elevation.[4]

 

Table 2.—Sequential sediment accumulation in Los Padres Reservior (source—R.M. Boyd[4] ).

Survey
date

Reservoir capacity1 (acre-ft.)

Loss in capacity (acre-ft.)

Annual rate of capacity loss (acre-ft.)

Nov 19472

3200

-

-

Nov 1977

2592.7

607.3

20.2

Sep 1978

2037.6

555

555

Oct 1980

1996.3

41.3

20.6

1 Below spillway elevation of 317.2 m. (1040 8 ft.) above mean sea level.
2 From pre-construction capacity curves developed by California Water and Telephone Company.

Sequential Changes in Bed Habitat Conditions

Habitat in the streams of the upper Carmel system is generally evaluated by its suitability for salmonid production. The local resource includes both steelhead and resident trout. Availabilities of suitable spawning and rearing habitats are considered factors limiting both populations, a common situation in streams of central California.

In riffles of boulder-bedded streams such as the upper Carmel River, both spawning and rearing occur in spaces or openings between the larger bed-forming rocks. Spawning occurs in bars and accumulations of gravels which form between the boulders or in their lees, locations partially protected from scour.

The epicycle of massive fill and scour following fires in this environment temporarily buries most of the limited habitat with finer material, largely sand. For this reconnaissance study, descriptors chosen to define the extent of burial and subsequent uncovering of habitat include:

1. net fill and scour, as measured by level-surveys following each major group of storms;

2. particle-size distribution of the bed surface, measured by censusing particles at the intersections of a grid;

3. percentage of bed area occupied by sand and finer material, also sampled on a grid; and

4. percent of the bed covered by material of sizes suitable for spawning, determined as above.

Net Fill and Scour

Minimal spawning or rearing habitat was available in the upper Carmel channels during the period of maximum fill. Habitat availability increased as the stored sediment was gradually scoured. A useful measure of these sequential changes is net mean fill or scour, determined from the change in mean bed elevation of the channel during each storm period. This change was quantified using repeated level-surveys of monumented cross-sections.

The sequence of fill and scour was recorded at six cross-sections in three riffles. The riffles were chosen shortly after the fire on the basis of observable habitat values for both spawning and rearing, their general alluvial character, absence of major unusual hydraulic properties, and presence in a long and straight reach. The last three criteria were necessary to meet the hydraulic requirement of the indirect discharge measurements used to determine the peak flows during each storm period. The sections were established in early November, 1977, fol-

[4] Bloyd, R.M. 1981. Letter of March 18 to Robert F. Blecker, hydrologist for Los Padres National Forest, which summarizes USDI Geological Survey studies of post-fire sedimentation in Los Padres Reservoir.


137

lowing the fire but prior to any measurable runoff. Cross-sections were resurveyed after each significant flood event during the winter of 1977–78, and again following the wet season of 1979–80. An example of data collected at one section describing the sequential changes in elevation and configuration of the bed is presented in figure 2.

The fill and scour cycle observed at each riffle is summarized in table 3. Fill occurred immediately after the first storms in December, 1977, and continued at some sections through the major storm period in January, 1978. By the end of the first winter, the bed was being scoured at all six sections, a process which continued through the second and third rainy seasons. The final column in table 3 traces the proportion of maximum net fill removed during each period.[5] By the end of the first season, 57–102% of the maximum observed net fill had been scoured. "Recovery percentages" of 80–151% were recorded by the end of the third year. At four of the six sections, 80–90% of the maximum observed fill had been removed by the end of the third year. Mean scour exceeding the mean maximum fill was limited to the riffle at Carmel Camp, where about half of the mean scour is attributable to lateral erosion of the lower bank area on one side of the channel.

figure

Figure 2.
Bed configuration and high-water marks during the fill and scour
cycle following the Marble-Cone fire, looking downstream.
Some high-water profiles slope toward the right bank, discussed below in the text.

[5] Maximum fills may have been greater during one of the storm periods. Ephemeral bed conditions during storm crests may not have great importance in defining spawning or rearing habitat value; thus the methodology is appropriate for the purposes of this study. The reader is cautioned that recovery percentages in table 3 may underestimate the removal of within-storm fill maxima.


138
 

Table 3.—Sequential changes in net fill and scour.

   

Mean Bed Elevation
(ft.)

Net Fill (+)
or Scour (–)
(ft.)

Percent1 Recovery

Carmel River
   at Bluff Camp

       

Lower Section

11/05/77

96.82

 

12/25/77

97.72

+0.90

 

01/28/78

97.832

+0.11

0

 

03/25/78

97.25

–0.58

57

 

11/08/80

96.93

–0.32

89

Upper Section

11/05/77

99.48

 

12/25/77

100.492

+1.01

0

 

01/28/78

99.89

–0.60

59

 

03/25/78

99.68

–0.21

80

 

11/08/80

99.68

0.00

80

Carmel River
   at Carmel Camp

       

Lower Section

11/06/77

93.82

 

12/26/77

94.232

+0.41

0

 

01/28/78

94.00

–0.23

56

 

03/25/78

93.81

–0.19

102

 

11/09/80

93.61

–0.20

151

Upper Section

11/06/77

95.24

 

12/26/77

95.482

+0.24

0

 

01/29/78

95.40

–0.08

33

 

03/26/78

95.30

–0.10

75

 

11/09/80

95.15

–0.15

138

Miller Fork
   above Carmel R

       

Lower Section

11/06/77

91.50

 

12/26/77

91.562

+0.06

0

 

01/29/78

91.562

0.00

0

 

03/26/78

91.52

–0.04

67

 

11/09/80

91.51

–0.01

83

Upper Section

11/06/77

94.18

 

12/26/77

94.29

+0.11

 

01/29/78

94.532

+0.24

0

 

03/26/78

94.27

–0.26

74

 

11/09/80

94.23

–0.04

86

1 Defined as whole channel change in mean bed elevation (MBE) by the relation 100 (MBEm –MBEi )/(MBEm –MBEo ), with subscripts m, i, and o identifying maximum net fill, measured, and original post-fire conditions, respectively.
2 Maximum net fill.

Size Distribution of Bed Material

The particle-size distribution of bed material is commonly quantified in the course of habitat assessments, either by a visual estimate or by a grid-by-number census. The latter approach was used in this study.

Particle-size distributions of bed-surface material were determined by measurement made at the same five riffles in the early fall months of each year, prior to the onset of rains. This is the season in which rearing habitat is most likely to be constrained by sediment. An area-stratified random sample of the entire riffle bed was drawn by stretching cloth measuring tapes between rows of eight to ten iron pins at the top and base of each riffle. Lengths of intermediate axes of particles immediately beneath preselected points on the tapes were measured and grouped in standard size-classes. This procedure is an adaption for use in boulder-bed channels of Wolman's (1954) now-standard methodology. A sample of 50 to 100 rocks is generally considered sufficient to describe bed-surface populations; larger samples were drawn following the 1978 storms as a wider range of size-classes were observed.

Sequential changes in the size distribution of bed material are shown in table 4. Sizes at the key descriptive percentiles generally decreased following the fire, then subsequently have increased. Relative changes were more pronounced at the 16th and 50th percentiles than in the larger materials, as might be expected.

Much, and probably most, of the change in particle-size distribution occurred during the first year following the fire. It was not feasible to recensus the bed between storms due to the unusually high flows of the winter of 1978. In most cases, the minimum sizes probably were associated with the December, 1977, or January, 1978 storm periods. Had no more storms occurred during the winter of 1978, a much greater effect on habitat conditions would have been observed during the summer and fall of 1978.

Sand-Covered Bed Areas

Aquatic biologists have often identified percent bed area covered by sand (or finer material) as a significant influence on the distribution of species in the channel, and as a factor affecting salmonid egg viability. The distribution of sand and finer material on the bed of mountain stream riffles appears to be controlled by different geomorphic processes than those governing the coarser sizes. In this study, sand is considered as a separate population, one whose variability is also best described by the percentage of the riffle bed which it covers. In this study, the sand-and-finer percentage of the bed surface was determined in the course of the particle-size measurements. Intermediate axial lengths of particles smaller than 4 mm. could not be readily measured under field conditions; these were grouped in a single class informally labelled "fines."[6]

[6] Most standard classifications divide sands and gravels at 2 mm. In the upper Carmel environment, which is deficient in very fine gravels, any interpretive difficulty introduced by including 2–4 mm. material with the sands is minor.


139
 

Table 4.—Sequential changes in particle-size of bed material, upper Carmel watershed.

figure

 

Sequential changes in the sand-covered portion of the bed are shown in figure 3. The abundance of fines increased markedly with the first storms after the fire. At the Bluff Camp riffle, the percentage of bed area covered by sand or finer debris on December 25, 1977, was visually estimated to be 40% in the riffle and 95% in the pool beneath it. By the end of the first year, the fines abundance at the five sites averaged only very slightly greater than at the time of the fire. As with the particle-size changes, the sequential variations in fines abundance were greatly accelerated by the unusually high runoff conditions of the 1978 water year.

Availability of Spawning-sized Material

Salmonid spawning habitat in the upper Carmel watershed may be limited by the availability of material of suitable sizes in riffles. The relative abundance of this material can be quantified for the Carmel channels as the percentage of the bed surface occupied by rocks within the range of suitable sizes, as no appreciable armoring of the bed was observed. For this study, it is assumed that the range of 4 mm. to 90 mm. defines the bulk of material found in and above freshly-constructed redds in streams of comparable size, slope, and underlying rock types (e.g., Orcutt etal . 1968, Platts etal . 1979).[7]

The availability of spawning-size material increased markedly at four of the five riffles in the first year after the fire. The percentage of the bed occupied by this size-range has remained slightly elevated, although depletion has probably occurred since 1978, particularly in the smaller sizes. To an appreciable degree, the increase has been manifested as expanded bars in

[7] Percentages of bed area occupied by material of other ranges may be computed from table 4 by those who would prefer to consider different sizes.


140

figure

Figure 3.
Sequential changes in bed area occupied by spawning-sized
material and sand-and-finer debris following the Marble-Cone
fire. Runoff events substantially exceeding bankfull discharge
are considered major storms. Sites are numbered as on figure 1
and table 4.

the lees of larger boulders, a location preferentially used for spawning in boulder-bedded channels. The role of fires in the supply of gravels in high-gradient streams merits study.

Supplemental Observations

Other processes related to post-fire sedimentation also affected the channels and riparian corridors. These were observed in a more general way.

1. The fill and scour cycle in pools and glides (or "runs") was greater in absolute magnitude than in riffles. Several traditional swimming holes were completely filled during the December and January storms following the fire. The relative rates of recovery in pools and glides seemed to be similar to or slightly slower than those in the riffles of this boulder-bedded channel.

This study was limited to describing sequential changes in riffles, where indirect discharge estimates and bed-material census are customarily made. Equally important in this decision was the historical emphasis placed on riffles by aquatic biologists. Subsequent research has clarified and quantified the importance of rearing habitat within pools and glides in salmonid production (e.g., Bjornn etal . 1977; Kelley and Dettman 1979). Future studies of post-fire changes in habitat should include pools and glides.

2. Few secondary slope instabilities were induced by the fire. Landslide-related sediment delivery to the main channels was probably of negligible magnitude; this presumably contributed to the rapid rate of sediment depletion in the channels. The relative stability of the slopes is considered to be primarily a function of bed-rock type.

3. Interception of sediment on the lowermost terrace was widespread, particularly at the mouths of ravines, chutes, and small tributaries. Much of this material is of gravel or pebble size. Relative to the volume of coarse material deposited in and above Los Padres Reservoir since the fire, the volume of debris intercepted on the terrace was small, perhaps 1–3%. This is a smaller amount, but somewhat similar to the fire-related sediment still stored in the main channels at least above the tailwater areas of Los Padres Reservoir. Delayed delivery of coarse material stored in these debris cones may be a factor in maintaining the supply of spawning-sized material during extended periods between major fires and floods.

4. Floods following the fire removed much of the organic matter which had accumulated in the channel. Most fallen trunks and limbs on or spanning the streambed were dislodged, then either washed through to Los Padres Reservoir or wedged between the trunks of larger riparian trees distributed along the banks. These small debris jams generated significant eddies during flood periods. As an example, the high-water marks of the December, 1977, February, 1978, and February, 1980 floods indicate that the water-surface profile sloped toward the right bank, the result of a small debris jam 12 m. (40 ft.) upstream. Nearly continuous lines of broken twigs and other fine organic matter accumulated in these eddies during each storm. Each line contained an appreciable amount of material, generally 0.5 to 5 cm. thick. Partial incorporation of this material into the soil was clearly visible by November, 1980. Post-fire additions of organic material to soils at or slightly above the active floodplain may be an appreciable factor in the development of soils in the riparian zone.

Conclusions

1. Sequential changes in riffle conditions in the upper Carmel watershed following the Marble-Cone fire were observed using four physical descriptors of salmonid habitat:


141

a. mean fill and scour;

b. particle-size distribution of the bed surface;

c. percent of the bed surface covered by sand and finer debris;

d. percent of the bed surface occupied by material of sizes suitable for spawning.

2. Riffles in the master channels of the upper Carmel watershed filled up to 0.3 m. (1 ft.) during the first storms following the Marble-Cone fire, primarily with sand. By the end of the first year, most of the fill had been scoured; much of what remained was of pebble and cobble size. By the end of the third year, all descriptors had returned to within 20% (relative to the maximum measured disruption) of their pre-fire conditions. Other on-going watershed processes were probably more important than residual effects of the fire as influences on habitat conditions by the end of the third year.

3. Effects of the fire on runs and pools were not measured. Maximum mean channel fill was generally observed to be several times greater than in riffles. Recovery of habitat values appears to occur at relative rates similar to or slightly slower than those in the riffles.

4. A substantial volume of sediment, primarily gravels and cobbles, was intercepted in the riparian and terrace areas. Delayed delivery to main channels is likely to be an important factor in maintaining the availability of spawning-sized material between major disruptive events.

Acknowledgments

This study was conducted in cooperation with the USDA Forest Service, Pacific Southwest Forest and Range Experiment Station, as part of the Chaparral Management Research and Development Program. Suggestions and assistance were contributed by Wade G. Wells and C. Eugene Conrad of the station; Robert F. Blecker (Los Padres National Forest); Gene H. Taylor (Monterey County Flood Control and Water Conservation District); and Vincent Piro and Randal Benthin (California Department of Fish and Game). Special thanks are extended to friends and colleagues who assisted in the field work, often under wet and cold conditions: Robert Herman, David F. Hoexter, Mark Jansen, G. Matt Kondolf, Yane Nordhav, Mark Springer, and Philip B. Williams. Wade Wells, David Hoexter and Nicholas M. Johnson reviewed the report in draft form.

Literature Cited

Bjornn, T.C., M.A. Brusven, M.P. Molnau, J.H. Milligan, R.A. Klamt, E. Chacho, and C. Schaye. 1977. Transport of granitic sediment in streams and its effects on insects and fish. University of Idaho Forest, Wildlife, and Range Experiment Station Bull. No. 17. 43 p.

Griffin, J.R. 1978. The Marble-Cone fire ten months later. Fremontia 6(2):8–14.

Kelley, D.W., and D.H. Dettman. 1980. Relationships between streamflow, rearing habitat, substrate conditions, and juvenile steelhead populations in Lagunitas Creek, Marin County. Report to the Marin Municipal Water District. 36 p. D.W. Kelley and Associates, Newcastle, California.

Orcutt, D.R., T.R. Pulliam, and A. Arp. 1968. Characteristics of steelhead trout redds in Idaho streams. Trans. Amer. Fish Soc. 97(1):42–45.

Platts, W.S., M.A. Shirazi, and D.H. Lewis. 1979. Sediment particle sizes used for spawning, with methods for evaluation. US Environmental Protection Agency Pub. 3-79-043. Cincinnati, Ohio. 32 p.

Wiebe, R.A. 1970. Relations of granitic and gabbroic rocks, northern Santa Lucia Range, California. Geol. Soc. Am. Bull. 81(1):105–116.

Wolman, M.G. 1954. A method of sampling coarse river-bed material. Trans. Am. Geophys. Union 35(6):951–956.


142

Flood Control and Riparian System Destruction

Lower San Lorenzo River, Santa Cruz County, California[1]

Gary B. Griggs[2]

Abstract.—A 1959 flood control project on the lower San Lorenzo River in Santa Cruz County, California, involved levee construction and excavation below the river's natural grade. Subsequent siltation has greatly reduced the channel's capability to contain flood waters. Annual dredging has destroyed the riparian corridor and has not significantly increased flood protection.

Introduction

The San Lorenzo River drains 357 km2 of the central California Coast Ranges (fig. 1). Annual rainfall in the redwood-forested basin averages 150 cm., and flooding has been common within the communities which occupy the river's floodplain. Steep slopes, landslides, and unstable soils combined with high-intensity precipitation have led to severe erosion in certain parts of the basin. Logging, quarrying, and the grading and vegetation removal that accompany urban and rural developments have compounded the erosion and sediment-production problem.

Excluding the population of the city of Santa Cruz at the river's mouth, the watershed is home to 33,000 people. Most of the population is concentrated along the stream bottoms of the river and its tributaries.

As a result of disastrous flooding within the city of Santa Cruz during December 1955, the US Army Corps of Engineers (CE) proposed a flood-control project along the lower San Lorenzo River. The project consisted of levee construction and channel dredging for 4 km. upstream from the river mouth. Changes in channel equilibrium have produced heavy siltation which has greatly reduced the project's flood control capacity. For the past four years the city has annually removed all river-bottom vegetation and bulldozed the accumulated sediment into windrows in the hope that the river would scour out its bed. Scouring has not taken place, but loss of riparian system has occurred.

figure

Figure l.
Index map showing the San Lorenzo River
watershed and its location in California.

[1] Paper presented at the California Riparian Systems Conference. [University of California, Davis, September 17–19, 1981].

[2] Gary B. Griggs is Professor of Earth Sciences, University of California, Santa Cruz.


143

Flooding

Flooding is the most widespread geologic hazard in the United States, accounting for greater annual property loss than any other single hazard. Despite the construction of ever-increasing numbers of dams, channels, and levees for "flood control" purposes, losses from flooding have continued to increase primarily due to expanded use, re-occupation, and development of downstream floodplains.

There is little doubt that river control works accelerate floodplain development. Once a sense of security from flooding has been established, the conversion of open space to densely populated areas has become commonplace. Although flood control projects do offer protection from all events smaller than the design flood, if properly designed, they will not be effective against the infrequent larger events. In other words, all flood control ends somewhere; we simply cannot afford to provide protection from the 500- or 1,000-year flood. Thus, as "protected" floodplain areas are more intensively developed, the potential damage from a great or catastrophic flood, which cannot be contained, continues to rise.

Developments located in the floodplain are not only more susceptible to damage, but also reduce the capacity of the floodplain to transport and store floodwaters, and may actually increase the depth and areal extent of inundation. Virtually the entire downtown portion of Santa Cruz lies within the 100-year floodplain of the San Lorenzo River, as do certain residential areas along the river's upper reaches.

Logging and land clearing activity can contribute to flooding problems. Logjams can form as logs and other debris are swept downstream during high flows. Considerable damage during past floods in the densely wooded and heavily logged San Lorenzo basin was apparently caused by logjams occurring at bridges, followed by river back-up and over-bank flooding.

Continued heavy rainfall during December, 1955, led to severe flooding throughout the San Lorenzo basin. Fifty centimeters of rain fell between 15 and 28 December at Boulder Creek, with almost half of that (23 cm.) falling on 22 December. The gauging station at Big Trees in Felton recorded a 6.88-m. stage with a discharge of 861 cu. m. per second (30,400 cfs). Overflow occurred from the headwaters to the mouth, resulting in the maximum flood on record. Numerous logjams and other channel obstructions diverted the floodflows, causing streams to change from their normal alignments and undercut and scour out numerous bridges, road fills, and private developments (US Army Corps of Engineers 1973). Seven persons lost their lives, 2,830 people were displaced from homes, and damages amounted to $8.7 million; most of this was within the city of Santa Cruz itself.

Flood Control

Almost two years before the 1955 flood, in the spring of 1954, the CE applied to Congress for $2.265 million for the construction of a flood control project on the lower 4 km. of the San Lorenzo River and lower Branciforte Creek in the city of Santa Cruz (fig. 2). Preliminary designs had already been completed using discharge from a 1940 flood.

The December 1955 flood apparently interrupted work and necessitated a re-evaluation of the "standard project flood" (the 150-year event), but it also provided the CE with even stronger justification for proceeding with the project. Construction began in 1957, after the following revisions in the discharge capacities of the project: a 25% increase for the San Lorenzo, and a 110% increase for Branciforte Creek, to 1,303 cu. m. per second (46,000 cfs) and 238 cu. m. per second (8,400 cfs) respectively (US Army Corps of Engineers 1957).

The CE project consisted of the construction of levees for 4 km. upstream from the mouth, and the excavation of about 590,000 cu. m. of sediments from the existing channel, to increase the slope and capacity of the new channelized reach. The "design" channel bottom was lowered as much as 2.1 m. below the natural or original river-bottom (fig. 3). In conjunction with the excavation, the CE design utilized flow velocities of 2.4–7.5 m. per second (7.9–24.7 ft. per second) to move the necessary water volumes through the various design cross sections.

In July of 1959 the project was completed and was deeded to the City of Santa Cruz by the CE. The city agreed to maintain the channel to design specifications and was provided with a maintenance plan and procedure. Annual maintenance costs were estimated by the CE at $25,000. Total project cost at the time of completion was $6,466,000. The CE departed at this point, absolved of all further responsibility. Considering the awesome reputation of the CE and the docile mentality of the times, it is not surprising that no one questioned the wisdom of dredging the channel and altering the gradient, the velocities used in the design, or the size of the channel. Because the CE presumably had the most experience in the field, it was assumed that the project as planned was the best long-term solution.

Flood protection assured, Santa Cruz intensively redeveloped the "former" floodplain of the


144

figure

Figure 2.
The city of Santa Cruz and the San Lorenzo River Flood Control Project in 1971. Dashed line delineates
the floodplain. Numbers refer to individual bridges—1) Highway 1, 2) Water Street, 3) Soquel Avenue,
4) Riverside Avenue. Arrow indicates point where Branciforte Creek enters San Lorenzo River.

now-tamed San Lorenzo River over the next 10 years. A shopping mall became the showpiece of a downtown renovation project. The early 1970s, however, brought some threatening revelations about the safety of downtown Santa Cruz and the condition of the channel. A 1975 channel centerline survey showed that at least 306,000 cu. m. of sediment had accumulated, significantly reducing the project's capacity. Annual dredging to project depth was not performed by the city, as public works officials felt that high winter flows would scour the accumulated sediments out to sea.

In an effort to aid this process, the city began to utilize a bulldozer with ripper blades to uproot all river-bottom vegetation along the entire 4-km. length of the flood control project, believing that the roots held sediment in place, thereby preventing scour. Scour, however, still did not occur. Subsequent surveys have shown only minor variation in the amount of channel fill, which now stands at about 350,000 cu. m. (figs. 3 and 4).

The California Department of Water Resources (DWR) discovered the situation in 1976. DWR threatened to assume responsibility for clearing the channel and charge the City of Santa Cruz for the dredging later. Responding to these official warnings, the city began to bulldoze sediment up into windrows within the last four years, again, hoping for winter scour to remove the sand (fig. 5). The city also started to remove sediment on a small scale; as of June 1981 less than 40,000 cu. m. had been removed. This has led to nearly total destruction of the riparian vegetation on an annual basis, as well as an unsightly downtown river channel. However, the city is unable to


145

figure

Figure 3.
Changing gradient of the San Lorenzo River as it passes through Santa Cruz. Note the contrast between
original or design river bottom after dredging and surveys taken in the late 1970s. Baseline survey refers
to channel condition prior to commencement of flood control project in 1959. Station numbers refer to
distance upstream from the river mouth in hundreds of feet (Station 20 = 2,000 feet).

finance the total removal of the accumulated sediments, with the cost estimated to be as much as $3 million initially and at least $200,000 annually to maintain. These are considerably different figures (even allowing for inflation) than the CE estimated in 1959 ($25,000/year). As a result, the city is concerned both about the cost of removing sediment and the potential flood hazard of leaving the sediment in the channel.

With no scouring during a large storm, it has been determined that some individual cross sections could only contain the 25- to 30-year flood. This is of immediate concern because the city is now hydrologically, as well as legally, back within the 100-year floodplain, as it was prior to the construction of the "flood control" project. No federal monies should thus be available for projects in the area; flood insurance coverage is also in question. Santa Cruz is stuck with a poorly designed project, a difficult dilemma, and a financial and ecological disaster. Why has this happened? Are there any solutions? And can we learn something from this expensive mistake?

The Effect of Altering the Natural Channel Gradient

Stream equilibrium is a dynamic process that is continually reacting to changing hydraulic conditions and basin sediment production. Water velocity, channel slope, and sediment transport capacity are adjusted in response to variations in discharge, channel morphology, and sediment availability.

In removing 590,000 cu. m. of sediment during construction of the flood control project,


146

figure

Figure 4.
Selected channel cross sections along San
Lorenzo River in Santa Cruz showing extent
of channel fill above original design channel
bottom. Station locations refer to Figure 3. All
elevations are in feet relative to mean sea level.

the CE increased the channel slope 32% over its last 4 km. and upset the equilibrium conditions established over thousands of years. Sea level is the ultimate base level for the San Lorenzo and most other rivers; however, due to channel excavation, high tides could extend 4 km. inland to the Highway 1 bridge. During a spring tide of 2 m. (mean sea level), 1.7 m. of standing water would occur at the bridge.

The anticipated hydrologic response of flowing water upon entering a standing body of seawater would be a reduction in velocity with accompanying deposition of sediment load. The "improved" channel was actually a sink that would eventually be filled in with sediment from the watershed, much like a dam or reservoir traps sediment. This process would continue until the channel returned to an equilibrium slope. Periodic surveys of the channel centerline and various cross sections indicated that equilibrium was gradually reestablishing, and it has now been reached.

However, the new equilibrium channel has a different profile than either the original or the design channel in the reach between Soquel and Highway 1 bridges (see fig. 3). The increased channel width and an increase in river sediment load have created a new equilibrium gradient in this reach. The channel bottom is now 2 m. above the initial design bottom and 0.9–1.2 m. above the original natural channel.

The estimated quantity of sediment that must now be removed in order to restore the design channel is about 350,000 cu. m. The CE made no mention of deposition problems in their design manual except to note frequent dredging would be required to maintain the channel grade. Effects of the sediment removal on the river's aquatic system and riparian vegetation were also not discussed. The basis for the CE estimate of annual dredging cost is unknown, but no sediment discharge measurements from the watershed had been made at the time the project was initiated.

Sediment Yield and Transport

Sediment yield within the San Lorenzo watershed is high and volumes of material transported by major runoff events can be very large. The natural basin conditions (steep and unstable slopes, highly erodible soils, and high intensity precipitation) combined with the vegetation removal and soil disturbance accompanying logging, quarrying, road-building and construction activities have all contributed to high erosion rates and the production of large volumes of sediment. Much of the construction and population growth in the watershed (the population tripled from 1960 to 1979, from 11,600 to 33,000 people) has occurred in areas with soils which are particularly erosion-prone. The San Lorenzo River Watershed Management Plan estimates that the two- to four-fold increase in sediment production during these years is directly attributable to human disturbance of the basin's soils.

Suspended sediment and limited bedload measurements have been intermittently collected at two stations within the basin since 1973. Using the sediment transport curves, flood frequency distribution, and particle size breakdown, projections can be made for the magnitude of sediment transport under various flood conditions as the river passes through


147

figure

Figure 5.
San Lorenzo River channel immediately downstream from the Water
Street bridge showing efforts by the City of Santa Cruz Department of
Public Works to pile up sediment in hopes of flushing by high flows.

Santa Cruz (table 1). For example, the 10-year flood can carry over 800,000 metric tons per day (520,000 cu. m.) of sand-sized or larger material in suspension. Bedload would increase this by 5% to 10%. If a sink (as was created in the "flood control" project) or tide water was encountered by material of this size in transit, it seems probable that much of it would be deposited. Again, although flood conditions would not normally persist for 24 hours, even eight hours of the 10-year storm could produce 173,000 cu. m. of sediment. Significant volumes of sediment can be transported by the two- or five-year events. Even if the channel were to be dredged to original project design, sediment carried by one large floodflow (or even the cumulative effect of several years of moderate flow conditions) could soon fill the channel back to an equilibrium grade. This raises serious questions about the effectiveness of annual dredging as a solution to the flood control problem.

The unavoidable conclusions are the following. 1) The San Lorenzo River channel is now at equilibrium grade, and the sediment fill appears from all evidence to be stable. 2) The channel can no longer carry the 100-year event, and in fact cannot, in all probability, hold the 30- to 40-year flood. 3) Downtown Santa Cruz is endangered and has far less protection than is required by the Federal Flood Insurance Act. The $6.5 million flood control project designed by the CE grossly underestimated the sediment load being carried by the river and also failed to account for the changes in channel equilibrium gradient which would be produced by the alteration of channel morphology.


148
 

Table l.—Sediment transport capacity of the San Lorenzo River below Branciforte Creek in Santa Cruz.

Event
(Recurrence interval)

Discharge (cfs)

Suspended Sediment (Tons/Day)

Suspended Sediment (>Sand Size-Tons/Day)

Suspended Sediment (Sand Size-Cu. Yds./Day @ 100 lbs/ft3

2 years

7,528

175,000

56,000

41,000

5

16,864

1,000,000

320,000

237,000

10

24,375

2,600,000

832,000

616,000

25

34,317

5,000,000

1,600,000

1,185,000

50

41,698

7,000,000

2,240,000

1,659,000

100

48,862

12,000,000

3,840,000

2,844,000

Future Options

There are no simple solutions to the flood hazard which the city of Santa Cruz is currently faced with, but any solution clearly involves the riparian corridor and the life it supports and the natural beauty it can present. This problem is not unique to Santa Cruz and the San Lorenzo River, but develops anywhere major "flood control" projects have been carried out. Through dams and reservoirs, aquatic systems are totally flooded; through "channel improvements" (levees, dredging, and channel straightening) these same systems are destroyed or eliminated, temporarily if not permanently. Thus, the price of flood control using engineering works is riparian corridor elimination in most cases. The San Lorenzo River is an extreme example in that the annual river-bottom vegetation removal and sediment shuffling has not even produced the anticipated protection from flooding.

Two important factors to consider in any proposal dealing with Santa Cruz and the San Lorenzo River are: 1) is the solution permanent and does it deal with the root cause, or is it simply a temporary stopgap approach; and 2) how will it ultimately affect the riparian corridor?

We invariably select engineering rather than planning solutions because these are more visible, more impressive, and they are also driven by institutional inertia. In addition, once the engineering structure is in place, additional engineering is the usual solution to shortcomings or flaws in the original design. (The reality is, however, that large natural systems, such as rivers and the ocean, simply can never be totally controlled by man-made structures).

A number of possibilities exist or have been proposed.

Option l.—Dredging and removal of all the accumulated sediment from the channelized reach of the river would cost about $3 million today. Although this would reduce the immediate flood threat to the city, it would offer only temporary protection. At average annual sand transport rates of 40–80,000 cu. m., either channel capacity would soon be reduced or expensive (estimated $100–200,000) yearly dredging would be required, thereby producing annual riparian corridor destruction. The city currently is using this dredging approach, but has only been removing sediment from the channel on a very modest scale. Channel surveys indicate that upstream sand input from winter flows is keeping pace with the sand removal operations.

Option 2.—A combination of erosion control measures and sediment or debris basins could be used to reduce downstream sediment transport in the San Lorenzo River. This effort would have to be accompanied by initial dredging of the channel reach through Santa Cruz in order to provide the required flood protection. Although any erosion control measures in the watershed would be beneficial, the costs of land acquisition and maintenance, and biological effects of a number of large sediment traps on the San Lorenzo River or major tributaries are serious negative factors. For comparison, costs for 20 such structures, each impounding one square mile watershed, would approximate the initial outlay and annual costs of maintaining the downtown channel.

Option 3.—A single large dam on the San Lorenzo itself or several smaller dams on major tributaries could reduce flood peaks by 20,000 cfs, such that the present channel could convey the reduced floodflows. No suitable site exists on the San Lorenzo for a dam of this sort without producing major inundation of populated areas. Construction costs and environmental impacts of the number of smaller dams required make this alternative an unattractive one.

Option 4.—The levees and bridges could be raised in order to increase the channel capacity such that the 100-year flood could be effectively contained. This option essentially enables the channel gradient to remain at its equilibrium position and allows for increased flood capacity


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through raising the banks. The costs for the replacement of four bridges and a six-foot increase in levee heights is estimted to be $20 million, over three times the cost of the original project (Jones-Tillson and Associates 1979). Any engineering solution of this sort has an obvious economic limitation, and the 100-year flood may well occur and top the banks despite the expenditure of $20 million. Should a flood large enough to breach the levees occur, the height of the floodwaters above the channel floor would provide a hydraulic head that could quickly erode the levee and inundate downtown Santa Cruz.

Perhaps the all too obvious solution is not to have built our cities on floodplains to begin with. History is against us however, and it is senseless to blame our ancestors for settling on the fertile flatlands adjacent to our rivers and streams. Although it may be cheaper and safer in the long run to relocate many floodplain communities, this is unlikely to ever occur without the occurrence of major floods which totally destroy those communities.

A compromise of sorts may be obtained by allowing a river to develop some sort of natural course, within the broader confines of a flood control structure. In the case of the San Lorenzo, a width increase of 18–34 m. would increase the channel capacity to original design conditions (approximately accomodating the 100-year flood). This proposal presents some challenges and opportunities in allowing the river to reconstruct some of its natural meanders and retain its natural gradient (both eliminated by the present levee system).

Utilizing a meandering pattern would only require rebuilding one of the levees at any particular location. A survey of land adjacent to the river shows that streets, parking lots, used car lots, parks, and tennis courts occupy much of the 18 to 34 m. of land in question. These uses could be continued after excavation occurs. The widening of the river could be designed such that a smaller pilot channel could hold perhaps the five- to 10-year event. Much of the remaining channel could be vegetated as a downtown park and green belt such as the recessed park which presently exists between Soquel and Water streets adjacent to the river. Other higher floodplain land could be used for the previously mentioned parking and streets except during and immediately after major flood events. The pilot channel could also provide an adequate flow depth for anadromous fish migration.

Existing bridges could probably be extended, obviating the complete bridge replacements necessitated by Option 3. Some houses and small commercial buildings may have to be removed, but initial investigation indicates that displacement need not be extensive. Much of the required land is city property which would lower acquisition costs.

Conclusions

In any attempt to control a natural system, we must realize that we are usually going to disturb a delicate equilibrium. By excavating the San Lorenzo River's bed to increase its slope and capacity to transmit floodwaters, we also created a disequilibrium to which the river had to adjust. As a result of the river aggrading its channel back to an equilibrium gradient, flood control capacity has been significantly reduced. Because the channel can no longer contain the 100-year event, the entire downtown area of Santa Cruz is apparently no longer covered by the Federal Flood Insurance Act. The stopgap bulldozer approach presently being used has led to yearly destruction of the riparian corridor and no significant alleviation of the flood hazard.

We must begin to focus our efforts on controlling our own activity, rather than persisting in the ineffective historical approach of an increasingly expensive system of dams, levees, and channels. All flood protection ends somewhere. We can never afford complete flood protection, as a community, a state, or a nation. The continued increase in annual flood losses despite the construction of an ever-increasing number of "flood control" structures is clear testimony to the failure of this approach.

Literature Cited

US Army Corps of Engineers. 1973. Flood plain information—San Lorenzo River, Felton to Boulder Creek. US Army Corps of Engineers, San Francisco, Calif.

US Army Corps of Engineers. 1957. General design memorandum—San Lorenzo River flood control project. US Army Corps of Engineers, San Francisco District, San Francisco, Calif.

Jones-Tillson and Associates and Water Resources Engineers. 1979. San Lorenzo River reconnaissance study. US Army Corps of Engineers, San Francisco, Calif.


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Photodocumentation of Vegetation and Landform Change on a Riparian Site, 1880–1980

Dog Island, Red Bluff, California[1]

Stephen A. Laymon[2]

Abstract.—This study used ground and aerial photos taken over the past 100 years to trace the development of the present riparian vegetation. The photos show the changes in the Sacramento River channel which have led to the present configuration of the area. Principles illustrated by these photos are: 1) the dynamic nature of the riparian system showing rapid and dramatic changes at this site; 2) the rapidity with which riparian vegetation develops; and 3) the use of historic and present day photography to document changes in a riparian environment.

Introduction

During the course of my 5-year study at Dog Island, Tehama County, I became interested in the development of the present day landforms and riparian vegetation at this site. I was able to follow up on this interest in connection with a job as archivist at the Tehama County Library and in a physical geography seminar at California State University, Chico.

Little or no work has been done to document changes at riparian sites. This study was undertaken to show the changes at this particular site, but more importantly to show the potential resources available to document land use, landforms, and vegetation pattern changes, and to show the dynamic nature of the riparian system. The use of ground photos to compare past with present conditions is a common practice in forest and rangeland situations. Problems were encountered in this study when an attempt was made to apply this technique to a flat Sacramento Valley site with tall riparian vegetation.

Methods

Research Techniques

Early ground photos were obtained from the collection of the Tehama County Library and several longtime local residents. Attempts to rephotograph these views of the study area met with limited success since the vegetation had grown so much in the ensuing 100 years, blocking the view from most angles.

The aerial photos were obtained from the United States Soil Conservation Service, US Army Corps of Engineers, and the California Department of Water Resources. Overlay projection using a photographic enlarger was used to document boundary changes.

Study Area

Dog Island, or Walton's Pasture, as it was known in the early days, has long been a favorite picnic spot for the people of Red Bluff. Now a small island in the Sacramento River, the site's amenities included an area of still water, where the land sloped gently to the river, in contrast to the high, steep bluff for which the city is named. Here the city had its waterworks, which originally consisted of a horse and wagon delivering water door to door. Later, the city pumped water directly from the river, and still later from deep wells.[3] Here also, local youths spent their days cutting school classes, and in the early days this is where most of the local people learned to swim.

In the mid-1960's the area was donated to the city of Red Bluff by the Samuel Ayers family for use as a city park and natural area. The city has kept development at a fairly low level, with a footbridge to the island, a parking lot

[1] Paper presented at the California Riparian Systems Conference. [University of California, Davis, September 17–19, 1981].

[2] Stephen A. Laymon is a Graduate Student in the Department of Forestry and Resource Management, University of California, Berkeley.

[3] Walton, T. 1956. Tehama County centennial oral history interview. Tehama County Library oral history tape.


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with landscaping, two restrooms, and trails. One loop road which was put in on the mainland portion has since been closed to vehicles due to a high level of vandalism.

The origin of the name Dog Island remains a mystery since long time residents say that the area was always called Walton's Pasture, and that the dairy cattle from Walton's Dairy on the bluff to the south grazed there. One story has it that an old man ran a kennel on the island in the 1880's, but since no island existed at that time, this is impossible. A more plausible explanation is that park officials asked some local truants what they called the area and "Dog Island" was the answer.

Landforms and Topography

The Dog Island study area consists of the river, the island, the channel around the island, the mainland plain, the red bluff, Brewery Creek, and the gently sloping area from the parking lot to the footbridge (see fig. 1). The entire study area has a remarkably narrow elevation range, with 95% lying between 77.1 m. and 79.2 m. above sea level. On the northwest side, the red bluff known as Duncan Hill rises almost vertically to a height of 97.5 m., or 20.4 m. above the river level. The parking lot at the west edge of the area is between 82.3 and 85.3 m. elevation. From there the land slopes in two terraces to the side channel 76 m. away. The highest point on the island is not more than 3 m. above the gross pool level of the Red Bluff diversion dam.

figure

Figure l.
Map of Dog Island study area and environs.

Despite having such a narrow elevation range, the area is not level, having many channels which have waterflow during flood stage. The three most prominent are old river channels that have been silted in over the years. One of these lies east of the bluff near the north boundary of the park, and was the 1850 river channel. Another lies near the east end of the footbridge. The third is found on the southeast side of the island, and was the main river channel prior to the 1937 flood.

The Sacramento River at Dog Island ranges from 170 m. to 250 m. in width. As a result of the diversion dam below Red Bluff, it is kept at a constant 77.1 m. above sea level. This is 2.4 m. higher than the river level would be without the influence of the dam. The water level is lowered slightly to 76.5 m. in the winter when no water is being diverted for irrigation. During flood stage the waters at times rise to 81 m. covering the entire area except the bluff and the parking lot. The river channel that separates the island from the mainland ranges in width from 20 m. to 41 m.

Brewery Creek is an intermittent stream which flows into the study area from the west. It was named for the brewery which was located along it near here in the 1880's. The creek has two main branches, the longer of which is 4.8 km. in length. It drains 8–10 km2 of highly eroded impermeable soils. During heavy local rains the runoff is great and the creek runs high, carrying with it heavy bedloads of rock, gravel, and soil. This is building up a delta in the side channel which may in the future connect the island to the mainland. The creek has cut a deep channel on the north side of the parking lot, and is responsible for the gently sloping gap between the red bluffs of Duncan Hill to the north and the city to the south.

Soils

Soil is the base for the vegetation of any area. Ninety percent of the soils in the study area are fertile loams, so the dense vegetation found here is not surprising.

Five types of soils are found on or near Dog Island. The island itself is an alluvial soil known as Red Bluff loam. It consists of up to 15% gravel, and has both high available water and high moisture-holding capacity (USDA Soil Conservation Service 1967).

The low area to the north of the island is made up of the Columbia loam complex, ranging from mixed soils of silt and gravels to fine sandy loams. These soils generally lie above all but the highest floods, are well drained, and have moderate permeability. They are brown to pale brown in color and are neutral to slightly acid. These are very fertile soils, favored for farming (ibid .).

The soil in the sloping area to the south of Brewery Creek is an Arbuckle gravelly loam. It


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is an easily channeled soil with poor waterholding characteristics, very slow permeability, and a clay substrate (ibid .).

Duncan Hill, the bluff on the northwest side, is made up primarily of Newville gravelly loam. This soil is yellowish-brown on the surface and is slightly acidic. The subsoil is a reddish-brown gravelly clay. It is made up of sediment from conglomerate and silt stone of the Tehama formation. In addition, a portion of the hill consists of a mixture of Corning-Redding gravelly loams, a medium acidic, reddish-brown soil with a red clay subsoil. This soil has low permeability and high runoff (ibid .).

Vegetation

The vegetation-types that are found in the study area are floodplain riparian woodland, blue oak woodland, cattail marsh, and landscape plantings. Of the aforementioned vegetation-types, the latter three are the least important since they form such a small portion of the total area. The blue oak woodland found on the hill north of Brewery Creek covers only 1% of the land area. Scattered blue oaks (Quercusdouglasii ) form the canopy here, reaching up to 10 m. There is no understory, and the shrub layer consists of scattered buckbrush (Ceanothuscuneatus ). The groundcover primarily consists of introduced grasses.

The landscape plantings are found around the main parking lot, restrooms and waterworks facilities. They consist mainly of several introduced cedars and pines, a border of live oaks (Quercus sp.) along the highway, several pyracantha (Pyracantha coccinea ) hedges, scattered introduced flowering shrubs, and approximately 0.25 ha. of lawn. These are planted around several native blue oaks.

The two marsh areas are the most important of the minor vegetation-types. They cover about 1% of the area. The marsh on the southern part of the island has a thick growth of cattail (Typha sp.) with a border of willows (Salix spp.). The water is up to 0.3 m. in depth at this spot. The open areas of water are thick with small aquatic plants such as duckweed (Azollafiliculoides ). The land area around the pond that is not covered with cattail and willows is grown up with dense stands of grasses. The marsh on the mainland is just north of the mouth of Brewery Creek. It is higher than river level and only contains water after a flood or heavy rain. The cattail here is much more scattered and intergrown with grasses, herbs, shrubs, and willows, a pattern that has accelerated over the past seven years.

The primary vegetation-type in the study area is riparian woodland. Various forms of this plant community cover 95% of the land. It is an exceptional vegetation-type in the arid West. The riparian vegetation in the study area is quite diverse. Various species of trees are dominant on different portions of the area, often forming stands of clumps or bands of a single species. The western border of the island, facing the slough, is primarily old-growth cottonwood (Populusfremontii ) reaching 40 m. in height, with scattered willows (fig. 2). An understory of box elder (Acernegundo ), willows, black walnut (Juglanshindsii ), and elderberry (Sambucusmexicana ), and bands of shrubcover and groundcover layers of wild blackberry (Rubusursinus and R . vitifolius ), and the introduced Himalayan blackberry (R . discolor ) are found. The central part of the northern third of the island is the most open. It has a cottonwood canopy with a scattered understory of box elder, valley oak (Quercuslobata ), blue oak, and buckeye (Aesculuscalifornica ), and a groundcover of mugwort (Artemisiadouglasiana ) sometimes reaching 2.5 m. The northern tip of the island is a white alder (Alnus rhombifolia ) and willow thicket with no groundcover, surrounded by a blackberry thicket. The northeastern side of the island also has a cottonwood canopy with an understory of box elder, willow, and elderberry, and a shrub and groundcover of blackberry and herbaceous growth. The border of vegetation closest to the water is a dense mixture of white alder, Oregon ash (Fraxinuslatifolia ), and willows. Further south this band of alders and willows widens to about 30 m.

Cottonwoods are absent from the southeast quarter of the island. This area has a very dense canopy of alder, box elder, and willow reaching to 15 m. The trees are closely spaced, allowing very little light penetration. Groundcover is lacking in the thickly forested areas, but bands of blackberry and herbaceous growth are found in the more open spots. One alder thicket of almost 0.75 ha. is especially interesting; the trees have grown to 18 m. and many are now dying. There is no groundcover, but an understory of sycamores (Platanusracemosa ) and Oregon ash is developing. At the southern tip of the island there is a willow thicket reaching 8 m. in height and 30 m. across.

The vegetation on the mainland, south of Brewery Creek, is similar to the western part of

figure

Figure 2.
Footbridge to Dog Island showing dense vegetation
along side channel, looking north (August, 1979).


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the island, with a cottonwood canopy to 40 m., a well-developed understory of box elder, alder, and willow, and a groundcover of blackberry. This type of growth also extends along the northwest side of the slough, from 50 m. north of Brewery Creek to the freeway bridge. Also found in this area, in the slightly lower and more open spots near the slough, are several dense willow thickets reaching 7 m. in height and up to 30 m. across.

Along Brewery Creek the vegetation also has a canopy of scattered cottonwoods reaching 25 m., but the understory is much less typically riparian, with live oaks, blue oaks, toyon (Heteromelesarbutifolia ) mixed with the willows, Oregon ash, and box elders. The groundcover is a mix of grasses, blackberries, and herbaceous growth.

Black walnut is the dominant tree in the area just north of Brewery Creek and along the base of the bluff. The trees are not large, reaching only 20 m., and do not form a closed canopy. This allows light penetration and the formation of a dense ground layer of blackberries with patches of willows and elderberries. Also in this area are a number of introduced species such as mulberry (Morus sp.), black locust (Robinia pseudoaccacia ), osage orange (Maclura pomerifera ), plum (Prunus sp.), fig (Ficus carica ), and pyracantha.

At the north end of the bluff the dominant tree species is valley oak. The largest of these trees reaches 35 m. in height, and some are at least 100 years old. This site has a groundcover of grasses and a scattered understory of box elder and black walnut. The valley oak area borders the field to the north for about 300 m. and merges into an area with a canopy of black walnut and cottonwoods. In this location there is also a dense osage orange thicket of about 1 ha. which is devoid of groundcover.

The center of the mainland portion is the most open of the entire study area. Until 1975 it was a large, grassy meadow with a few scattered clumps of box elder, plum trees, and two dense box elder thickets. When the park loop road was constructed, the grass in the meadow was mowed to cut down on fire danger and provide a more "park-like" atmosphere. The meadow instantly became a defacto parking lot, the gathering place for the local teenagers, which totally denuded large areas of it. Due to reduction of competition from the grasses, the box elders began to grow rapidly and now are large trees reaching 15 m. and covering a much more extensive area. The tall rye and Johnson grasses that previously covered the meadow provided a vegetation-type that is now missing. More information on this area can be found in Laymon (1983).

Results

As static as the scene appears today at this bend in the river, as little as 40 years ago the island was very different in appearance, and as recently as 100 years ago the entire study area was litte more than a sandbar, devoid of vegetation. With the use of maps, aerial photographs, ground photos, and local legend, I was able to reconstruct the development of Dog Island over the past 100 to 130 years.

Two basic types of geologic formations are found in the study area. They are the recently formed alluvial deposits of the island and low regions to the east, and the red bluffs consisting of Pleistocene and Pliocene nonmarine sedimentary deposits to the west (USDA Soil Conservation Service 1967). This hard, red soil has been an effective barrier to westward river movement for many thousands of years. One can picture the river migrating without restraint eastward across the valley many times, always to return to the west and to stop at this 23-m. bluff.

In the early 1850's when the first settlers came to Red Bluff, they found the river flowing against these bluffs from the center of the study area to 3.2 km. (2 mi.) south of town.[3] Maps from 1850 to 1900 show no evidence of even a sandbar in the river at this location. A photo taken in 1881 from the bluff adjacent to the study area looking south toward Red Bluff (fig. 3) shows a bare bluff with the river running at its base. On the right (west bank) a small delta from Brewery Creek was beginning to build up. The closest brick building on the right was the city waterworks. The building is still located at the site.

Another photo (fig. 4) taken from Red Bluff, looking north, circa 1900, shows the sides of the bluff and the rest of the study area, devoid of vegetation except for a few low willows on the sandbar in the river, a valley oak at the far right, and scattered blue oaks on top of the bluff. The amount of deposition at the foot of the bluff can be seen by comparing figures 3 and 4. Alluvial deposits had built out 30 to 50 m. in 20 years.

The next photo (fig. 5), taken in 1912, shows the area from the west, looking past the waterworks toward the Tuscan Buttes to the east. This photo illustrates the lack of vegetation and shows the river flowing towards the waterworks building (today the main flow is directed 350 m. south of that point due to deflection by Dog Island). No sandbars are seen in the river, but the west bank above the Brewery Creek outlet is in the same position as it is today. The area appears to be much lower than at present, indicating continued deposition on the mainland since the picture was taken. The first band of trees to the west of the river is very likely the 1850 river channel.

Figure 6 shows the river, looking towards Red Bluff, circa 1910, with the waterworks building on the right. One interesting feature is the amount of vegetation that has grown on the bank between 1881 and 1910.


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figure

Figure 3.
Dog Island area from bluff looking south toward Red Bluff, 1881 (courtesy of Tehama County Library collection).

figure

Figure 4.
Dog Island from bluff at Red Bluff looking north,  circa  1900 (courtesy of Tehama County Library collection).


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figure

Figure 5.
Dog Island from Garrett home looking east toward Tuscan
Buttes, 1912 (courtesy of the Wetter collection).

figure

Figure 6.
Dog Island area from bluff looking south toward Red Bluff, 1910 (courtesy Tehama County Library).

I found it impossible to rephotograph any of the four historic photos of the area. The vegetation had grown up so much that the scenes were not repeatable. An oblique aerial photo (fig. 7), taken in 1979, was an attempt to duplicate figure 4. This photo illustrates the dramatic growth of vegetation at the site. Any photo taken at the point from which the photo in figure 4 was taken would today show only the first row of cottonwoods on the south end of the island.

Figure 5 was taken from an upstairs balcony of the Garrett house, a 1900 Victorian, on the west side of Main Street. I was not able to attempt a photo from this spot, but did try one from the front porch. All that could be seen from this point was the live oaks along Main Street. From the balcony, possibly the first row of cottonwoods along the slough could have been seen. I was able to take figure 8 from a point on the bluff, along the river, two blocks to the south. This photo, with Tuscan Buttes in the background, again shows how strikingly the area has changed.


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figure

Figure 7.
Oblique aerial photo looking north, 1979.

figure

Figure 8.
Dog Island area looking east from Red Bluff with Tuscan Buttes in the background, 1981.

The aerial photos (fig. 9, 10, 11, and 12) were taken in 1942, 1956, 1970, and 1980. This sequence illustrates the increase in riparian vegetation at the site during the 38-year period. In 1942 only 15% of the island was covered with riparian vegetation. This had increased to 50% by 1956; to 90% by 1970; and to 100% by 1980. The mainland portion shows a similar pattern with the most dramatic increase between 1970 and 1980, when the box elders filled in the center of the mainland plain.

The first aerial photos of the Sacramento Valley were taken in 1938. I was able to study the photo of the Red Bluff area. In Figure 13 the 1938 land boundaries, the pre-1937 flood boundary, and the present boundaries are shown. From this composite map one can see the recent changes in the area. Prior to the 1937–38 flood, the land that later became the eastern portion of Dog Island was part of the mainland on the east side of the river. During the floodwaters, 65 m. of bank were carved off. The end of the peninsula was cut off, forming an island.[4] By 1952 this channel had widened to about three times the 1938 width, and the channel between it and the other island had filled in, leaving the area with its present shape.

Discussion

It is unfortunate that aerial photo coverage of the study site and the Sacramento River only go back as far as 1938. Quantitative land use changes can only be derived using these photos as a baseline. At Dog Island I was fortunate to find historic photos dating back 100 years. At most sites one would not be so lucky. Also, without the use of geographic and man-made landmarks, as I had at this site, it would be very difficult to tell where the early photos were

[4] Wetter, Judge Curtis E., Red Bluff, California. Personal communication, September, 1978.


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figure

Figure 9.
Aerial photo, Dog Island, 1942 (courtesy
of the US Army Corps of Engineers).

figure

Figure 10.
Aerial photo, Dog Island, 1956 (courtesy
of the US Army Corps of Engineers).

figure

Figure 11.
Aerial photo, Dog Island, 1970 (courtesy
of the US Army Corps of Engineers).

figure

Figure 12.
Aerial photo, Dog Island, 1980 (courtesy
of the US Army Corps of Engineers).

taken. Areas where photos would be most readily available would be near towns.

The technique of rephotographing a scene to document vegetation changes on a site appears to have limited usefulness in a riparian setting of low relief. Even at Dog Island where the 20 m. bluffs were available, it was not successful since the vegetation had grown so much and views were blocked from all previously photographed angles.


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figure

Figure 13.
Geographical changes at Dog Island, 1937–1980.

Significant changes have occurred at this site and the reasons are not obvious. I believe that the deposition at Dog Island is part of the normal east-west migration of the Sacramento River. When the early settlers arrived in the late 1840's, the river had reached the red bluffs on the west. Gradually, since then, it has been moving back to the east. This process was accelerated by the 1937–38 flood which cut off the tip of the peninsula on the east side of the river. This stabilized the west side at Dog Island by deflecting the main force of the water away from the island area, such that it hit a full 1.5 blocks farther south on the red bluff. This process has slowed again since the mid-1960's when the Red Bluff diversion dam was built and some attempt was made to stabilize the banks on portions of the pool by limited use of riprap.

The increase in vegetation is a natural process as new land is being formed, but it is likely that man has accelerated the process here. The first of these factors is the construction of Shasta Dam. This dam controls the level of flow on the Sacramento River throughout the year by storing the winter floodwater and releasing it for agricultural use during the summer and fall. This creates much higher flows in the summer than would normally occur and gives more free water to the riparian vegetation than would normally be available during this period of water stress.

Possibly the most significant reason for this increase in vegetation is the raised water table created by the Red Bluff diversion dam. This dam created Lake Red Bluff which is held at a constant water level throughout the growing season. This provides the vegetation with an unlimited supply of water. At no place on the area (except the bluff itself) is water a limiting factor to plant growth.

It will be interesting in the years to come to see what landform and vegetational changes take place on the island. It is doubtful, with the bank stabilization that has taken place near the area, that major changes in the shape of the site will occur. The most significant change that is now taking place is the silting in of the side channel. Riparian vegetation will be growing here within 20 years if this process continues. Young valley oaks and black walnuts are found on higher portions of the area and these species will likely become more dominant as the years pass.

When considering the study area and the riparian woodland system in general, two concepts must by held foremost in one's mind when making management decisions. The first concept is that change is the essence of the riparian zone. In 120 years, major changes have taken place here and the current vegetation structure is a product of this change. If man insists on a stagnant situation through the use of channelization, the riparian community will not survive.

The second concept is that of the rapid growth and resistance of this vegetation-type. In a period of 40 years this area has been transformed from a gravelbar to a mature cottonwood/willow riparian woodland. The successional changes are still taking place, and in another 40 years a valley oak/black walnut riparian woodland will have taken its place. The land is the important resource, and if man can refrain from plowing, grazing, or riprapping it, the forest will return in a very short time.

Literature Cited

Laymon, Stephen A. 1983. Riparian bird community structure and dynamics: Dog Island, Red Bluff, California. In : R.E. Warner and K.M. Hendrix (ed.). California Riparian Systems. [University of California, Davis, September 17–19, 1981.] University of California Press, Berkeley.

USDA Soil Conservation Service. 1967. Soil survey, Tehama County, California. U.S. Department of Agriculture.


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4—
AQUATIC/RIPARIAN INTERACTIONS IN RIVERINE SYSTEMS

figure


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The Importance of Riparian Vegetation to Stream Ecosystems[1]

Allen W. Knight and Richard L. Bottorff[2]

Abstract.—Riparian vegetation is very important in determining the structure and function of stream ecosystems. Most aquatic organisms, both invertebrates and fish, are directly or indirectly dependent on inputs of terrestrial detritus to the stream for their food. Natural changes in riparian vegetation and the biotic processing of detritus, as well as other factors, determine the kinds and abundance of aquatic invertebrates living in streams, from headwaters to large rivers. Removal of riparian vegetation will significantly affect stream organisms by: 1) decreasing detrital (food) inputs; 2) increasing the potential for primary production in aquatic plants; 3) increasing summer water temperatures; 4) changing water quality and quantity; and 5) decreasing terrestrial habitat for adult insects.

Introduction

The manner in which riparian systems are managed and protected is commonly related to their value as buffer strips, stream bank stabilizers, and fish and wildlife habitat. These strips of streamside vegetation may be the only habitat remaining for some wildlife species. As riparian vegetation is modified or destroyed by grazing, logging, urbanization, road construction, water development, mining, and recreation, interest in its importance is increasing. Our objective is to briefly review the role of riparian vegetation in the structure and function of stream ecosystems, especially headwater streams. We also explore the possible effects of vegetation modification or destruction in headwater streams. Whenever possible, our review emphasizes conditions found in Sierra Nevada streams.

Headwater Streams

Headwater streams are greatly influenced by riparian vegetation since they function as processors of natural organic matter coming from the watershed (Cummins and Spengler 1978). These small streams are characteristically shaded and kept cool by overhanging riparian vegetation, which also contributes dead organic matter (detritus) to the stream. Shading not only affects water quality but influences the activities of primary producers such as algae and aquatic macrophytes. Riparian vegetation supplies organic matter in the form of dead leaves, needles, twigs, branches, logs, bud scales, fruit, droppings of terrestrial animals (frass), and dissolved organic matter (DOM).

The direct input of organic matter from riparian vegetation is substantial: annual values range from about 100 gm. per m2 to more than 1,000 gm. per m2 (Bray and Gorham 1964; Anderson and Sedell 1979), and values for standing crops can be much higher (Naiman and Sedell 1979). The addition of this organic matter is fundamentally important to the stream biota since this is often its major energy source, which is supplemented by lesser amounts of autochthonous production (Hynes 1963; Cummins 1974). Dead organic matter may contribute as much as 99% of the annual energy input to headwater streams covered by a dense forest canopy (Fisher and Likens 1973). Particulate detritus accounted for 53% of the annual energy input to Bear Brook, New Hampshire, and DOM input accounted for 47%; autochthonous primary production by mosses contributed very little. These streams are termed "heterotrophic", because in effect they consume organic matter produced by adjacent terrestrial systems.

Although allochthonous detrital input to streams continues throughout the year, seasonal pulses do occur. Detritus is added in autumn from deciduous leaf-fall and plant die-off. In winter and spring it is washed in by higher runoff (Minshall 1968; Fisher and Likens 1973;

[1] Paper presented at the California Riparian Systems Conference. [University of California, Davis, September 17–19, 1981].

[2] Allen W. Knight is Professor of Hydrobiology, University of California, Davis. Richard L. Bottorff is Research Assistant, Department of Land, Air, and Water Resources, University of California, Davis.


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Hobbie and Likens 1973). Additional pulses may include bud scales in spring and frass in summer. Tree branches broken by wind and snow may drop into streams in winter. Rainstorms periodically wash in DOM exuded from plants or collected on leaves from arboreal animals, while groundwater continuously brings in DOM.

Although the heterotrophic nature of headwater streams enclosed in forests has been well emphasized by recent research (Fisher and Likens 1973; Cummins 1974), headwater streams in unforested or sparsely-forested regions can be autotrophic, receiving most of their energy from primary production of aquatic macrophytes and algae (Minshall 1978). Autotrophy has been documented in desert streams lacking riparian vegetation and shading (Naiman 1976; Minshall 1978; Busch and Fisher 1981) and has been suggested for high-altitude streams (Cummins and Klug 1979), especially in western montane regions (Wiggins and Mackay 1978). Headwater streams within forests can also change seasonally from heterotrophy to autotrophy, depending upon natural variations in light intensity, nutrients, hydrologic factors, and detrital input (Naiman and Sedell 1980).

Data are currently lacking to classify Sierra Nevada headwater streams as either heterotrophic or autotrophic. The vegetation, climate, and geology of Sierra Nevada mountains vary substantially from location to location. Thus headwater streams may vary widely in their heterotrophy/autotrophy balance. The extensive forests and chaparral on the western slope of the Sierras do suggest that detritus from riparian vegetation is very important to stream energetics. Even above the timberline, dense growths of willow, alder, grasses, and herbs overhang the small stream channels, supplying detritus and shading the water. Only at high elevations when streams flow over granite bedrock is riparian vegetation sparse and the stream unshaded.

Organic Matter Processing

The importance of organic matter contributions from riparian vegetation to stream ecosystems has been fully appreciated for only about 10 years (Cummins 1974). The manner in which aquatic organisms utilize and process organic matter at different seasons and locations along streams is a current research topic (Cummins 1973, 1975; Cummins and Klug 1979; Anderson and Sedell 1979; Hawkins and Sedell 1981). We briefly summarize here the role of aquatic organisms in continually processing and transforming organic matter from the time it enters the stream (fig. 1).

figure

Figure l.
Schematic diagram depicting the processing of dead organic matter in
headwater streams (redrawn from data in Cummins and Spengler 1978).


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Coarse particulate organic matter (CPOM: > 1 mm. diameter), such as leaves, starts leaching DOM once it enters the water. Up to 30% of dry weight may be leached in the first day; deciduous leaves leach faster than coniferous needles (Cummins 1974; Hynes etal . 1974). Fungi and bacteria rapidly colonize the leaves undergoing leaching. Although most of these microbes can metabolize cellulose, only some can use lignin (Cummins and Spengler 1978). Certain aquatic insects such as some stonefly nymphs, midge larvae, cranefly larvae, and caddisfly larvae shred or break down leaves (CPOM) during feeding and are called "shredders" (Cummins 1973). The microorganisms that colonize the leaves are an important source of shredder nutrition.

Shredder and microorganism feeding eventually breaks down CPOM into fine particulate organic matter (FPOM: < 1 mm. diameter). However this process is only one source of FPOM. FPOM may result from: 1) shredder and microorganism feeding on CPOM; 2) physical abrasion of CPOM by stream turbulence; 3) fine particles eroded from streambed algae; 4) fine material washed or blown in from the surrounding watershed; and 5) conversion from DOM by chemical and microbial activity (Cummins 1974). Dissolved organic matter leached from CPOM, plus DOM entering from the watershed, aquatic plants, and microbial excretions, can be partially converted into FPOM. This conversion is accomplished by physical flocculation and microbial assimilation, processes dependent on water turbulence, temperature, pH, and various ionic concentrations (Lush and Hynes 1973).

FPOM is the food for aquatic organisms known as "collectors". These animals obtain FPOM either by gathering it from stream substrate deposits or by filtering it from the flowing water. Deposit feeders include certain midge larvae and mayfly nymphs. Filter feeders have diverse ways of capturing FPOM from the passing water (Wallace and Merritt 1980). Blackfly larvae possess fan-shaped structures on their heads for filtering FPOM and transferring it to their mouths. Some caddisfly larvae construct detailed silk nets capable of sieving out FPOM. The net is often held between small twigs or stones exposed to the current, and the larva hides in a tube just behind. The collected FPOM contains bacteria on its surfaces, which increases the quality of the food for the collector. Particle size is very important to collectors since their mouthparts and sieving devices have specific shapes and openings for obtaining and handling FPOM.

A thin film of algae covers most stream substrates and contributes to instream primary production, especially when light intensity and nutrient concentrations are high. Microscopic diatoms are often the most abundant algal group, but larger filamentous green and blue-green algae are also common. Aquatic organisms known as "scrapers" have well-adapted mouthparts for scraping up and consuming this algal film, which also includes some FPOM and microscopic animals. Scrapers in Sierra streams include many mayfly nymphs, water penny beetles, riffle beetles, and some midge larvae.

Some aquatic invertebrates and vertebrates prey on shredders, collectors, scrapers, and each other; they are known as "predators". Predators in Sierra streams include many stonefly nymphs, dragonfly nymphs, some midge larvae, alderfly larvae, and dobsonfly larvae. Most aquatic insects in streams, even those that are predatory, are potential prey for trout and many nongame fish species.

The amount, kind, and timing of riparian vegetation additions to the stream and the shading provided by streamside plants will determine which feeding groups (shredders, collectors, scrapers, predators) prosper at any site. Thus, the population abundance of stream animals and community composition of the stream ecosystem are dependent on riparian vegetation.

The River Continuum Concept

The structure and function of aquatic communities along a river system have recently been organized into the River Continuum Concept (Cummins 1975; Vannote etal . 1980). This concept involves several stream factors—temperature, substrate, water velocity, stream morphology, and energy inputs from allochthonous and autochthonous sources—which interact to influence the availability of food for stream animals. These factors should vary in a predictable fashion from headwaters to downstream locations, and should produce predictable distributions of the four feeding groups along the continuum (fig. 2).

Since headwater streams (orders 1-3) are often heavily shaded and receive large amounts of organic matter from riparian vegetation, these streams are heterotrophic. Their ratio of gross photosynthesis (P) to respiration (R) will be less than one. Coarse substrates predominate, since stream gradients and erosive power are high. Shredders reach maximum abundance in these upper stream sections because of the abundant CPOM. FPOM and DOM are used and exported downstream. Because many Sierra headwater streams originate within coniferous forests, they may differ from typical headwater streams originating within deciduous forests of the eastern United States in detrital input and lighting conditions.

Organic matter input and shading are less important in medium-sized rivers (orders 4-6) because of the greater widths and more open canopy. Increased primary production shifts these streams from heterotrophy into autotrophy, and a P:R ratio greater than one. Increased algal production allows scrapers to be abundant. Collectors are also common, and a few shredders are still present. FPOM and DOM are again used and exported downstream.


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figure

Figure 2.
The relationship between stream size and the progressive shift in structural and functional
components of streams. Box graphs of feeding groups are provided to compare Sierra streams
with eastern streams. The relative number of organisms in each feeding group is indicated
by rank-ordered lists, from large to small (from Cummins 1975; Vannote  et  al . 1980).

Riparian vegetation has little direct influence on large rivers (orders > 6) since the wide channels are open to sunlight, and the input of terrestrial detritus relative to water volume is small. However, FPOM from upstream sources is very important, and for this reason collectors are the predominant aquatic organisms of large rivers. Although these rivers are open to sunlight, increased turbidity restricts both light penetration and primary production by algae on the fine river substrates. Instead, phytoplankton may be important primary producers in the upper water layers, although turbidity may restrict the depth of their production. Therefore, large rivers are thought to be heterotrophic and have a P:R ratio less than one.


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Shredders and scrapers are essentially absent because their food resource and coarse substrate are lacking.

Streams on the western slope of the Sierra Nevada typically pass through several plant communities—subalpine forests (conifers), red fir forests, mixed conifer forests, oak woodlands, chaparral, and grasslands—each of which contributes different organic matter inputs and shading effects. In addition, alpine tundra, montane meadows, and montane chaparral may be locally important. It is not known if all aspects of the river continuum concept apply to Sierra streams.

It is possible to summarize predictions of the river continuum concept (Vannote etal . 1980), especially as they are thought to be true for many streams in forested regions. Exceptions are known to occur for desert streams (Minshall 1978), and possibly for western montane streams (Wiggins and Mackay 1978). Some of these predictions have recently been tested in four Oregon streams, and shown to support the river continuum concept (Naiman and Sedell 1980; Hawkins and Sedell 1981).

Width, depth, and discharge increase as stream order increases. Substrate size changes from coarse to fine going from headwaters to large rivers. Diel changes in water temperature increase to a maximum in medium stream orders (3–5), then decrease downstream.

CPOM and riparian vegetation shading decrease in importance downstream, and FPOM increases in importance. This causes the CPOM:FPOM ratio to decrease as stream order increases. The particle size of detritus decreases downstream.

DOM diversity decreases downstream as labile components are used by microorganisms, causing refractory components to accumulate.

P:R ratio < 1 for stream orders 1–3—heterotropic condition.
P:R ratio > 1 for stream orders 4–6—autotrophic condition.
P:R ratio < 1 for stream orders >  6—heterotrophic condition.

Shredders decrease downstream as CPOM becomes less abundant.

Collectors increase downstream as FPOM becomes more important.

Scrapers increase to a maximum abundance in medium-sized rivers (orders 4–6) as the canopy opens and admits light to the substrate, but then decrease in larger rivers (orders > 6) because turbid water shades algae on the stream substrate.

Predators maintain approximately constant abundance along the continuum.

Biotic diversity is low in the headwaters, increases to a maximum in medium stream orders (3–5), and decreases in larger rivers.

Effects of Riparian Vegetation Removal

Some of the major inputs of riparian vegetation to instream systems are shown in figure 3. Effects on stream invertebrates of disruptions to five of these inputs will be discussed: 1) decrease of detrital inputs; 2) loss of shade as it affects primary production; 3) loss of shade as it affects stream temperature; 4) water quality and quantity alterations; and 5) loss of terrestrial habitat. The intensity of these effects is related to the degree of modification of the vegetation.

Decrease of Detrital Inputs

Riparian vegetation often supplies large amounts of organic matter (energy) to the stream, forming a dependable food base for stream invertebrates year after year. Many of these animals have complex structures, behaviors, and life cycle events which are specially adapted for using different kinds and sizes of detritus as food. Decrease of detritus will cause decreased populations of these species, although instream production may still maintain some at lower densities.

Loss of Shade

Effect on Primary Production

Riparian vegetation is a major control on light intensities reaching algae and macrophytes in headwater streams, and therefore on the level of primary production that can occur. Shade removal has been demonstrated to increase primary production and cause algal mats in small streams, both in the field (Brown and Krygier 1970; Likens etal . 1970; Granoth 1979), and in the laboratory (McIntire and Phinney 1965; Brocksen etal . 1968). For example, vegetation removal along a small stream in Kansas changed it from heterotrophy to autotrophy (Gelroth and Marzolf 1978). Also, in laboratory streams exposed to two different light levels, the stream receiving twice as much light had twice the gross plant production (Brocksen etal . 1968). If nutrients or other factors are not limiting, increased illumination due to shade removal will increase primary production and the food resources used by scrapers.

Loss of Shade

Effect on Stream Temperature

Shade from riparian vegetation moderates stream temperatures, often preventing excessive summer temperatures that may be lethal to invertebrates or fish. Field studies have demonstrated significant increases in summer water temperatures and decreases in winter temperatures when shade is removed from small streams (table 1).


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figure

Figure 3.
Relationships between riparian vegetation and stream components.

 

Table l.—Water temperature changes in small streams caused by riparian vegetation removal, in relation to undisturbed conditions.

   

Temperature change

 

Location

Forest type

Summer1

Winter

References

Oregon

Coniferous

+8(a)

Brown and Krygier (1970)

   

+15(b)

 
   

+8(a)

0

Levno and Rothacher (1967, 1969)

Alaska

Coniferous

+5(a)

0

Meehan etal . (1969)

Kansas

Deciduous

+5(c)

Gelroth and Marzolf (1978)

New Hampshire

Deciduous

+5(c)

+

Likens etal . (1970)

   

+4(d)

 

West Virginia

Deciduous

+8(a)

–2

Aubertin and Patric (1974)
Lee and Samuel (1976)

North Carolina

Deciduous

+7(a)

–2

Greene (1950)