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

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.

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, Alnus rhombifolia can become dominant. When water tables are relatively deep, Platanus racemosa is the usual dominant when aeration of the intervening soil is high and Quercus lobata 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).

Deciduousness and Productivity

Mediterranean-type climates, with their mild, wet winters and dry summers, are well known for their sclerophyllous evergreen vegetation (Mooney et al . 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 , Ilex cassine , I . coriacea , I . myrtifolia , I . opaca , I . vomitoria , Magnolia virginiana , Myrica cerifera , M . heterophylla , Persea borbonia , P . palustris , and Quercus laurifolia (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 et al . 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 .

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 de facto 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.

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

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 Fimbristylis vahlii , 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 et al . 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 et al . 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

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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Thompson, K. 1977. Riparian forests of the Sacramento Valley, California. p. 35–38. In : A. Sands (ed.). Riparian forests in California: their ecology and conservation. Institute of Ecology Pub. No. 15. 122 p. University of California, Davis.

Thorne, R. 1976. A phylogenetic classification of the Angiospermae. p. 35–106. In : M. Hecht, W. Steere, and B. Wallace (ed.). Evolutionary biology. Volume 9. Plenum, New York, N.Y.

Thornthwaite, C. 1948. An approach toward a rational classification of climate. Geogr. Rev. 38:55–94.

Thornthwaite, C., and J. Mather. 1955. The water balance. Drexel Inst. Technol. Pub. Climatol. 8:1–104.

Tucker, J. 1980. Taxonomy of California oaks. p. 19–29. In : T. Plumb (tech. coord.). Proceedings of the symposium on the ecology, management, and utilization of California oaks. [Claremont, Calif., June 26–28, 1979]. USDA Forest Service GTR-PSW-44. 368 p. Berkeley, California.

US Department of Agriculture. 1941. Climate and man: yearbook of agriculture. 1248 p. US Department of Agriculture, Washington, D.C.

US Department of Commerce. 1970. Climate of California. In : Climates of the states: climatography of the United States, 60–4. 57 p. US Depatrment of Commerce, Washington, D.C.

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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.

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

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 (Quercus lobata ) 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 et al . 1915). Fremont cottonwood (Populus fremontii ), California sycamore (Platanus racemosa ), willow (Salix spp.), and valley oak are common upper canopy species found throughout the Valley. Such species as box elder (Acer negundo 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 (Vitis californica ), poison oak (Rhus diversiloba ), Dutchman's pipe vine (Aristolochia californica ), 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 (Baccharis viminea ), wild rose (Rosa californica ), 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

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 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.

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 et al . 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

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.

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-

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 et al . 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 et al . 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.

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.

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 et al . 1980). Based on figures compiled by Bury et al . (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.

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. Nussbaum3 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 (Dicamptodon ensatus ) 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 (Desmognathus fuscus ) 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 (Clemmys marmorata ) 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 (Diadophis punctatus ) 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

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

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 (Eumeces gilberti ) 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

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 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 Ascaphus truei 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, Ascaphus truei . J. Herpetol. 4: 179–189.

Fitch, Henry S. 1975. A demographic study of the ringneck snake (Diadophis punctatus ) 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 Ascaphus truei Stejneger. Copeia 1931:97–101.

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.

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:

". . . 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 human numbers 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-

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

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

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

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

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.

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).

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).

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.

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:

areas:

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 et al . (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.

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.

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.

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.

Figure l.
Location map.

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.

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.

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.

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 et al . (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 et al . (1977) and Michny et al . (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.

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 et al . (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

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.

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

different in species composition than regeneration in the established forests.

Discussion

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.

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 Populus deltoides along the Missouri River in southeastern South Dakota. Amer. Midl. Nat. 83(2):330–342.

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 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 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).

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 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).

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 in toto , 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

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 Populus fremontii surrounding

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 Quercus lobata 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. Vitis californica and Rubus procerus occupy the landward margins, whereas Typha latifolia and Juncus effusus 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 (Cyperus alternifolius , Alisma sp., and Marsilea vestita ) to plants usually found in open, droughty habitats (Centaurea melitensis , Briza minor , and Cynodon dactylon ). 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 , Brodiaea californica , 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: Stipa pulchra , Brodiaea hyacinthina , and Calochortus luteus . In general, species

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 Quercus lobata 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

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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.

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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.

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

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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.

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

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 13 —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

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

Human Impact