Volume 1/Chapter 1/Sierra Nevada Ecosystems

* Critical Finding

Introduction

Rock and Soil

* The SNEP Study Area

Climate

WATER

Plants and Vegetation

* Ecosystems

* Insect Species Found Only in the Sierra

Animals

Humans In The Sierra

Social Institutions

* Land Ownership and Reserve Allocation in the Sierra Nevada

The Sierra Nevada of the Future

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Water

Water is an essential and often limiting factor for life. Given strong seasonal mediterranean patterns, high annual variability of climate, natural aridity of the eastern flanks, and the constant thirst of plants, animals, and burgeoning human communities adjacent to the Sierra, water remains a subject of intense competition for all Sierran biota.

Water partitions the Sierra into twenty-four readily discernible river basins or watershed units (figure 1.2). The Sierran crest divides water flow either west to the Pacific Ocean or terminating in the San Joaquin valley, or east into the Great Basin, where the water evaporates. To the west, the major watersheds are defined by the Feather, Yuba, American, Cosumnes, Mokelumne, Stanislaus, Tuolumne, Merced, San Joaquin, Kings, Kaweah, and Kern Rivers; to the east, by the Truckee, Carson, Walker, and Owens Rivers. Streams, creeks, and temporary waters define subwatersheds at increasingly smaller scales within these areas.

FIGURE 1.2 (ACTUAL VIEW 20K)

Boundaries of the core Sierra Nevada ecoregion, the study area, and the twenty-four river basins used by SNEP in its assessments.

Watersheds at each scale are important to creatures that inhabit water. Sierra Nevada waters are home to a diverse aquatic biota, including fishes, amphibians, invertebrates, and plants. To denizens of rivers, the landscape is defined and limited by linear connections; the arterial nature of water systems isolates aquatic populations. Watersheds also isolate aquatic organisms, so that entirely different aquatic biotas may exist from one watershed to another. Rivers and their watersheds extend beyond the geologic edges of the Sierra Nevada to their final destination in ocean, valley, or basin. Fish and other aquatic life have evolved to occupy habitat zones within certain elevations along the rivers, but they do not have sharp or readily defined downstream or upstream boundaries (figure 1.5).

FIGURE 1.5 (ACTUAL VIEW 27K)

Aquatic and riparian ecosystems in healthy condition provide critical habitat for Sierra plants and animals. (Photo by Jerry F. Franklin.)

At middle and low elevations, the Sierra Nevada once supported a diverse fish population, including anadromous species such as chinook salmon. Extensive and abundant populations of frogs and salamanders inhabited Sierran streams, lakes, and meadows. The largest numbers of aquatic species in the Sierra Nevada are the little-known invertebrates. The many lakes of the high Sierra, once mostly fishless, originally supported a diversity of aquatic amphibian and invertebrate species. These groups of aquatic animals have been extremely vulnerable to changes in their habitat, and the story of their composition and distribution is now quite different from that of the past.