Treesearch

Amphibians are declining worldwide for a variety of reasons, including habitat alteration, introduction of non-native species, disease, climate change, and environmental contaminants. Amphibians often play important roles in structuring ecosystems, and, as a result, amphibian population declines or extinctions are likely to affect other trophic levels (Matthews and others 2002). Avoiding declines or reversing the declines of amphibian populations that are already underway should be a major concern of land and wildlife managers.

The Sierra Nevada Ecosystem Project provided the first comprehensive status report on the condition and history of natural resources of this mountain region (Centers for Water and Wildland Resources 1996). The report concluded that aquatic habitats were the most altered and impaired ecosystems, after exposure of Sierra watersheds to 150 years of landscape changes resulting from activities such as hydraulic mining, damming and diversions of streams, road building, livestock overgrazing, timber harvest, hard-rock mining, and introductions of exotic species. Continued assessment of watershed...

Lake Tahoe, widely renowned for its astounding clarity and deep blue color, lies at an elevation of 1,898 meters (m) in the central Sierra Nevada, astride the California-Nevada border. The volume of the lake is 156 cubic kilometers (km3), and its surface area is 501 square kilometers (km2), 38 percent of the total basin area of 1,313 km2. The eutrophication of the lake has been studied intensively since the early 1960s (Goldman 2000), when scientists and farsighted political leaders and private citizens began to recognize that human activities, especially the accelerated input of nutrients...

Cumulative effects result from the combined impact of multiple activities over space and time. Land and aquatic resource managers are particularly concerned with cumulative watershed effects (CWEs). CWEs can encompass a broad range of concerns, but primary issues are changes in runoff, water quality, channel morphology, and aquatic ecosystems at the watershed scale (Reid 1993). CWEs are a class of cumulative effects defined by multiple sources within a watershed that share a common delivery mechanism, the drainage network (fig. 1).

Federal and state legislation, such as the National Environmental Policy Act and the California Environmental Quality Act, require that responsible agency staff consider the cumulative impacts of proposed activities before permits are issued for certain kinds of public or private projects. The Council on Environmental Quality (CEQ 1997) defined a cumulative impact as "...the impact on the environment which results from the incremental impact of the action when added to other past, present, and reasonably foreseeable future actions regardless of what agency (federal or non-federal) or...

The earliest explorers of the Sierra Nevada hailed the mountain range for its unsurpassed scenery. Although a significant component of that beauty was an especially rich assemblage of plants and animals, it was not until many decades later that the Sierra Nevada's wealth of biodiversity was appreciated fully and documented in earnest. Indeed, by the time naturalists, including the legendary John Muir, began to write of the range’s biological assets, features such as ancient forests, alpine meadows, and stream corridors were under full assault from unsustainable levels of logging, livestock...

The Sierra Nevada is a topographically and floristically diverse region of the western United States. While it comprises only a fifth of the total land area of California, half of the native plant species in the state occur within the range. In addition, more than 400 plant species are endemic to the Sierra Nevada and many of these are listed as threatened or have other special conservation status (Shevock 1996). As in many areas of the world, the biodiversity of the Sierra Nevada region is undergoing change due to alterations in human uses and fire regimes, climate change, and invasions...

Carnivores play important roles in structuring communities, and their populations are useful indicators of ecosystem condition (Wennergren and others 1995, Buskirk 1999, Crooks and Soulé 1999, Terborgh and others 2001). As many as 4 of 20 native mammalian carnivore species have been extirpated from the southern Cascade Mountains and Sierra Nevada, with unmeasured effects on ecological communities. Given the loss of a number of significant carnivores from the system, understanding the status and ecological roles of the remaining species has assumed new urgency. Mesocarnivores (intermediate...

In California, hundreds of different public and private organizations are involved in prioritizing and acquiring new conservation lands (California Environmental Dialogue 1999, California Continuing Resources Investment Strategy Project 2001). Although the State of California owns less than 3 percent of the land (Davis and Stoms 1998), it plays a significant role in the conservation of biodiversity, public open space, and commodity production. State government funding for land acquisitions and conservation easements comes from a variety of sources, including special funds, park-related...

The Sierra Nevada’s biological distinction and diversity are almost as legendary as its spectacular peaks and beautiful granite landscapes. The Sierra Nevada is recognized as a zoogeographic region on the basis of the coincidence of species ranges (for example, Udvardy 1969, 1975; Welsh 1994). Udvardy (1969) defined the Sierra Nevada bioregion as bounded by the Great Basin to the north and east, the Mojave Desert to the south, and the Central Valley of California to the west. Welsh (1994) further delineated the Sierra Nevada into three latitudinal segments, recognizing shifts in species...