 SCOPE AND BACKGROUND OVERVIEW OF SIERRA NEVADA ECOSYSTEMS AND ASSESSMENT STATUS MANAGEMENT STRATEGIES FOR ECOSYSTEM SUSTAINABILITY INSTITUTIONAL INTEGRATION OF ASSESSMENTS AND SOLUTIONS
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rev. Jun. 17, 1996 |
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Animals About 400 species of terrestrial vertebrates (including mammals, birds, reptiles, and amphibians) use the Sierra Nevada, although only a fraction are restricted to the range. Animals that live in the Sierra Nevada depend greatly on the distribution and quality of vegetation for their habitat and food needs. Many native Sierran species are adapted to habitats maintained by the presettlement fire regime. Although only a handful of species require late successional habitats, many more depend on the presence of large, old trees, snags, and logs in Sierran woodland and forest communities for some part of their life cycle. Late successional and riparian forests are important habitats to wildlife, as are the low-elevation foothill woodland types. In the latter zone especially, conversion of habitat and loss of ecological function have dramatically altered the suite of species that flourish in these communities. A common and important pattern for Sierran birds is their migration up and down slopes, following seasons. When a specific habitat needed for completion of a critical life stage (e.g., foothills for breeding) is disrupted, species may be put at risk even if they are able to use alternative habitat for other needs. Three modern species once well distributed are now gone from the Sierra Nevada. These are grizzly bear, Bells vireo, and California condor. Fifteen terrestrial vertebrates now well established in the Sierra are not native to the range. Several of these have had significant detrimental impacts on the ecology of the Sierra and its native species. The most serious effects have been produced by the brown-headed cowbird, which arrived in the range early in the twentieth century. The spread of this nest-parasitizing bird has mirrored the spread of farmland, grazing, clear-cut logging, and suburban development. Cowbirds are implicated or directly charged with the decline of several songbirds in the Sierra Nevada, especially willow flycatcher, Bells vireo, yellow warbler, and chipping and song sparrows. The conversion of oak woodlands has had substantial effects on terrestrial vertebrates. This zone once supported some of the highest species densities in the range. Lower elevations in this region provided key habitats to many Sierran species that are short-distance altitudinal migrants. Now many of these habitats are gone or greatly diminished in quality and extent, with concomitant effects on animal species. Loss of riparian habitats in this zone has been especially critical. Humans in the Sierra Humans are an integral part of Sierra Nevada ecosystems, having lived and sustained themselves at various elevations in the region for at least 10,000 years. Indigenous populations were widely distributed throughout the range at the time of European immigration. Archaeological evidence indicates that for more than 3,000 years Native Americans practiced localized land management for utilitarian purposes, including animal hunting, forest burning, seed harvesting, pruning, irrigation, and vegetation thinning. These practices no doubt influenced resource abundance and distribution in areas of early human settlement. On a longer timescale, humans may have played a role in the decline of large vertebrates during prehistoric times. Extinction of a large and diverse megafauna throughout western North America, including the Sierra Nevada, at the end of the last major ice age (around 10,000 years ago) coincided with the arrival of humans in North America. Some scientists link these extinctions to overhunting by humans of animals already stressed by changing environments. Immigration of Euro-American settlers in the early 1800s began a period of increasingly intense resource use and settlement. By the late 1800s, parts of the Sierra had been transformed as a result of intense interest by these immigrants in Sierran resources. For example, grizzly bear and foothill bighorn sheep were driven to extinction locally, and mountain meadows were transformed by the excessive grazing of this period. Agriculture, mining, logging, and grazing activities were extensively practiced in many regions of the Sierra. The need to divert water to support resource extraction and settlement led to a major reordering of natural hydrological processes through a vast network of ditches and flumes. In some areas, impacts from early use of the Sierra created rapid and irreversible changes from presettlement conditions. By the early 1920s, a new phase of Sierran history was emerging, in which resource use was more regulated and forest and range protection was emphasized. Suppression of fires became a primary goal of federal, state, and private efforts, controls were imposed on the timing and locations of grazing, and timber harvest was systematized under government and industrial forestry programs. Although trends of use have varied over the last 150 years, increasing population pressure and complex demands on Sierran resources pose serious ecological threats in some regions and severe management challenges elsewhere. Settlement patterns and resource use have historically reflected the export value of Sierra Nevada resources as commodities. The foothills became a focus of early attention for Mother Lode gold deposits, timber, water, and agriculture. An estimated 150,000175,000 people moved into the Sierra Nevada from 1848 to 1860. The population in 1970 was about 300,000, and by 1990, over 650,000 people were living in the Sierra. About 70% of the current population are located on the west-side foothills of the Sierra Nevada, with other concentrations in the vicinities of the main Sierran highways. Projections suggest that the entire Sierra Nevada will grow in population to somewhere between 1.5 million and 2.4 million residents by the year 2040. New residents are increasingly drawn by the amenity values of Sierra Nevada resources as they seek a high-quality living environment. Retirees, commuters, and exurban migrants are all coming to the Sierra Nevada at the same time that employment is declining in the traditional resource-extraction industries, changing the social, economic, and ecological fabric of the region. The new residents are decreasingly dependent on resource extraction and increasingly bring outside sources of income into the region. Over the past twenty years, the economy of the Sierra Nevada region, like the population, has more than doubled. The major commodity-based sectorsagriculture, timber, and miningexperienced little or no growth in employment. On a rangewide basis, recreation and tourism provide more jobs and roughly the same total amount of wages as all the commodity-based sectors combined. The economic stimulus from new businesses, commuters, and retirees is now far greater than that provided by all the commodity and recreation-based employment in the region. One of the major implications of this trend is that the economic character of the region is less influenced by the major resource industries and agencies and is becoming more similar to the diverse economy and society of California as a whole. Community well-being in the Sierra is undergoing transitions consistent with changing settlement patterns and resource uses in the region. About 15% of the Sierra population live in communities with high well-being. More than half of these communities are in the Sacramento commuter counties of Nevada, El Dorado, and Placer. About 20% of the total population of the Sierra live in communities with low levels of well-being. More of these communities are in the northern Sierra than other regions, although scattered communities with low or high well-being exist throughout the region. Some communities, such as the greater Lake Tahoe Basin area, have distinct patterns of unequal distribution of wealth and well-being, with areas of extreme poverty surrounded by communities of wealth and high community capacity. For many residents, air quality is an important aspect of quality of life in the Sierra Nevada. Air quality varies greatly depending on region. Northern airsheds, with the exception of some local communities where winter woodsmoke creates health hazards, generally are among the cleanest in the nation. Southern airsheds, by contrast, are heavily impacted by ozone and have some of the poorest air quality in the nation. Ozone damage is occurring in conifer forests of middle and high elevations, particularly in the southern western forests. We know little about the levels of ozones and other particulates that are acceptable to biota, but federal standards for humans may be inadequate for some other species. Dust storms over the alkali and dry lakes of the eastern Sierra create episodic health hazards to humans and presumably to plants and other animals as well. Air quality in the Sierra Nevada is at a critical point, with moderate to severe degradation becoming all too often accepted as the status quo. Unlike other areas in the state, the Sierra has ozone levels that are not declining. Except at a few places like Lake Tahoe, Mono Lake, and some urban communities, little effort is being made to address reduced visibility in the Sierra, the source of which primarily is the Central Valley. 
 
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