 * CRITICAL FINDING INTRODUCTION ROCK AND SOIL * Insect Species Found Only in the Sierra * Land Ownership and Reserve Allocation in the Sierra Nevada The Sierra Nevada of the Future
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* CRITICAL FINDING
Climate Change During the period of recent human settlement in the Sierra Nevada, climate was much
wetter, warmer, and more stable than climates of the past two millennia; successful
ecosystem evaluations and planning for the future must factor climate change into
analyses. IntroductionThe Sierra Nevada evokes images particular to each individuals experience of the range. These images take on the quality of immutability, and we expect to find the range basically unchanged from one year to the next. The Sierra Nevada, however, including its rocky foundations and the plants and animals that inhabit it, changes continually through time. Ecosystems respond to cumulative effects from the past; the old-growth forests in the Sierra today evolved under different conditions from those of the present. To understand how the landscapes of the Sierra Nevada are changing, and what role humans have in shaping the future, we benefit by knowing what makes up the current Sierra as well as key factors influencing change. This was the point of departure for the Sierra Nevada Ecosystem Project. A brief introduction to the Sierra Nevada and the context of the study are presented here; subsequent chapters summarize the studys findings. Rock and SoilAt its foundation, the Sierra Nevada is an enormous deposit of granitic rock whose exposed slopes are readily visible at the crest of the range. The gradual west slope rising from the expansive Central Valley to the Sierra crest is dissected by deep, west-trending river canyons. At the eastern edge of the uplift, the high peaks dominate the uppermost elevations, forming rolling highlands in the northwith elevations mostly less than 9,000 feet (figure 1.1) and expansive, highly dissected mountains in the broad southern alpine zones, where Mount Whitney (highest peak in the contiguous forty-eight states) rises to 14,495 feet. The range ends abruptly at the eastern escarpment, dropping with a shallow gradient in the north, but in the south plunging more than 10,000 feet from the Sierran crest to the floor of the Great Basin.  FIGURE 1.1 (ACTUAL VIEW 23K) Northern Sierra montane aerial view. (Photo by Jerry F. Franklin.) As a geological feature, the Sierra Nevada is relatively distinct. The western boundary is defined as a contact between old, harder rocks of the Sierra Nevada and their eroded and redeposited younger by-products at the edge of the Central Valley. At the north, the older rocks of the Sierra Nevada are overlain by younger volcanic rocks of the southern Cascades in the Mount Lassen area. The eastern edge of the range follows the base of the Sierran escarpment. At the south, the geologic Sierra Nevada abuts the structurally distinct Tehachapi Mountains, forming a discernible boundary in southern Kern County. The Sierra Nevadas environmental history has been shaped over several hundred million years by varying intensities and forms of uplift, erosion, volcanism, and glaciation. Plate tectonics and climate variations acting at millennial, decadal, and annual timescales interact to influence the intensity of these events and their impacts on the landscape. These diverse geological activities have produced a broad suite of rock formations in the Sierra Nevada, dominated by granite but including many types of igneous, sedimentary, and metamorphic rocks, with ages from Cambrian (about 500 million years ago) to Quaternary (the past 2 million years). Most evidence suggests that the modern range is about 10 million years old, although very recent and controversial evidence suggests a much older age. Rocks of the Sierra Nevada interact with climate, topography, surface processes, and biota to create Sierra Nevada soils. Because the Sierra Nevada is underlain by mostly granitic rocks, soils that develop from these foundations are thin and rocky. Although the nutrient capital (fertility) of the soil in general over the Sierra Nevada is rather low, the range contains some of the most productive sites for conifers in the world. Soil types form a mosaic across the Sierra, influencing vegetation, erosion, wildlife distribution, water quality, fertility, and a myriad of human uses. Such a complex geological and soil foundation has dramatic implications for human uses of Sierra Nevada ecosystems. Mesozoic deposits (more than 100 million years old), altered through pressure and heat and exposed through erosion or buried deep underground, form the gold and silver that attracted a rush of miners and began the period of Euro-American settlement. Abundant sediments from ancient seafloors, lake beds, and water-carried deposits create the ore and gravel resources that are the contemporary valuable rocks of the Sierra (plate 1.1). Persistent seismic activities, especially along volcanic vents of the eastern escarpment near Mammoth Lakes and Markleeville, are a focus of concern for urban development in these areas, yet those same vents provide geothermal power for existing communities. The rich and fertile soils that have formed on the western edges of the Sierra Nevada continue to support a diverse agriculture that had its origins in the Native American communities that occupied the region. Volcanic and seismic activity is highly localized but ongoing in the Sierra Nevada. New volcanic craters have been built, vents have erupted, hot springs have formed, faults have slipped, and volcanic-induced mud slides have occurred as recently as the past hundred years in a few regions. Volcanic events will undoubtedly persist as agents of change affecting local ecological and human elements of Sierran ecosystems and demanding local attention. 
 
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