| Summary: | Alpine tundra is an important indicator system of environmental change (Grabherr et al. 1996; Beniston and Fox 1996). This ecosystem occurs at all latitudes, with its lower altitudinal limit at timberline inversely related to latitude (Woodward 1993). Thus, the global distribution of alpine tundra and the fact that this system exists near the limits of vascular plant tolerance to temperature, moisture, and growing season duration makes it an excellent system for monitoring environmental change across the globe (e.g., Körner and Larcher 1988). In addition, the functional integrity of this system is critical to lower elevation ecosystems because substantial amounts of water and elements are intercepted by the alpine, filtered, and transported to lower elevations (Williams et al. 1996; chapter 4). Alpine tundra has been spared most of the large-scale disturbances associated with human development and resource extraction that have occurred in lower altitudinal ecosystems. This is probably due to its climatic severity and lack of renewable resources that can be exploited (e.g., trees, fast-growing forage for grazing). Some high-altitude sites have been impacted by recreational development (e.g., ski areas, trails, roads), mining, and grazing. In addition, changes in native herbivore populations, particularly elk and deer, due to extirpation of predators by humans (chapter 12), may have significantly influenced tundra vegetation (chapter 14). However, the indirect effects of human activities associated with the burning of fossil fuels are of greater current and future concern as the dominant anthropogenic influences on alpine tundra ecosystems. At a global scale, climate change is of concern for all ecosystems, whereas at a more-regional scale, there is concern for the impact of N and acid deposition near centers of industrial and urban growth (Galloway et al. 1995). Niwot Ridge, and possibly much of the Colorado Front Range, has experienced significant increases in the rate of N deposition (Sievering et al. 1996; ...
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