over the last two millennia, one-fourth of all bird species are believed to have gone extinct as a result of human activities (Olsen, 1989). This increase in species extinctions is in part because extinctions are occurring on the time scale of human economies, but evolution typically occurs more slowly (except for microorganisms, including those that cause disease).
Despite convincing scientific evidence, there seems to be a general lack of public awareness concerning the global decline in biodiversity, related ecological and societal impacts, and the fact that biodiversity changes are not amenable to mitigation after they occur (Chapin et al., 2000) (Figure 5.8 ). Overall, land transformation is identified as the primary driving force in the loss of biodiversity worldwide (Vitousek et al., 1997). It is estimated that 39 to 50 percent of available land has been degraded by human activity (Vitousek et al., 1986; Kates et al., 1990). Human influences include loss of permeable surfaces to pavement and increases in greenhouse gases, aerosols, and pollutants. Humans use over half the world’s accessible surface fresh water, and more nitrogen is fixed by humans than by all natural sources combined (Vitousek et al., 1997). After land transformation, the next most important cause of extinctions is invasion of nonnative species. Many biological invasions are irreversible, degrade human health, and cause large economic losses. The impact of the zebra mussel on the US Great Lakes states is one such example.
Montane ecosystems are valued highly even though they are small in area compared to other major biomes. Recognized by scientists for their importance to hydrological, biochemical, and atmospheric processes, they are particularly sensitive to climate change because of their many ecotones (Spear et al., 1994) and limited spatial area. Montane areas are scenic, relatively pristine, and often provide water for many urban and agricultural areas (Walker et al., 1993).
Changes in snowfall and snowpack in montane regions have a large impact on treeline and plant communities (Patten and Knight, 1994). The timing of snowmelt affects plants in many ways, including the alteration of leaf traits, the changing of leaf production, shoot growth (Kudo et al., 1999), and flowering (Inouye and McGuire, 1991). In addition, changes to the timing of snowmelt will alter the exposure to late spring frosts (Inouye, 2000). A decrease in synchrony associated with phenological events at high and low altitudes may pose problems for animal species that migrate between altitudinal zones (Inouye et al., 2000). For example, marmots are presently emerging from hibernation 38 days earlier than they did 23 years ago in the Rocky Mountains (Inouye et al., 2000). As this example relates