Climate is a major driver of Sierra Nevada ecosystems. The cumulative effects of past and present climates, in concert with geologic factors (such as soil type) and processes (such as fire), largely determine current hydrology and species distribution patterns in the Sierra Nevada. Accelerated climatic change related to anthropogenic influences is expected to result in significant ecosystem effects in western montane systems, including reduced snowpack, altered fire regimes, and modified species vulnerability (CIRMOUNT Committee 2006). In the Sierra Nevada, atmospheric warming is resulting in an increase in the fraction of rain to snow, a decrease in maximum snowpack water content, and earlier snowmelt (Cayan et al. 2001; Dettinger 2005). Climate scientists expect climatic change to interact with and exacerbate other ecosystem stressors, such as altered fire regimes, air pollution, and non-native species invasions (IPCC 2007)-stressors that already rank among the most threatening to Sierra Nevada ecosystem resilience (Mutch et al. 2008).