ABSTRACT
Introduction ............................................................................................................ 164 Biogeographic Focus ............................................................................................. 165
Paci¡c Northwest .............................................................................................. 165 Sierra Nevada .................................................................................................... 165 Northern Rocky Mountains ............................................................................... 166 Central Rocky Mountains ................................................................................. 166 Southern Rocky Mountains ............................................................................... 166
Collaborative Approach ......................................................................................... 167 Status and Trends in Western Mountain Ecosystems ............................................. 168
Snow, Ice, and Hydrology ................................................................................. 168 Forest Ecology, Demography, and Die-Off ....................................................... 172 Tree-Line Dynamics .......................................................................................... 174 Ecological Disturbance and Interaction of Stressors ........................................ 175 Simulating Ecosystem Response to Climatic Change ...................................... 178 Developing Adaptation Science ........................................................................ 180
Understanding, Forecasting, and Adapting-The Next Phase ............................... 182 Summary ................................................................................................................ 183 References .............................................................................................................. 184
Mountains in western North America are beginning to see changes in ecosystem processes primarily from climate-forced changes in water dynamics. With earlier snowmelt and increasing proportions of rain versus snow (Mote 2003; Stewart et al. 2005; Knowles et al. 2006), drought stress is increasing. Cascading effects include increasing vegetation mortality (van Mantgem et al. 2009), dieback of entire forest stands (Allen and Breshears 1998; Breshears et al. 2005), longer and more intense ¡re seasons (McKenzie et al. 2004; Westerling et al. 2006; Littell et al. 2009a), and increased susceptibility to insects and pathogens (Carroll et al. 2004; Breshears et al. 2005; Hicke et al. 2007). Model projections (Littell et al. 2009) suggest that all these phenomena will become even more pronounced in coming years (IPCC 2008; Milly et al. 2008).
