Global climate is expected to change rapidly over the next century (Thompson et al. 1998; Houghton et al. 2001; IPCC 2008). This will affect forest ecosystems both directly by altering biophysical conditions (Neilson 1995; Neilson and Drapek 1998; Bachelet et al. 2001) and indirectly through changing disturbance regimes (Baker 1995; McKenzie et al. 1996; Keane et al. 1999; Dale et al. 2001; McKenzie et al. 2004; Westerling et al. 2006). Changes in biophysical conditions could lead to species replacement in communities and latitudinal and altitudinal migrations (Iverson and Prasad 2002; Neilson et al. 2005). Expected increases in the frequency, size, and severity of wildfires (Mearns et al. 1984; Overpeck et al. 1990; Solomon and Leemans 1997; IPCC 2008), and other disturbances such as insect outbreaks, may further amplify changes in vegetation structure, species composition, and diversity (Christensen 1988; McKenzie et al. 2004). These shifts in distributions of plant species may have large impacts on many aspects of ecological diversity and function (Peters and Lovejoy 1992; Miller 2003).