Climate variables were derived from 4-km monthly climate normals (1961-1990) based on a combination of PRISM (Daly et al. 2002 ) and WorldClim (Hijmans et al. 2005 ) climate data. The western North America portion of these data are described in Wang et al. (2011 ). We used a set of 17 derived bioclimatic variables presumed to adequately summarise boreal climate conditions (see below). Our models were developed for prediction purposes only; we do not intend to interpret the importance of individual climate variables. Thus the correlation among climate variables was not of concern.
Derived bioclimatic variables used in the Maxent models