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Climate Inputs to Distribution Modelling

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

  • average winter (Dec/Jan/Feb) temperature
  • average summer (Jun/Jul/Aug) temperature
  • winter (Dec/Jan/Feb) precipitation
  • summer (Jun/Jul/Aug) precipitation
  • precipitation as snow
  • number of frost-free days
  • mean warm month (Jul) temperature
  • mean summer (May-Sep) precipitation
  • mean cold month (Jan) temperature
  • mean annual temperature
  • mean annual precipitation
  • frost-free period
  • degree days above 5° C
  • degree days below 0° C
  • climate moisture index
  • climate moisture index (Jun/Jul/Aug)
  • potential evapotranspiration