Climate change, mountain pine beetle, and the decline of whitebark pine, a keystone species of high-elevation ecosystems in British Columbia, Canada

Warming climates are expanding the geographic range of mountain pine beetle (Dendroctonous ponderosae) and creating more suitable habitat for beetle populations at higher elevations. This means that whitebark pine (Pinus albicaulis), a keystone species of high-elevation ecosystems in western North America, may be more vulnerable to beetle outbreaks than ever before. Whitebark pine is already in peril due to an introduced pathogen, and mountain pine beetle outbreaks will likely exacerbate its decline.  We used a modelling approach to quantify the effects of climate change on the vulnerability of whitebark pine to beetle outbreaks in British Columbia.  Based on empirical relationships describing the direct and indirect influences of climate on mountain pine beetle persistence, we constructed landscape-wide projections of climatically suitable beetle habitat from 1921 to 2070 using historical weather records and future climate conditions predicted by the CGCM1 global circulation model (assuming a doubling of atmospheric CO₂ by 2100).  These projections were overlayed onto the geographic range of whitebark pine in British Columbia to quantify changes in the distribution of suitable beetle habitat and vulnerability of whitebark pine to beetle outbreaks. We found that warming climates have already increased the risk of whitebark pine to beetle outbreaks.  Furthermore, the climate change scenario derived from CGCM1 suggests that the amount (ha) of whitebark pine at moderate and severe risk to beetle outbreaks will double by 2070.  Such potentially massive losses of whitebark pine will jeopardize the species and have cascading ecosystem impacts.