A Provincial and Regional As sessment of the Mountain Pine Beetle Epidemic in British Columbia: 1999-2008

Abstract

Western Canada is currently experiencing an epidemic infestation of mountain pine beetle (Dendroctonus ponderosae Hopkins). In British Columbia, the infestation extends over more than 13 million ha and has resulted in a wide-range of social, economic, and ecological impacts. In this study, we compile the known environmental drivers of the infestation and assess these drivers against the actual outcomes of the infestation to date. To support our investigation, we defined the population at risk to mountain pine beetle attack as the spatial extent of pine in British Columbia (approximately 525,329 km^2 ) and used a range of driver variables known to influence the location and success of beetle infestations (i.e., proportion of pine, climatic factors, and l atitude adjusted elevation) as inputs to a two-step clustering algorithm. We generated 15 cl usters representing unique combinations of these driver variables. Variables that represent resulting conditions or infestation outcomes (i.e., cumulative amount of pine killed, proportion of pine remaining, distance to nearest infestation, or stand susceptibility) were then used to characterize these clusters and to identify areas of the province with similar drivers, but with different infestation conditions and outcomes. When the entire study area is considered, our findings indicate that th e most susceptible areas of pine in British Columbia were attacked by the beetle fi rst and that heretofore uninfested areas with similar conditions were likely sp ared from infestations initially due to their abundance of im mature pine. However, infestations in less optimal areas increased ma rkedly in 2007 and 2008, as the competition for hosts increased. A regional assessment of the clusters (for areas in the north, cen tral, and southern regions of British Columbia) further indicated that the beetles may have opportunities to expand in northern and central areas-depending on short-term climatic conditions. By relating our current understanding of infestation drivers to the 2008 infestation, we were able to identify those areas of the province that are most vulnerable to continued infestation. Our results confirm that mountain pine beetle will likely continue to be the dominant forest health concern in British Columbia for many years to come.

Keywords: mountain pine beetle, infestation, sp read, susceptibility, 2-step clustering