Changes in tree community composition within high elevation whitebark pine stands following mountain pine beetle (Dendroctonus ponderosae) outbreaks

Whitebark pine, Pinus albicaulis, is a keystone species of high elevation ecosystems throughout western North America.  Aerial detection surveys have documented increasing mortality throughout central Idaho and ground observations estimate that in some areas, up to 90 percent of the whitebark pine overstory has been killed.  Two of the primary biotic agents that are causing tree mortality are white pine blister, Cronartium ribicola, and mountain pine beetle, Dendroctonus ponderosae.  To document stand composition before beetle outbreaks for comparison with the species composition of tree community regeneration, we surveyed thirty-two whitebark pine stands on five National Forests in Idaho, Montana and Wyoming that had recent outbreaks of mountain pine beetle.  All surveyed stands show the impact of mountain pine beetle activity and there were varying levels of blister rust occurrence across the sites.  Overstory and understory stand composition varied greatly across the sites.  Based upon composition of the understory tree community, some stands appear to be retaining a high percentage of whitebark pine while others appear to be having whitebark pine replaced by tree species such as subalpine fir.