Ghost Forests, Global Warming, and the Mountain Pine Beetle (Coleoptera: Scolytidae)

The mountain pine beetle, Dendroctonus ponderosae Hopkins, is a significant ecological force at the landscape level. The majority of the life cycle is spent as larvae feeding in the phloem tissue (inner bark) of host pine trees. This feeding activity eventually girdles and kills successfully attacked trees (Amman and Cole 1983, Furniss 1997). Outbreaks of this insect can be truly spectacular events (Fig. 1A; Amman and Logan 1998). Most western pines are suitable hosts for this insect, but ponderosa pine, Pinus ponderosae Lawson, and lodgepole pine, Pinus contorta Douglas, currently are the most important host species. The distribution of the beetle generally reflects this primary host range, although lodgepole pine extends further north and ponderosa pine extends further south than the current geographic range of the beetle. The mountain pine beetle is a native insect, having co-evolved as an important ecological component of western pine forests. The inter-relationship between beetle-caused mortality and subsequent fire has resulted in a basic ecological cycle for many western forests (Schmidt 1988).