Impacts of mountain pine beetle (Dendroctonus ponderosae) (Col., Scolytidae) infestation on future landscape susceptibility to the western spruce budworm (Choristoneura occidentalis) (Lep., Tortricidae) in north central Washington

Current and future western spruce budworm [Choristoneura occidentalis (Freeman)] hazard was evaluated for a 400 ha (1000 acre) landscape in north central Washington state using computerized growth and hazard-rating models. The landscape has recently suffered extensive overstory lodgepole pine [Pinus contorta (Dougl. ex Loud.)] mortality due to a mountain pine beetle [Dendroctonus ponderosae (Hopkins)] infestation. To evaluate the impact of this lodgepole pine mortality on future susceptibility to western spruce budworm outbreaks, computer simulations in which overstory lodgepole pine was retained or removed were compared. Susceptibility to western spruce budworm attack increases more rapidly and intensely with overstory lodgepole pine mortality. Additional scenarios included silvicultural treatments to reduce stand density and alter species composition. Results suggest that a variety of management options are available to reduce landscape-level western spruce budworm risk.