Release of a thinned budworm-infested Douglas-fir/ ponderosa pine stand.

Abstract

Eighty-yr-old Pseudotsuga menziesii in a thinned stand of mixed conifers in western Montana showed less impact due to defoliation by western spruce budworm Choristoneura occidentalis than firs in an adjacent unthinned stand. Radial growth of thinned fir increased 57%; Pinus ponderosa 38%; whereas unthinned fir grew very slowly. In both stands, radial growth of pine increased substantially, even before thinning, probably because defoliation weakened the competing fir. Thinning may reduce budworm impact by increasing larval mortality, enhancing host tree growth, or stimulating the tree's defensive chemistry.-Authorswestern spruce budworm Choristoneura occidentalis Pseudotsuga menziesii Pinus ponderosa