Stand Conditions and Spruce Budworm Damage in a Western Montana Forest

This paper reports the relationship of site quality, crown closure, and percent Douglas-fir (Pseudotsuga menziesii Mirb. [Franco]) to defoliation caused by spruce budworm (Choristoneura fumiferana [Clem.]) on a western Montana forest. Significantly less defoliation was observed on moist bottomland sites than on drier hillsides. Open stands, and stands with low percentage of Douglas-fir also incurred considerably less defoliation than did dense stands and stands composed mostly of Douglas-fir. Silvicultural control of budworm defoliation seems unfeasible on the area studied. Defoliation on good quality sites is not severe enough to warrant such control measures; on poor sites, only undesirably low-stocking levels, or low percentages of Douglas-fir would create a condition having low defoliation risk.