Site and Stand Characterists
USDA Forest Service, Technical Bulletin
Outbreak of western budworm occur over a wide geographic range, and populations are successful from warm, dry interior Douglas-fir types to cool, moist subalpine fire/spruce types. This wide distribution across environmental gradients and forest types could simple suggest that the budworm has broad adaptability. Outbreak frequency and infestation intensity vary considerably, however, which suggests budworm populations may be responding to an ecological similarity that exists among these seemingly diverse habitats. The common feature appears to be physiological stress in host trees.
Wulf, N. and Cates, R. (1987). Site and stand characterists. In: MH Brookes et al. (eds) Western Spruce Budworm, pp. 90-115. USDA Forest Service, Technical Bulletin 1694.