ABSTRACT
The post-outbreak forest is less dense and more diverse, and surviving trees are more productive than in the pre-outbreak forest. Although dead trees increase the risk of subsequent fire until the dead trees fall and decompose, the post-outbreak forest typically is more sustainable under prevailing environmental conditions. The spruce beetle, Dendroctonus rufipennis, is the most important mortality agent in spruce forests in Canada and Alaska, as well as high elevation forests through the Cascade Range and Rocky Mountains. The eastern spruce budworm, Choristoneura fumiferana, is one of the most destructive defoliators in spruce and fir forests of eastern North America. The related western spruce budworm, Choristoneura occidentalis, is the most widespread and destructive defoliator of coniferous forests in western North America. The fall webworm, Hyphantria cunea, is native throughout continental USA, southern Canada and northern Mexico. It has been introduced accidentally into many parts of Europe and Asia.
