Development of spruce-fir stands following spruce beetle outbreaks

Logged and unlogged stands of Engelmann spruce-subalpine fir were evaluated in spruce beetle outbreak areas infested about 15, 25, 50, and 100 years ago. Seedling regeneration was generally adequate except in heavily logged areas, although seedlings were often damaged, apparently by animals. Species composition was dramatically altered in favor of fir in the unlogged spruce-fir type. In the overstory, fir may predominate for many years but eventually the spruce will replace it. When the forest reaches a basal area of 150 to 200+ ft2 per acre in predominantly large spruce, the potential for spruce beetle outbreaks increases. Changes in species composition with different intensities of beetle infestations and over several centuries are hypothesized.