Effects of a spruce beetle (Coleoptera: Scolytidae) outbreak and fire on Lutz spruce in Alaska

The spruce beetle, Dendroctonus rufipennis (Kirby), has had a major effect on the spruce forests of southcentral Alaska. In one area of the Chugach National Forest, 51% of the Lutz spruce, Picea glauca X lutzii Little, or nearly 90% of the commercial stand volume was killed by spruce beetles during a 16-yr period. The majority of the tree losses occurred during the first 10 yr of the outbreak. Tree species composition remained essentially the same after the outbreak. Forest structure changed with decreased tree density, and species richness declined significantly on the unburned, spruce beetle-effected plots. This reduction in plant diversity was probably a result of the significant increase, and competitive advantage, of bluejoint grass, Calamagrostis canadensis (Michaux) Beauvois, and fireweed, Epilobium angustifolium L., in the heavily beetle-effected plots. Although species richness did not change 7 yr after a prescribed fire, species composition did change. Specifically, the occurrence and percentage of bluejoint and fireweed cover significantly increased.