Girdled versus Bark Beetle-created Ponderosa Pine Snags: Utilization by Cavity-dependent Species and Differences in Decay Rate and Insect Diversity 1

Snags are a natural component of forest ecosystems and provide a variety of functions and values to forests and their constituents. Snags provide important feeding substrates, nesting sites, and habitat for a variety of invertebrates and vertebrates, and many of these functions continue after the snag eventually falls and becomes a log (coarse woody debris). Some forest landscapes are thought to be “snag deficient ” for wildlife needs because of the direct action of forest managers or because of natural events such as winter storms or fire. Therefore, it is not unusual for forest managers to desire to create snags by various means. In this study we compared snags created by mechanical girdling (chainsaw) and bark beetle (western pine beetle aggregation pheromone) attack to determine acceptability and suitability to cavity dependent species, tree decomposition characteristics, and insect diversity. After 6 years we have found differences in the rate of deterioration (tree fading rates, branchlet retention, bole failure, top breakage, bark sloughing), woodpecker feeding activity, cavity excavation, and insect diversity. Our data indicate that bark beetle-killed trees provide a more biologically rich snag that is both suitable and acceptable to cavity dependent species.