Windstorm disturbance effects on forest structure and black bear dens in southeast Alaska

We examined the relationships among forest susceptibility to windstorm damage, forest structure, and black bear winter den site selection in the coastal temperate rain forests of southeastern Alaska, USA. Forest susceptibility to maritime windstorms was determined by applying a wind-disturbance model (WINDSTORM) to two study areas where bear dens had been identified by radio telemetry. We evaluated model predictions for forest structure against field data for one study area. As predicted, forests in wind-protected landscapes contained features indicative of later stages of forest development where larger and older trees are more abundant. By contrast, forests located in storm-susceptible locations contained higher tree densities, less variation in tree diameters, smaller trees, and less evidence of large, old trees with heart rot. Analysis of habitat use relative to its availability on the landscape indicates that bears selected wind-protected landscapes over storm-prone landscapes in both study areas for winter dens. The majority (58%) of den sites were located in forests most protected from catastrophic storm effects. By contrast, only 6% were located in forests most exposed to storm damage. Results suggest that forests most protected from catastrophic windstorm disturbance contain more suitable overwinter habitat for black bears as evidenced by den site selection.