Black Bears Select Large Woody Structures for Dens in Southeast Alaska

Abstract

Timber interests target coastal temperate rainforests, and within them stands composed of large trees potentially selected by American black bears (Ursus americanus) for denning. We identified the location of 75 black bear dens (used ≥14 days) in an intensively logged area on Prince of Wales Island, Alaska, USA. We ground‐visited a subset (n = 43) of these sites to measure the diameter of living trees and woody structures used by black bears for denning. We contrasted dens with random trees available in the study area in a series of models to characterize black bear den selection. All but 1 of 43 ground‐visited dens were located within woody structures, and all but 2 of these structures were >1 m diameter at breast height (dbh). We built resource selection functions (RSFs) to investigate black bear den selection across a range of spatial scales, though estimated selection was generally scale invariant. Black bears strongly selected large‐diameter woody structures (dead or alive) as dens at the home‐range scale, with the estimated relative strength of selection (RSS) for a 2‐m‐diameter tree approximately 166 times that of a 1‐m‐diameter tree. The estimated RSS of logged forest was unexpectedly greater (2.75 times) than that of the remaining commercially valuable old‐growth forest. Selection for den structures within stumps in previously logged stands suggests features of the woody structure may be of greater importance to black bears selecting dens than attributes of the surrounding forest. There was no observed correlation between bear den selection and second‐growth age, indicating that stumps may persist as suitable dens well after logging. Because denning is an important part of their life history and the denning structures used by black bears on Prince of Wales Island will eventually decay, retaining habitat value for bears in areas intensively managed for timber harvest requires strategies to recruit very large, old trees throughout the landscape. © 2021 The Wildlife Society.

Den supplementation for black bears in coastal British Columbia

“…Large western redcedar stumps with sufficiently sized cavities were easily converted into functional bear dens by creating a roof over the internal chamber with plywood. The success of this approach is not unexpected given that black bears have been documented using high‐cut stumps with intact cavities as dens elsewhere on Vancouver Island (Davis 1996) and other areas of coastal North America (e.g., Washington‐Lindzey and Meslow 1976; Alaska‐Porter et al 2021). This method could prove beneficial in areas where low levels of natural den retention has occurred and regenerating trees have not yet grown large enough to form dens.…”

“…Coastal black bears need to select structures for denning that provide protection from potential predators and adverse weather, and, in coastal temperate rainforests, these are usually found in large‐diameter woody structures (Lindzey and Meslow 1976, Noble et al 1990, Davis 1996, Porter et al 2021). On Vancouver Island, black bears establish dens in cavities associated with large‐diameter hollow trees (x̄ = 159 cm dbh) or structures derived from trees (i.e., logs, root boles and stumps), primarily in western redcedar ( Thuja plicata ) or yellow‐cedar ( Callitropsis nootkatensis ) trees (Davis 1996).…”