Big, sick, and rotting: Why tree size, damage, and decay are important to fisher reproductive habitat

Abstract

To gain a better understanding of the factors affecting selection of reproductive habitat by female fishers ( Martes pennanti) in boreal mixed-wood forests, we identified structures, sites, and stands used by 12 radiotagged female fishers for reproduction between 2005 and 2009 near Dawson Creek, British Columbia, Canada. We deployed a used-unused design to evaluate the support by the data for a series of candidate models at each scale using information-theoretic inference. All dens occurred in internal cavities in large, diseased, and decaying trembling aspen ( Populus tremuloides; x ¯ DBH = 50 cm , SD = 11, n = 20) or balsam poplar trees ( Populus balsamifera spp. balsamifera; x ¯ DBH = 58 cm , SD = 11, n = 11). Female fishers appeared to select reproductive denning structures based upon the difference between the diameter of the tree (cm) from the mean DBH of trees within the site and whether the tree showed signs of damage and visible signs of decay. At the site scale, selection was positively related to mean DBH of aspen and balsam poplar trees and vertical diversity index, and negatively related to density of hard logs (pieces ha −1). Females selected stands for reproduction based upon mean DBH of trees ⩾15 cm and the position of the stand within their non-denning home range. In the boreal mixed-wood forests of north-eastern British Columbia, reproductive habitat for fishers was strongly linked to infection courts in large, diseased, and decaying aspen and balsam poplar trees. Our data suggests that tree size, damage, and decay play critical roles in the suitability of habitat for reproduction, and forest managers should consider retaining and promoting ecological processes that result in the recruitment of trees with these features if conservation of reproductive habitat for fishers is a concern.