The Effect of Time and Forest Disturbances on the Structural and Functional Characteristics of Fisher (Pekania pennanti) Resting Structures

Abstract

The fisher is a mammalian carnivore that chooses resting locations each day. Refugia are essential, thus most of the fisher's resting locations are cavities in large live or dead trees. Tree growth and decomposition influence the creation of cavity-bearing structures, which may take centuries, but they can be lost to fire or harvest in an instant. Thus, the conservation of the fisher relies on an equilibrium between the loss of structures via disturbance and their creation. In the mid-1990s we studied fisher resting habitat by following radio-marked individuals to their resting locations. In 2016, roughly 20 years later, we assessed the risks that the resting structures were exposed to by overlaying the perimeters of fires and tree harvest units on the location of 192 resting structures. We also assess the effect of disturbance by examining 36 of them in the field. The mean distance from a resting structure to the nearest harvest unit was 651 m, with 16.8% estimated to be within a harvest unit. The mean distance of the resting structures to the nearest fire was 635 m with 51.0% estimated to be within a fire. Of 36 resting structures that were reevaluated or relocated in the field, 16 (44.4%) were of questionable use in 2016. Based on GIS analyses of disturbance coupled with field data on relocated structures, approximately 15–25% were potentially usable after 20 years. Managers planning actions should consider this a background level of loss of resting structures over 20 years—a background against which additional vegetation management can be considered.