Long-term demographic changes of deer mouse (Peromyscus maniculatus) populations in a forest landscape with cumulative clearcutting

Abstract

The deer mouse (Peromyscus maniculatus) is a generalist species and is widespread among the various early-successional forest habitats associated with post-clearcut landscapes. Deer mice seem to occupy clearcuts more than undisturbed late successional forest, at least for abundance, because harvested sites apparently act as dispersal sinks. We investigated the responses in abundance of P. maniculatus populations to cumulative clearcutting of coniferous forests on a landscape that had four independent clearcutting events (Periods 1 to 4) over a 42-year interval from 1979 to 2020 in south-central British Columbia, Canada. We tested three hypotheses (H) that populations of P. maniculatus would (H1) increase in abundance owing to the ongoing availability of early seral post-harvest habitats associated with cumulative clearcutting; (H2) have higher mean abundance, reproduction, and survival in clearcut than forest sites owing to greater food resources; and (H3) occupy clearcut sites as dispersal sinks thereby having lower adult body mass (a proximate measure of condition) and reduced reproductive output than in forest sites.Mean annual abundance of P. maniculatus was highest and similar in Periods 2 and 4 with comparable numbers in Period 1 for the first four post-harvest years of these clearcutting periods. This pattern did not support H1 that P. maniculatus would increase in abundance associated with cumulative clearcutting over the 42-year period. Deer mouse populations reached relatively high densities (range of 23 to 53 per ha) on clearcut sites and these irruptions were likely related to supply of lodgepole pine seed from cones in logging debris. Overall mean abundance of P. maniculatus ranged from 1.4 to 3.6 times higher in clearcut than forest sites, thereby supporting the abundance part of H2. Recruitment, number of successful pregnancies, and breeding young-of-the-year deer mice were all higher in clearcut than forest sites, thereby supporting the reproduction part of H2. However, equivocal measures of overall survival did not support this hypothesis. The general similarity in mean body mass of adult mice between treatment sites and higher reproductive output in clearcut than forest sites did not support H3 that clearcut sites would act as dispersal sinks for deer mice. This study is the first to measure the long-term demographic responses of deer mice to cumulative clearcutting over a coniferous forest landscape. Clearcut sites may provide high-quality habitat for deer mice in this forest landscape.