Responses of mustelids and small mammal prey to combined retention on clearcuts: Woody debris, green trees, and riparian structures

Abstract

Small mustelids such as the American marten (Martes americana) and short-tailed weasel (Mustela erminea) are important furbearers in temperate and boreal forests and are negatively affected by clearcutting. A major prey species, the southern red-backed vole (Myodes gapperi), also disappears from clearcuts and does not return to abundance levels of uncut forest for many decades. We tested the hypotheses (H) that on newly clearcut sites, (H1) the presence of small mustelids, (H2) abundance, species richness, and species diversity of the forest-floor small mammal community, and (H3) reproduction of the major species: M. gapperi and the deer mouse (Peromyscus maniculatus), would be greater on sites with combined retention treatments of woody debris piles, riparian, and green-tree retention than on sites with no retention. A fourth hypothesis (H4) predicted that the above response variables on sites with combined structural retention would be comparable to or higher than those in uncut old-growth forest. Mustelid presence and populations of forest-floor small mammals were sampled on five replicated (n = 4) treatment sites from 2017 to 2020 in south-central British Columbia, Canada.Mean presence (index of activity patterns) of mustelids was statistically similar among sites but in the combined treatments was 1.4 to 2.9 times higher than that in the dispersed (no retention) and uncut forest sites and was likely biologically important. Mustelid presence was particularly evident in the debris piles and riparian sites. Mean abundance of M. gapperi was 11.1 to 16.6 times higher in the combined retention and uncut forest sites than the dispersed sites. Mean abundance of P. maniculatus was higher in the dispersed than uncut forest, but similar in the combined retention to these treatments. Mean total abundance, species richness, and species diversity of eight small mammal species were all higher (1.3 to 1.6 times) in the combined retention sites than the dispersed and uncut forest sites. Although not formally significant (P = 0.08), results for mustelid presence tended to support H1 that these small carnivores would occur more frequently on sites with combined structural treatments than the dispersed and uncut forest sites. The overall high total numbers (and species richness and diversity) of small mammal prey species supported H2 that abundance would be greater on sites with the combined retention than on the dispersed sites with no retention. Reproduction and survival followed the pattern of abundance for the major species, and hence H3 was supported. Higher mean total abundance in combined retention sites than in uncut forest supported H4 in 2017–2018 but not in 2019–2020 when an influx of generalist species increased total abundance in the dispersed sites. This study is the first to measure the responses of small mustelids and small mammal prey species to combined structural retention. One or more of these retention treatments is highly recommended during most harvesting regimes in these forests.