Mammalian responses to windrows of woody debris on clearcuts: Abundance and diversity of forest-floor small mammals and presence of small mustelids

Abstract

Forest harvesting often leaves excess woody debris on the forest floor that could provide habitat for small mammals and mustelid predators. A windrow or series of piles constructed from woody debris may connect patches of mature forest and riparian areas to allow small mammals and some of their predators to use clearcut openings. We tested two hypotheses (H) that woody debris arranged in windrows connecting reserves of uncut forest, on newly clearcut sites, would increase (H1) abundance of the major vole species and total abundance, species richness, and species diversity of the forest-floor small mammal community, and (H2) presence of small mustelids in response to abundance of small mammal prey; compared with sites of dispersed woody debris or uncut forest. We measured abundance and diversity of small mammals and the presence of small mustelids (American marten, Martes americana; short-tailed weasel, Mustela erminea; long-tailed weasel, M. frenata) from 2012 to 2016 in replicated treatments of woody debris in windrow and dispersed sites compared with uncut forest sites at two study areas near Elkhart and Golden in south-central British Columbia, Canada.At Elkhart, mean abundance of total voles and total small mammals per index-line were higher in the windrow than dispersed sites, and higher or similar to forest sites. At Golden, mean abundance of total voles was similar, but the dispersed and windrow sites had higher numbers of total small mammals than the forest sites. Mean species richness and diversity were highest in the windrow sites at both study areas. Thus, the predictions of H1 were supported, except for total voles at Golden. Mean abundance of the southern red-backed vole (Myodes gapperi), a principal prey species for mustelids, was higher in windrow than dispersed sites, and similar or lower than forest sites. M. gapperi, along with the long-tailed vole (Microtus longicaudus) dominated the overall vole population in windrows at Elkhart. M. longicaudus dominated the windrows and dispersed sites at Golden. Deer mice (Peromyscus maniculatus) and northwestern chipmunks (Neotamias amoenus) were at similar numbers in dispersed and windrow sites, but shrews (Sorex spp.) showed a positive response to windrows. Overall mean presence by marten and small weasels were, on average, 3.3–4.8 times higher in windrow than dispersed sites, and higher or similar to forest sites, which supported H2. Our study is the first to connect windrows to patches and larger units of uncut forest and to cover a 5-year period since harvest. Responses in mean total abundance, species richness, and diversity of small mammals in windrows were maintained throughout the 5-year period. This consistent result was likely related to the connectivity between windrows and uncut forests. Strategic management of post-harvest woody debris in a network of windrows or piles will help to maintain abundance and diversity of forest mammals, both predator and prey species, on clearcuts.