Green-tree retention and recovery of an old-forest specialist, the southern red-backed vole (Myodes gapperi), 20 years after harvest

Abstract

Context Populations of many mammalian species are reduced as a result of clearcutting, despite the concurrent objectives of wood production and conservation of mammal diversity on cutover forest land. To help ameliorate this decline, green-tree retention (GTR) leaves large live trees after harvest to provide mature forest habitat and increase structural diversity of the regenerating stand. Aims To test the hypotheses (H) that, at 20 years after harvest, (H1) abundance, reproduction and survival of the southern red-backed vole (Myodes gapperi), as well as (H2) abundance and species diversity of the forest-floor small mammal community, would increase with the basal area (BA) and density of residual trees after harvest. Methods Small mammals were live-trapped in 2015–16 in replicated clearcut, dispersed retention, aggregated retention, patch cut and uncut forest sites in mixed forests of Douglas fir (Pseudotsuga menziesii var. glauca) and lodgepole pine (Pinus contorta Dougl. var. latifolia) in southern British Columbia, Canada. Key results Mean BA and density of overstory coniferous trees were significantly different at 20 years post-harvest, being higher on patch cut and uncut forest sites than on the clearcut and GTR sites. M. gapperi populations were significantly greater in aggregated retention and uncut forest sites than in the other sites, but demographic parameters were similar among sites, and therefore H1 was partly supported. Mean total abundance of small mammals differed significantly among sites, with the highest overall numbers occurring in the aggregated retention (16.2), clearcut (13.6) and uncut forest sites (11.9). Mean species richness and diversity were highest in the GTR and clearcut sites. Thus, H2 was not supported. Conclusions Recovery of M. gapperi in aggregated retention sites with 10m2 ha–1 BA of residual trees, as a group, occurred at 20 years post-harvest. Implications Aggregated retention of residual trees should help provide some habitat to conserve forest mammals on harvest openings, but successional development up to 20 years post-harvest may be required.