Long-term responses of ecosystem components to stand thinning in young lodgepole pine forest: II. Diversity and population dynamics of forest floor small mammals

Abstract

A variety of silvicultural practices may be used to diversify second-growth forests that have regenerated from clearcut harvesting. These young stands are structurally simple and amenable to practices such as variable-density and conventional thinnings to accelerate ecosystem development. This study was designed to test the hypotheses that (i) abundance and diversity of forest floor small mammals, and (ii) population dynamics (reproduction, recruitment, and survival) of the southern red-backed vole ( Clethrionomys gapperi) would be maintained at levels recorded in old-growth forest, by large-scale thinning to various densities in young lodgepole pine ( Pinus contorta) forest. Replicate study areas were located near Penticton, Kamloops, and Prince George in south-central British Columbia, Canada. Each study area had three stands thinned to densities of ∼500 (low), ∼1000 (medium), and ∼2000 (high) stems/ha, with an unthinned young pine and old-growth pine stand for comparison. Forest floor small mammal communities were sampled intensively in 2000, 2001, and 2002 at 12–14-years after the pre-commercial thinning treatment. Mean total abundance of small mammals was similar among stands with the highest overall numbers recorded in 2002. Mean species richness and diversity of small mammals were similar among stands. Mean abundance of C. gapperi was similar among stands and increased significantly with time. This pattern of abundance of C. gapperi will likely be consistent except perhaps in years of high numbers when productivity of this species may be highest in old-growth forest. Reproduction, recruitment, and early juvenile survival of C. gapperi was similar among stands; Jolly–Seber summer survival was higher in the thinned than unthinned stands with no difference in winter survival among stands. Our results supported hypotheses (i) and (ii) that abundance and diversity of forest floor small mammals and the demographic attributes of C. gapperi populations would be maintained in young managed lodgepole pine stands (thinned or unthinned) at levels recorded in old-growth forest.