Small mammals and stand structure in young pine, seed‐tree, and old‐growth forest, southwest canada

Alternative silvicultural systems to clearcutting are receiving considerable attention in Pacific Northwest forests of North America. Understanding the implications of these harvesting systems on stand structure and biodiversity through time is a fundamental aspect of forest ecosystem management. This study was designed to test the hypothesis that diversity of stand‐structure attributes and forest floor small‐mammal communities will increase from young pine to seed tree to old‐growth forest. The study area was within mixed Douglas‐fir (Pseudotsuga menziesii)–lodgepole pine (Pinus contorta) forests within the Montane Spruce biogeoclimatic zone near Summerland in south‐central British Columbia, Canada. This retrospective study had three replicate stands each of 17‐yr‐old “young pine” (clear‐cut harvested), “seed tree” composed of young pine with Douglas‐fir seed trees, and uncut “old‐growth” composed primarily of Douglas‐fir and lodgepole pine. Stand‐structure attributes (coniferous tree layers and understory vegetation) were measured in each stand. Small‐mammal populations were sampled intensively from 1995 to 1997 in all stands. The mean total percentage cover and crown‐volume index of herbs and mosses were similar among treatment stands, but for shrubs–deciduous trees were highest in young pine and lowest in old growth. Mean species richness of herbs and coniferous trees was similar among treatment stands, but for shrubs–deciduous trees was highest in the young pine. Mean species diversity of herbs and shrubs–deciduous trees was similar among treatment stands, but for coniferous trees was higher in the seed‐tree and old‐growth stands than in the young pine stands. Mean richness of layers of herbs and shrubs–deciduous trees appeared consistently highest in the young pine, but for coniferous trees was highest in the seed‐tree stands. Mean abundance of red‐backed voles (Clethrionomys gapperi) was consistently higher in the old‐growth than in young pine or seed‐tree stands. Mean numbers of Northwestern chipmunks (Tamias amoenus), heather voles (Phenacomys intermedius), western jumping mice (Zapus princeps), montane shrews (Sorex monticolus), and common shrews (S. cinereus) were higher in the seed‐tree or young pine stands than in old growth. Mean abundance of meadow voles (Microtus pennsylvanicus) was highest in seed‐tree stands. Deer mice (Peromyscus maniculatus), long‐tailed voles (M. longicaudus), and short‐tailed weasels (Mustela erminea) had similar mean numbers among treatment stands. Mean species richness and diversity of small mammals was higher in the seed‐tree and young pine stands than in old growth. Each of these stand types offers its own structural diversity to the forest landscape and should help manage for a range of biodiversity goals.