Silvicultural Use of Herbicide in Sub-Boreal Spruce Forest: Implications for Small Mammal Population Dynamics

Abstract

Vegetation management in northern coniferous forest ecosystems may have implications for small mammal communities. This study was designed to test the hypothesis that herbicide-induced habitat alteration would reduce small mammal populations in early-successional stages of sub-boreal spruce forest. A secondary objective was to determine the long-term influence of herbicide treatment on reproduction, survival, and growth attributes of deer mouse (Peromyscus maniculatus) and southern red-backed vole (Clethrionomys gapperi) populations. Small mammal populations were intensively sampled in 4 pairs of control and treatment sites dominated by early-successional vegetation (5-10 yr after clearcut harvesting) near Prince George, British Columbia, Canada. Sampling was conducted during 1987 (pretreatment year) 1988-89 (first and second posttreatment years), and in 1991-92 (fourth and fifth posttreatment years). Higher mean numbers of red-backed voles (P = 0.03) and shrews (Sorex spp.; P = 0.001) were present on control than treatment sites during 1988-92. Mean abundance of meadow voles (Microtus pennsylvanicus; P = 0.69) and deer mice (P = 0.20) were similar on control and treatment sites throughout the study. Short-tailed weasels (Mustela erminea) and long-tailed weasels (Mustela frenata) were commonly captured on both control and treatment sites. There were no consistent differences between control and treatment populations in body mass, total biomass, or proportion of adult male and female red-backed voles and deer mice in breeding condition. However, there was a higher mean number of successful pregnancies in control than treatment populations of red-backed voles (P = 0.02) but not deer mice (P = 0.18) during posttreatment years. Mean Jolly-Seber estimates of survival of red-hacked voles (P = 0.01) but not deer mice (P = 0.70) were higher in treatment than control populations. The magnitude of observed demographic effects from herbicide treatment were well within the mean values of natural fluctuations of these variables. Herbicide treatment of areas dominated by early-successional vegetation in northern coniferous forests should be staggered in time and space to allow recovery (2-3 yr) of vegetation and small mammal species sucl as red-backed voles and shrews.