SILVICULTURAL USE OF HERBICIDE IN SUB-BOREAL SPRUCE FOREST - IMPLICATIONS FOR SMALL MAMMAL POPULATION-DYNAMICS

Vegetation management in northern coniferous forest ecosystems may hav e implications for small mammal communities. This study was designed t o test the hypothesis that herbicide-induced habitat alteration would reduce small mammal populations in early-successional stages of sub-bo real spruce forest. A secondary objective was to determine the long-te rm influence of herbicide treatment on reproduction, survival, and gro wth attributes of deer mouse (Peromyscus maniculatus) and southern red -backed vole (Clethrionomys gapperi) populations. Small mammal populat ions were intensively sampled in 4 pairs of control and treatment site s dominated by early-successional vegetation (5-10 yr after clearcut h arvesting) near Prince George, British Columbia, Canada. Sampling was conducted during 1987 (pretreatment year), 1988-89 (first and second p osttreatment years), and in 1991-92 (fourth and fifth posttreatment ye ars). Higher mean numbers of red-backed voles (P = 0.03) and shrews (S orex spp.; P = 0.001) were present on control than treatment sites dur ing 1988-92. Mean abundance of meadow voles (Microncs pennsylvanicus; P = 0.69) and deer mice (P = 0.20) were similar on control and treatme nt sites throughout the study Short-tailed weasels (Mustela erminea) a nd long-tailed weasels (Mustela frenata) were commonly captured on bot h control and treatment sites. There were no consistent differences be tween control and treatment populations in body mass, total biomass, o r proportion of adult male and female red-backed voles and deer mice i n breeding condition. However, there was a higher mean number of succe ssful pregnancies in control than treatment populations of red-backed voles (P = 0.02) but not deer mice (P = 0.18) during posttreatment yea rs. Mean Jolly-Seber estimates of survival of red-backed 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 herbi cide treatment were well within the mean values of natural fluctuation s of these variables. Herbicide treatment of areas dominated by early- successional vegetation in northern coniferous forests should be stagg ered in time and space to allow recovery (2-3 yr) of vegetation and sm all mammal species such as red-backed voles and shrews.