Townsend's chipmunk populations in Douglas-fir plantations and mature forests in the Oregon Coast Range

Abstract

Despite the abundance and ecological importance of Townsend's chipmunks (Tamias townsendii) in coniferous forests in the northwestern United States and southwestern Canada, little is known about either the habitat associations of the species or the influence of forest structure on population density. We livetrapped chipmunks in three mature, fire-regenerated coniferous forests (>140 years old) and nine 10- to 35-year-old Douglas-fir plantations in the Oregon Coast Range to examine patterns of their population density and habitat associations. Estimations of density of chipmunk populations among stands ranged from 0.0 to 23.8/ha. Population density within a stand did not significantly change between autumn and spring. Population density, mean maximum distance moved, and sex ratio did not differ significantly between young and mature stands, although mean body mass of chipmunks in mature forests was greater than mean body mass of those in young stands during autumn. Chipmunk population density was correlated with the percentage of salal (Gaultheria shallon) in the understory, suggesting that forest stand structure plays an important role in determining habitat quality for this species. Habitat characteristics in the Oregon Coast Range are highly favorable to Townsend's chipmunks, probably because of mild winters, high rates of primary production, structural characteristics of the stands, and minimal competition from other species of sciurids.