Estimating woody browse availability for ungulates at increasing snow depths

In northern temperate environments., assessments of ungulate winter range in forested ecosystems commonly focus on measuring availability of browse because the dietary proportion of browse is typically high in winter. In many cases, these efforts ignore reductions in browse availability due to snow burial because this effect is difficult to measure. In this paper, we show how consideration of snow burial can alter the relative availability of browse in 6 forest communities common in the east slopes of the Rocky Mountains of the Alberta, Canada. We developed species-specific allometric relationships of stem diameter and woody twig biomass and height for the common shrub species and used these models to predict the decline in the proportion of total biomass/stem available to ungulates relative to stem height. Based on measures of stem densities, we then compared declines in browse availability for all browse species and for preferred browse species with increasing snow depths. Species compositional differences between forest types influenced the decline in browse availability as snow depth increased. Our stem-based approach is more flexible than previous plot-based approaches because it does not assume a distribution in stem heights but uses local information. Adjustments in browse availability are essential in habitat and food selection studies of ungulates where snow accumulates (c) 2005 Elsevier B.V. All rights reserved.