Effect of high elevation birch forest on snow stability

Abstract

Forest and especially evergreen conifers like pine and spruce are known to reduce avalanche formation due to their physical anchoring effect and their influence on snow pack layering through changed temperature, radiation, wind speed etc. Research shows that percentage covered by the crown reflects the forests ability to reduce avalanche danger, and crown cover is therefore often used as a measure of the forest's efficiency as protection forest. Crown cover is highest in evergreen conifer forests, but in Scandinavia, the deciduous tree species birch (Betula pubsens, subspecies alpine betula) is the most common tree species in higher elevations near the tree line. This is a small and often thin stemmed, flexible tree. Their crown is thin and field observations show that in avalanche terrain the stems of such trees have a form heavily affected by snow creep and glide and the trees are in many cases bent under the snow cover. Thus, this type of forest does not fulfill the common criteria set for protection forests and its effect on the snow cover is largely unknown. In this study we question whether typical birch forests can reduce the probability of avalanche formation through snowpack effects and anchoring. We look at cases of small avalanches in birch forest, stem densities and snow profiles inside and outside birch forest and compare observations to results from models for calculating anchoring effects.