Snow forces on forest plants due to creep and glide

Snow forces impede afforestation in the subalpine region; in particular juvenescent trees can be damaged by extraction from the ground. Such forces are mainly triggered by intense snow gliding which is a frequent phenomenon on slopes with a smooth ground surface.In this article we have investigated the effects of snow gliding processes on forest plants. The study area was situated on a south-facing slope (altitude 1900 m, inclination 30°) in the Stubai valley, Tyrol, Austria. The site is characterized by a smooth ground surface (stagnation depth of about 10 m) and high glide rates leading to a great number of damaged plants almost every winter season.The investigations included snow gliding measurements and experiments to determine those forces which are necessary to uproot juvenescent trees from the ground. The experiments were carried out on Swiss stone pine and larch trees with a height of 0.6–0.9 m (diameter 0.02 and 0.045 m).Our measurements revealed glide rates of up to 46.5 mm d−1 and forces between 1000 and 3500 N as sufficient to uproot juvenescent trees.The downslope force was determined by the applicable snow pressure equations and compared with the results of our experiments. The investigations show that the calculated values are in close agreement with those measured on the plants. Provided that an impact of 50% of the measured forces will no longer result in damage to the trees (extraction or breakage), we calculated that the stagnation depth has to be reduced to about 1.5 m.