Snow and avalanche: the influence of forest on snowpack stability

Snow avalanches are among the most important disturbances that affect mountain ecosystems, influencing forest dynamics, establishment and mortality processes. At the same time, forests can affect the likelihood of avalanche release and can thus protect human settlements and infrastructures. The forest protective role is largely a function of forest stand structure, snow characteristics and topography. Starting from winter 2003/2004 the snowpack evolution within forested areas of the Aosta Valley (Italy) has been monitored, in order to increase the present knowledge on complex relationship between forest and snowpack. Since 2005, a specific research was carried out focused on detection and analysis of those avalanches that released within forested areas. First, an analysis of the Regional Avalanches Cadaster of the Aosta Valley was done to determine the number of avalanches, about 5 %, with a starting zone located into forested areas. Afterwards, 15 sites were chosen to compare forest characteristics with neighbouring areas located at same altitude, aspect and slope, where no avalanches occurred. The resulting data were used to evaluate the minimum requirement for selected parameters (e.g. tree density, basal area, canopy cover) that a forest must have in order to supply the protective function with respect to avalanche release and snowpack conditions derived from Avalanches Bulletin of Aosta Valley. By increasing the current data-base, it might be possible to relate forest structural characteristics to the reduction of snowpack instability. As defense measure from avalanches, in some cases it should be preferable to use sustainable practices such as suitable silvicultural approach instead of traditional and permanent defence structures.