Snow avalanche release in forest ecosystems: A case study in the Aosta Valley Region (NW-Italy)

Snow avalanches are among the most important disturbances that affect mountain ecosystems, in fl uencing forest dynamics, establishment and mortality processes. At the same time, forests can affect the likelihood of avalanche release and can, in some cases, protect human settlements and infrastructure. Yet, since the ability of a forest to protect settlements is largely a function of its stand structure and composition, snow characteristics and topography, under particular conditions, avalanches can be triggered in forested areas. The aim of this work is to identify forested areas in the Aosta Valley (NW Italy) where at least an avalanche release occurred and to determine, through case studies, the main forest features that may prevent an avalanche release. Based on analysis of the regional avalanches cadastre, 5.4% of all the recorded avalanches released from a forested area. A sample of 15 avalanche sites with a release zone within a forested area was chosen, to compare the structural characteristics with neighboring forested areas located at the same altitude, aspect and slope, where no avalanches occurred. Most of the avalanches released at the end of winter and in the early spring, during periods when the danger level was equal or higher than 3- considerable. In our case studies, stem density (stems/ha) was the most important factor for snowpack stabilization, while the shrub canopy cover increased the probability of avalanche release. By enlarging the current database, it might be possible to relate forest structural characteristics to the snowpack structure, and consequently to avalanche release. In some cases, it might be preferable to use sustainable practices, such as suitable silvicultural approach, instead of permanent defense structures (less ecologic and often more onerous) in order to achieve a satisfactory avalanche protection.