Item: Avalanche starting zones below the timber linestructure of forest
Title: Avalanche starting zones below the timber linestructure of forest
Proceedings: Proceedings of the 1992 International Snow Science Workshop, Breckenridge, Colorado, USA
Authors: Martin Schneebeli and Martin Meyer-Grass
Abstract: Avalanches starting in small clearings of forests are not uncommon in Switzerland. Forests covering steep slopes are the main means to shelter roads and buildings from the adverse effects of avalanches. It is therefore of great interest which density of trees and maximal size of clearings are permissible. During the winters 1986 to 1991 most of the avalanches starting below the timber line in the Swiss alps have been surveyed. The survey is looking at the topographic features of the starting zone using high resolution topographic maps, the snow profile at the crown of the avalanche, the weather conditions from the moment of the release five days backward, and a detailed measurement of the forest structure within the starting zone and a the same measurements in the immediate vicinity of the starting zone. In total more than 50 parameters are measured. The statistical evaluation shows the importance of tree density and size of clearings for avalanche release. The different tree communities are not equally efficient in preventing avalanches. This difference is difficult to influence, because it is caused by the local climate and soil type. In the zone with mixed stands of the evergreen spruce (Picea abies) and the deciduous larch (Larix larix) as well as in pure larch stands the density of the trees seems to be of greater importance than the species. Unfortunately, most pure larch stands are dispersed, which may lead to the impression that they are worse than evergreen trees.
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Keywords: starting zone, release, density
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