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Snow Avalanches in Forests of the Swiss Alps
Reference
Teich, M., Marty, C., Gollut, C., Gret-Regamey, A. and Bebi, P. 2012. Snow and weather conditions associated with avalanche releases in forests: Rare situations with decreasing trends during the last 41 years. Cold Regions Science and Technology 83-84: 77-88.

Background
The authors write that "so-called 'forest avalanches' are important disturbances that affect mountain ecosystems and can pose substantial hazard to human settlements and infrastructures as well as to the forest cover itself (Bebi et al., 2009)," adding that "the assessment of avalanche activity under changing climate conditions is also an important issue with respect to risk management in the future (Martin et al., 2001)."

What was done
In their study of both new snow forest avalanches, which release in periods of heavy snowfall and under stormy and permanently cold conditions, as well as old snow forest avalanches, which release after periods of high insolation and an increase in air temperature, Teich et al. analyzed 21 different snow and weather variables associated with 189 naturally-released forest avalanches that occurred in the winters between 1985/86 and 2005/06, which events were evenly spread across the Swiss Alps and over elevations ranging from 700 to 2200 meters above sea level, after which they tested for long-term trends in the occurrence of favorable meteorological conditions for both sets of forest avalanches during a total of 41 winters (1970/71-2010/11).

What was learned
The five Swiss researchers report that "the number of potential forest avalanche days decreased at 11 of 14 snow and weather stations [79%] in the Swiss Alps for new snow forest avalanches and at 12 of 14 stations [86%] for old snow forest avalanches, independent of elevation and climatic region."

What it means
In the words of Teich et al., "these negative trends suggest a further decrease of snow and weather conditions associated with avalanche releases in forests under current climate change." And they add that "in combination with the currently observed increase in forest cover density in the Swiss Alps (Bebi et al., 2001; Brandli, 2010; Krumm et al., 2011), it is thus likely that avalanche releases in forested terrain will become less frequent in the future."

References
Bebi, P., Kienast, F. and Schonenberger, W. 2001. Assessing structures in mountain forests as a basis for investigating the forests' dynamics and protective function. Forest Ecology and Management 145: 3-14.

Bebi, P., Kulakowski, D. and Rixen, C. 2009. Snow avalanche disturbances in forest ecosystems - state of research and implications for management. Forest Ecology and Management 257: 1883-1892.

Brandi, U.-B. 2010. Schweizerisches Landesforstinventar. Ergebnisse der dritten Erhebung 2004-2006. Birmensdorf: Eidgenossische Forschungsanstalt fur Wald. Schnee und Landschaft. Bundesamt fur Umwelt, Wald und Landschaft, Bern, Switzerland.

Krumm, F., Kulakowski, D., Spiecker, H., Duc, P. and Bebi, P. 2011. Stand development of Norway spruce dominated subalpine forests of the Swiss Alps. Forest Ecology and Management 262: 620-628.

Martin, E., Giraud, G., Lejeune, Y. and Boudart, G. 2001. Impact of a climate change on avalanche hazard. Annals of Glaciology 32: 163-167.

Reviewed 27 February 2013