Increasing storm damage to forests in Switzerland from 1858 to 2007

The most severe damage to forests in Central Europe occurs during winter storms caused by Northern Hemispheric mid-latitude cyclones. Storm events in the winter semesters of the past 150 years were investigated to quantify changes and evaluate whether damage rates, forest properties and climate had changed. Records of damage extent (wind throw/snap/breakage), forest area and growing stock in Switzerland were comparatively analysed. Storm damage (m(3)) was 17 times greater during the period 1958-2007 than during the period 1908-1957 and 22 times greater than in the period 1858-1907. Forest area in Switzerland has increased by 63% and growing stock by 292% over the past 150 years. The significant recent increase in storm damage could only partially be explained by increased growing stock. Weather reports prior to storms indicated that severe storm damage occurred almost always when soils were unfrozen (96%) and wet (96%). During the observation period mean winter temperature has increased by nearly 2 degrees C and winter precipitation has increased by nearly 50% in the study region. In the Zurich region, daily maximum gust wind speed and storm damage were compared. Maximum gust wind speed above 35 m s(-1) was associated with extensive storm damage. Catastrophic storm damage and maximum gust wind speed measured during storms have increased during recent decades. In conclusion, increasing growing stock, warm winter temperature and high precipitation, and even more markedly, increasing maximum gust wind speed have all contributed to the recent increase in windstorm damage to forests. (C) 2009 Elsevier B.V. All rights reserved.