Framework for assessing the windthrow risk to Norway spruce forests in Switzerland

If forests are to satisfy all our demands in the long term, then they must be managed purposefully. Disturbances that could jeopardise the provision of ecosystem services occur repeatedly. To better deal with these disturbances, knowing what damage and consequences can occur is important. In Switzerland, storms are the biggest large-scale disturbances in forests. No simple framework exists to characterise storm risk to forests. In this work, an extreme value statistic was used to generate a frequency-intensity distribution of storms. In addition, a correlation between gust peaks, i.e. intensity, and quantitative damage, i.e. consequence, for different tree heights of Norway spruce was constructed based on a relationship between tree height and damage percentage found by Schmidt et al. (Can J For Res 40:1636-1652, 2010). The combination of the two resulted in a frequency-consequence distribution. Although many uncertainties still exist due to sparse loss data and lack of long measurement series, this study provides a framework that can be used for risk assessment. The resulting expected damage can be used to study the effects on forest development and to optimise forest management accordingly.