Windwurf und Borkenkäferepidemien im Alptal nach Vivian und Lothar | Windthrow and bark beetle attacks in the Alptal after the wind storms Vivian and Lothar

After the strong winter storms Vivian (1990) and Lothar (1999), many Swiss forests have been severely infested by bark beetles. Based on detailed forest management information from 28 forest compartments this study tested a set of potential explanatory variables as predictors for the occurrence of bark beetle damage in the Alptal valley (northern Swiss Prealps). For each storm we developed a separate multiple linear regression model. Bark beetle occurrence was measured as the sum of insect-damaged wood within five years after the winter storms. Two predictors (wind-damaged wood during a winter storm and occurrence of adult spruce) explained more than 50% of the variance of bark beetle occurrence. Our results support the idea that windthrow damage is highly conducive to subsequent bark beetle attack of the surrounding forests. Additionally, the occurrence of larger spruce trees (diameter at breast height > 40 cm) explains a significant fraction of the remaining variance of bark beetle occurrence, which underpins the importance of forest age structure for windthrow and insect damage as causes of tree death. Methodologically, our study highlights the value of historical forest management data in the context of ecological modeling.