Quantifying the probability of bark beetle induced damage in central German Norway spruce forests

Norway spruce ( Picea abies ((L.)H.Karst) ) is a tree species of great relevance to central and northern European forests and forest management, mainly due to its production potential and its natural dominance on certain higher altitude and latitude sites. However it is also prone to abiotic and biotic disturbances, frequently leading to economic damage and management challenges. Storms, bark beetles and droughts, in particular, contribute to such events. The European Spruce Bark Beetle ( Ips typographus (L.) ) has expanded its range, caused large scale disturbances in recent years and is predicted to further expand its range and damage potential due to climate change. Recent outbreak events are questioning the viability of spruce as a dominant forest tree species across central Europe. In order to investigate the probability of bark beetle induced damage occurrence and its contributing factors in the predominantly secondary spruce stands in central Germany, we developed a model based on forest management and environmental data. The predictor variables comprise stand, soil and climate quantities as well as information on previous damage. We combined a large empiric data basis with the restrictive application of prior knowledge to ensure ecological plausibility, which enhances the potential of generalization. Our results indicate a limited mitigation potential of several proposed silvicultural counter measures in relation to the estimated impact of climate factors. The model will be used to evaluate and map the current and future risk of bark beetle induced damage in spruce stands, which can aid forest management in the prioritization of counter measures and tree species selection.