Towards an improved understanding of bark beetle and other insect herbivore infestation in conifer forests

European forest ecosystems are increasingly exposed to stressors such as storm, drought episodes and mass attack of forest insect pests. Sustainable forest management requires a fundamental understanding of causal relationships between forest structures and the occurrence of disturbance events, as well as a well-functioning transfer of scientific knowledge into practice. Risk or predisposition assessment, phenological models or prediction of deficits in stand water supply can serve as decision support for prophylactic and protective measures in forestry. This overview addresses the theoretical approaches to insect pest-related mortality in forests that form the basis for such models. Many insect herbivore species benefit from increased temperatures and drought. For example, there is a clear correlation between bark beetle infestation and summer temperatures, storm damage and precipitation deficits. Drought stress is one of the main factors predisposing conifer forests to bark beetle infestation and significantly impacts interactions among Picea abies, Ips typographus and its associated ophiostomatoid fungi. A multi-year study focused on the effects of drought on the defence capacity and attractiveness of Norway spruce to I. typographus. The empirical dataset gained in field and laboratory experiments provides new insights into defence responses of this important tree species against biotic infestations under drought.