Anna Maria Jönsson

For exploring forest performance in the future, dynamic vegetation models are important tools. Tree mortality is a crucial process in these models, but explicit representations of major agents of mortality have often been relatively underdeveloped. In needle-leaved forest in the temperate and boreal zones, bark beetles are often important for the mortality pattern. The European spruce bark beetle (SBB, Ips typographus) has, in recent years, replaced wind as the most important disturbance agent in European forests. Historically, SBB damage is typically triggered by wind storms as they create breeding material with no defences to overcome for the beetles. Drought can contribute to increased damage and prolonged outbreaks by lowering the defence of the trees, but it has also been the main ultimate driver of some of the European forest damage by bark beetles in the last decade. In this study we implemented an SBB damage module in a dynamic vegetation model (LPJ-GUESS) that includes representation of wind damage and forest management, with the aim to present a general concept that can be used for other bark beetle species as well. The module was calibrated against observations of storm and SBB damage in Sweden, Switzerland, Austria and France. The model was driven by SBB phenology, drought, storm felled spruce trees and a dynamic beetle population density. The model was able to catch the start and duration of outbreaks triggered by storm damage reasonably well, but with discrepancies in levels which can be at least partly related to salvage logging of storm felled forest and sanitary cutting of infested trees. The model showed increased damage in the most recent years with warm and dry conditions, although below the level reported, which may suggest that the drought response of spruce in LPJ-GUESS is underestimated. The new model forms a basis to explore vulnerability of European forests to spruce bark beetle infestations.