With ongoing climate change, the European spruce bark beetle (Ips typographus) represents a growing threat for Norway spruce (Picea abies) forests, causing widespread mortality of trees that in turn causes losses of essential ecosystem services, such as protective function. Understanding the processes predisposing trees to bark beetle attacks is crucial to define correct management guidelines, for preserving forest services and functions. Having an early detection of infested or susceptible trees can allow to identify small- to mid-scale infestations before they escalate into larger outbreaks.
This contribution aims to explore the main predisposing factors to bark beetle infestation at the tree level. At this purpose, forest structural data and increment cores were collected in bark-beetle killed and living stands in mountain protective forests in south-eastern Switzerland, in the canton of Grisons. Particularly, statistical modelling, tree-ring analysis and the comparison of drought responses were combined to have a better overview of bark beetle attack dynamics.
We did not observe significant differences in drought responses between bark beetle-killed and living trees. Furthermore, the models outlined that forest structure variables were the most important predictors of bark beetle-induced mortality. Specifically, trees closer to forest gaps and with lower species mingling in neighbourhood were more prone to bark beetle attack. These findings provide valuable insights to support forest management in mountain protective forests. They suggest that strategies to reduce bark beetle infestations should focus on the spatial arrangement of forest gaps and increasing tree species diversity. This information can help forest managers to identify more accurately high-risk areas, allowing for better resource allocation to prevent larger outbreaks and maintain the protective effect of the forest.