Beetles, wind, and fire: integrating disturbance predisposition assessments into decision support systems for climate-adapted management of mountain forests

Strategic long-term planning of mountain forests in the European Alps requires a balancing act between sustaining forest biodiversity and ecosystem services (BES) and mitigating disturbance risks, particularly under climate change. In this context, close-to-nature forestry (CNF) is considered an effective strategy to adapt mountain forests to climate change while sustaining BES. However, it remains unclear for forest management whether current CNF strategies sufficiently reduce forests’ predisposition to climate-change-induced shifts in disturbance regimes.

Decision support systems (DSSs) can help address this challenge by integrating climate-sensitive forest modelling with indicator frameworks for evaluating BES provision and disturbance predisposition, including risks from bark beetle infestations and windthrow. These DSS frameworks have proven a flexible applicability across various forest models, spatial scales, forest types, and environmental conditions. However, climate-change-induced changes of disturbance regimes require adaptations of existing DSS frameworks by accounting for emerging disturbance agents, such as forest fires.

To address this complexity, we integrated the forest gap model ForClim with a disturbance predisposition assessment system (PAS) and assessments of BES provision. Specifically, we integrate a novel forest fire predisposition indicator with an established PAS for bark beetle and windthrow disturbances, along with an indicator framework for evaluating BES. Simulations were conducted for a forest enterprise in the Central Swiss Alps, covering a large elevation gradient, under three climate scenarios (historical, SSP2-4.5, and SSP5-8.5) and six management strategies, including CNF variants with different management intensities and climate-adapted approaches.

Our results indicate that climate change will dynamically alter disturbance predisposition across elevation gradients. Site-related predisposition to fire and bark beetle infestation generally increased under climate change, while stand-related predisposition varied with climate scenario and elevation. Under moderate warming (SSP2-4.5), stand-related predisposition to fire and windthrow increased across all elevations. In contrast, under severe warming (SSP5-8.5), long-term reductions in stand-related predisposition to fire, bark beetle infestation, and windthrow occurred at lower elevations due to declining forest productivity, while predisposition increased at higher elevations with improved growing conditions. CNF emerged as a balanced approach for reducing predisposition to bark beetle infestation and windthrow while maintaining BES. However, CNF promoted stand characteristics that increase stand-related predisposition to forest fires. Our results further show that increasing management intensity generally reduces stand-related disturbance predisposition but can also lead to trade-offs, such as reduced BES provision.

We conclude that climate-adapted forest management must account for both stand-related and site-related predisposition to prioritize disturbance-prone ‘hotspots’, especially in areas of high BES value. Proactively reducing disturbance predisposition may involve short-term trade-offs regarding BES provision but may be crucial to avoid larger, long-term BES losses from severe disturbances. Our study underscores the need for decision support systems to support informed decision-making in mountain forest management.