Impact of forest management on the future resilience of German Norway spruce (Picea abies (L.) H. Karst) forests to abiotic and biotic threats in the changing climate

Abstract

The impacts of biotic and abiotic disturbances, such as bark beetles and wind storms, on European forests are likely to increase due to climate change, and forest management must adapt accordingly. Productive coniferous tree species, such as Norway spruce, are particularly vulnerable to these effects. Diverse forest management options should allow for divergent trajectories in forest dynamics. In this context, we model the effects of three distinct management strategies under two future climate pathways (RCP 4.5 and 8.5) utilising storm gust speeds at the national scale across Germany from 2020 to 2046. We then integrate a wind storm damage event and a subsequent bark beetle attack with simulated forest growth, to quantify stock losses in Norway spruce forests. We simulate forest growth with the 3-PGmix model, model wind damage susceptibility with the ForestGALES model and calculate the subsequent beetle damage with the IpsR model. To provide a reference point for the national-scale wind damage simulations, an initial reference comparison with a statistical wind damage model, calibrated and validated for south-western Germany, was undertaken, which showed a slightly greater pessimistic trend in the ForestGALES model. Under the future climate, when no damage was considered, the “Standard Thinning” strategy yielded the highest standing and harvested volume, while a height-limited “Adapted Thinning” strategy performed best when wind and bark beetle damage were incorporated. While bark beetle damage rates were identical between “Standard Thinning” and “No Thin” management, the “No Thin” management strategy performed the worst when wind and beetle damage was taken into account, due to its greater standing volume. Therefore, a risk averse management strategy for Norway spruce, to avert the worst effects of climate change and increased likelihood of biotic and abiotic disturbances, is a potentially effective future risk mitigation solution.