From calamity to infestation: linking windstorm tree damage to bark beetle outbreak through forest structure and meteorological analysis

Abstract

In recent years, we have witnessed worldwide, an increase in natural forest disturbances, particularly windstorms, which have caused significant direct and indirect forest damages, often triggering largescale bark beetle outbreaks. In this study, we investigated the interaction between windstorm-induced tree damage and subsequent bark beetle outbreaks in the northeastern Italian Alps (Province of Belluno and Bolzano), focusing on the 2018 Vaia windstorm and the successive bark beetle infestation started in 2021. Additionally, we aimed to determine whether this potential correlation is influenced by forest structural characteristics such as forest height heterogeneity (HH), forest density, and forest mean height using LiDAR data, or by meteorological factors (mean temperature and cumulative precipitation) through in-situ spatialized information. Our research findings, based on a methodology centered on spatial interactions, indicate a potential link between the bark beetle outbreaks and the windstorm event Vaia occurred three years before. Our results suggest that forest structural variables are, in most of the cases, significantly similar across all areas affected by the bark beetle. This similarity is observed both in forests impacted by the Vaia windstorm and in other Picea abies forests not affected by the windstorm, indicating that these forest structural variables may not be a trigger for the bark beetle outbreak. Our findings do not show a clear and consistently significant difference in meteorological conditions. This variability can be attributed to the specific areas affected by the Vaia windstorm, which are predominantly mountainous regions characterized by distinct temperatures and precipitation compared to the rest of the provinces. When analyzing the combined influence of structural and meteorological variables in both study areas, our results indicate that none of these factors were ultimately significant predictors of the interaction between bark beetle infestations and areas affected by the Vaia windstorm. Our study suggests that, as climate change increases the frequency and severity of these disturbances, adaptable forest management framework to enhance forest resilience and sustainability are needed, helping forests to better withstand and recover from future natural disturbances.