Mitigating bark beetle damage in Norway spruce stands: Insights from Belgium's latest outbreak

For several years, Europe has witnessed a significant dieback of diverse forest tree species, and the Norway spruce, a common species across the continent, is no exception. The combination of drought events and bark beetle infestations appears to play a significant role in these widespread diebacks, raising concerns about the future viability of this species in some regions. The Ardenne, located in southern Belgium where spruce is not native, has also experienced significant dieback during the 2017–2022 period. An analysis of the drivers related to spruce bark beetle attacks was performed to better anticipate probable future significant spruce dieback. The available cartographic data describing potential climatic, growth-condition and management drivers influencing these diebacks have been gathered using GIS tools (Geographic Information Systems) and linked with the Norway spruce health map that have been produced using Sentinel-2 satellite imagery from our previous research, helping to identify affected areas. Lidar flights conducted prior to the outbreak provide detailed descriptions of the forest stands. All our analysis were conducted with a huge quantity of cartographic and remote sensing data covering the entire Belgian spruce forest (120,000 ha). A random forest analysis followed by a profile model assessment, was employed to pinpoint the key drivers contributing to dieback. Statistical analysis showed that stands with greater dominant height and closer distance from bark beetle hotspots in previous years were associated with higher dieback intensity. Stands located in bioclimatic zones characterized by low altitude, or those with climatic conditions marked by a summer water deficit (P-ETP) or a more rapid decrease in summer water deficit during the 2010–2021 period, were associated with increased damage in Norway spruce stands. These results were interpreted to propose management guidelines for limiting the impact of future bark beetle outbreaks in spruce stands, which will be increasingly stressed in this century's climate. High-resolution remote sensing data can identify variations within seemingly uniform forests, providing insights into disease outbreak patterns.