An approach to detect and map forest canopy layers in Swiss mountain forests using nationwide airborne laser scanning data

Understanding vertical forest structure is essential for forest management and is strongly linked to ecosystem functioning. In countries with protective forests, sustainable management is key to protecting humans and infrastructure from natural hazards. Well-structured forests usually feature multiple canopy layers, enhancing resistance and resilience to natural disturbances, reducing vulnerability to natural hazards, and improving adaptation to environmental changes. Forests with a single canopy layer often require prioritised and targeted management to increase their structural complexity. Hence, mapping forest canopy layering is crucial for effective forest management and risk mitigation.We developed a reproducible method for large-scale mapping of forest canopy layering to support sustainable forest management. Using airborne laser scanning data, we combined tree- and area-based methods to distinguish between single- and multi-layered forest areas in Switzerland. Our study encompasses four forest ecoregions, seven altitudinal vegetation belts, and a variety of topographic and climatic conditions. The resulting canopy layering map (resolution 10 x 10 m) was validated against two forest structure data sets, one from the Swiss National Forest Inventory (279 plots) and an Independent Forester Assessment (198 plots), yielding overall accuracies of 68 % and 81 %, respectively. Our study provides a robust and scalable method for mapping forest canopy layering across large mountain areas, which is transferable to other regions. Validation across various environmental settings demonstrates the suitability of the approach for nationwide use. Our forest canopy layering map supports sustainable, climate change-adapted forest management decisions, helping to set management priorities that promote well-structured forests for the future.