Recovery of the forest's protective effect after stand-replacing wind disturbances.

Forests in mountain areas provide an indispensable ecosystem service by protecting people and infrastructure from natural hazards. However, open questions remain regarding its long-term and reliable provision, which will amplify with climate change. In particular, natural disturbances, such as wind storms, can cause temporary losses of the forest's protective effect against natural hazards, such as rockfall, snow avalanches or landslides, potentially leading to higher risks for settlements and infrastructures. In this study, we analyzed the recovery of the protective effect of a large number of windthrow areas in the Swiss Alps using high-resolution canopy height models and single tree detection. We observed a considerable recovery of tree height (67 % on average), forest cover (90 %) and stem density (46 %) 31 years after the storm. Basal area showed a lower recovery of 16 % on average with 25 % of the studied areas showing a retarded recovery of ≤ 6 %. This highlights the extended timescales required for full recovery of the protective effect against certain hazard types, such as rockfall or landslides. Recovery rates were most importantly influenced by temperature, precipitation, local topography, gap size and lithological substrate, underlining the importance of local environmental conditions when predicting recovery. The study highlights future research gaps, including the role of deadwood as well as species mixture in the recovery of the forest's protective effect after disturbances.