Unabated forest expansion despite increased rockfall frequency at Täschgufer slope, Switzerland

Rockfall activity and forest dynamics interact closely in alpine talus environments, where climate warming is altering both geomorphic processes and vegetation patterns. This study provides a comprehensive assessment of the coupled dynamics between forest expansion and rockfall activity at the talus-forest ecotone of the Täschgufer slope (Swiss Alps). By integrating dendrogeomorphic analyses, high-resolution aerial imagery, and satellite-derived vegetation indices, we reconstruct changes in rockfall frequency and forest dynamics over the past five decades. Our results demonstrate a persistent upslope forest migration despite increasing rockfall disturbances driven by enhanced permafrost thaw. This suggests that rising temperatures and prolonged growing seasons have created favorable conditions for tree recruitment and growth and that these processes can offset increasing geomorphic disturbance. However, comparison between the mitigated and unmitigated segments of the talus slope indicates that rockfall activity alone does not control tree colonization, and that the underlying structure of the talus slope also plays a critical role in constraining the biogeomorphic balance. Our study positions the talus-forest ecotone, like the treeline, as a highly sensitive indicator of climate change, particularly given limited anthropogenic influence in these environments. The integrated methodological framework presented here provides a valuable baseline for investigating these geomorphologically disturbed ecotones and highlights the importance of multidisciplinary approaches to inform sustainable management and conservation in sensitive alpine environments.