Complex Greening in the Meretischitälli Catchment

In recent decades, greening has been a widely observed phenomenon across the European Alps, and the importance of biogeomorphic feedbacks in mountain environments has been increasingly recognised. Yet, research remains limited on the extent to which these vegetation changes interact with geomorphic activity and slope stability at catchment scale. Understanding these interactions is essential for improving interpretation of the development of alpine landscapes under ongoing climate forcing, as they influence sediment redistribution, slope stability and downstream ecosystem functioning.
This research investigates how these vegetation-slope dynamics interact in alpine environments, with particular focus on the development of the treeline ecotone, species-specific contributions to greening and the control of landform-specific variations on vegetation dynamics. We focus on the Meretschi catchment, a geomorphically dynamic valley in the Swiss Alps. Greening is quantified using NDVI from Landsat imagery (1984-2024) and tree establishment mapping in the treeline ecotone from historical orthophotos. Species-level field surveys were conducted, terrain variables were derived from a digital elevation model, and a detailed geomorphological map was constructed. All these aspects were compared across space and time to assess the controls on greening and their interactions.
Vegetation greening, indicated by NDVI increase, was strongest between 1900-2500 m, coinciding with the treeline ecotone. Tree establishment shifted upslope and intensified over time, with densification in localised microclimatic patches contributing more to greening. Clusters of more than 20 trees contributed significantly more to greening, highlighting the importance of both tree density and establishment rate.
Species contributions varied, with Larix decidua dominating greening among newly establishing trees compared to Pinus cembra. Across the catchment, woody vegetation (dwarf shrubs and forest) contributes more to greening than grassland and pioneers only recently started contributing. These patterns appear to be largely controlled by species functional traits and microclimatic sensitivities, but also by anthropogenic effects, in particular grazing practices.
Geomorphic activity strongly influenced greening, with more stable landforms with high soil development potential showing more pronounced greening compared to rocky, unstable landforms, and with gravitational landforms displayed the highest variability. This variability reflects episodic disturbance and recovery, which highlights the impact of biogeomorphic feedbacks.
Overall, the research shows that alpine greening in the Meretschitälli catchment develops from a synthesis of climatic facilitation, species traits, geomorphic activity and anthropogenic influence, producing spatially heterogeneous vegetation change. By linking greening to geomorphic activity and characteristics, this research advances our understanding of catchment-scale eco-geomorphic feedbacks and provides a basis for predicting how vegetation-slope-species interactions may shape alpine landscape with ongoing climatic changes.