Effect of pastoral management and climate change on Alpine pasture vegetation: An assessment over two decades

Alpine pasture vegetation is jointly shaped by climate and grazing, yet long-term studies addressing the drivers of vegetation change have rarely accounted for the spatial and temporal variability of grazing intensity. This study resurveyed 51 GPS-referenced vegetation plots in five actively grazed pastures of the Western Italian Alps after 19 years (2003–2022). Vegetation surveys and weather-station records were integrated with two complementary grazing metrics: official annual stocking-rate trajectories at the pasture scale and a slope-derived Site-Use Intensity (SUI) index representing potential livestock use at the plot scale. Changes in six dominant Social Behaviour Types (SBTs), plant diversity, and pastoral value were related to climatic and management predictors using machine-learning models. All pastures experienced warming, whereas precipitation and stocking-rate trends varied among sites. Only species typical of meso-eutrophic grasslands and oligotrophic acidophile montane swards increased significantly in cover. Both SBTs showed their largest increases at intermediate SUI, but their climatic and grazing responses diverged. The increase in species associated to meso-eutrophic grasslands was linked with faster increases in mean annual temperature and precipitation and was weakly related to stocking-rate trends. Oligotrophic montane acidophile species increased mainly under moderate warming and greater water availability, but declined with rapid warming, longer dry spells, and sharp stocking-rate increases. Climate and management had comparable and mainly additive importance, while SUI was the most influential individual predictor of both SBT cover changes and community evenness. Species richness and pastoral value remained stable, whereas the Effective Number of Species increased by 11.8%, indicating a redistribution of relative cover rather than net species accumulation. By separating pasture-scale livestock pressure from plot-scale potential use, this study showed that local grazing distribution may be more informative than livestock numbers alone for explaining long-term vegetation change. Adaptive management should therefore align stocking rates with pasture-specific vegetation carrying capacity, manage livestock distribution within pastures, and adjust occupation and recovery periods to interannual variation in vegetation growth and water availability.