Abstract
The impact of ongoing climate change on plant communities varies according to vegetation type and location across the globe. Snowbed flora count among the most sensitive vegetation due to their dependence on long-lasting snow patches. This is especially the case toward their rear distribution edge, where warming has already induced a marked decrease in snow deposition. Thus, analysing the dynamics of snowbed plant communities is crucial for understanding the ecological processes that condition their persistence under new environmental conditions. The Pyrenees represent the southern distribution limit of several eurosiberian snowbed species. We surveyed eight snowbeds based on permanent plots, where the presence of each taxon was recorded annually between 2012 and 2019. We analysed vegetation patterns between sites and plots, related them to environmental gradients, and assessed temporal trends of community dynamics. We detected important between-site differences regarding species composition. However, these differences were not supported by species' biogeographical patterns, which suggests that local abiotic factors filter species with distinct autecology. In parallel, temporal community turnover was observed through the expansion of widespread grassland species, which supports the hypothesis of colonisation of snowbeds by common alpine taxa. Such changes could be related to a decrease in snow cover over recent times, which releases extreme environmental constraints to plant growth. Therefore, it is crucial to characterise fine-scale ecological conditions to forecast plant community dynamics and provide reliable information for conserving snowbed vegetation across the Palearctic.