Abstract ID: 3.13977 | Accepted as Talk | Talk/Oral | TBA | TBA

In temperate high mountains, snowbeds are those environments covered by snow until mid-summer, where only a set of specialised species, which depend on the particular microclimatic conditions found in snowbed patches, are able to thrive. The Pyrenees represent one of the southernmost refugia for many of them, but the reduced dimensions of snowbed patches and their scattered distribution throughout the range make them extremely sensitive to climatic changes. Indeed, the rising temperatures and the reduction of winter snowfall related to climate change are causing an earlier snowmelt, favourable to the growth of the more competitive generalist species from the neighbouring alpine grasslands. Within this context, between years 2003-2005 we established permanent transects in 9 acidic Pyrenean snowbed patches, and resampled them the periods 2013-2015 and 2023-2024. Transects cover the short but steep snowmelt gradient, beginning in an alpine grassland and ending in the snowiest part of the snowbed. In each transect we sampled species composition and coverage in plots of 10 x 50 cm distributed at regular 20 cm-intervals throughout the snowmelt gradient. To analyse the data, for each period and transect we grouped the plots into different vegetation groups based on their floristic similarity by means of fuzzy-c-means non-hierarchical clustering. After that, we analysed the changes in species richness in each vegetation group, as well as the changes in species frequencies and distribution, considering snowbed specialists and a set of the main grassland generalists found in neighbouring grasslands. Preliminary results evidence the rapid colonisation of snowbed patches by a set of competitive grassland species in 20 years. Concerning snowbed specialists, we observe two contrasted responses depending on their specificity on the snow cover duration. Those species characteristic of the snowiest part of snowbeds show a contraction of the area occupied, whereas those characteristic of the periphery show an increase towards the snowiest part of the snowbed. Overall, these results show rapid composition changes in 20 years related to the changing micro-environmental conditions throughout the snowmelt gradient, and evidencing the vulnerability of some snowbed specialists within the context of climate change.