Short-term vegetation shifts in an alpine grassland under current and simulated climate change

Questions: Recent years have been characterised by extreme climate conditions. Given that high elevations are undergoing enhanced warming and alpine ecosystems provide important services, we ask: Have alpine grasslands experienced rapid vegetation changes over the last five years? Which species are more sensitive to warmer and/or drier conditions? Location: Carex curvula grassland in the southern Alps (Italy). Methods: Species cover was visually estimated in 20 permanent plots, including both control and climate-manipulated plots, during the period 2017–2022. Climate manipulations, that is, increased temperature and/or reduced precipitation during the snow-free period, started from 2018. Principal component analysis, redundancy analysis and generalised least-squares or linear mixed-effect models were employed to investigate variations in species assemblage and species-specific responses. Results: Detectable changes were found in species cover over time and between climate manipulations, with warmed plots experiencing greater shifts in species composition compared to controls. At the species level, however, both increases and decreases in cover were observed over time, with only two non-dominant forbs, Phyteuma hemisphaericum and Leucanthemopsis alpina, showing either increased cover in warmed plots or lower cover values under drier conditions. No treatment effects and the lowest variation across years were found for the two dominant species (the sedge Carex curvula and the forb Alchemilla pentaphyllea) which together make up more than 70% of vascular plant cover. Despite the short time period investigated, a major cover reduction was observed in all treatments for some snowbed species. Conclusions: The plant species assemblage of the target alpine grassland was found to be sensitive to short-term manipulations simulating future climate changes, with individual species exhibiting idiosyncratic responses to manipulations and different cover dynamics over time. A decline in some snowbed specialists already seems to be taking place even in these late-successional grasslands — at a rate likely to increase in the future — with the majority of other vascular species exhibiting greater resistance to changing environmental conditions.