BACKGROUND AND AIMS: Climate change, particularly the increased frequency of extreme climatic events, poses significant challenges to the biodiversity and functionality of semi-natural grasslands. However, the response of plant functional traits of grassland communities to climate extremes is still an unresolved issue. Using data from a long-term experiment, we aimed to characterize the functional response of a grassland community to simultaneous long-term effects of grazing and climate extremes. METHODS: For a 20-year period, we monitored the species composition of grazed and ungrazed grassland plots. We measured functional traits defining the leaf economics spectrum (LES) and the hydraulic safety-efficiency (HSE) trade-offs, and we identified the temporal dynamics of single traits at the community level as well as the changes in functional strategies among grazed and ungrazed communities. Then, we assessed the role of climatic extremes in driving the changes in functional composition. KEY RESULTS: Grazed plots, in the first few years, were dominated by fast-growing species with more acquisitive strategies compared with ungrazed plots. However, both communities showed a reorganization in functional structure over time, pointing towards a selection of trait combinations favouring more conservative, stress-tolerant strategies. The joint effect of grazing and climate extremes significantly altered the functional composition of the grazed community, leading to a shift from species with grazing-tolerant traits to species with grazing-avoidant, and drought-tolerant, traits. CONCLUSIONS: We found that grazing pressure generally promoted functional diversity but led to rapid shifts in community composition when combined with prolonged drought events. In contrast, the ungrazed community, dominated by species with conservative resource-use strategies, showed more stable functional richness and divergence, as well as a reduced sensitivity to climatic extremes. These results underscore the importance of carefully evaluating grazing in the context of climate change, particularly to guide restoration and conservation efforts.

BIOME Lab Department of Biological Geological and Environmental Sciences Alma Mater Studiorum University of Bologna 40126 Bologna Italy

Czech University of Life Sciences Prague Faculty of Environmental Sciences Department of Spatial Sciences 16500 Praha Suchdol Czech Republic

Department of Biology University of Padova 35121 Padova Italy

Department of Environmental Biology University of Rome 'La Sapienza' 00185 Rome Italy

Department of Life Sciences University of Siena 53100 Siena Italy

Department of Life Sciences University of Trieste 34127 Trieste Italy

Institute of Agricultural and Environmental Sciences Estonian University of Life Sciences 51006 Tartu Estonia

Institute of Ecology and Earth Science University of Tartu 50409 Tartu Estonia

NBFC National Biodiversity Future Center 90133 Palermo Italy

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