Effects of climate change on the coenological and functional structure of sub-Mediterranean grassland communities

Climate change and extreme events are having strong repercussions on the various ecosystems present in the world; those most affected are the mountain ecosystems in which plant species often live at the limits of environmental tolerance. In the Apennines, mountain grassland communities (important hotspots of biodiversity) are also affected by socio-economic changes that lead to grassland abandonment. In relation to climate change, the alteration of existing precipitation and temperature regimes has led to a shift in the mountain meadows' functional and coenological structure, making them particularly vulnerable. The distribution of plant communities has been shaped by ecological factors such as the intensity of winter cold stress and summer drought stress. The change in the intensity and duration of environmental stresses, cause plant species to be maladapted to the new conditions, leading to changes in community composition and posing a possible risk of extinction on the local or even the global scale for the most threatened species. On the other hand, the cessation of traditional agricultural practices linked to socio-economic issues has favored the expansion of shrubs and forests, besides the invasion of tallgrass species with competitive stress-tolerant strategies, increasing the vulnerability of mountain grasslands. The joint action of these two factors is causing the loss of biodiversity and the ecosystem services provided by the mountain semi-natural grasslands. This Thesis aims to understand how mountain meadows will respond to global warming in terms of biodiversity, and functional and coenological composition. To understand the vegetation dynamics that occurred, an approach based on the resampling of historical vegetation plots associated with vegetation maps was chosen, being the result of a compromise between the availability of historical data and the reliability of their reallocation, as proven by other investigations in semi-natural grasslands (e.g., Bennie et al., 2006; Wesche et al., 2012; Stevens et al., 2016). To evaluate these effects, climatic data and bioclimatic indices were compared between the periods 1952-1972 and 2000-2020, and historical phytosociological relevés referred to communities surveyed by Pedrotti in 1969 (Cortini Pedrotti et al., 1973) were compared with relevés carried out in 2021- 2022 (116 in all) regarding species and coenological composition, functional traits, and ecological indicators. The results indicated that climate change was not the main driver of change in species and functional composition. Changes in plant communities distributed in the outer and dryer parts of the basin can be ascribed to a management change (from mowing to grazing, reduction of mowing frequency, increase in grazing intensity), which modified the disturbance regimes. Vegetation changes in the humid meadows distributed in the central part of the basin were probably due to the reduction of grazing pressure, increasing the diversity of functional traits adapted to non-selective disturbance. In the dolines and along the main collector that drains water to the sinkhole, the wetland vegetation underwent minor composition changes, probably due to the substantial constancy of summer rainfall. However, the reduction in the abundance of some high-conservation-value species, such as Carex buxbaumii, poses a warning about the possible negative trend of the populations of these species, deserving proper monitoring programs and conservation actions.