The Biodiversity of Semi-Natural Grasslands: Implication of Land-Use and Climate Change on the European Alps

Semi-natural grasslands are of great conservation values given the high rate of biodiversity that they sustain. The diversity of these habitats is the result of both the environmental conditions in which they occur and millennia of pastoral and agricultural activities. However, as land-use and climate change continue to intensify, alpine grassland habitats are threatened to lose their ecological and functional values. Grazing intensification mainly occurs as a consequence of the abandonment of traditional pastures in more remote locations. The abandonment leads to a drastic reduction of semi-natural grassland’s surface and to changes in their floristic composition. Whereas those areas increasingly heavily loaded with livestock are widely exposed to the risk of degradation and eutrophication. Additionally, global climatic change is another factor that can threatens the biodiversity of grasslands by affecting the distributional range of their habitats, modifying the composition and structure of plant communities. The forecasted changes in temperature and precipitation patterns, with an increase in extreme climatic events, are expected to have a wider impact on the distribution of biodiversity. The latter as major implications onto spatial prioritization planning and conservation actions which will need to better include climate change scenarios. Firstly, we investigated the effects of land-use intensification and abandonment on grassland plant communities by addressing key ecological concepts of community dynamics. We attempted to unravel the relative importance of assembly rules driving community composition under various land-use scenarios. A thorough understanding of these dynamics requires the implementation of taxonomic, phylogenetic and functional diversity, by considering also different scale of diversity (α- and β-diversity). For this, we locally collected data through vegetation relevés to detect the successive change in plant community composition and structure under grazing disturbance and after disturbance release. For α-diversity, we considered diversity within communities, the community weighted means of plant functional traits to observe species response to their environments, and also the correlation among the three components of diversity to gain knowledge on how they relate to each other in response to disturbance. For β-diversity, we considered dissimilarity among communities under the three components of diversity where total β-dissimilarity was decoupled between its turnover and nestedness components. Our results suggest that various grazing intensity and different stages of abandonment directly affect plant communities both at the α- and β-diversity in some cases in contrasting ways; and taxonomic, phylogenetic and functional diversity resulted to correlate with opposing trends among them, revealing insights on the role of assembly rules in community assembly dynamics. We highlight the importance to consider all aspect of diversity and different scales to provide different information enabling to better unravel the complex dynamic’ features of nature. Secondly, we shifted our approach towards quantitative and empirical models of species-environment relationship to investigate shifts in the habitat suitability of the diagnostic species of four grassland habitats (6110*, 6210(*), 6239,6240) of the Alps caused by future climate change. Here, we used available online database holding species distribution-point data and environmental variables thought to influence species distribution to build up species distribution models (SDMs) and project future changes under five global circulation models, two climate change scenarios for the time period 2070-2100. Our results demonstrate a loss of habitat suitability for more cold adapted species (6230*) across the five geographical sectors of the Alps (SW, NW, NE, CE, NE). Whereas more thermophilous species undergo a shift in their distribution range towards northern and eastern parts of the Alps as a consequence of increased temperatures, disruption in precipitation regimes, and intensification of extreme events, which are found more pronounced in the SW Alps. Conclusively, climatic awareness can improve the way we interact with, plan to manage, and conserve grasslands habitats by locating hotspot of biodiversity loss both due to climate change and land-use change, thus sustaining conservation prioritization and planning. Therefore, land-use change must be of mayor concerns for those who addresses climate change, and vice versa.