Effects of Past and Current Land Use on Biodiversity: from a semi-natural grassland on Öland (Sweden) to a European perspective

Abstract: Concerns are increasing about the loss of biodiversity under land use change and how this will affect the ecosystem services provided by natural and semi-natural communities and consequently how this will threaten human well-being. The thesis examines the impact of present and past land use on different aspects of biodiversity; namely species diversity, traits and functional diversity and on ecosystem services. It also focuses on exploring and understanding how communities are assembled and to what extent past and current environmental filters affect the coexistence of species. A key aspect was the investigation of functional traits distribution within species communities. This thesis has a broad range of scales, from working with semi-natural grassland fragments on a 25km2 study area to a more European perspective. Studying different aspects of species diversity and functional diversity provides a more complete picture on the community-level consequences of past and current habitat conditions. Species evenness and species richness show independent responses to past and current habitat conditions, suggesting that the species evenness should be more systematically included in the assessment of the taxonomic component of biodiversity. Functional metrics were not completely reflected by taxonomic metrics, leaving uncertainty about the extent to which taxonomic indicators fully characterize biodiversity changes in response to land-use change and calling for an integration of taxonomic and functional indicators. Both species and functional diversity were associated with present and past habitat conditions, suggesting that both components of biodiversity may exhibit relatively long time-lagged responses to changes in habitat conditions. Therefore, the development of reliable indicators of biodiversity change would greatly benefit from the integration of both past and present biodiversity drivers. Species coexistence could be explained by different processes acting on different scales, reflecting the degree of environmental heterogeneity. At the scale where species share physically the same environment, species coexistence could be explained by the limiting similarity in a variety or combination of their ecological strategies, leading to the high fine scale species richness observed in semi-natural grasslands. Further research with a larger pool of traits in order to have a more complete picture of the trade-offs between coexisting species, as well as research at different scales are required to further understand the mechanisms governing species coexistence. Limiting similarity could be more common within each abundance class, especially within the subdominants, than between abundance classes, suggesting the need for further investigations to link the dissimilarity processes within each abundance class to the context of functional redundancy. This may influence the ecosystem resilience of the semi-natural grasslands in the context of the ongoing abandonment of traditional grazing management, which are threatening the diversity of this ecosystem. Finally, linking biodiversity to the provision of ecosystem services together with further research into the recognition of the multifunctionality of ecosystems should promote a better conservation planning of those component of biodiversity that contribute to preserve human well beings.