Site dependence of local-scale variations in taxonomic and functional diversity of semi-natural dry grasslands

Grasslands represent biodiversity hotspots in temperate Europe and, for this reason, have been extensively studied in the last century. Because such diversity is the result of a multitude of processes that shape communities, the adoption of a multifaceted approach (i.e., encompassing taxonomic and functional facets simultaneously) is fundamental to assessing the biodiversity of grassland habitats. Moreover, considering different spatial scales of investigation is crucial to properly evaluate short- and broad-scale processes simultaneously. Accordingly, we adopted a broad approach, taking into account alpha and beta diversity components of diversity to assess whether small-scale changes in grassland biodiversity are site-dependent. Additionally, such framework has been improved addressing a multi-faceted perspective, thus considering both taxonomic and functional diversity. The grasslands investigated are classified as high conservation priority habitats, and we surveyed them in two biogeographical regions in Italy. In each area, on a small scale, the grassland habitat has two distinct ecotypes, and in each of these, we surveyed vegetation and measured four plant traits. Our results showed that α-diversity differed taxonomically and functionally only between the two sites, while β-diversity also showed local functional differentiation. Furthermore, we demonstrated that while taxonomic β-diversity is mostly due to species turnover, functional β-diversity is equally due to turnover and nestedness. Therefore, our findings may shed light on how processes shape the different facets of semi-natural grassland biodiversity.