How Do Tree Canopy and Soil Nutrients Drive Distinct Facets of Diversity and Community Assembly in Sub‐Mediterranean Grasslands?

Question How do tree canopy cover and soil nutrients shape the taxonomic, phylogenetic, and functional diversity of sub‐Mediterranean grasslands? Location Valdebezana's valley (Burgos, Northern Spain). Methods We measured 10 above‐ and belowground plant functional raits related to resource acquisition strategies and dispersal ability from four sub‐Mediterranean grasslands dominated by species with different biogeographic origins (Eurosiberian vs. Mediterranean). Then, we estimated patterns in taxonomic composition and compared the levels of taxonomic, phylogenetic, and functional diversity indices among communities and estimated their phylogenetic and functional assembly patterns, together with the decoupled functional diversity. Additionally, we estimated the influence of tree canopy and soil nutrients in shaping such patterns. Results Communities segregated according to their biogeographic origin (Eurosiberian vs. Mediterranean) along a soil resource gradient, matching the economics spectrum expectation. Taxonomic diversity differed significantly between biogeographic origins, but phylogenetic or functional diversity did not. Assembly patterns showed phylogenetic over‐dispersion accompanied by functional clustering, with a significant effect of decoupling. Differences in taxonomic diversity were driven by edaphic factors, while canopy closure mainly influenced phylogenetic and functional patterns. Conclusions Sub‐Mediterranean grasslands are highly rich in all facets of biodiversity (taxonomic, phylogenetic, and functional) and in assembly processes. In these habitats, local conditions may influence the structure and composition of herbaceous plant communities, highlighting the fragility of ecotones to environmental variations. Our results underline the need to develop proper management actions to preserve ecotone grassland communities; for instance, the creation of heterogeneous environments combining forest patches with open areas to maximize their biodiversity and functionality.