How fine‑scale abiotic and biotic variations affect taxonomic diversity in abandoned sub‑Mediterranean grasslands

Abandonment of semi‐natural grasslands throughout Europe is causing the invasion of coarse tall grasses with competitive stress‐tolerant strategies, leading to a decrease in biodiversity (Louault et al. 2002). Our questions were i) Does the variation in micro‐ and mesic‐scale features affect dominant species and taxonomic diversity of plant communities? ii) Does the increase of dominant species affect negatively taxonomic diversity? The study area was “Montagna di Torricchio” Natural Reserve (central Apennines). In abandoned grasslands dominated by Bromus erectus Huds., Sesleria nitida Ten. and Brachypodium rupestre (Host) Roem. & Schult., we randomly selected 53 plots (5x5 m) recording plant species cover, topographic and soil variables. We ran RDAs to investigate the effect of abiotic variables on dominant species and the effect of both biotic and abiotic variables on species richness, evenness and exponential of Shannon index. We assessed the single contribution and combination of abiotic variables, dominant species, and B. rupestre cover on taxonomic diversity through Variation Partitioning. S. nitida was found dominating less dry grasslands whereas B. erectus the xeric grasslands. Furthermore, B. erects and B. rupestre were found on sites which had deeper soils, suggesting the soil as the main driver for the spreading of B. rupestre. Both abiotic features exerted a significant effect on plant community. Flat landforms and deep soils tend to enhance taxonomic diversity. Finally, we found a negative effect of B. erectus and S. nitida on plant community, in agreement with the prediction of competitive exclusion exerted by dominant species (Grime 2001).