Taxonomical, coenological and functional approach to analyse the effect of multi-year mowing on sub-Mediterranean invaded grasslands

The cessation of semi-extensive farming or underutilization of grasslands is leading to vegetation changes throughout Europe, as well as in semi-natural sub-Mediterranean mountains. At the community level, these changes foster the invasion of unpalatable tall grasses, mostly with competitive stress-tolerant strategies, affecting species diversity and decreasing the nutrient value of pastures ecosystem. In the Italian peninsula, two perennial species of Brachypodium are fostered by grazing cessation or by a livestock pressure below the theoretical carrying capacity of pasture: B. rupestre (Host) Roem. et Schult. in the sub-Mediterranean hills and low mountains, and B. genuense (DC.) Roem. et Schult. over 1300–1400 m a.s.l. These species can spread over a wide range of abiotic conditions, shifting their strategy thanks to their high intraspecific trait plasticity. Consequently, finding proper management practices to restore invaded grasslands is an important issue to preserve their biodiversity and economic value. This research was aimed to understand the effect of multi-annual mowing events on the recovery of a grassland community invaded by Brachypodium rupestre. In particular, we analysed the effects on taxonomic diversity, coenological composition, and trait composition (space occupation strategies, vegetative propagation, presence of storage organs, and flower- ing phenology) at the plant community level, and changes in B. rupestre traits. The study site was located next to the “Montagna di Torricchio” Natural Reserve (central Apennines) undergrazed since at least 30 years. We fenced one homogeneous area of 2 ha invaded by B. rupestre: half of the surface was mown twice a year since 2010, and hay and litter were removed after each mowing event; the other half was unmown and used as a control. Species cover (%) was recorded in 30 random plots (0.5 m × 0.5 m) in late June, before the start of the experiment and in the following six years. We collected also data on B. rupestre traits in mown and unmown areas (plant height, leaf area, leaf dry mass, seed mass, hypogeogenous rhizome dry matter content, and aboveground phytomass), and calculated Specific Leaf Area. B. rupestre cover and aboveground phytomass strongly decreased over time; species richness and transformed Shannon and Gini-Simpson indices increased, while Shannon’s evenness showed fluctuations. Fringe habitat and successional species, indicators of ongoing dynamic processes, decreased in cover, along with caespitose species, grasses, and species with rhizomes and runners as vegetative propagation modes. The cover of species that are typical of managed grasslands increased, as well as that of rosulate species, species with compact shoots with innovation buds at the axil of basal leaves, and species flowering in mid-late summer. The resulting species composition was consistent with that of central Apennines’ managed pastures. B. rupestre Specific Leaf Area did not show a significant trend, while both leaf area and leaf dry mass, as well as plant height and seed mass, decreased. These results suggest that B. rupestre reduces the amount of dry matter (e.g. structural and storage carbohydrates) inside the rhizomes and the investment in growth (horizontally and vertically) and in sexual reproduction. In summary, recurring mowing twice a year could represent the proper management practice to restore invaded grasslands, enhancing species diversity.