Comparing the impacts of Carpobrotus spp. and Opuntia stricta on plant and invertebrate communities in small Mediterranean islands.

Our study aims to assess the impacts of these species on native plant and invertebrate communities in Giglio and Capraia, two small islands of the Tuscan Archipelago (Italy). We sampled 24 square plots of 4 m2, 12 for each island and species. In both case, 6 of them were randomly placed in invaded patches and 6 of them in natural communities as control. All these plots were located within habitats of conservation interest. For each of them, we recorded data on plant species occurrence, their abundance. Furthermore, we collected soil samples for the Berlese funnel method and for soil microbiota analysis and sampled ants using pitfall traps. Preliminary results show a decrease in plant species richness in the invaded areas compared to the uninvaded ones in both cases. We detected a greater loss of plant species for Carpobrotus invasion than in the case of Opuntia invasion, given the ability of the former to build suffocating monospecific mats. As regards the impacts on the soil fauna, Opuntia does not seem to change completely soil structure and invertebrate communities, while Carpobrotus significantly modify edaphic properties and invertebrate communities.