Evidence of short-term response of rocky cliffs vegetation after removal of invasive alien Carpobrotus spp.

Abstract

Invasive alien plant species are among the major drivers of change in natural ecosystems; therefore, their eradication or control is a common and effective conservation tool to reverse biodiversity loss. The LIFE LETSGO GIGLIO project was implemented with the objective of controlling the invasion of Carpobrotus spp., among the most threatening invasive alien species in Mediterranean ecosystems, on the Island of Giglio (Tuscan Archipelago, Italy). The management of Carpobrotus spp. was conducted across an area of approximately 33,000 m2 of coastal habitats. The main intervention was conducted during the winter of 2021–2022, primarily through manual removal, with a limited use of mulching sheets. Subsequent years saw the continued removal of seedlings. We monitored the habitats of vegetated sea cliffs and coastal garrigues (both protected under Directive 92/43/EEC), as these were the two habitats most affected by the control actions. A total of 24 permanent plots were sampled annually from 2020 to 2023 in a Before-After-Control-Impact (BACI) design. We analysed the variation pre- and post-removal of Carpobrotus spp. cover and litter and of native plant cover and diversity, as well as the changes in the composition of native plant communities. Our results show that already two years after the main intervention of removal, thus in the short term, the community’s composition shifted considerably towards the pre-invasion set of species. This recovery was also evident in terms of diversity indices, although the impact of Carpobrotus spp. on ecological parameters (mainly soil) favoured nitrophilous species. Furthermore, we highlight the need for yearly removal of Carpobrotus spp. seedlings for the next 5–10 years, in order to continue promoting the recovery of native communities.