Consequences of iceplant (Carpobrotus) invasion on the vegetation and seed bank structure on a Mediterranean island: response elements for their local eradication

Biological invasions are one of the world’s leading causes of biodiversity loss. Islands are particularly good models for studying the impact of invasive species. Bagaud island (58 ha), which is part of Port-Cros National Park (southeastern France), is currently suffering an invasion of Carpobrotus. A restoration project has been established with the aim of eradicating these species to protect native ecosystems. The objective of the present study was to examine the plant composition of the local vegetation and seed bank (in litter and soil) focusing on (i) Carpobrotus patches and (ii) native plant communities, with the ultimate goal of determining whether Carpobrotus removal is followed by native plant community colonization. A further objective of this study was to help identify the most effective protocol for adequate ecological restoration. Native plant communities found around Carpobrotus patches can vary depending on whether the patch is located on the coast or inland; we can therefore expect a variety of plant communities to form following Carpobrotus removal. Even though Carpobrotus litter can frequently contain seeds of native species, such Atriplex prostrata, Frankenia sp. and Sonchus asper, it also contained many more Carpobrotus seeds (77.6%). Therefore, it is important to remove Carpobrotus litter to prevent large numbers of Carpobrotus seeds from recolonizing after eradication. We conclude that the most effective ecological restoration protocol consists of the following: (i) the removal of living Carpobrotus plants and (ii) the removal of Carpobrotus litter. This protocol can be made even more effective by following it up in the near and mid-term by periodic and thorough checks for Carpobrotus reinvasion.