Carpobrotus acinaciformis vs Carpobrotus edulis: Are there any differences in their impact on coastal dune plant biodiversity?

Coastal sand dunes are widely acknowledged as fragile and dynamic ecosystems. Among the several threats affecting the native biodiversity of these systems, invasive plants are one of the most troubling ones. The genus Carpobrotus has been recognized as one of the most abundant invasive genera along the Mediterranean coast, particularly in coastal sand dunes. In Italy, two taxa belonging to this genus have been identified: C. edulis and C. acinaciformis. Given that the taxonomic identification of these two species is still subject of debate, we investigate whether there are differences concerning their ecology in terms of their impact on native plant communities in central Italy coastal dunes. To do so, we analyzed their relative impact on species richness, diversity and relative abundance. Vegetation sampling was carried out through paired-plots, comparing invaded to non-invaded plots. Although our results show a general decrease in native species richness in all the invaded plots, there were no significant differences between the richness and diversity of the native communities invaded by C. edulis and that of the communities invaded by C. acinaciformis, although slight differences on native species' relative cover was observed. In addition, we observed a higher occurrence of C. edulis in the areas closer to the seashore. We conclude that even though there are no meaningful differences in the impacts of the two taxa on native biodiversity, further analyses are needed to exclude potential differences in their relative ecological adaptations to the changing abiotic conditions found along the coastal zonation.