Structural and diversity changes in coastal dunes from the Mexican Caribbean: the case of the invasive Australian pine (Casuarina equisetifolia)

The coastal dune at the natural protected area of Cozumel Island has been impacted by the invasive Australian pine (Casuarina equisetifolia), which is highly competitive with the native species and only few native plant species can grow under its canopy. Our goal was to demonstrate that the Australian pine’s presence reduces the cover and vegetation diversity of the coastal dune’s native species. We used ten sampling plots (100 m each), five of which included Australian pine (invaded), and five that did not (non-invaded). We recorded the number of different plant species and their cover, height, and diameter in each plot. We found 43 plant species belonging to 40 genera, from which 37 species were found in the non-invaded plots, while only 26 plant species were present in the invaded ones. The vegetation density (3547 ± 709 individuals ha) and the cover (65%) in the plots that lacked Australian pine were higher compared to the density (2785 ± 802 individuals ha) and cover (35%) of the plots that included it. According to our analyses, Australian pine presence negatively influenced the species composition and abundance of the native species. Moreover, we found significant differences in the native plant diversity between the invaded and non-invaded plots. Our results demonstrated that invasive species, such as the Australian pine, negatively affected the native plant community in the coastal dune because it constrained its community structure.