The alien flora on the island of Menorca, a biosphere reserve

Abstract Biological invasions are a major threat worldwide, and their impacts are especially harmful on islands. The establishment and expansion of alien plant species is strongly dependent on the characteristics of the species such as their ability to reproduce, disperse, and compete with native plants, and the characteristics of the invaded habitats. Here, we assessed the current status of the alien flora on the island of Menorca, a Biosphere Reserve. We focus on (i) the habitats and land uses they occupy, (ii) their distribution across the island to detect the most invaded areas, and (iii) their life forms and biogeographic origin. We divided the island into 12 grids of 10 × 10 km and explored eight habitat types and five land-uses. For each grid, we visited three sites per habitat and compiled a floristic inventory, using DAFOR method to estimate plant species abundance. In total, we found 117 alien taxa in 247 inventories. Most alien taxa were phanerophytes, therophytes and chamaephytes, and the most common origin was Neotropical, African, and Nearctic. The cover was higher in streams than in forests and dunes, and the roadsides exhibited a higher richness than cliffs and dunes. Urban coastal areas exhibited more species or higher cover than sites surrounded by natural or protected areas. We recommend to focussing on the management of alien plant species in well-conserved areas to avoid new introductions therein.