Non-native and invasive alien plants on fluvial islands in the São Francisco River, northeastern Brazil

This paper is the result of a survey of the alien flora present on fluvial islands in the Sao Francisco River, northeastern Brazil. The floristic similarities between the islands wereassessed, as well as the relationship between area size and species richness. The study covered eight islands in the Sao Francisco River Valley and was carried out in a period of eight months. Thirty one alien species were registered, six of them ( Amaranthus viridis , Calotropis procera , Cenchrus ciliaris , Enneapogon cenchroides , Prosopis pallida and Ricinus communis ) present on all islands. The highest number of invasive alien species (26) was recorded on Massangano Island. The floristic similarity between the islands varied between medium and very high, while the number of alien species present was positively correlated with area size. The study demonstrates that the biodiversity on these eight fluvial islands is endangered, especially due to the presence of alien species capable of invading natural areas.