The alien and invasive plant species that may be a future conservation threat to the Lesotho Afro-alpine Drakensberg area

Abstract In this study, we documented and compared similarities of the alien plant species richness between South Africa represented by three provinces: Free State (FS), Eastern Cape (EC), and KwaZulu-Natal (KZN), and Lesotho—an important water source area for southern Africa. We tested the prediction that alien plant species in Lesotho are a subset of South Africa’s species partly because of the short geographical distances between the provinces and Lesotho, and environmental similarity. Overall, 7124 records containing 1040 individual alien plant species belonging to 147 families were documented. South Africa had significantly greater alien plant species records than Lesotho. Of 147 plant families, 44 were represented in both countries, and 101 families did not occur in Lesotho. Against the study prediction, the Geraniaceae and Orobanchaceae families occurred in Lesotho but not in three provinces. KwaZulu-Natal had a significantly greater number of species than Lesotho but not the other provinces, and 49% of species in three provinces originated from the Americas (i.e. South and North), Europe, and Asia. A similar pattern was observed in Lesotho. Woody and herbaceous alien plants, habitat transformers, dominated three provinces, while herbaceous species dominated Lesotho. The 62% of 1040 alien species were not listed in the South African national regulations, indicating their negative impacts are also unknown in the study region. Plant nurseries were a dominant species dispersal pathway in South Africa, while home gardens were prominent in Lesotho. We conclude that invasive plant species constitute a future threat to the Lesotho Drakensberg highlands water catchments and recommend prioritising their management and improving cross-border biosecurity between Lesotho and South Africa.