Alien flora of Nigeria: taxonomy, biogeography, habitats, and ecological impacts

Abstract

Biological invasions remain one of the greatest threats to biodiversity and livelihoods, and this is predicted to increase due to climate change and globalization. In this study, we produced a comprehensive checklist of alien plants in Nigeria from online flora databases, herbarium records, published field surveys, and questionnaires administered to botanical gardens. The resulting alien flora was classified into naturalized, invasive, and cultivated plants. We then fitted a random forest model to identify the attributes which facilitate the naturalization of alien plants in Nigeria. We also used separate chi-squared tests to investigate if the frequency of these attributes is statistically significant between the naturalized and invasive plants. The results include 1,381 alien plant taxa, comprising 238 naturalized, 190 invasive, and 953 cultivated species. The naturalized and invasive plants (428 species) spread across 91 families, with Fabaceae and Poaceae having the highest representations. The random forest model showed that life forms and local economic uses were the most important drivers of alien plant naturalization in Nigeria. Chi-squared tests revealed a non-random distribution of life forms (P < 0.001), higher frequencies of naturalized plants from the Indomalaya (P = 0.006) and the Neotropics (P = 0.04), greater introductions during the British colonial rule, and are used mostly for medicinal, ornamental, food, and fodder. Naturalized and invasive plants were recorded in all regions of Nigeria and are mostly found in urban ruderal and agricultural landscapes. This baseline information can support further ecological studies and conservation actions in Nigeria.