Invasion risk of the currently cultivated alien flora in Southern Africa is predicted to decline under climate change

Alien species can have massive impacts on native biodiversity, ecosystem
functioning, and human livelihoods. Assessing which species from currently
cultivated alien floras may escape into the wild and naturalize is
essential for efficient and proactive ecosystem management and
biodiversity conservation. Climate change has already promoted the
naturalization of many alien plants in temperate regions, but whether it
is similar in (sub)tropical areas is insufficiently known. In this study,
we used species distribution models for 1,527 cultivated alien plants to
evaluate current and future invasion risks across different biomes and 10
countries in southern Africa. Our results confirm that the area of
suitable climate is a strong predictor of naturalization success among the
cultivated alien flora. In contrast to previous findings from temperate
regions, however, climatic suitability is generally predicted to decrease
for potential aliens across our (sub)tropical study region. While
increasingly hotter and drier conditions are likely to drive declines in
suitability for potential aliens across most biomes of southern Africa, in
some the number of potential invaders is predicted to increase under
moderate climate change scenarios (e.g., in dry broadleaf forests and
flooded grasslands). We found that climatic suitability is expected to
decline less for aliens originating from continents with the tropical
biome or from the Southern Hemisphere. In addition, we found that the
climatically suitable area will decline less for aliens that have already
naturalized in the region. While the number of potential invaders may
decrease across southern Africa under future climate change, our results
suggest that already naturalized aliens will continue to threaten native
species and ecosystems.