Predicting Shifts in the Geographical Distribution of Two Estuarine Plant Species from the Subtropical and Temperate Regions of South Africa

Climate suitability maps are useful to determine changes in the distribution of species. The aim of this study was to predict the future distribution of two estuarine species (Bassia diffusa and Hibiscus tiliaceus) from two biogeographical regions under climate change. The Bioclim and Maxent modelling algorithms were used to calculate current climate suitability and were projected onto future climate data to develop climate suitability maps. The trained area under a receiver operating characteristic curve (AUC) values ranged from 0.723 to 0.936 for both species under the current climatic conditions, and from 0.695 to 0.933 for future conditions. Distribution range contraction for Bassia diffusa is predicted along its eastern distribution limit (South-East coast) in South Africa, suggesting extirpation in 42 out of 62 estuaries. This may allow mangroves to expand into areas where B. diffusa will be lost. Low suitability was predicted for H. tiliaceus in warm temperate estuaries which may limit further expansion. Future climate change scenarios in this region predict that temperature will not increase above the minimum temperature tolerance of H. tiliaceus. This approach can be applied to determine the potential range shifts of other estuarine species, supporting the development of proactive strategies to reduce climate change impacts on biodiversity.