James Ayuk – University of Fort Hare
Lincoln Raitt – University of the Western Cape
Guy Midgley – University of Stellenbosch
This research investigated the water regime of three Restionaceae species and the implications of possible changes in soil hydrology caused by climate change in communities within the Cape floristic region. Vegetation survey counts for the presence of these species along with measurements of soil water table depth and moisture content generated from eight small-scale plots (50 x 50 m) were used to investigate possible hydrological niches. A comparative analysis of the effects of two Representative Concentration Pathway (RCP), RCP 2.6 and RCP 8.5, climate extremes on plant water regimes was carried out. MaxEnt modelled species hydrological niches at very fine spatial scale. The visual assessment showed a match between the actual (observed) sampled occurrences and the predicted (modelled) locations. This made the outputs valid for the interpretation of community structure and deemed fit for predicting the potential future species distributions based on novel environmental conditions introduced by climate change. Staberoha distachyos might remain stable at altitudinal conditions but is mostly predicted to disappear at most places where they presently occur. Additionally, the species population is seen to expand under RCP 2.6 scenario conditions but, on the other hand, shrink under RCP 8.5 scenario conditions. A similar trend is expected for Elegia filacea, Hypodiscus aristatus and Staberoha cernua. Hydrological factors are considered ecologically important as they account for the differences in the species responses. Species distribution has mainly been underpinned by a moisture gradient rather than by the overarching climatic variations seen in larger settings. Finally, the results derived from different possible climatic scenarios may guide future decisions on conservation. While the direction to which species change would definitely take remains uncertain in the future, these results are a firm pointer towards the most likely future paths.