Predicting the extent of succulent thicket under current and future climate scenarios

Abstract

Using data from the distribution records of the facultative CAM succulent shrub Portulacaria afra, and high resolution climate response surfaces, we developed a spatially explicit model of the potential distribution of the species in the Thicket Biome of the eastern and southern Cape, South Africa. The resultant map shows a close relationship with the expected distribution of P. afra prior to the advent of intensive ranching by goats in the region. In field situations where P. afra is known to have been cleared by agricultural activities, the map showed the potential of the site for this species. It also demonstrated the absence of the species in areas where it does not occur e.g. fynbos, grasslands, forest and Nama-karoo. A weakness of the model is the lack of a measure of the density of P. afra. Under the CSM (coupled ocean-atmosphere model) climatic change scenario, 80.3% of the grid-cells would remain suitable and 19.7% would become unsuitable.