Patterns of plant species richness and growth form diversity in critical habitats of the Nama-Karoo Biome, South Africa

Abstract

The distribution patterns and determinants of biodiversity in the Nama-Karoo Biome are poorly known. This poses a problem for conservation given the impact that future developments (e.g. uranium mining, fracking) and global climate change are likely to have on the region's biodiversity. This study investigated the potential role that several environmental and climatic variables play in determining species richness, relative cover, and growth form diversity in two habitat types: plains and rocky dolerite hillslopes. The study area extended over a 600 km longitudinal environmental gradient in the Upper Karoo in which mean annual precipitation varied from 100 to 600 mm from west to east. A pairwise floristic survey approach was implemented, using modified Whittaker plots in each habitat type at 30 sites within the shale gas exploration area in the Upper Karoo bioregion. The results showed that total species richness was significantly higher (p < 0.01) in slope habitats than in plains habitats across the environmental gradient. The greatest diversity in both habitat types in terms of species richness and relative cover was in the low woody shrubs growth form. Similar plant associations on slopes aggregated spatially and conformed closely to their respective vegetation types, while those in plains habitats were interspersed with no clear clustering. A combination of soil, environmental and climatic parameters emerged as significant explanatory variables for modelling total species richness and relative cover of the five dominant growth forms. Habitat type was a significant explanatory variable for total species richness and relative cover. In the current vegetation map of South Africa, the vegetation types for the Upper Karoo bioregion are coarse, giving the impression of homogeneity in what is a highly heterogeneous landscape. Further mapping of fine-scale biodiversity patterns is needed in order to better inform conservation and management practices in the Nama-Karoo Biome.