Maintaining plant diversity of a species-rich montane grassland system in the face of global change
The rich grassland-plant diversity of the Drakensberg mountain region, which has persisted under heterogeneous fire and herbivory regimes, and significant fluctuations in climate, has come to face its most formidable threat—land transformation, which involves habitat destruction and land use intensification. Over the last ca. 200 years, human settlement in the northern Drakensberg study area, the Mdedelelo-Cathkin landscape in South Africa, has markedly increased, but the influence of human pressure on plant diversity has been largely unexplored, leaving an uncertain future for this biodiversity. This thesis aimed to reduce uncertainty around the influence of socio-ecological systems, represented by communal, private and protected land tenure systems, on grassland habitat and associated plant diversity. Analysis of changes in land use and land cover and field-based sampling of plant diversity revealed a conservation conundrum. Although grassland-plant diversity was maintained at higher levels on private systems, these systems were especially vulnerable to transformation. And while communal systems were less vulnerable to transformation, they were associated with heavy-continuous grazing that transformed grasslands into a novel state depauperate of plant diversity. Protected systems were, however, largely successful in maintaining primary grasslands, and their plant diversity. On these systems, where fire is the principal disturbance agent, the previously unexplored, multidecadal influence of heterogeneous fire regimes, was explored. A novel characterisation of heterogeneity in fire-return intervals and season of burning identified a threat of increasing fire regime homogeneity. The influence of socio-ecological systems, and their particular fire and herbivory disturbance regimes were framed by a construct termed, “socio-ecological disturbance regimes” (S-EDRs), which successfully reflected the interconnected nature of human society, disturbance regimes, and plant diversity. The transformation of a quarter of the landscape’s primary grassland over the 71-year period of assessment should draw urgent attention from conservationists and society. The S-EDR framework highlighted the critical responsibility society has in maintaining plant diversity. For the conservation of grassland-plant diversity a cross-societal approach is necessary, valuable plant diversity was found across the socio-ecological systems evaluated. Moreover, protecting Drakensberg-grassland ecosystems and their plant diversity will contribute to the global effort to mitigate the looming influence of climate change.
A thesis submitted in partial fulfilment of the requirements for the degree of Doctor of Philosophy to the Faculty of Science, University of the Witwatersrand, 2022
Plant diversity, Rich grassland-plant diversity, Drakensberg mountain region