Assessing the level of habitat fragmentation of the KwaZulu-Natal sandstone sourveld.

Abstract

Numerous processes, including habitat loss and fragmentation, contribute to ecosystem degradation, resulting in the loss of ecosystem functioning and diversity. The KwaZulu-Natal Sandstone Sourveld (KZN SS) is a grassland ecosystem type that is currently classified as endangered due to extensive habitat loss. A large percentage of this ecosystem has been converted through agriculture and development. This is due to the fact that this vegetation type occurs in a prime agricultural area for timber and sugar cane plantations. This has led to the physical fragmentation of the KZN SS, the exacerbated effects of which could diminish the biological persistence of this ecosystem. Apart from a few conserved areas (only several hundred hectares), most remnant patches of KZN SS are exposed to frequent fire and stressful levels of grazing. Very little is known about this vegetation type and thus the current level of habitat fragmentation and connectivity of the landscape is presently unknown. Furthermore, there is currently no standard method used to quantify habitat fragmentation. The overall aim of this study was to quantify habitat fragmentation of the KZN SS using measures of structural and functional connectivity. Through the use of various measures of habitat fragmentation and connectivity, this study identified priority areas of KZN SS, and designed landscape corridors to improve landscape connectivity. There are numerous measures that can be implemented to assess landscape and habitat connectivity, including graph theory. The Conefor Sensinode software, which employs graph theory, was chosen to aid in assessing the level of habitat fragmentation. The integral index was chosen as the best connectivity index to use in determining landscape connectivity. Once the data had been processed within Conefor, it was then imported into a Geographical information system (GIS) where the data was finally represented. A least-cost analysis was then run in ArcGIS to determine the best route for a landscape corridor to undertake within the eThekwini Metropolitan area. This analysis took into account the priority areas of KZN SS identified, the protected areas network, and the DMOSS (Durban Metropolitan Open Space System). The study ascertained that the KZN SS is a highly fragmented landscape, which has resulted in very low levels of connectivity between fragments in the eThekwini Metro. Priority areas have been identified and landscape corridors have been suggested. This situation needs to be addressed if species within the KZN SS are to persist. This study recommends that the eThekwini Municipality can safeguard the biodiversity of this endangered ecosystem by focusing on managing the patches of KZN SS that have been identified as having a high level of importance within the landscape.