The impact of fire and land use on the Kwazulu-Natal Sandstone Sourveld.

Abstract

The KwaZulu-Natal Sandstone Sourveld (KZNSS) is one of the most prominent South African grassland types and has undergone large-scale transformation through the years. This endangered, species-rich grassland is endemic to KwaZulu-Natal. Much of the KZNSS remains in patches within the eThekwini Municipality area (EMA), many of which are in communal areas and some in nature reserves. These remnants are under-conserved and under-researched. Fire and land use are focal when conducting research and implementing management and conservation practices in these grasslands. Therefore, this study aimed to determine the effect of long-term burning history on species composition and structure in protected and communal agricultural land in KZNSS grassland remnants within the eThekwini Municipality area. The objectives were to examine fire regime variations over 20 years (2002 – 2022) in reserves and communal agricultural areas found in KZNSS remnants within the EMA using Geographic Information Systems (GIS) and remote sensing. Additionally, to determine: 1) the effect of land use; 2) the effect of fire and 3) the effect of the interaction between fire and land use on grassland plant species composition, richness, evenness, and diversity; veld condition and tree density in the burnt and unburnt patches of the study areas. Remote sensing was used to obtain fire records for the last 20 years, of these remnant patches. Within the selected reserves and communal area study sites, one area with a high fire frequency (burnt five or more times in the last 20 years) and one with a low frequency (two or three times over 20 years) or which had not burnt in these 20 years were sampled. Quadrat sampling was utilised to quantify grassland composition in four communal areas (KwaCele, Qadi, Zwelibomvu, and Toyane) and four reserves (Silverglen, New Germany, Roosfontein, and Krantzkloof). A veld condition assessment (VCA) was conducted in these sites. Additionally, tree density was assessed to account for the woody encroachment in these areas. Over the past 20 years, the communal agricultural areas had a higher fire frequency than protected areas. It was also observed from the fire records that the season of burning was consistent over the years, both communal agricultural and protected areas burning mostly in the dry season. However, the percentage area burnt in these grassland patches fluctuated, with the proportion of areas burnt being highest in earlier years. Overall, fire, land use, and their interaction influenced the plant species (grasses and forbs) composition. Land use had an effect on plant species richness, evenness, and diversity. Fire, nor the interaction of fire and land use, had a significant effect on these variables. Communal agricultural areas had the highest plant species richness, evenness, and diversity. This could be explained by the fact that over 20 years, communal agricultural areas had a higher fire frequency than nature reserves. This higher frequency of fire encourages diversity as fire removes dominant vegetation, thereby allowing other plant species to grow, which prevents there just being one dominant species that outcompetes the others. For the veld condition assessments, unburnt patches in the protected areas had greater veld condition scores due to overgrazing and stocking rates being low. However, fire and land use, as well as their interaction, did not affect the tree density observed in the study areas. For the KZNSS to remain healthy and functional, land use and fire, as well as their interaction, are essential aspects. Therefore, to maintain biodiversity, effective management necessitates a balanced strategy that considers both ecological needs and human activities.