Can High Density, Short Duration Grazing Replace Fire in a South African Mesic Grassland?

Can High Density, Short Duration Grazing Replace Fire in a South African Mesic Grassland?

High density grazing (HDG), defined as the concentration of many livestock on a small area for a short period of time has become increasingly popular in the South African mesic grassland yet little is known about it impact. HDG is usually applied without fire, based on the assertion that it is a key contributor to desertification of grasslands. However, fire plays an important role in the development and growth of most South African mesic grassland plant species, as it stimulates resprouting and reduces competition for light. The aim of this study was to determine the impacts of high density grazing on plant species composition and soil physical properties in a South African mesic grassland. Using a fence-line contrast, the objectives were to compare the impact of HDG with annually burnt firebreaks; one which was grazed and the other one which was not grazed, on soil compaction, ground cover and species composition. Soils under HDG and annual burning with grazing were 54% and 32% more compacted, respectively compared to annual burning with no grazing. High density grazing compared to annual burning irrespective of grazing resulted in four-fold more litter accumulation that can reduce irradiation received by plants and limit growth. Grass species diversity was 10% lower under HDG and annual burning with grazing compared to annual burning with no grazing. Forb species diversity was similar between HDG and annual burning with no grazing. However, Jaccard’s dissimilarity index, showed a forb species turnover of 22%, with HDG having 3 and annual burn with no grazing having 2 unique species, indicating that fire dependent species may have been replaced with fire independent species under HDG. Findings from this study indicate that HDG cannot replace the role of fire and potentially has a negative impact on a South African mesic grassland.