How stable is the tuft structure of a mesic Drakensberg grassland under various burning regimes?

Abstract

Management options to maintain the stability of Drakensberg grasslands need to incorporate their dynamic nature in response to fire. This study addressed the lack of information on the spatial and temporal changes of these grasslands at a small (tuft) scale. The basal area of every tuft in three 0.25 m2 quadrats per replicate (3) of four burning treatments was mapped over two years in a long-term burning trial using a pantograph. The extent of change in size and shape of tufts indicated the dynamic nature of these grasslands from year to year. Basal cover of Themeda triandra was high in the annual winter (62.5%) and biennial spring (50.5%) burns, lower in the five-year burn (36.1%) and low in the biennial summer burn (11.5%). The bare area in the biennial summer burn increased by 5.6%, remained the same in the annual winter, and decreased in the biennial spring (6.1%) and five-year (7.8%) burns. The disappearance of Stiburus alopecuroides from the summer burn and increase in basal cover of Tristachya leucothrix indicates a directional change in composition that is likely to be irreversible. The biennial spring burn, where the three dominant species were in a state of equilibrium, is recommended for stability.

Keywords: basal cover, fire, mapping, South Africa