Frequent burning maintained a stable grassland over four decades in the Drakensberg, South Africa

Abstract

The mesic montane grasslands of the uKhahlamba-Drakensberg, which produce cured flammable fuel, have evolved under and are sustained by recurrent fires. The Brotherton burning trial (12 replicated treatments) was established at Cathedral Peak (1 890 m asl) in 1980 to understand how burn season and frequency control the composition and diversity of the montane catchment grassland. Multivariate methods were used to examine the long-term (almost 40 years). compositional stability under different burning regimes. The species composition deviated steadily and markedly from the initial state (Bray–Curtis dissimilarity) by 43.4 ± 9.32% with quinquennial burning (alternating autumn/spring) and by 64.6 ± 2.24% with attempted fire exclusion (three unplanned burns). Composition was rapidly transformed (by 53.1 ± 4.6%) by biennial summer burning (discontinued in 1991). Dominance shifted from Themeda triandra to other grasses (Stiburus alopecuroides, Tristachya leucothrix, Harpochloa falx) with biennial summer and infrequent burning. In contrast, regular dormant season burning annually or biennially (in autumn, winter, or spring) maintained a stable grassland close to the original composition (mean deviation 23.08%). Burning homogenised the composition, overriding the initial extant small-scale spatial variation. Results support the current practice to burn biennially in the dormant season to maintain stable grassland in the Drakensberg catchments.