Interactive effects of prescribed fire and livestock grazing on Seriphium plumosum in South African sour bushveld

Abstract

Documented increases in woody plant abundance worldwide can reduce land value and grazing capacity. Throughout many grasslands and savannas in South Africa, Seriphium plumosum, an encroaching woody plant, has been rapidly displacing desirable native species. Cost-effective management techniques are required, in order to prevent encroachment. However, the effects of fire and grazing on S. plumosum are not well understood. We established a full factorial, completely randomised experiment to evaluate interactive effects of fire and livestock grazing on woody plant density and native plant diversity. Sixteen 100 m² plots were aggregated within an area of rangeland and randomly assigned four treatments, including: i) ungrazed, not burned: ii) ungrazed, burned, iii) grazed, not burned, and iv) grazed, burned. Results indicate fire can reduce S. plumosum height (p < 0.01) and canopy cover (p < 0.01), while simultaneously maintaining the herbaceous community composition (p = 0.33). However, this treatment effect was not significant 24 months after a single treatment. This suggests that although fire holds promise for S. plumosum management, follow-up treatments are necessary to control the shrub. Additional research into the effects of altering components of the fire regime in combination with grazing could provide insight into more effective management.

Keywords: bankrupt bush, plant community dynamics, Stoebe vulgaris, Stoebe plumosa, woody plant encroachment