Moderate grazing sustains plant diversity in Afromontane grassland

Abstract

Abstract Aims Natural disturbances drive plant assemblages in Afromontane grassland. Our aim is to assess how intensity of cattle grazing and time since last fire influence plant species richness, dominance and assemblage composition. Location Central Midlands, KwaZulu‐Natal province, South Africa. Methods Sites differed in grazing intensity (light, moderate and heavy) and time since last fire: recently burned ( RB ) vs unburned ( UB ). We sampled plants in 24 vegetation quadrats (1‐m 2 ) randomly located within each site (~1000 m 2 ). We used linear regression models for species richness and dominance, IndVal to identify indicator species and CCA for assemblage composition. All analyses were conducted at quadrat and site level. Results Species richness was significantly influenced by time since last fire ( RB > UB ), grazing intensity (light < moderate > heavy) and the fire–grazing interaction at quadrat level. Dominance reciprocated the response of species richness to time since last fire ( UB > RB ), but did not respond consistently to grazing intensity (light > moderate > or < heavy). Plant assemblage composition was significantly influenced by time since last fire, grazing intensity and vegetation structure (live vegetation cover and vegetation height). Indicator species of species‐poor, heavily grazed sites included alien species, such as Cirsium vulgare and Conyza bonariensis . Conclusion Response of species richness to grazing intensity conforms to the predictions of the intermediate disturbance hypothesis. Burning and moderate grazing should be part of grassland management. To prevent species loss and influx of alien species, heavy grazing should be minimized. As development of grassland ecological networks in a timber matrix is being pioneered in South Africa, these findings indicate a way forward for the management of similar systems elsewhere in the world.