Forb community responses to an extensive drought in two contrasting land-use types of a semi-arid Lowveld savanna

Abstract

Projected increases in the frequency and severity of drought events are expected to impose changes in the ecology of native forb communities in semi-arid ecosystems. We examined the state of forb communities during, and directly after an extreme drought event across two contrasting land-use types, which included a protected area (high diversity of free roaming wild herbivores) and communal rangeland (long history of intensive cattle grazing) in a semi-arid Lowveld savanna of the Gazankulu area, South Africa. Forb floristic data were collected towards the end of the drought and repeated after the drought release a few months later. Forb community composition was significantly different among land-use types. Community changes were not induced by annual forb emergence alone, but through species-specific dominance shifts, which differed among land-use types. Forb richness, diversity and biomass were equally low at both land-use types and increased significantly after the drought release, although the magnitude of response was much stronger in the protected area, whereas drought contributed to a directional change in the protected area with a complete post-drought turnover in both annual and perennial forb species, much less variability was observed in the communal rangeland, which may suggest long-term effects imposed by land-use history.

Keywords:

• climate change
• diversity
• grazing
• herbivory
• rainfall variability