Plant community structure and possible vegetation changes after drought on a granite catena in the Kruger National Park, South Africa

Abstract

A preliminary study investigated the associations between vegetation communities along catenary soil gradients in 2015. The severe drought of 2016 in South Africa presented the opportunity to study post-drought savanna vegetation changes. This hillslope transect was surveyed for five successive seasons. The Braun-Blanquet method was used, and the data were analysed by means of the TWINSPAN algorithm, which resulted in the classification of different communities on the crest, sodic site and riparian area. Change in herbaceous and grassy vegetation composition and diversity in the transect is compared between rainfall years, wet and dry seasons, and three different zones (crest, sodic site and riparian areas). Spatial and temporal autocorrelation of the woody component shifted the focus to variance within the graminoid and herbaceous layers. Clear vegetation changes were observed on the crest and the sodic sites, whereas changes in the riparian area were less obvious. In all three habitats, species richness decreased after the drought and did not reach pre-drought levels even after two years. However, plant species diversity was maintained as climax species were replaced by pioneer and sub-climax species. These changes in community structure, which had reverted to systems dominated by climax species by the end of the sampling period, might be an indication of the savanna ecosystem’s resilience to drought conditions. Conservation implications: Although clear vegetation changes were observed in the five successive seasons after the drought, this study showed that the savanna ecosystem is relatively resistant to drought and that human intervention is not needed.

Keywords

• drought
• vegetation classification
• savanna
• diversity
• catena