Biodiversity-based evaluation of thicket thresholds at different levels of elephant impact – Towards assessment and monitoring of thicket vegetation

Abstract

Assessing the health status of thicket requires an understanding of the structure, composition and plant diversity of this vegetation type. With the wide variety of herbivores supported by thicket vegetation, factoring in individual species impacts is difficult. This study aims to utilise elephants (since they are umbrella species and ecosystem engineers) to assess the health of the thicket vegetation by comparing various vegetation metrics with elephant densities in the Addo Elephant National Park (AENP). When these metrics were related to the NDVI values obtained in the areas surveyed, the results produced a predictive model that could be used as an effective monitoring tool to assess the health of thicket vegetation within, and outside, the park. Healthy thicket vegetation can be described as having an NDVI range between 0.43 and 0.52, a species richness of 28–41 species, a species diversity (H) of 2.25–2.96, a canopy integrity between 31% and 55% and a total plant cover of 113–172%. In the AENP, this state of healthy thicket vegetation is achieved at an elephant density recommendation of 0.81 elephant/km2. In addition, at this prescribed elephant density, the appropriate plant cover is complemented by diversity – in particular the health of geophyte and succulent components of thicket.