Local extirpation of woody species in Colophospermum mopane woodland under chronic utilisation by elephants

Abstract

The hypothesis that certain woody species may be prone to local extirpation under chronic elephant utilisation was examined for Colophospermum mopane open woodland, for an area within the foraging range of elephants from permanent water. Elephant density increased from nearly absent in the 1970s to >3 elephants km⁻², with 0.62 adult bulls km⁻², by 2022. Study components of vegetation impact included a long-term elephant exclosure, a fence-line contrast with an adjacent communal area, comparison with an adjacent wildlife reserve carrying a fifth of the elephant density and the use of historical studies of the vegetation. A history of elephant utilisation resulted in woodland becoming hedged through pollarding of tree stems by elephants. Impacted woodland was characterised by a slightly lower tree density, reduced average height of trees, altered shrub composition and lower species richness. The dominant C. mopane and sub-dominant species had persisted. However, about 14 species were potentially trending towards local extirpation on account of very high levels of adult mortality, but had persisted because of a low level of seedling recruitment. Fleshy fruits were a shared attribute among most extirpation-trending species, which, together with a reduction in woody species richness that affects browsers, has ramifications for trophic flows.