Elephant herbivory of knob‐thorn (Senegalia nigrescens) and ivory palm (Hyphaene petersiana) in Bwabwata National Park, Caprivi, Namibia: The role of ivory palm as a biotic refuge

Abstract

AbstractAfrican elephants have major impacts on vegetation, particularly at high densities. Knob‐thorns (Senegalia nigrescens) are typically ring‐barked by elephant, and high levels of mortality are common at high elephant densities. Our study aimed to test whether ivory palm clusters (Hyphaene petersiana) form a biotic refuge for knob‐thorn against elephant herbivory. We measured the density, damage and mortality of knob‐thorns in sites differing according to ivory palm presence and elephant density, and thus, the probability of knob‐thorn encounter by elephants. The site with palms and low elephant density, had a high density of knob‐thorns, but lower proportions of damaged and dead trees, than sites without palms but with similar or higher elephant density. In the former, knob‐thorns were associated with palm clusters, particularly saplings and young adults. In this site, low proportions of damaged and dead knob‐thorns were recorded in palm clusters, compared with outside clusters, and to those in the other sites. Our study also showed that juvenile palms which protected knob‐thorns, suffered low mortality in contrast to subadult palms. We have no evidence but implicate elephants and suggest that in palm clusters, subadult palms are more accessible to elephants than knob‐thorns because of the different methods of utilisation.