Tall trees survival in relation to bottom-up and top-down drivers in Hluhluwe-iMfolozi Park, South Africa

Abstract: Tall trees are in decline throughout many national parks in South Africa. Many studies have found that trees within a certain size are preferred by elephants which damage trees by either bark stripping, breaking tree branches and/or stems or by knocking over trees (toppling). The decline of trees in relation to growing elephant populations is of growing concern, as tall trees are a key stone feature in the savanna ecosystem. One of the parks where elephant populations are increasing is in Hluwhluwe-iMfolozi Park, KwaZulu-Natal. To investigate whether trees within the park are in decline, we set out to revisit previously tagged trees from 2007 to reassess their condition. When revisiting trees a total of 260 trees were found, resulting in a 92.5% success rate in relocation of individual trees. The analyses showed that elephant impact was not descriptive of tree mortality within the park. Two tree species however, Combretum molle and Spirostachys africana, had a lower mortality risk. The risk of elephant impact was mediated by several abiotic variables, such as slope, aspect and elevation. The results of this study further accentuates the need to research the interaction between various factors to understand the causative agents of tall tree mortality.