Complexities associated with elephant impact on Sclerocarya birrea subsp. caffra in the Greater Kruger National Park

Abstract

African elephants Loxodonta africana are habitat modifiers, with the ability to impose heavy impact on trees. Conservation managers are concerned about increasing elephant impact on keystone tree species such as the marula Sclerocarya birrea subsp. caffra, however, a variety of natural and management-based factors influence the likelihood of a marula receiving elephant impact. Our study focused on a marula population in the Greater Kruger National Park which has been exposed to elephants for five years. Our objectives were to (1) examine the potential factors responsible for the decline of adult marula, (2) evaluate elephant impact across marula size classes, and (3) evaluate elephant impact on male and female marula. We modelled tree mortality as a response variable to factors, which included previous elephant impact, sex of the tree, distance to water, distance to roads, and termite presence. Of the sampled trees, 38% were dead. We found that a combination of elephant impact and termite presence within trees best explained tree mortality, with the presence of water and roads having relatively uniformed effects on tree mortality because of an overabundance of these features. Trees in the smaller height classes had the highest annual mortality levels, whilst female trees had heavier impact levels in comparison to males. Our results highlight the complexity of a marula tree mortality, and how both natural and management-based factors can influence tree survival. We propose that environmental management alterations can decrease elephant-tree encounter rates and increase tree survival.