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Title: Elephant versus other browsers' long-term influences on savanna woodland dynamics : synergistic influences of elephant and other large mammalian herbivores on the structure and composition of woody plant communities in Hluhluwe-iMfolozi Park, South Africa
Author: O'Kane, Christopher Anthony John
ISNI:       0000 0004 2744 3442
Awarding Body: University of Oxford
Current Institution: University of Oxford
Date of Award: 2012
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A crucial question in the debate about reintroducing elephant culling is whether the long-term effects of elephants and mesobrowsers on woodlands are similar. Sufficiently high biomass-densities of mesobrowsers may, following reduction or removal of elephants, continue to heavily impact earlier life-history stages of a similar suite of woody plants that elephant impacted, preventing these species from maturing. Thus a similar end-point for woodland structure and composition is achieved. No study exists in the literature where woody plant and habitat utilisation of the savanna browser guild has been determined in the same locality over the same period. A review of 49 years of literature implied that the two groups impact the same core woody-species in the same habitats. Dietary and habitat utilisation of guild members was determined in Hluhluwe-iMfolozi Park, South Africa. A small suite (n = 8) of woody species formed the core diet of all guild members. Herbivores’ densities were determined using a novel GIS approach; all members of the guild showed extensive overlap in habitat use. GPS collars and a GIS were then used to detect zones of different density of impala in the landscape, thus defining, for the first time, a natural fine-grain browsing gradient. Densities of woody seedlings were significantly less (average 48% reduction) in areas of high versus low impala density. A simple browse-browser model, incorporating, in a novel approach, functional groups of plant species, was parameterised from these results and an extensive review of the literature. Outputs suggest that over the long-term (100 years), impala will have a similar impact on woodland structure as elephant. An apparently strong synergistic effect between impala and elephant impact, suggests that reduction or removal of either impala or elephant will radically reduce long-term destruction of woodlands. In smaller or medium sized reserves, where control of mesobrowser populations is practical, profitable and more acceptable than elephant culling, these findings imply a re-direction of management efforts. Management should consider the biomass-density of both groups, rather than just focus on the system’s perceived ‘keystone’ species. Such principles may also apply to temperate and other systems.
Supervisor: Macdonald, David W. Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Ecology (zoology) ; zoology ; ecology ; savanna ecology ; ungulates ; ecosystems ; competition ; African elephants