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Do elephants over-utilize mopane woodlands in northern Botswana?

Published online by Cambridge University Press:  10 July 2009

Raphael Ben-Shahar
Raphael Ben-Shahar
Affiliation:
Department of Zoology, University of Oxford, South Parks Road, Oxford 0X1 3PS
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Abstract

Evidence from southern African semi-arid savannas suggests that high elephant densities in nature reserves cause the over-utilization of woodlands. Northern Botswana, with its prolific elephant population, is expected to follow such a pattern unless the densities of elephants which could be sustained by indigenous woodlands are determined and maintained at carrying capacity. Above ground biomass production was estimated for mopane (Colophospermum mopane) woodlands, a principal food source for elephants, which grows over much of northern Botswana. Densities of trees and shrubs, dimensions of plants and elephant densities were recorded within stratified plots situated according to a regional rainfall gradient. Mean estimates of above ground biomass (foliage and twigs) were 9.41 and 7.83 t ha−1 for shrubs and trees respectively. A logistic model described the maximum levels of biomass removal from plants before over-utilization of mopane occurred. Variables incorporated in the model included above ground biomass of mopane shrubs and trees, growth rates of plants and expected off-take by elephants. The model predicted a complete biomass regain within 10 y if no elephant browsing occurs. Intensive elephant browsing in woodlands containing 15 elephants km−2, however, can suppress biomass production if growth rates of plants fall below 70% of the maximum annual rate. Nonetheless, there was no substantial evidence to suggest that elephants will reduce the biomass of mopane woodlands in northern Botswana below a sustainable level if their numbers are allowed to increase considerably beyond the current estimate.

Keywords

biomassBotswanaColophospermum mopaneelephantsproductionrainfallsavannashrubstrees
Type
Research Article
Information
Journal of Tropical Ecology , Volume 12 , Issue 4 , July 1996 , pp. 505 - 515
Copyright
Copyright © Cambridge University Press 1996

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