Feeding choices and impacts of extralimital giraffe on two keystone tree species in the Kgalagadi National Park

Edmund February,Eleanor Shadwell,Storme Viljoen,Dawood Hattas

doi:10.4102/koedoe.v59i1.1454

Edmund February, Eleanor Shadwell + Show 2 more

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https://doi.org/10.4102/koedoe.v59i1.1454

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Abstract

In this article we determine the effect of an extralimital megaherbivore on the reproductive potential and vegetation structure of two keystone tree species in the Auob River in the south western Kalahari Desert of southern Africa. Using spoor and dung counts we establish the presence of giraffe in three predetermined density zones by walking 50 transects across the river in each zone. We also photographed six trees from each species in each zone and use these photographs to determine browse impact on reproductive potential, canopy volume as well as the percentage dieback on the extremities of the canopy. We then perform stable carbon and nitrogen isotope analysis on the leaves of the trees and compare these relative to the isotope ratios of giraffe dung to ascertain dietary preference. Crude protein was determined as a guide to nutritive value. Finally, we determine both chemical and physical defences for the two species. Our results show a significant negative impact of giraffe browse on tree canopies, no significant differences in recruitment and a noticeable decrease in flowers and pods at the giraffe browse height of 2 m – 5 m. No significant differences in crude protein or condensed tannins were found but significant differences in spinescence. Giraffe are not endemic to the Auob River and our study shows that the introduction of these animals is having a negative impact on the canopies of Vachellia haematoxylon. While there are, as yet, no significant impacts on reproductive potential we speculate that this will happen with time.Conservation implications: Our study shows that giraffe are significantly impacting the canopies of two common tree species in the Auob River in the arid Kgalagadi Transfrontier Park. Without management intervention an increasing population of giraffe will result in substantial changes to the plant community vegetation structure of the river.

Highlights

For many tourists, the primary reason for visiting an African national park is to see a diversity of large mammals (Grünewald, Schleuning & Böhning-Gaese 2016)
In 1991 8 giraffe were introduced into an enclosure near the Craig Lockhart borehole on the Auob River in the Kgalagadi Transfrontier Park in southern Africa, and in 1998 35 animals were released into the park from this enclosure (Bezuidenhout, Herbst & Ferreira 2010; Rowland 1991)
This impact is far greater for V. haematoxylon than for V. erioloba and if allowed to continue could lead to substantial changes in the plant community vegetation structure of the Auob River

Summary

Introduction

The primary reason for visiting an African national park is to see a diversity of large mammals (Grünewald, Schleuning & Böhning-Gaese 2016). To meet this expectation, giraffe (Giraffe camelopardalis) have been introduced into several reserves in South Africa (Bond & Loffell 2001; Parker & Bernard 2005). In 1991 8 giraffe were introduced into an enclosure near the Craig Lockhart borehole on the Auob River in the Kgalagadi Transfrontier Park in southern Africa, and in 1998 35 animals were released into the park from this enclosure (Bezuidenhout, Herbst & Ferreira 2010; Rowland 1991). Giraffe in particular have been shown to exert extreme browse pressure on some Vachellia species to the extent that these may be eliminated from the environment (Bond & Loffell 2001)

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