notes and records

© 2000 East African Wild Life Society, Afr. J. Ecol., 38, 175–177

Notes and records

Wildfire reduces elephant herbivory on Colopho-spermum mopane (Fabaceae)

Andrew D. Kennedy*Centre for African Ecology, University of the Witwatersrand,Private Bag 3, WITS 2050, South Africa

Colophospermum mopane Kirk ex J.Leon (Fabaceae), com-monly known as mopane, is an example of a tree speciesthat is heavily browsed by elephants Loxodonta africana(Blumenbach) (Ben-Shahar, 1993). Young mopaneleaves are favoured by elephants because of their highcrude protein content of 17.5% (Styles & Skinner, 1997).Stems are also browsed on account of their mineral value,particularly of phosphate and calcium (Van Wyk, 1994).Being semideciduous, the tendency for C. mopane toretain some of its leaves during the dry season is con-sidered crucial to sustaining high elephant populationsthrough this resource-deficient time of year.

Colophospermum mopane often grows in savanna habi-tats that are prone to wildfire. The high resin content ofits foliage causes the shrub to burn readily, even whenthe leaves are green. It may be hypothesized that thiscombustion process alters the palatability of C. mopaneshrubs to herbivores. Selective browsing by elephantsupon the charred tips of C. mopane branches has beenreported (Brynard & Pienaar, 1960; Van Wyk & Fairall,1969) and it is widely believed that elephants prefer thecrisp, darkened shoots of burnt C. mopane to the sinewy,fibrous stems of unburnt plants (I. White, pers. comm.).This selectivity has been attributed to changes in thechemical content of woody material induced by the burn-ing process.

To test the hypothesis that elephants feed selectivelyupon burnt C. mopane a survey of elephant damage to C.mopane shrubs was undertaken in the Letaba Exper-imental Burning Plots (LEBPs) in the Kruger National

* Present address and correspondence: Department of Geography,

The University of Western Australia, Nedlands, Western Australia

6907.

175

Fig 1 Map showing the location of the Letaba Experimental

Burning Plots in the Kruger National Park, South Africa.

Park (Fig. 1). The LEBPs comprise a series of 56 rec-tangular plots, each of surface area 6.5 ha, arranged ina randomised block design. A variety of prescribed firetreatments has been applied to these plots since 1958.Elephants roam freely throughout the Letaba region andno attempt has ever been made to exclude them from theLEBPs.

For the purpose of this study a total of 225 C. mopaneshrubs were selected randomly from within nine pairedplots in such a manner that 75 were derived from eachof the biennial August burn, biennial October burn andcontrol treatments. These treatments conform with mid-dry season wildfires, early wet-season wildfires andunburnt conditions, respectively.

Selection of trees was carried out as follows: withineach 360 × 180 m plot, five parallel transects of length180 m were laid out at 72-m intervals. Five points wererandomly delimited along each transect so that no two

176 Notes and records


points occurred within 10 m of each other. To minimizeedge effects no points were allocated within 10 m of thefirebreaks at either end of the plots. The nearest C. mopanetree to each point was then selected.

The total incidence of elephant herbivory is shown inTable 1. Of the 225 C. mopane individuals examined dur-ing this project 84 showed visible signs of elephantdamage. This varied from single shoots that had beensnapped or twisted to the breaking of branches and theuprooting of larger trees. Of those shrubs examined inburnt sites, 27.5% had experienced elephant damagerelative to 57% in unburnt controls. A x2-test on thesedata indicates that the difference in elephant damage toburnt versus unburnt shrubs is significant at theP ³ 0.01 and P ³ 0.001 levels for the August–Controland October–Control comparisons, respectively.

Comparison of elephant damage to the August andOctober burning plots reveals that slightly more damagewas inflicted upon C. mopane in plots that were burnt inthe middle of the dry season than at the start of the wetseason. A total of 32% of shrubs showed evidence ofelephant browsing in the first treatment against 23% ofshrubs in the second treatment. However, this differenceis not significant at the P ³ 0.05 level. This suggests thatwildfire during the rainy season may render C. mopaneless palatable to elephants than wildfire occurring at thepeak of the dry season, but further data are required totest this.

The results of this study suggest that elephants do notfeed preferentially upon burnt C. mopane. Instead thesinewy, fibrous stems of unburnt plants appear to beselected over the crisp, darkened shoots of burnt plants.Such selectivity conforms with what is known about thefeeding behaviour of elephants in the Luangwa Valley,Zambia, where unburnt C. mopane trees are often strippedof their cambial/bark layer (Lewis, 1991). The resultsalso support the observation of Bell & Jachmann (1984),who found that elephants in the Kasungu National Park,

Table 1 Number of

Colophospermum mopane shrubs damaged

and undamaged by elephants in

plots with different fire

histories

August October

wildfire wildfire Control

Total number of trees examined 75 75 75

Number of trees with elephant damage 24 17 43

Number of trees without elephant damage 51 58 32

Percentage elephant damage 32 23 57

Malawi, avoided burnt areas of Brachystegia woodlandand congregated instead in areas unaffected by fire. How-ever, the earlier observations of selective browsing onthe charred tips of C. mopane (Brynard & Pienaar, 1960;Van Wyk & Fairall, 1969) in the Kruger National Parkare not supported.

The results of this study have broader ecological sig-nificance. Wildfires and elephant herbivory are recog-nized as two of the principal determinants of the structureand composition of African savanna vegetation (Laws,1970; de Booysen & Tainton, 1984). Although theimpact of each individual factor is relatively well under-stood, the interaction between the two factors has notbeen fully explored. The results of this study suggestthat elephants find burnt C. mopane less palatable thanunburnt C. mopane. This implies that fire and herbivorydo not operate independently of each other but insteadshow interaction. At an applied level, the results suggestthat elephant distributions may be manipulated throughthe application of prescribed wildfires, a conclusion thatwill be of considerable interest to national park managersseeking to manage elephant populations through non-destructive means.

Acknowledgements

I am grateful to Harry Biggs, Andre Potgieter, JohanOelofse and Johane Baloyi of the National Parks Board,South Africa, for assistance during this project. BarabaraLederer of the University of Bern helped to collect fielddata.

References

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of Brachystegia woodland by elephants. Afr. J. Ecol. 22, 157–

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Notes and records 177

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BRYNARD, A.M. DE V. & PIENAAR, U. (1960) Annual report of the

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LEWIS, D.M. (1991) Observations of tree growth, woodland

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Luangwa Valley, Zambia. Afr. J. Ecol. 29, 207–221.

STYLES, C.V. & SKINNER, J.D. (1997) Seasonal variation in the

quality of mopane leaves as a source of browse for mammalian

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VAN WYK, P. (1994) Field Guide to the Trees of the Kruger National

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(Manuscript accepted 18 February 1999)

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