International Journal of Ecology

International Journal of Ecology / 2013 / Article

Research Article | Open Access

Volume 2013 |Article ID 769587 |

J. J. Viljoen, H. C. Reynecke, M. D. Panagos, W. R. Langbauer, A. Ganswindt, "Seasonal Selection Preferences for Woody Plants by Breeding Herds of African Elephants (Loxodonta africana) in a Woodland Savanna", International Journal of Ecology, vol. 2013, Article ID 769587, 10 pages, 2013.

Seasonal Selection Preferences for Woody Plants by Breeding Herds of African Elephants (Loxodonta africana) in a Woodland Savanna

Academic Editor: Bruce Leopold
Received19 Nov 2012
Revised25 Feb 2013
Accepted25 Feb 2013
Published26 Mar 2013


To evaluate dynamics of elephant herbivory, we assessed seasonal preferences for woody plants by African elephant breeding herds in the southeastern part of Kruger National Park (KNP) between 2002 and 2005. Breeding herds had access to a variety of woody plants, and, of the 98 woody plant species that were recorded in the elephant's feeding areas, 63 species were utilized by observed animals. Data were recorded at 948 circular feeding sites (radius 5 m) during wet and dry seasons. Seasonal preference was measured by comparing selection of woody species in proportion to their estimated availability and then ranked according to the Manly alpha (α) index of preference. Animals demonstrated a selection preference in feeding on woody vegetation, and Grewia hexamita, Grewia bicolor, Grewia flavescens, and Grewia monticola were selected consistently more over all seasons. In addition, our results indicate that elephant herds have a low preference for at least some of the woody species prone to extirpation and that feeding preferences for woody plants do not account for the association of elephants and riparian fringe habitat.

1. Introduction

The transformed and fragmented South African landscape has resulted in a lack of suitably sized protected areas for elephants, thus creating major challenges for managing elephant populations relative to their effects on ecosystem processes, vegetation structure, and species of plants and other animals [1]. Prolonged periods of locally high densities of elephants can alter vegetation structure, and the impact can intensify, especially when animals are confined to small or medium sized fenced reserves [2, 3]. This is especially challenging in fenced reserves smaller than 1000 km² to which elephants have been reintroduced by 2001 in South Africa [4, 5]. Subsequent to the introduction of elephant in these small areas, these savannas are exposed to intensive management, and decision makers are increasingly challenged to choose options which can balance needs of locally high elephant numbers with the maintenance of vegetation and ecosystem diversity.

Elephant feeding behaviour in combination with natural processes, for example, climate and fire, is the architects in different African landscapes and has been the focus of numerous studies describing elephant diet [611]. However, many of these studies failed to define selection preferences at the plant species level and only describe preferences at the broad level of growth forms [12, 13]. This gap resulted in incorrectly assigning certain responses in the environment to elephants [14]. White and Goodman [15] used quantitatively collected field data and concluded that differences in the structure and the diversity of woody vegetation in Mkhuze Game Reserve, South Africa, were unrelated to elephant use. Similarly, Landman et al. [16] used a microhistological analysis of faecal material to determine composition of elephant diet and thereby refuted the popular belief that elephant herbivory was the major driver of decline of important plants in the Addo Elephant National Park, South Africa.

Food resources are distributed heterogeneously across the landscape and vary in quality and quantity between seasons [14] which might explain elephants altering their selection from green grass during wet seasons to browse foliage during dry seasons [1820]. Therefore, it could be assumed that elephants might feed through a wide variety of vegetation communities for food species that permit efficient and effective nutrient intake and that specific plants meeting these criteria vary seasonally. Currently, only limited information is available regarding seasonal-dependent variability in food of African elephants, although such information would be important to avoid making suboptimal management decisions.

We describe the seasonal relative availability and species-specific preference for woody vegetation by free-ranging African elephant breeding herds in the southern part of the Kruger National Park (KNP).

2. Material and Methods

2.1. Study Area

Data were collected from March 2002 to September 2005 in the KNP within the Granite Lowveld, Delagoa Lowveld, Tshokwane-Hlane Basalt Lowveld, Gabbro Grassy Bushveld, and the Northern Lebombo Bushveld [21]. The KNP covers an area of 19000 km² and can be longitudinally divided into resistant granites in the west succeeded by Ecca shales, basalt, and rhyolites in the east that give rise to different soil types and associated flora and fauna [22]. Average rainfall varies from 500 to 750 mm/year [23]. From May to July is the early dry season, the late dry season is from August to October, the early wet season is from November to January, and the late wet season is from February to April [24].

2.2. Study Animals

We selected, as our focal herd, the first breeding herd of elephants in the southern region of KNP spotted from a helicopter after the take-off. On January 14, 2001, the matriarch was fitted with a VHF radio collar (Africa Wildlife Tracking cc, South Africa) which was replaced in August 2002 with a GPS satellite collar (Africa Wildlife Tracking cc, South Africa) for easier location. We trailed the breeding herds on foot which provided us the means to study patterns of woody plant use in all terrains, thus eliminating the sample bias that would be introduced if elephants were studied only in areas where elephants were regularly seen or areas that were easily accessible by road. To ensure that the collared group’s feeding behaviour was not atypical, following the same protocol as above, we recorded selection of noncollared breeding herds randomly sighted in the study area. To avoid collecting from the same breeding herds, we included data from about 20 different herds. Different individuals joined and left the core group from time to time, and contacts with these breeding herds were not continuous throughout the study period. Family groups (breeding herds) are defined as individuals who are seen together more than 70% of the time [25]. We did not collect data of all-male groups or solitary elephant bulls, as sexual dimorphism affects their feeding behaviour [26].

2.3. Data Collection

We collected data during two wet seasons and two dry seasons in the early and late phases of each season, commencing in March 2002 and ending in September 2005. Two criteria were used to define a feeding area prior to the recording of floristic data (Figure 1).

Firstly, average feeding time measured among at least three individuals in the breeding herd had to exceed 1.5 min. Secondly, the distance between feeding paths within a feeding area had to exceed 25 m. Individual elephants in breeding herds tend to move closer together as a unit when not feeding and especially when crossing open areas or when they perceive imminent danger (J. J. Viljoen, H. C. Reynecke, pers. obs.). Recording data during real-time observations following these criteria eliminated suppositions of the source and nature of the impact due to, that is, chance, accidental, fire, frost, droughts, natural mortality, other herbivores, or elephant bulls [27]. We then identified, using current field guides [28], all woody plants, available to elephants in feeding sites and recorded them as either utilised or notutilised. Feeding sites had a radius of 5 m (area = 78.5 m2) measured from the sighting of the first elephant from the herd feeding, assuming that this area would contain the impact of an individual [6, 26].

Once data had been collected at the feeding site observed to have been browsed, an alternative feeding path in the feeding area was followed to limit the chance of collecting data from the same individual’s selection. We collected data from four feeding sites selected in the feeding area occupied by a herd to allow for a better representation of the woody species present in the area. Cerling et al. [29] reported that isotope patterns in hairs of different individuals from the same elephant herd were similar which represented dietary preferences and behaviour of the entire group. Similarly, Buss [18] concluded that food habits and other behaviour of individuals within each group were similar based on field observations on feeding behaviour of elephants on the savanna lands in the Murchison Falls National Park region of Uganda.

Field data recording commenced anywhere between 10 and 60 min after a breeding herd had left the observed feeding area. Field crews (at least two observers) maintained a safe distance from the animals to minimize disturbance and always avoided being positioned upwind of the herd to avoid detection. Direct field observations in Uganda on feeding behaviour of elephants indicated that the primary feeding periods occurred most frequently during early morning and only minor or secondary quantities of food were selected at various times of day and night which supplemented their diets [18].

Each elephant within the breeding herd left behind numerous feeding sites on the feeding path, while moving slowly through the feeding area before regrouping and moving towards the next feeding area or to water.

2.4. Data Analysis

An animal which has access to a variety of food items will show preference for some and avoid others [30]. Preference was measured by comparing selection of woody species in proportion to their estimated availability. Seasonal preferences for woody species were then ranked according to Manly’s alpha (α) index of preference [30]: Where is Manly’s (preference index) for woody species is the proportion of woody species or selected ( and ), is the proportion of woody species or in the environment, and is the total number of tree species available.

If the index value /, then the woody species is given preference for selection, whereas if /, the woody species is neglected.

Data recorded from the woody plant species utilised and not utilised from the collared and noncollared herds were collated according to season. Availability and selection of woody species in the sample sites for all seasons were categorised with a frequency distribution into classes. A woody species with an observed frequency between 0 and 100 in all feeding sites was categorised as rare and with a frequency >100 as common. Similarly, woody species with a selection frequency between 0 and 25 were categorised as low selection and >25 as high selection. Statistica version 7 was used for all analyses [31].

3. Results

Average annual rainfall for the Lower Sabie area during the study period measured 549 mm during the wet seasons and 25 mm for the dry seasons. Areas traversed by observed herds during the study period extended from the Sabie and Crocodile River Thickets, Delagoa Thorn Thickets, Sclerocarya birrea subsp. caffra, Vachellia nigrescens Savanna, Mixed Combretum Woodlands to the Lebombo Mountain Bushveld. We sampled 237 feeding areas which included 468 wet season feeding sites and 480 dry season feeding sites (Figure 2). We recorded 98 woody species within the feeding areas and of this number; 63 species contributed to the elephant’s diet across all seasons.

Based on average percentages of the Manly alpha index values, the woody plants neglected decreased from the wet seasons (65%) to the dry season (41%) (Figure 3). This is confirmed by the values <0.1 for woody plants in the early wet, late wet, and early dry seasons indicating a low proportion of woody plants being selected (Tables 1 and 2). During the late dry seasons 34 woody plant species had values ranging from 0.1 to 1.0 (Table 2). This change towards a greater proportion of woody species recorded in the dry seasons indicates that the herds selected different vegetation types in the dry season compared to wet seasons. This change might be from the low grass production during the dry season and availability of a diversity of woody plant species in southern KNP [32].

Early wet season ( = 0.0227)Late wet season ( = 0.0263)

Manilkara mochisia 0.0866SVachellia nilotica 0.0963S
Schotia capitata 0.0866SBoscia mossambicensis 0.0963S
Strychnos madagascariensis 0.0866SOzoroa obovata 0.0723S
Bolusanthus speciosus 0.0577SClerodendrum glabrum 0.0642S
Peltophorum africanum 0.0469SAlbizia harveyi 0.0482S
Carissa bispinosa 0.0433SSclerocarya birrea 0.0482S
Combretum molle 0.0433SXimenia americana 0.0482S
Grewia hexamita 0.0408SGrewia bicolor 0.0351S
Boscia albitrunca 0.0371SGrewia monticola 0.0341S
Sclerocarya birrea 0.0371SBoscia albitrunca 0.0321S
Lannea schweinfurthii 0.0334SSearsia gueinzii 0.0321S
Albizia petersiana 0.0289SStrychnos spinosa 0.0321S
Dombeya rotundifolia 0.0289SLannea schweinfurthii 0.0321S
Ozoroa engleri 0.0266SGrewia  flavescens 0.0299S
Cassia abbreviata 0.0217NGrewia hexamita 0.0282S
Mundulea sericea 0.0217NManilkara mochisia 0.0241N
Cissus cornifolia 0.0204NTerminalia prunioides 0.0222N
Diospyros mespiliformis 0.0200NCombretum apiculatum 0.0218N
Grewia bicolor 0.0192NCombretum zeyheri 0.0201N
Grewia  flavescens 0.0164NZiziphus mucronata 0.0186N
Searsia gueinzii 0.0162NCombretum imberbe 0.0161N
Pterocarpus rotundifolius 0.0156NAlbizia forbesii 0.0140N
Ximenia caffra 0.0144NDalbergia melanoxylon 0.0139N
Euclea divinorum 0.0131NPterocarpus rotundifolius 0.0129N
Albizia forbesii 0.0124NDiospyros mespiliformis 0.0126N
Combretum zeyheri 0.0124NEuclea divinorum 0.0114N
Dichrostachys cinerea 0.0118NVachellia tortilis 0.0113N
Ehretia amoena 0.01100NEhretia amoena 0.0098N
Dalbergia melanoxylon 0.0107NGymnosporia buxifolia 0.0092N
Vachellia nigrescens 0.0105NGymnosporia senegalensis 0.0089N
Flueggea virosa 0.0084NDichrostachys cinerea 0.0084N
Vachellia robusta 0.0081NCombretum hereroense 0.0075N
Combretum collinum 0.0072NVachellia robusta 0.0064N
Combretum hereroense 0.0069NVachellia nigrescens 0.0057N
Ziziphus mucronata 0.0064NPhilenoptera violacea 0.0055N
Vachellia gerrardii 0.0054NCombretum paniculatum 0.0044N
Gymnosporia senegalensis 0.0052NGrewia villosa 0.0040N
Combretum paniculatum 0.0048NFlueggea virosa 0.0019N
Grewia villosa 0.0040N
Vachellia tortilis 0.0036N
Combretum apiculatum 0.0029N
Euclea undulate 0.0024N
Philenoptera violacea 0.0022N
Cienfuegosia hildebrandtii 0.0012N

Early dry season (1/m = 0.0161)Late dry season (1/m = 0.0145)

Manilkara mochisia 0.093736SBoscia mossambicensis 1S
Searsia gueinzii 0.065615SCommiphora mollis 1S
Grewia monticola 0.06249SCroton megalobotrys 1S
Vachellia xanthophloea 0.056241SGrewia occidentalis 1S
Grewia bicolor 0.04838SPeltophorum africanum 0.9286S
Ozoroa engleri 0.046868SVachellia xanthophloea 0.8571S
Rhoicissus spp. 0.046868SSchotia brachypetala 0.5714S
Terminalia sericea 0.043263SGrewia monticola 0.5616S
Ziziphus mucronata 0.04166SEuclea natalensis 0.5S
Vachellia gerrardii 0.040534SKigelia africana 0.5S
Combretum imberbe 0.037494SSpirostachys africana 0.5S
Grewia hexamita 0.036896STerminalia sericea 0.5S
Dombeya rotundifolia 0.035151SGrewia bicolor 0.4901S
Peltophorum africanum 0.031245SGrewia hexamita 0.4419S
Schotia brachypetala 0.031245SVachellia gerrardii 0.4S
Lannea schweinfurthii 0.027269SCombretum imberbe 0.3636S
Pterocarpus rotundifolius 0.027102SAlbizia forbesii 0.2941S
Vachellia nigrescens 0.024996SGrewia villosa 0.2895S
Albizia petersiana 0.022318SCombretum zeyheri 0.2857S
Vachellia robusta 0.020377SDalbergia melanoxylon 0.2787S
Diospyros mespiliformis 0.019228SVachellia tortilis 0.25S
Ozoroa obovata 0.018747SManilkara mochisia 0.25S
Euclea divinorum 0.017439SMundulea sericea 0.25S
Combretum hereroense 0.017267SSearsia gueinzii 0.25S
Dalbergia melanoxylon 0.015539NDiospyros mespiliformis 0.2143S
Albizia forbesii 0.013339NEuclea divinorum 0.1912S
Grewia  flavescens 0.012226NCombretum paniculatum 0.1818S
Sclerocarya birrea 0.010415NOchna inermis 0.1667S
Vachellia tortilis 0.008521NVachellia nigrescens 0.1386S
Dichrostachys cinerea 0.008497NOzoroa engleri 0.125S
Ximenia caffra 0.006695NGrewia  flavescens 0.1134S
Gymnosporia senegalensis 0.006465NVachellia robusta 0.1132S
Grewia villosa 0.003125NCommiphora pyracanthoides 0.1111S
Flueggea virosa 0.001644NGymnosporia senegalensis 0.1111S
Ehretia amoena 0.001103NVachellia erubescens 0.1S
Vachellia erubescens 0NPterocarpus rotundifolius 0.0976S
Vachellia exuvialis 0NVachellia exuvialis 0.087S
Bolusanthus speciosus 0NDichrostachys cinerea 0.07S
Boscia foetida 0NZiziphus mucronata 0.0455S
Cissus cornifolia 0NEhretia amoena 0.0323S
Combretum apiculatum 0NCombretum apiculatum 0.0313S
Commiphora mollis 0NCombretum hereroense 0.0238S
Commiphora pyracanthoides 0NBoscia foetida 0.0213S
Croton megalobotrys 0NVachellia grandicornuta 0N
Ehretia rigida 0NAlbizia petersiana 0N
Euclea natalensis 0NBalanites maughamii 0N
Euphorbia ingens 0NBerchemia discolor 0N
Grewia occidentalis 0NBolusanthus speciosus 0N
Gymnosporia buxifolia 0NBoscia albitrunca 0N
Gymnosporia maranguensis 0NCarissa bispinosa 0N
Hyperacanthus amoenus 0NCommiphora africana 0N
Oncoba spinosa 0NEhretia rigida 0N
Ormocarpum trichocarpum 0NEuclea undulata 0N
Philenoptera violacea 0NFlueggea virosa 0N
Phoenix reclinata 0NGardenia volkensii 0N
Phyllanthus reticulatus 0NGymnosporia buxifolia 0N
Senna petersiana 0NLannea schweinfurthii 0N
Spirostachys africana 0NMystroxylon aethiopicum 0N
Strychnos madagascariensis 0NOncoba spinosa 0N
Terminalia phanerophlebia 0NOrmocarpum trichocarpum 0N
Terminalia prunioides 0NPhilenoptera violacea 0N
Ximenia americana 0NPhyllanthus reticulatus 0N
Ptaeroxylon obliquum 0N
Schotia caffra 0N
Sclerocarya birrea 0N
Senna petersiana 0N
Strychnos spinosa 0N
Terminalia phanerophlebia 0N
Ximenia americana 0N

Three Grewia species, namely, Grewia bicolor, Grewia flavescens, and Grewia monticola which have a wide distribution in the landscape, were selected in all seasons except in the early wet season, and Grewia hexamita was the only woody plant recorded as being highly selected in all four seasons (Table 3). van Wyk and Fairall [33] reported that Grewia species were sought after by elephants in the southern region of the KNP. Rarity of occurrence, that is, species occurring at low frequencies (less than 100 individuals in all feeding sites), did not stop elephants from actively seeking out these plants. Of the 63 plants selected across all seasons, only 10 plants were common, and 53 plants were classified as rare (Table 3).

SpeciesEarly wetLate wetEarly dryLate dry

Grewia hexamita h, rh, rh, rh, r
Grewia bicolor h, ch, ch, c
Grewia  flavescens h, cl, rl, r
Grewia monticola h, ch, rh, r
Searsia gueinzii h, rh, rh, r
Manilkara mochisia h, rh, rh, r
Ozoroa engleri h, rh, rl, r
Peltophorum africanum h, rh, rh, r
Schotia brachypetala h, rh, rh, r
Lannea schweinfurthii l, rh, rh, r
Sclerocarya birrea l, rh, rl, r
Vachellia gerrardii h, rh, r
Vachellia nigrescens h, rl, c
Vachellia robusta l, rl, r
Vachellia tortilis l, rh, c
Vachellia xanthophloea h, rh, r
Albizia forbesii l, ch, r
Combretum hereroense l, rl, r
Combretum imberbe h, rh, r
Dalbergia melanoxylon l, ch, r
Dichrostachys cinerea l, cl, c
Diospyros mespiliformis l, rl, r
Euclea divinorum l, rl, c
Grewia villosa l, rh, r
Gymnosporia senegalensis l, cl, c
Pterocarpus rotundifolius h, cl, r
Terminalia sericea h, rh, r
Ziziphus mucronata h, rl, r
Boscia mossambicensis h, rh, r
Ozoroa obovata h, rl, r
Albizia petersiana h, rl, r
Dombeya rotundifolia h, rh, r
Boscia albitrunca h, rh, r
Vachellia erubescens l, r
Vachellia exuvialis l, r
Boscia foetida l, r
Combretum apiculatum l, r
Combretum paniculatum l, r
Combretum zeyheri h, r
Commiphora mollis h, r
Commiphora pyracanthoides l, r
Croton megalobotrys h, r
Ehretia amoena l, r
Euclea natalensis l, r
Grewia occidentalis h, r
Kigelia africana h, r
Mundulea sericea h, r
Ochna inermis l, r
Spirostachys africana l, r
Ziziphus mucronata l, r
Terminalia sericea h, r
Flueggea virosa l, r
Rhoicissus spp.h, r
Ximenia caffra l, r
Vachellia nilotica h, r
Albizia harveyi h, r
Clerodendrum glabrum h, r
Strychnos spinosa h, r
Ximenia americana h, r
Bolusanthus speciosus h, r
Carissa bispinosa h, r
Combretum molle h, r
Schotia capitata h, r

4. Discussion

Although it is reported that elephants have a preference for the riparian fringe [34] and are frequently associated with that plant community (Figure 2), our results suggest that they do not have any feeding preference for woody plants in the riparian fringe. Tree species generally associated with riparian vegetation such as Ficus sycomorus, Breonadia salicina, and Nuxia oppositifolia are commonly found along rivers in the study area. However, the feeding sites actively selected by breeding herds in our study did not contain these woody species. Thus, the association of elephants with riparian fringes might rather be for regulating body temperature and feeding on the reed Phragmites australis in the riverbeds (J. J. Viljoen, H.C. Reynecke, pers. obs.).

As there are insufficient quantitative data available, no clear prediction has emerged about which woody species are prone to extirpation and under what circumstances [35]. Kerley et al. [12] made reference to the lack of quantitative studies in terms of species contribution in diet of elephants as well as the plethora of studies that indirectly infer elephant diet from plant-based studies. For example, Sclerocarya birrea is a woody plant that is deemed a species susceptible to extirpation [35, 36]; yet, our data show that this plant had a high selection frequency only in the late wet season at a low Manly alpha index value of 0.048. Although present in the feeding areas in the early dry and late dry seasons, this plant was neglected by the breeding herds of elephants.

To a large degree climatic and biological variability in African savannas explain differences in heterogeneity and productivity of vegetation at landscape and regional scales [14, 35]. These explain the differential use of habitats and seasonal changes in the distribution of elephants [7, 3744]. This study shows that the selection preference of elephant herds corresponds with seasonal changes [29, 44]. In the feeding areas frequented by the observed elephant breeding herds, 64% of the available woody species were browsed by elephants during the four seasons. This relatively high proportion of sought after woody species suggests that breeding herds select areas that permit efficient and effective nutrient intake [29, 45]. Functional traits of selected woody species, that is, their phenology and life history, probably vary seasonally, which could explain these selection patterns. Future research should investigate the causal mechanisms underlying selection preferences, which might include plant nutrients in the soil, leaves, fruits, and flowers of woody species.

Although our observations were restricted to diurnal hours due to safety issues and visibility, we propose that the woody plant species available and selected during the night did not differ from those selected during daytime [18].


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