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Effects of elephants on ecosystems and biodiversity

January 2008

Authors:

Graham I. H. Kerley

Nelson Mandela University

Marietjie Landman

Nelson Mandela University

Laurence M. Kruger

Organzation for Tropical Studies and University of Cape Town

Norman Owen-Smith

University of the Witwatersrand

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Exponential decline in the abundance of mistletoes (Viscum 2 rotundifolium, Viscum crassulae, Viscum obscurum) in the presence of elephants in 3 4 5

…

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Chapter 3 1

Effects of elephants on ecosystems and biodiversity

Lead author: Graham I.H. Kerley 1

Authors: Marietjie Landman 1, Laurence Kruger 2, Norman Owen-Smith 3

Contributing authors: Dave Balfour 4, Willem de Boer 5, Angela Gaylard 6, Keith

Lindsay 7 & Rob Slotow 8

1 Centre for African Conservation Ecology, Department of Zoology, Nelson

Mandela Metropolitan University

2 Organization for Tropical Studies/Botany Department, University of Cape Town

3 Centre for African Ecology, School of Animal, Plant and Environmental Sciences,

University of the Witwatersrand

4 Eastern Cape Parks

5 Resource Ecology Group, Wageningen University

6 South African National Parks

7 Amboseli Trust for Elephants/Amboseli Elephant Research Project

8 Amarula Elephant Research Programme, School of Biological and Conservation

Sciences, University of KwaZulu-Natal

Introduction...............................................................................................................4

Elephants as megaherbivores ..................................................................................6

Feeding behaviour ....................................................................................................7

Discarded forage.....................................................................................................8

Sexual dimorphism and feeding .............................................................................9

Diet........................................................................................................................10

Ecological processes influenced by elephants.......................................................12

Effects of elephants.................................................................................................14

Individual plants and species................................................................................14

Mechanisms of impact on individuals......................................................................15

Case studies of species-specific impacts ..................................................................17

Assessing species-specific vulnerability...................................................................21

SECOND DRAFT Assessment of South African Elephant Management 2007 1

a. Plant traits -...........................................................................................................22

b. Landscape and management unit characteristics – Vulnerability to e..................22

Fauna.........................................................................................................................22

Invertebrates..............................................................................................................23

Reptiles and amphibians...........................................................................................24

Birds..........................................................................................................................24

Bats ...........................................................................................................................25

Small terrestrial mammals........................................................................................25

Large terrestrial mammals........................................................................................25

Communities & Ecosystems.................................................................................27

The population and species level impacts brought about by elephants (documented

in part above) may be expressed at the community and ecosystem level, including

emergent properties of such systems, such as nutrient cycling, vegetation structure

and dynamics. ...........................................................................................................27

Nutrient cycling ........................................................................................................28

Soil resources............................................................................................................29

Seed dispersal ...........................................................................................................29

Comparison among ecosystems................................................................................30

Illustrative case studies.............................................................................................31

Contrasts across biomes and ecosystems..................................................................37

Gaps in knowledge ...................................................................................................39

Rates of change........................................................................................................39

Megaherbivore release ...........................................................................................40

Spatial perspectives ................................................................................................41

Piosphere effects...................................................................................................42

Impacts in confined areas/small reserves..............................................................44

Constraints to identifying elephant effects...........................................................44

Conceptual/modelling framework for contextualizing elephant effects............45

General assessment.................................................................................................47

Breaking and toppling...........................................................................................47

Plant resistance .....................................................................................................47

Bark stripping: Little known.................................................................................48

Assessment: Elephants and Biodiversity..............................................................48

Overall Assessment...............................................................................................49

SECOND DRAFT Assessment of South African Elephant Management 2007 2

Concluding comments ............................................................................................49 1

References................................................................................................................50

Figures

Figure. 3.1: Damage to baobabs by elephants in the Chobe National Park,

Botswana (Photo: W. Trollope)..................................................................................8

Figure. 3.2: Regression analysis at the 90th quantile of recent elephant use of

baobabs in the Kruger National Park and the Inaccessibility value calculated for

these. Elephant browsing drops below 100% at 7o slope and below 20% at the 18o

slope cut-off (Edkins et al. 2007)..............................................................................18

Figure. 3.3: Exponential decline in the abundance of mistletoes (Viscum

rotundifolium, Viscum crassulae, Viscum obscurum) in the presence of elephants in

the Addo Elephant National Park (Magobiyane, 2006)............................................21

Graphs

Table 3.1: The relative role of elephant in broad ecological processes (n = 19),

modified from Kerley & Landman (2006), operating in subtropical thicket in

relation to other megaherbivores (2 sp.), mesoherbivores (19 sp.), omnivores (3 sp.)

and carnivores (18 sp.)..............................................................................................13

On the following morning we were up before the sun, and, travelling

in a northerly direction, soon became aware that we were in a

district frequented by elephants, for wherever we looked, trees were

broken down, large branches snapped off, and bark and leaves

strewn about in all directions, whilst the impress of their huge feet

was to be seen in every piece of sandy ground.

Selous (1881, page 39, north of Gweru, Zimbabwe in 1872).

SECOND DRAFT Assessment of South African Elephant Management 2007 3

Introduction 1

The issue of the effects of elephants within ecosystems has emerged strongly since

the formulation of the concept of the “elephant problem and the concerns that

elephants may irrevocably alter the remaining areas which are available to them”

(Caughley, 1976a). Two perspectives need to be kept in mind when these concerns

are raised. Firstly, the order of Proboscideans (including the modern elephants)

evolved in Africa, as part of a unique group of mammals (the Afrotheria - Robinson

& Seiffert, 2003), with their roots going back 80 million years. Subsequently, over

160 species of Proboscideans are thought to have evolved, with all the continents

except Australia and Antarctica being colonised (see Sukumar (2003) for a

comprehensive summary of Proboscidean evolution). The modern African elephant

(Loxodonta africana) emerged about 3 million years ago. These megaherbivores,

therefore, need to be seen as part of the evolutionary history of African ecosystems,

with opportunity for extensive co-evolution with African biodiversity. Hence, at

some spatial- and temporal-scale, elephants and African biodiversity can coexist.

From another perspective, we need to recognise that all herbivores, which by

definition are consumers of plant tissue, have an influence – to a greater or lesser

extent – on communities and ecosystems (Huntly, 1991). Even relatively small

herbivores can have profound effects in shaping ecosystem structure, particularly

when they occur at high densities. For example, Cote et al. (2004), writing about the

increase in deer abundance, had the following to say:

They affect the growth and survival of many herb, shrub and tree

species, modifying patterns of relative abundance and vegetation

dynamics. Cascading effects on other species extend to insects, birds,

and other mammals. Sustained over-browsing reduces plant cover

and diversity, alters nutrient and carbon cycling, and redirects

succession....simplified alternative states appear to be stable and

difficult to reverse.

Similarly, smaller herbivores with specific manners of feeding can alter ecosystems,

although their abundance and overall use of resources may not be high. For

SECOND DRAFT Assessment of South African Elephant Management 2007 4

example, Yeaton (1988) and de Villiers & van Aarde (1994) showed that

preferential feeding by porcupines Hystrix africaeaustralis on the bark of red

syringas Burkea africana exposed the xylem to fire, with consequent increases in

tree mortality, and ultimately shifts in tree community structure. Rodent granivory

and seedling predation leads to the mortality of plants and may alter plant

communities (Brown & Heske, 1990). Thus, it must be recognised that elephants

are in no way unique among herbivores in the manner in which they shape their

communities and in causing the mortality of their forage species (predator-like

behaviour). What is of interest, however, is the scale and rate of these processes

when driven by elephants, and how this is affected by elephant density.

From the above, it is apparent that we need to be clear on what is considered an

“elephant” effect and what is an “elephant density” effect (Cowling & Kerley,

2002). The former would reflect the ability of elephants to influence biodiversity

(by virtue of the special characteristics of elephants), while the latter would reflect

the consequences that elephants can have on an ecosystem in relation to the

numbers present (typical of the concerns when elephants are concentrated or

confined in small conservation areas). Bearing this in mind, this chapter addresses

the following questions in an attempt to bring together the existing knowledge on

the effects of elephants on ecosystems and biodiversity.

• Are elephants special in the nature of their feeding, and hence their

impacts, by virtue of features such as body size, the trunk and tusks?

• How do elephants impact on individual plants, species and communities

and how is this expressed at an ecosystem level?

• What ecosystem processes do elephants influence that could possibly

affect the structure and functioning of these ecosystems?

• What are the cascading or knock-on effects of elephants on biodiversity?

In addition, we attempt to identify what we still need to find out in order to better

understand the impacts of elephants. The approach is to use these questions as a

framework to guide the contents of this chapter.

Across Africa, elephants occupy a broad range of terrestrial ecosystems (Laws,

1970; Boshoff et al., 2002), excluding only extreme deserts (where they are limited

SECOND DRAFT Assessment of South African Elephant Management 2007 5

to major water courses by the need for shade, forage and surface water). Central to

the debate around elephant management is their putative impact on savanna and

forest systems, with more recent interest in subtropical thicket systems. The focus of

this assessment is on South Africa, and particularly on savanna and subtropical

thicket; forests are of less importance as elephant habitat in South Africa.

Elephants as megaherbivores

The African elephant is the largest herbivore alive today, with females attaining a

maximum body mass of over three tons and males over six tons. Hence, they are

regarded, along with other species exceeding a ton in adult body mass (i.e. rhinos

and hippos), as “megaherbivores” (Owen-Smith, 1988). Coupled with this large

size, is a fairly simple digestive system with most digestion taking place in the

capacious hindgut comprising the small intestine and colon. Throughput is

relatively rapid, with mean retention-time of around 24 h independent of the daily

food intake (Clauss et al., 2007; Davis, 2007). This fast passage (compared with

other large herbivores) means that digestive efficiency is quite low, with less than

half of the ingested food being assimilated and the remainder passed out as faeces.

On the other hand, large amounts of fibre can be ingested without slowing

throughput, in contrast to the situation for ruminants (Janis, 1976). Because of their

large size (hence, relatively low external surface area to volume ratio) elephants

have a low metabolic rate per unit of body mass, which enables them to obtain

adequate nutrition yields from low nutrition plant material. Hence, their relative

daily food intake (in dry mass terms) is also low, around 1-1.5% of body mass per

day (compared with 2-3% for cattle). Nevertheless, as a consequence of their large

size, the absolute amount of vegetation that each elephant consumes per day is

huge, estimated to be over 60 kg for a fully grown male weighed as dry mass, or

around 180 kg weighed wet (Owen-Smith, 1988).

SECOND DRAFT Assessment of South African Elephant Management 2007 6

Feeding behaviour 1

Elephants display a variety of feeding behaviours, and have long been known as

robust and wasteful feeders (Selous, 2006). As with other vertebrate herbivores,

they can ingest forage directly by biting with the mouth, although this occurs

infrequently (about 10% of browsing events in subtropical thicket – Lessing, 2007).

Alternatively, forage is plucked (broken off the plant or the entire plant uprooted)

with the trunk and passed to the mouth where it is ingested through a single bite or

multiple bites, or material may be stripped off a branch with the trunk and passed to

the mouth. They also run branch tips through their teeth to strip off the bark,

discarding the interior wood. At certain times of the year they strip off and discard

leaves before consuming the bark, while at other times they may eat the leaves of

these same species (Barnes, ). 1982

The trunk, a specialised foraging adaptation with surprising dexterity, plays a

crucial role in enabling elephants to achieve a high rate of food intake, in part by

allowing them to chew and handle material simultaneously. Food intake has been

estimated to approach an instantaneous rate of 2 kg.min when feeding on succulent

shrubs (Lessing, 2007). The trunk, together with their high shoulder height, also

allows them to forage up to 8 m above ground level (Croze, 1974). Elephant have

also been observed adopting a bipedal stance in order to reach higher (Croze, 1974).

Most browsing, however, is between 0.5 and 2.5 m (Guy, 1976; Jachmann & Bell,

1985; Chafota, 2007; Lessing, 2007).

-1

The tusks may also be used for specialised feeding, particularly in stripping the bark

of trees, which is most common during the latter part of the dry season and the early

growing season (Barnes, 1982). They are probably gaining from the carbohydrates

stored within, and flowing through this bark prior to leaf flush (Barnes, 1982).

When hard pressed for food, elephant may gouge quite deeply into the trunks of

soft-stemmed trees like baobabs Adansonia digitata (Fig. 3.1). They also dig up

roots to feed on the root tips of some woody and succulent species (Barnes, 1982;

Lessing, 2007).

SECOND DRAFT Assessment of South African Elephant Management 2007 7

Figure. 3.1: Damage to baobabs by elephants in the Chobe National Park, 2

Botswana (Photo: W. Trollope).

Elephants may also use their feet to dig out (kicking or scraping) geophytes or grass

tussocks and may knock grass tussocks held in the trunk against their legs to

dislodge soil (Owen-Smith, 1988).

Elephants may fell or uproot trees up to 60 cm in basal diameter (Chafota, 2007).

Sometimes they may feed on the branch tips or roots of these trees, but on other

occasions they walk away from the fallen tree without feeding. It has been

suggested that some of the tree felling may be a social display unrelated to feeding

(Midgley et al., 2005), but this has proved hard to confirm. Trees pushed over in

Kasungu National Park Malawi showed a height mode of 4-5 m for favoured

species, but only 2-3 m for species generally rejected as food (Jachmann & Bell,

1985).

Discarded forage

Elephants do not ingest all the forage they harvest. This “wasteful” feeding may

include material accidentally dropped or discarded (Ishwaran, 1983). Paley (1997)

provided a crude estimate that the discarded material may represent more than half

SECOND DRAFT Assessment of South African Elephant Management 2007 8

of the forage requirements of elephants in the Addo Elephant National Park (Addo),

South Africa. Lessing (2007) estimated that about 25% of the forage removed per

pluck may be discarded in Addo. It has been hypothesized that this discarded

material may alter the size, distribution, nutrient levels and, hence dynamics of litter

in subtropical thicket ecosystems (Kerley & Landman, 2006). Elephants are not

unique in this behaviour, as for example kangaroo rats (Dipodomus sp.) also discard

a large proportion of the forage they harvest (Kerley et al., 1997). T

his aspect of

elephant foraging is poorly described and understood, but may have profound

cascading effects on ecosystem function and biodiversity patterns.

Sexual dimorphism and feeding

Elephant males are on average 1.3 times larger than females and adult males attain a

body mass twice that of adult females (Lee & Moss, 1995). They, therefore, can be

expected to exhibit differences in feeding behaviour and hence impacts, due to both

allometric effects, and differences in energetic and nutritional demands of

reproduction (Stokke & du Toit, 2000; Greyling, 2004; Lagendijk et al., 2005;

Shannon et al., 2006a). In addition, differences in social structure (group living

cows vs. largely solitary bulls) will influence foraging (Dublin, 1996).

Sex-based differences have been observed in savanna habitats, including differences

in diet, diet quality and tree toppling, with bulls typically feeding more robustly on

fewer plant species (but a wider range of plant parts – Stokke & du Toit, 2000) and

including more low quality items. In the South African Lowveld, Greyling (2004)

showed that family units more frequently debarked and defoliated woody plants,

while bulls tree-felled and ate roots more frequently. In addition, males generally

consumed a higher proportion of grass than females. Adult bulls had greater bite

and break diameters than family units (Cransac et al., 1998; Stokke, 1999; Stokke &

du Toit, 2000; Greyling, 2004; Shannon et al., 2006a). Differences in habitat use

have been ascribed to the differential need to access water with breeding females

being found closer to water (Stokke & du Toit, 2002), and Shannon et al. (2006b)

found no habitat selection in areas where water spatially limiting. There have

therefore been suggestions that elephant sexes may occupy different feeding niches

(Stokke & du Toit, 2000; Shannon et al., 2006a) in savanna.

SECOND DRAFT Assessment of South African Elephant Management 2007 9

In contrast, in subtropical thicket, males and females showed large overlaps in

feeding height, pluck size and foraging rates, which did not differ between sexes

(Lessing, 2007). Males, however, did access the largest biomass (branch size) per

pluck, and tended to harvest more multiple stem portions per pluck (compared to the

females who tended to use single stem plucks).

Diet

It is generally presumed that elephant herbivory is an important mechanism that

structures plant communities (e.g. Laws, 1970; Tafangenyasha, 1989; Stuart-Hill,

1992; Trollope et al., 1998; Mapaure & Campbell, 2002; Conybeare, 2004). Thus, it

is important to have an understanding of elephant diet, and particularly their dietary

preferences, in order to predict these impacts. However, some plant species that are

not browsed by elephants respond to elephants through indirect mechanisms (e.g.

trampling and associated path formation – Plumtre, 1993; Landman et al. In Press).

In addition, the amount of forage ingested by elephants only represents a fraction of

their total forage off-take (Guy, 1976; Paley, 1997), hence, impacts on plant

communities are not a simple function of food requirements.

Although numerous studies describe the diet of elephant in a range of habitats (e.g.

wooded savannas, desert shrublands, fynbos and subtropical thicket – Buss, 1961;

Jarman, 1971; Barnes, 1982; Kalemera, 1989; Viljoen, 1989; Kabigumila, 1993;

Paley & Kerley, 1998; Steyn & Stalmans, 2001; Milewski, 2002; Greyling, 2004;

Minnie, 2006; Chafota 2007), many are not quantitative in terms of species

contribution, and for example may describe diet at very broad levels (i.e. growth

forms - Koch et al., 1995; Cerling et al., 1999; Codron et al., 2006). In addition, few

studies (Guy, 1976; Jarman, 1971; Viljoen, 1989; De Boer et al., 2000; Greyling,

2004; Minnie, 2006; Landman et al., In press) assess the relative availability of

dietary items, and are thus able to quantify preferences for specific species.

Moreover, the diet of elephant is often indirectly inferred from plant-based studies

(Penzhorn et al., 1974; Barratt & Hall-Martin, 1981; Midgley & Joubert, 1991;

Stuart-Hill, 1992; Moolman & Cowling, 1994; Lombard et al., 2001), assuming that

differences between elephant areas and areas where elephants have been excluded is

SECOND DRAFT Assessment of South African Elephant Management 2007 10

the result of elephant browsing. In this regard, Landman et al. (In Press) showed

that a significant number of such species are not eaten by elephants.

Elephants are mixed feeders, consuming a range of plants and plant parts from

grasses to browse, bark, fruit and bulbs. Their large body size and robust feeding

allow them to have a broad diet (e.g. 146 plant species in subtropical thicket –

Kerley & Landman, 2006). Elephant herbivory can, therefore, influence the fate of a

considerable number of plant species. However, the bulk of the daily dry matter

intake comes from a few species.

Elephants consume varying proportions of browse and grass depending on region,

vegetation cover, water availability, soil nutrient composition, and season

(Williamson, 1975; Field & Ross, 1976; Owen-Smith, 1988; Koch et al., 1995;

Cerling et al., 2004). Grasses are primarily consumed in the rainy season (40-70%

of the diet), and trees or shrubs in the dry season, when grass contributes only 2-

40% (Buss, 1961; Bax & Sheldrick, 1963; Wing & Buss, 1970; Jarman, 1971;

Field, 1971; Laws et al., 1975; Williamson, 1975; Guy, 1976; Barnes, 1982; Lewis,

1986; Kabigumila, 1993; Spinage, 1994; De Boer et al., 2000; Greyling, 2004).

When feeding on grasses, elephants favour leaves and inflorescences during the wet

season, turning more to leaf bases and roots during the dry season (Owen-Smith,

1988). Forbs (herbaceous plants besides grasses) are also commonly consumed, and

elephants may spend much time feeding in reed beds during the dry season. Under

dry conditions, wood, bark and roots may constitute 70-80% of the material eaten

(Barnes, 1982).

Elephants are selective feeders at the plant species level. For example, 40-70% of

the seasonal browse intake of elephants feeding in the Chobe River front region of

northern Botswana came from just three shrub species: Baphia massaiensis,

Bauhinia petersiana and Diplorhynchus condylocarpon, with a wider range of

species eaten during the hot-dry season than at other times of the year (Chafota,

2007). A similar pattern was observed in subtropical thicket, where 25 out of 146

species used, comprise 71% of the diet (Kerley & Landman, 2005). Common

dietary staples elsewhere include species in the genera Acacia, Azima,

Colophospermum, Combretum, Commiphora, Cordia, Cynodon, Dichrostachys,

SECOND DRAFT Assessment of South African Elephant Management 2007 11

Grewia, Faidherbia, Gardenia, Portulacaria, Premna, Schotia, Sclerocarya,

Tamarix, Terminalia and Ziziphus. Genera rejected as food, or eaten rarely, include

Baikiaea, Burkea, Capparis, Croton, Erythrophloem, Euclea, Ochna and Scolopia

(see diet references above). Several Combretum spp. are commonly eaten, others

rejected (e.g. Combretum mossambicensis – Skarpe et al., 2004).

There is conflicting evidence regarding the nutritional characteristics of plants

preferred by elephants. Some studies show preferences for plants with higher levels

of protein, sodium, calcium and magnesium (Dougall, 1963; Dougall & Sheldrick,

1964; Van Hoven et al., 1981; Jachman & Bell, 1985; Hiscocks, 1999), lower levels

of crude fibre (Field, 1971; Holdo, 2003), secondary compounds and lignin

(Jachmann, 1989). In contrast, Thompson (1975) could not show any differences in

mineral or crude protein content between the bark of five species of trees with

different apparent preference. Calcium, magnesium, sodium, potassium, total salts

and crude protein do apparently not determine elephant use among 16 species

assessed by Anderson & Walker (1974) in Zimbabwe. These relationships may be

confounded by factors such as soil nutrients, rainfall, plant availability etc. and need

to be further researched.

It has been hypothesised that because of their simple digestive system, involving

rapid throughput, elephants are less readily able (than ruminants) to handle plant

secondary chemicals (e.g. resins, tannins and other phenolics), which tend to be

concentrated in leaves (Olivier, 1978; Langer, 1984).

Ecological processes influenced by elephants

Elephants affect a broad variety of ecological processes through their feeding,

digging and movement. For example in subtropical thicket, Kerley & Landman

(2006) showed that the role of elephants (15 broad processes) was comparable to

that of the balance of the vertebrate herbivore community (21 species) in terms of

the number of ecological processes (Table 3.1). In addition, by virtue of their killing

of other herbivore species through aggressive competition (e.g. white rhinoceros

Ceratotherium simum and black rhinoceros Diceros bicornis - Slotow et al., 2001;

SECOND DRAFT Assessment of South African Elephant Management 2007 12

Kerley & Landman, 2006), elephants also play a role analogous to predation. The

significance of elephants in all these roles, and how this differs between landscapes,

has yet to be quantified. The focus on a few effects such as tree mortality may,

therefore, mask both the extent and the mechanisms of elephant impacts (Landman

et al., In press).

Table 3.1: The relative role of elephant in broad ecological processes (n = 19), 7

8 modified from Kerley & Landman (2006), operating in subtropical thicket in

9 relation to other megaherbivores (2 sp.), mesoherbivores (19 sp.), omnivores (3 sp.)

and carnivores (18 sp.). 10

Elephant formation of “browsing lawns,” where they reduce the height of mopane

veld and increase the quality of forage, may be considered “gardening”, analogous

SECOND DRAFT Assessment of South African Elephant Management 2007 13

to the formation of “grazing lawns” by other herbivores including snails, tortoises,

geese and wildebeest (McNaughton, 1984). This shrub coppice state is

advantageous for elephants through providing more food and better quality re-

growth within the 2-5 m height range favoured by elephants (Jachmann & Bell,

1985). There are also increases (provided the overall cover is not lost) in the

availability of forage for other herbivores (Guy, 1981; Smallie & O’Connor, 2000;

Styles & Skinner, 2000; Rutina et al., 2005; Makhabu et al. 2006). In addition, they

may excavate waterholes in dry riverbeds (Owen-Smith, 1988; Selous, 2007). The

paths that they develop in travelling to and from water, and around obstacles such as

mountainous ridges, can facilitate movements by other species (e.g. Skead, 2007).

Elephants also function as keystone species (Paine 1969), as, for example, shown by

their dispersal of seeds of a specific range of plant species (Kerley & Landman,

2006). These observations appear to be consistent with the “keystone herbivore”

concept, invoked to explain how the elimination of similar megaherbivores

elsewhere through hunting by early human colonists in the late Pleistocene

contributed to a cascading sequence of extinctions among other large mammal

species (Owen-Smith, 1987, 1989; Koch & Barnovsky 2006).

Effects of elephants

If we are to understand the impacts of elephants, it is critical that the connections

between elephants and the assumed impacts (defined here as changes brought about

by elephants) are clearly understood and demonstrated. Elephant impacts are

observed at a range of levels, from soils to coexisting mammals (reviewed below),

and in all instances of such impacts, the mechanisms need to be clearly identified.

Individual plants and species

Elephants impact on plants by breaking branches/stems, stripping bark, uprooting

plants and toppling trees. The persistence of a plant species eaten by elephants is

dependent on whether they can cope with herbivory of this nature (i.e. the relative

capacity of these species to restrict, resist or compensate for the damage inflicted by

resprouting and/or regrowth), or whether mortality is balanced or exceeded by

SECOND DRAFT Assessment of South African Elephant Management 2007 14

recruitment and regeneration. The ability to resprout is taxon-specific, e.g. Aloe

spp., Acacia goetzii, Acacia nigrescens, Acacia nilotica, Acacia polycantha,

Dalbergia melanoxylon (Luoga et al., 2004; Kruger et al., 2007) and various

Commiphora spp. (Kruger et al., 2007) have all been reported to be poor resprouters

following either cutting or elephant damage, while a range of other species coppice

readily. Responses to bark stripping also vary across taxa, e.g. Acacia xanthophloea

in Amboseli, Kenya, are relatively tolerant of bark stripping and branch removal by

elephants (Young & Lindsay, 1988). Brachystegia spp. seem highly susceptible to

elephant damage, despite their high coppicing ability, resulting in stands of tall trees

being converted to shrubby coppice regrowth (Thompson, 1975; Guy, 1989).

O’Connor et al. (2007) suggest that the sensitivity of woody species to elephant

browsing is a function of plant and landscape features. Through their feeding,

elephants can “negatively” impact plant species and cause extirpation (localised

plant species extinction - Penzhorn et al., 1974; Western 1989. O’Connor et al.,

2007) or conversely, trigger plant growth and regeneration (Stuart-Hill, 1992).

Mechanisms of impact on individuals

Toppling effects

The ecological effects of toppling may differ from pollarding (total breaking of the

stem) in that the roots may be removed from the soil in which case mortality

generally ensues. However, if the roots remain in the soil, many species can

resprout quite effectively (e.g. Combretum apiculatum - Eckhardt et al., 2000).

Factors that influence vulnerability to being toppled include strength of the wood,

the depth and extensiveness of the root system and substrate stability (O’Connor et

al., 2007). Shallow-rooted shrubs (e.g. Commiphora spp.) that are uprooted

completely by elephants may also be greatly reduced in their prevalence by

elephants, as has happened in sections of Tsavo East National Park, Kenya

(Leuthold, 1977), and in Ruaha National Park, Tanzania (Barnes, 1985).

Bark stripping

The impact of stripping on a plant species is dependent on the degree to which the

bark is stripped e.g. ring barking results in mortality; if some phloem remains intact,

SECOND DRAFT Assessment of South African Elephant Management 2007 15

the bark may regrow (Buechner & Dawkins, 1961; Laws et al., 1975; Williams et

al., 2006). This may vary between species, e.g. Mopane may lose up 95% of the

bark without visible signs of stress (Styles, 1993). Features of the tree influence

their vulnerability to being stripped, for example, elephants can cause more damage

to trees with stringy bark (e.g. Acacia spp.) vs. those with bark that breaks off in

chunks (e.g. Sclerocarya birrea) (O’Connor et al., 2007). Furthermore, toxins in the

bark or stem spinescence may reduce preference for bark stripping (Sheil & Salim,

2004; Morgan, 2007). Fluted or multistemmed trunks are better protected against

stripping (Sheil & Salim, 2004), e.g. Balanites maughamii, where 2/3 of the bark is

protected on account of fluting (Williams et al., 2006) or multistemmed trees that

avoid total stripping (O’Connor et al., 2007) e.g. various Combretum and

Gymnosporia spp. Further, Sheil & Saliem (2004) found that elephants selectively

stripped larger trees.

The effects of stripping may be exacerbated by borer infestation, rot and interaction

with fire (Laws et al., 1975; Thompson, 1975). Elephant bark stripping may

facilitate insect and fungal attacks in Brachystegia boehmii woodlands in northern

Zimbabwe (Thompson, 1975). However, Smith & Shah-Smith (1999) found no

relationship between elephant damage and fungal infection. Van Wilgen et al.

(2003) suggest that it is highly likely fire in conjunction with elephant impacts may

have resulted in the loss of large trees in the Kruger National Park between 1960

and 1989 (see Eckardt et al. 2000).

Vulnerability of seedlings

Few studies explore elephant impact on seedlings (but see Jachmann & Bell, 1985;

Kabigumila, 1993; Barnes, 2001), but there is evidence for species-specific impacts

(e.g. baobabs - Edkins et al., 2007; ca. 35% mortality in Acacia erioloba in Chobe

National Park, Botswana - Barnes, 2001). Elephants may cause mortality by ripping

seedlings from the soil or prevent recruitment into adult size classes through top

kill, maintaining the plants in a size class where they are caught in the “fire trap”

(Barnes, 2001).

SECOND DRAFT Assessment of South African Elephant Management 2007 16

Case studies of species-specific impacts 1

Baobab Adansonia digitata 2

Elephants are the only herbivores that can kill adult baobabs, and are frequently

linked to the reduction in baobab densities, e.g. Mana pools (Swanepoel, 1993),

Tanzania (Barnes et al., 1994) and Kruger (Whyte et al., 1996). Barnes et al.

(1994), in a ten-year study in Tanzania, found that baobab populations declined as

elephant numbers increased and that the baobabs recovered when elephant

populations declined due to poaching.

As with other species, the impact of elephants on baobabs is confounded by

interactions with drought (Whyte et al., 1996), other herbivores (Edkins et al.,

2007) and fire. Furthermore, the pattern of elephant effects on baobabs is

inconsistent across size-classes, either showing selection against small trees

(Weyerhaeuser, 1985; Barnes, 1985), or no size-class selection (Swanepoel, 1993).

Spatial refuges for baobabs may occur on steep slopes inaccessible to elephants

(Fig. 3.2; Edkins et al., 2007). Consequently, it is unlikely that elephants can

remove all baobabs from areas that include sufficient topographic relief (Whyte et

al. 1996; Edkins et al. 2007).

SECOND DRAFT Assessment of South African Elephant Management 2007 17

Figure. 3.2: Regression analysis at the 90th quantile of recent elephant use of 2

3 baobabs in the Kruger National Park and the Inaccessibility value calculated for

4 these. Elephant browsing drops below 100% at 7o slope and below 20% at the 18o

slope cut-off (Edkins et al. 2007). 5

Acacia spp. 7

Because Acacia spp. are commonly selected by elephants (Calenge et al., 2002),

and show little or no resprouting once mature, their densities may decline under

high elephant browsing pressure, e.g. Acacia tortilis, A. xanthophloea, A.

nigrescens, A. senegal or A. erioloba (van Wyk & Fairall, 1969; Pellew, 1983;

Ruess & Halter, 1990; Barnes, 2001). However, Acacia spp. have the capacity to

regenerate rapidly from seedlings (Western & Maitumo, 2004), and elephants tend

to ignore early stage and regenerating trees (Okula & Sise, 1986; Mwalyosi, 1987;

Mwalyosi, 1990; Pellew, 1983; Calenge et al., 2002). Thus, elephant damage may

not appear to affect Acacia populations overall (Balfour, 2005). In a comparative

study of eight co-occurring Acacia spp. in Hluhluwe-iMfolozi Park, while levels of

impact varied between the different species, no species were selected for or against

(Balfour, 2005). In contrast, Western & Maitumo (2004) showed that elephants

have have brought about the local loss of swamp-edge A. xanthophloea woodlands

in Amboseli, Kenya, their impacts overriding that of fire or other processes. Soil

chemistry confounds the latter results, however, as rising salinity levels were clearly

linked to A. xanthophloea mortality in non-swamp areas in both Amboseli, Kenya,

(Western & van Praet, 1973) and Ngorongoro, Tanzania (Mills, 2006).

SECOND DRAFT Assessment of South African Elephant Management 2007 18

Marula Sclerocarya birrea 2

Despite concerns of the impacts of elephant on marula, early studies (Coetzee et al.,

1979), suggested that these impacts did not constitute a threat. Gadd (2002) showed

that elephant impacts on marula are sustainable (low mortality rates, recovery of

affected trees, no selection for small trees) in three populations adjacent to the

Kruger. However, other studies have shown that marula trees have suffered severe

attrition due to elephants (e.g. Weaver, 1995). In the Kruger, Jacobs & Biggs (2002)

showed a 7 % mortality of marula trees, mostly ascribed to the breakage of main

stems by elephant. They also showed that these impacts varied in terms of the extent

(number of trees affected) and severity (amount of damage to a tree) across

landscape types. Jacobs & Biggs (2002) also highlighted the concern that elephant

damage could lead to increased mortality due to other factors such as insect or

pathogen attack and fire.

Mopane Colophospermum mopane 16

Elephants browse intensively on mopane trees, and prefer mopane to many other

trees (Ben-Shahar, 1993). However, mopane are well adapted to regenerate after

elephant browsing, and few mopane trees are killed by this browsing. While

unbrowsed mopane have treelike morphologies, mopane woodlands may be

converted to stands of shrubby coppice through the feeding impacts of elephants

(Lewis, 1991; Smallie & O’Connor, 2000; Styles & Skinner, 2000; Lagendijk et al.,

2005). Elephants inhibit height recruitment by repeatedly breaking leader shoots

(Anderson & Walker, 1974). However, elephants may have more impact in taller

mopane, where ring-barking, heavy browsing and toppling may cause mortality

(Caughley, 1976a; Lewis, 1991).

Several factors affect the degree of elephant damage on mopane. Proximity to water

sources appears, as in many other systems, to have the greatest effect on elephant

damage on mopane (Styles & Skinner, 2000). Soil type also appears important: soils

that promote shrub-like mopane yield less stable woodlands than soils that promote

SECOND DRAFT Assessment of South African Elephant Management 2007 19

tree-like growth of mopane (Lewis, 1991). Elephant browsing intensity also tends to

fluctuate with time of year, being greatest in summer (Styles & Skinner, 2000).

Spekboom Portulacaria afra 4

P. afra is one of the most abundant species in subtropical thicket, and probably the

best studied example of the species-specific impacts of elephants in Addo. The

roots, shoots and leaves are utilised extensively (contributing ca. 9 % to the diet),

usually in proportion to availability - Landman et al., In press). Elephants reduce the

height of individual plants (Stuart-Hill, 1992) and may remove more than 50% of

the biomass (Penzhorn et al., 1974). Despite these high levels of utilisation (and

thus large impacts), P. afra persists in the presence of elephants, except in areas

with extremely high elephant densities (Landman, In prep.). Stuart-Hill (1992)

argued that the species is adapted to the ‘top-down’ browsing by elephants, whereby

the lower rooted branches escape elephant browsing impacts, which facilitates

vegetative reproduction. The ‘top-down’ hypothesis is supported by observed

elephant browsing heights of above 50 cm in Addo. However, this hypothesis fails,

when the plants are uprooted and the roots are consumed (Stuart-Hill, 1992;

Lessing, 2007).

Mistletoes

Mistletoes (comprising Viscum rotundifolium, Viscum crassulae, Viscum obscurum,

Moquinella rubra) are highly nutritious (Midgley & Joubert, 1991) and are

preferred food items for elephants in Addo (Landman et al., In press). This guild is

treated as an entity here. Mistletoes show an exponential decline in abundance

(Figure 3.3) and richness with increasing levels of elephant browsing, with V.

crassulae disappearing in the presence of elephants (Magobiyane, 2006). V.

rotundifolium, however, persists at very low densities in elephant habitat. These

responses are rapid (a 60% decline in abundance within six years), and after a

decade of elephant browsing, mistletoe densities are too low to be used as measures

of elephant impact (Magobiyane, 2006).

SECOND DRAFT Assessment of South African Elephant Management 2007 20

Figure. 3.3: Exponential decline in the abundance of mistletoes (Viscum 2

rotundifolium, Viscum crassulae, Viscum obscurum) in the presence of elephants in 3

the Addo Elephant National Park (Magobiyane, 2006).

Aloe sp. Aloe africana 6

Aloes, in particular A. africana, have long been known to disappear from the

elephant area of Addo, presumably as a result of elephant browsing (Penzhorn et al.,

1974; Barratt & Hall-Martin, 1991). Only recently did Landman et al. (In press)

show that elephants actually consume A. africana, albeit in very small proportions

(ca. 0.1% of the diet). Aloes appear to be particularly sensitive to the impacts of

elephants (relative to P. afra and mistletoes) and disappear rapidly at very low

levels of herbivory. This suggests that alternative mechanisms of elephant impact

(e.g. trampling) may be responsible for the disappearance of the species (Landman

et al., In press).

Assessing species-specific vulnerability

The above examples show that plants respond differently to elephant use. Some

species decline rapidly, while others are able to persist in the presence of elephants,

SECOND DRAFT Assessment of South African Elephant Management 2007 21

albeit with altered growth forms. These responses are, however, difficult to interpret

due to the presence of a range of confounding variables (e.g. fire, soil nutrients,

other herbivores, elephant densities). O’Connor et al. (2007) provide a theoretical

framework for assessing the vulnerability of a plant species to

extirpation/extinction. They list a range of a) plant traits, b) landscape

characteristics that might influence the probability of elephant’s selection for these

species and c) management unit characteristics that exacerbate these.

a. Plant traits - A species would be considered vulnerable to extirpation by

elephants if it displays the following characteristics:

1. lacks the ability to sprout as adults and/or cannot re-grow their bark so that

mortality results as a consequence of pollarding or ringbarking,

2. are restricted to selected foraging habitats,

3. are highly selected for by elephants,

4. are frequently subjected to pollarding and ringbarking,

5. regenerates infrequently and/or usually in small numbers,

6. slow growing, and

7. displays episodic recruitment.

b. Landscape and management unit characteristics – Vulnerability to extirpation is

exacerbated:

1. terrain lacks topographical refuges,

2. there are no spatial refuges from elephant because distance from water is not

a foraging constraint,

3. where reserves are small,

4. reserve is located in semi-arid region with variable grass production, hence

heightened utilization of woody material, and

5. reserve is a degraded semi-arid savanna in which suitable grass is no longer

available and woody plants form the bulk of the diet.

Fauna

The direct effects of elephants on animals include direct mortalities and interference

competition (as opposed to resource competition). Thus, elephants may temporally

SECOND DRAFT Assessment of South African Elephant Management 2007 22

exclude other species from resources such as waterholes or other resources by

actively chasing them away (Owen-Smith, 1996). Alternatively, elephants may also

facilitate access to resources through, for example, excavating waterholes (Owen-

Smith, 1988) and increasing the availability and quantity of forage (e.g. Skarpe et

al., 2004). The understanding of these interactions is again limited due to

confounding factors, and the fact that these are normally cascading effects.

Invertebrates

There are few studies on the effects of elephants on invertebrates. Cumming et al.

(1997) found significantly lower richness of ant species in woodlands that had been

impacted by elephants than in intact woodlands. Furthermore, cicadas were only

recorded in the intact woodlands, not in the impacted woodlands.

Dung beetles are sensitive to habitat change (Klein, 1989). Disturbance in the form

of fire or elephants can have a significant effect on dung beetle species diversity,

and biomass (Botes et al., 2006). In Tembe Elephant Park, Maputaland, dung beetle

(Botes et al., 2006) and spider (Honiball et al., Unpublished) assemblages differ

between elephant impacted sand forest (a key endemic habitat type) and undisturbed

sand forest sites (including the loss of some forest specialist species). Elephants

may provide refugia for other species, particularly ground living invertebrates under

dung, and trunks of toppled trees (Govender, 2005).

Musgrave & Compton (1997) demonstrated a significant increase in phytophagous

insect feeding damage in the presence of elephants in Addo, and attributed this to an

increase in the quality of browsed plants through a decline in secondary chemical

compounds (e.g. tannins). This hypothesis has yet to be tested, nor has it been

shown which insect species were involved, and what their population or overall

insect biodiversity responses were. This apparent increase in nutritional quality of

plants needs to be weighed-up against the significant decline in overall plant

phytomass (Kerley & Landman, 2006).

SECOND DRAFT Assessment of South African Elephant Management 2007 23

Reptiles and amphibians 1

In an attempt to explain high tortoise abundance in Addo, Kerley et al. (1999)

hypothesize that elephant alteration of subtropical thicket habitat (through their

creation of open habitat patches and paths) may favour increased access for tortoises

(i.e. leopard tortoises Stigmochelis pardalis, angulate tortoises Chersina angulata).

Birds

Cummings et al. (1997) found a drop in species richness of birds and changes in

bird communities (from woodland species to non-woodland species) in response to

changes caused by elephants in Miombo woodlands, Zimbabwe. Reduced vertical

and horizontal heterogeneity in the elephant-impacted woodlands probably accounts

for their observed loss of species richness (c.f. MacArthur 1964).

In contrast, Herremans (1995), in assessing bird community species shifts in

riverine forest and Mopane woodland in northern Botswana, found that dramatic

woodland change associated with the high abundance of elephants did not result in a

reduction in bird diversity. This was possibly due to the fact that woodland

conversion was spatially restricted. However, gallinaceous birds were more

abundant in areas heavily impacted by elephants than elsewhere in the Chobe River

region (Motsumi, 2002).

Elephant removal of large standing trees in savanna (e.g. Eckhardt et al., 2000),

may decrease the availability of nesting sites for raptors, especially vultures and

other rare, open-savanna species (Monajem & Garcelon, 2005). Little is available in

the scientific literature on the nesting requirements of savanna raptors. More

research is needed to determine the outcomes of elephant-raptor interactions.

Chabie (1999) showed that in transformed thicket in Addo, there were significant

changes in the bird communities. At the guild level, there was a shift from

frugivores in intact thicket to a community dominated by insectivores and

granivores in opened-up thicket. In addition, there was a shift to larger bodied sized

species in transformed thicket. The hypothesis that elephants drive these changes

needs to be further tested.

SECOND DRAFT Assessment of South African Elephant Management 2007 24

Bats

The expected loss of large trees and snags due to elephants may decrease both

roosting sites of bats and available habitat for species that specialise on feeding

within dense vegetation (Fenton et al., 1998). However, Fenton et al. (1998) found

no drop in Vespertilionid and Molossid (airborne insectivores) bat species richness,

or a loss in specialists, with a reduction in woodland canopy cover.

Small terrestrial mammals

There are few studies on the impacts of elephants on small mammals. Keesing

(2000) suggested that the presence of elephants in East African savannas may result

in an increase in species richness of small mammals, through habitat alteration.

Large terrestrial mammals

Browsers

There is a general negative correlation between elephant biomass and the biomass

of browsers and medium-sized mixed feeders across ecosystems (Fritz et al., 2002).

A number of mechanisms for this have been proposed, including a) the reduction in

resources i.e. direct competition for resources, b) the alteration of habitats for

browsers and other ungulates, c) increase in visibility resulting in higher predation

levels, and d) competition for water (Owen-Smith, 1988; Skarpe et al., 2004; Valeix

et al., 2007). While the patterns are significant, and sometimes obvious, the

mechanisms are not yet clear: a possible explanation may be that elephants reach

highest abundances in areas of mopane and other vegetation types which they

exploit more effectively than other browsers.

The structural transformation from more wooded to more open habitat conditions

may benefit some browser species, but lead to a decline in others. The high

abundance of elephants that has persisted along the Chobe river and in Hwange

National Park, has been associated with an increase in kudu and impala (Skarpe et

al., 2004). The mechanism for this is not clear, however, on the Chobe river, it may

reflect the increase in Capparis tomentosa vines and C. mossambicensis shrubs,

SECOND DRAFT Assessment of South African Elephant Management 2007 25

which are readily consumed by kudu and impala, but not elephants. In contrast,

along the Chobe river, the abundance of bushbuck has declined substantially

following the opening of the riparian woodland by elephants (Addy, 1993).

In Addo, the opening of the succulent thicket vegetation by elephants appeared to

bring about a decline in bushpig Potamochoerus porcus, Cape grysbok Raphicerus

melanotis and bushbuck abundance (Novellie et al., 1996; Castley & Knight, 1997).

However, it is not known whether populations of these species outside the elephant

enclosure have remained unchanged over this period, or whether putative changes in

habitat structure are the consequences of elephant impacts (reasonably likely given

the trends reviewed here) or some other process such as global climate change

(Kerley & Landman, 2006).

The reduction of vegetation cover and density by elephants in Addo results in a

change in potential browse availability for black rhinoceros (Landman, In prep).

The increase in elephant paths, associated with increases in elephant densities,

initially facilitates access to browse by black rhinoceros, but the subsequent

dominance of the landscape by these paths results in a loss of foraging

opportunities.

Sigwela (1999) compared the diet of kudu in the elephant enclosure and botanical

reserves of Addo, and showed that elephants had no apparent effect on kudu diet

selection. This is surprising given that 1) extensive vegetation changes have

occurred in the elephant enclosure, 2) kudu diet (28 species) includes many of the

plant species recorded as being impacted by elephants, and 3) elephants consume all

the plant species recorded in the diet of kudu here. This suggests that food

availability is not limiting to either kudu or elephant at the present densities of

vegetation and browsers at these sites (Kerley & Landman, 2006).

Grazers

Given that grass forms a substantial part of the diet of elephants for much of the

year (Owen-Smith, 1988) elephants may be expected to compete with grazing

ungulates if forage is limited. On the other hand, elephants are able to open up the

SECOND DRAFT Assessment of South African Elephant Management 2007 26

woodland and increase the grass cover (Caughley, 1976b). However, in their broad

scale analysis, Fritz et al. (2002) could not detect any effect of elephants on grazers.

Western (1989) highlighted the role of elephants in East Africa in facilitating

pasture for medium and small ungulates, including domestic livestock.

In several cases, the decline of grazing species has been linked to the encroachment

of woody vegetation in the absence of elephants (Owen-Smith, 1988), for example

wildebeest Connochaetus taurinus, zebra Equus burchelli, waterbuck Kobus

ellipsiprymnus, and reedbuck Redunca arundinum in Hluhluwe-Imfolozi Park

(Owen-Smith 1989). In Tsavo East National Park, Parker (1982) reported an

increase in abundance of several grazing species, including oryx Oryx gazella,

warthog, and plains zebra, following the opening of shrubland by the increasing

elephant population. Young et al. (2004) found that by decreasing cattle grazing in

a grassland area, elephants reduced the effects of competition between livestock and

zebra.

Not all grazers benefit, for example the conversion of tall woodlands into shrub

coppice is likely to be adverse for sable antelope, although possibly not for roan

antelope (Bell, 1981).

Buffalo Syncerus caffer show a variety of responses to elephants. In the Chobe

region, buffalo herds favoured areas recently grazed by elephants, suggesting

facilitation rather than competition (Halley et al., 2003). Skarpe et al. (2004)

suggested that there is no evidence for competition between buffalo and elephants in

Chobe, however there is some evidence for competition between buffalo and

elephants in Tanzania (de Boer & Prins, 1990).

Communities & Ecosystems

The population and species level impacts brought about by elephants (documented

in part above) may be expressed at the community and ecosystem level, including

emergent properties of such systems, such as nutrient cycling, vegetation structure

and dynamics.

SECOND DRAFT Assessment of South African Elephant Management 2007 27

Nutrient cycling 1

Elephants typically constitute 30-60% of the large herbivore biomass in savanna

ecosystems, and are thus responsible for 25-50% (allowing for metabolic scaling) of

the plant biomass consumption by herbivores (Owen-Smith, 1988; Fritz et al.,

2002). About 50% of the material eaten passes through the gut undigested.

Furthermore, elephants process fibrous plant parts such as bark and roots (which are

generally not eaten by other herbivores) and thereby accelerate biomass recycling.

Their importance for biomass cycling is further enhanced through wasteful feeding

(Paley, 1997; Lessing, 2007) and toppling of trees (Owen-Smith, 1988).

This contribution by elephants to biomass recycling tends to be greater in nutrient-

poor than in nutrient rich ecosystems because of their capacity to exploit vegetation

components of low nutritional value. The removal of branch ends as well as leaves,

plus felling of mature trees, promotes compensatory regeneration by these plants

(Pellew, 1983; Fornara & du Toit, 2006: Makhabu et al., 2006) and, hence, greater

primary production and rates of nutrient recycling than would occur in the absence

of elephants. Termites contribute to the release of the nutrients in the fibrous tissues

in elephant dung, and fire to releasing the minerals held in the stems of trees toppled

by elephants. It has been hypothesised that, in the nutrient-deficient savanna

woodlands prevalent on Kalahari sands (with little capacity to retain nutrients),

much of the biologically available nitrogen and sodium pool may be held within

elephant biomass (Botkin et al., 1981).

Elephants may also play variety of roles in nutrient cycling, especially in nutrient-

deficient ecosystems. They may release the nutrients locked up in tree trunks and

roots (Botkin et al., 1981). By removing large trees, they reduce the role that these

trees play in extracting mineral nutrients from deep soil layers (Treydte et al.,

2007), and also the contribution of these trees to small-scale heterogeneity in soil

nutrients through the nitrogen-enrichment promoted by fallen leaves. This generally

decreases the availability of high quality forage resources beneath tree canopies, and

this could indirectly affect the persistence of grazers (Ludwig, 2001). By reducing

the prevalence of nitrogen-fixing legumes such as many Acacia spp. elephants may

suppress the role that these species play in nitrogen enrichment (Treydte et al.,

SECOND DRAFT Assessment of South African Elephant Management 2007 28

2007), although the absolute and relative extent of this effect has not been

quantified.

Soil resources

Because of their large biomass, the trampling effects of elephants on soil

compaction can also be substantial, with unclear consequences for vegetation

(Plumptre, 1993). The large increase in woody cover, associated with the exclusion

of elephants in the experimental plots in Uganda, dramatically increased soil

organic matter and thereby pH, and extractable Ca, K, and Mg levels. Organic C

and N also increased, but total P declined slightly (Hatton & Smart, 1984).

Kerley et al. (1999) showed that in the Addo elephant enclosure the proportion of

the landscape that represented run-on zones (i.e. where resources such as water,

litter, soil and nutrients are trapped during overland flow) declined, while the

proportion of run-off zones (i.e. where these resources are lost) increased. The

consequence of this was a decline in soil nutrients. Kerley et al. (1999) suggested

that elephant impacts were less deleterious than goat impacts, but that these studies

must be replicated.

Seed dispersal

Elephants may play an important role in facilitating the dispersal and germination,

and hence regeneration of a large variety of plant species through endozoochory.

Elephants are considered to be the only foragers (and hence dispersers) of the large

fruited Balanites wilsoniana, a canopy tree dominant in Kibale Forest, Uganda, as

well as other large fruited forest species (Chapman et al., 1992; Babweteera et al.,

2007). Elephants enhance seedling germination (Cochrane, 2003) and increase

seedling survival and growth by dispersing propagules far from adult trees

(Babweteera et al., 2007). In savanna, seed germination and seedling survivorship

of Sclerocarya birrea are also enhanced following fruit ingestion by elephants

(Lewis, 1987).

SECOND DRAFT Assessment of South African Elephant Management 2007 29

Despite their dietary breadth in subtropical thicket (i.e. 146 plant species – Kerley &

Landman, 2006), elephants are relatively poor seed dispersers in Addo, dispersing

only 21 plant species through endozoochory (Mendelson, 1999; Sigwela, 2004),

comparable to black rhinoceros and eland (both 20 species – Mendelson, 1999).

Why so few species are dispersed is not clear, but may reflect the rarity of most

plant species in the diet (25 out of 146 species comprise 71% of the diet – Kerley &

Landman, 2005), selective foraging behaviour in terms of plant phenology,

complete loss of propagules during digestion or inadequate sampling. The large

volume of forage intake (and faecal output) by elephants (Owen-Smith, 1988),

however, allows them to disperse large numbers of seeds (Sigwela, 2004), but their

role in plant regeneration through this process needs to be quantified. Levels of

zoochory vary between locations, as for example Robertson (1995) recorded 32

dicot species that were dispersed by elephants in nearby Shamwari Private Game

Reserve.

Mortality of seeds during passage through the digestive tract was significantly lower

in elephant compared to a model ruminant (the goat) (Davis, 2007). The effects of

passage through the elephant digestive tract on germination differed between plant

species (e.g. Acacia karroo germination declined, while Azima tetracantha

germination improved). In addition, patterns of germination after ingestion differed

between elephants, goats and pigs (Davis, 2007). This suggests that elephant effects

on endozoochory may not be replaced by other herbivores.

Comparison among ecosystems

Perceptions of the extreme impacts that burgeoning elephant populations can have

on vegetation have been strongly influenced by particular case studies. These

include the situations in Murchison Falls National Park, Uganda, which led to the

first major elephant culling operation implemented in Africa; Tsavo East National

Park, Kenya, where a need for drastic culling was proposed but not implemented in

the face of opposition; and Chobe National Park in northern Botswana, where high

elephant concentrations have developed in the vicinity of the Chobe River, and

culling has been repeatedly advocated but not undertaken because of practical

considerations. Most recently extreme vegetation changes ascribed to elephants

SECOND DRAFT Assessment of South African Elephant Management 2007 30

have been documented for Amboseli National Park in Kenya. A critical appraisal of

what these particular situations show, or do not show, will be presented before

turning to a more general assessment of ecosystem differences.

Illustrative case studies

Murchison Falls in Uganda

Murchison Falls National Park covers a 2400 km2 section of the northern part of the

Bunyoro district in western Uganda, divided between southern and northern

sections by the Nile River, with elephants spread more widely over a 3200 km2

range at the time of the study (Laws & Parker, 1970; Laws et al., 1975). The annual

rainfall of 1250 mm supported a moist Terminalia glaucescens/Combretum

binderanum savanna woodland, plus open grassland areas with scattered Acacia

sieberiana trees. In addition there were patches of closed-canopy forest (including

the Budongo Forest), which historically had apparently been much more

widespread, and a limited area of bushland. Soils are underlaid by basement igneous

rocks, with volcanic influences from the adjoining Rift Valley. Annual burns were

generally started early in the dry season. A population approaching 10 000

elephants had become compressed into the park by surrounding human settlements,

creating an effective regional elephant density of around 3 elephants.km-2. The park

also supported 6 000 hippos and 14 000 buffalos, plus numerous kob, hartebeest and

warthog, so that large herbivore biomass totalled 12 000 kg.km-2. Much of the

central region had been transformed into Hyparrhenia grassland with just the

stumps of the trees remaining. The challenge was to establish the relative roles of

fire and elephants in the vegetation transformation, and to project the likely

trajectory of the elephant population.

Vegetation changes were documented from aerial photographs (Laws & Parker,

1970; Laws et al., 1975). In one woodland section examined, a tree density of 5300

km-2 in 1958, of which 24% were dead (Buechner & Dawkins, 1961) had been

reduced to 1060 km-2 in 1967, of which 98% were dead. Furthermore, a radial

pattern of damage from the centre of the park outwards indicated that fire was not

the major cause. In some areas the woodland had been replaced by dense

SECOND DRAFT Assessment of South African Elephant Management 2007 31

Lonchocarpus taxiflorus shrubland, apparently resistant both heavy browsing and

fire. Two plots established in 1967 excluding elephants and other large herbivores

had become transformed to closed canopy A. sieberiana woodland 7-10 m high by

1981 (Smart et al., 1984). However, plant species richness had dropped to almost

half of that recorded in 1967, especially in the herbaceous layer. Following the

build-up of soil organic matter, there was a dramatic increase in extractable cations

associated with elevated soil pH (Hatton & Smart, 1984). Although total soil

phosphorus declined, available phosphorus and nitrogen both showed increases.

Furthermore, following drastic reduction of the elephant population during the 1978

civil war, abundant regeneration of dense acacia scrub was occurring through much

of former open grassland area of the park and also invading areas of former

Terminalia woodland. However, fires had also occurred less frequently than the

annual burns of the 1960s.

Because of the paucity of trees, 80-90% the diet of the elephants consisted of grass,

although the forest patches provided a refuge for a segment of the elephant

population (Laws & Parker, 1970). Estimates from cropped elephants indicated that

the population was declining under these conditions, with calving interval

lengthened to 5.6 years and age at first calving retarded to 20 years. Mortality of

elephants killed for crop protection contributed to this decline.

Tsavo East in Kenya

Tsavo East and West National Parks together cover an area of over 20 000 km2 in

south-eastern Kenya, divided by the Mombassa road and railway line, and adjoin

the extensive Galana concession to the north-east. The sparse annual rainfall

averaging only about 400 mm in central Tsavo supports vegetation consisting

predominantly of Commiphora shrubland on acid alluvial soils, with bands of tall

trees and other species flanking rivers. The total elephant population was estimated

to number 24 000 animals in 1967, by which stage woodland decline had become a

source of concern (Glover, 1963; Agnew, 1968). Acacia tortilis plants taller than 1

m declined by 65% in density between 1970 and 1974, while baobab trees had been

virtually eliminated by 1974, 20 years after first reports of vegetation damage by

elephants (Leuthold, 1977). Mature Commiphora shrubs were reduced in density

SECOND DRAFT Assessment of South African Elephant Management 2007 32

from 90 plants.ha-1 in 1970, to 5 ha-1 by 1974 in a 4400 km-2 section of Tsavo East,

but the rest of the park showed far less change (Myers, 1973). This period spanned a

severe drought, during which one third of the elephant population died of starvation.

Fire became a secondary factor contributing to further opening of the woodland.

The opening of the woody vegetation component led to increases in the abundance

of grazers such as Grevy’s zebra (Equus grevyi) and beisa oryx (Oryx gazella),

while browsers including lesser kudu (Tragelaphus buxtoni), gerenuk (Litocranius

walleri) and giraffe (Giraffa camelopardalis) declined (Parker, 1982). Black rhino

numbers also dropped drastically, but in their case poaching, facilitated by the

opened vegetation, was the direct cause.

Following the drought decline, the elephant population in Tsavo was reduced

further by poaching to a low of around 6000 animals by 1994. This lowered density

then allowed abundant woodland regeneration to occur by 1994, especially of

Acacia tortilis and in riparian fringes (van Wijngaarden, 1985; Leuthold, 1996).

Commiphora shrubs that had been pushed over also showed abundant resprouting

from the base of the stem or roots. Certain tree species not eaten by elephants

survived virtually unchanged from 1970. The only long-term impacts evident are

the virtual disappearance of baobab trees within the park, and virtual elimination of

black rhinos, the latter through poaching facilitated by the opening of the

vegetation. Long term consequences for animal populations have not been

documented.

Chobe River front and elsewhere in northern Botswana

The region of northern Botswana including Chobe National Park supported a

regional elephant population of about 40 000 animals within 80 000 km2 in 1980

(Spinage, 1990), which had grown to 140 000 by 2006 (Skarpe et al., 2004). Recent

dry season elephant densities along the Chobe River front region average around 4

elephants.km-2, dropping to 0.5 elephants.km-2 when these animals disperse during

the wet season. Simpson (1975) recorded the persistence of a narrow strip of

riparian forest fringing the river in 1970, although many of the large acacia trees

appeared to be dying. By 1980 most of the trees near the river, mainly Acacia

nigrescens and A. tortilis, had been reduced to standing dead trunks, while in the

SECOND DRAFT Assessment of South African Elephant Management 2007 33

shrub understory two species unpalatable to elephants, Capparis tomentosa and

Combretum mossambicense, had become predominant. Further back from the river

a shrubland including Combretum eleagnoides, Baphia massaiensis and Bauhinia

petersiana occurs on an alluvial terrace, while 3-5 km away from the river the

vegetation changes to sandveld woodland with Burkea africana predominant on

shallower sandy soils and Baikiaea plurijuga on deeper sands. Rainfall averages

around 700 mm. Aerial photographs indicated that the area covered by woodland

had decreased from 60% to 30% between 1962 and 1998, while the area of

shrubland had expanded from 5% to 33% (Mosugelo et al., 2002). Vegetation

adjoining the Chobe River had appeared quite open in 1874, before elephants were

eliminated in the region by ivory hunters (Selous, 1881). The alluvial terrace had

remained open through the 1930s, and grazing by cattle before the national park was

established, plus exclusion of fires, were suggested as factors contributing to the

thicket development (Simpson, 1978).

A study on the ecosystem consequences of these vegetation changes (Skarpe et al.,

2004) showed that little regeneration of the tree species reduced in abundance by

elephants was evident, largely because of the intense browsing pressure by a high

density of impala (locally >150 animals per km2) on seedlings. The shrub species

avoided by elephants were commonly browsed by ruminants (Makhabu et al.,

2006). Buffalo also appeared to be more abundant in areas of the floodplain where

elephants had been feeding than elsewhere. The abundance of both small mammals

and gallinacaeous birds (guinea fowl and spurfowl) appeared to be affected

favourably rather than adversely by severe elephant impacts. The Chobe River front

also showed an exceptionally high density of land birds in general, but more

especially of migrants (Herremans, 1995). However, the opening of the woody

vegetation cover by elephants was associated with a substantial reduction in the

abundance of bushbuck, to a third or less of their former abundance at the time of

Simpson’s previous study during 1969-70 (Addy, 1993). Fire was not a factor in the

vegetation changes occurring near the Chobe River, being blocked by the main road

paralleling the river, but contributed to an opening of the sandveld woodland away

from the river.

SECOND DRAFT Assessment of South African Elephant Management 2007 34

The area severely affected by elephant impacts extended over a distance of 20-30

km along the Chobe River, with human settlements to the east and west. Further

west along the Linyanti River, a similar pattern of woodland conversion is in

progress, mostly outside the national park. Extremely high local concentrations of

elephants develop here during the late dry season, up to 20 elephants.km

-2. By 1991

over 40% of the trees in the riparian fringe were dead (Coulson 1992; Wackernagel,

1992). Acacia spp were especially severely affected, with two-thirds of A. erioloba

and 45% of A. nigrescens trees dead, in many cases due to debarking by elephants.

However, wind-throw and natural senescence were additional factors contributing to

this mortality, and other species such as Diospyros mespilliformis and Combretum

imberbe growing in the riparian woodland showed much less elephant damage.

Repeated aerial photographs indicated a net loss rate of canopy trees of only 2% per

year between 1992 and 2001, but tree felling was patchy and much of this loss

occurred in the patches were the above two Acacia spp were prevalent (Bell, 2003).

These pictures also revealed that an expanding shrub layer largely of Combretum

mossambicense had developed by 2001.

Amboseli Basin in Kenya

The Amboseli Basin covers 8 500 km2 in southern Kenya, with the central lake

being the remnant of a much vaster lake generated by drainage from the slopes of

Mount Kilimanjaro to the south in Tanzania (Western, 2007). The area set aside as

Amboseli National Park occupies 388 km2. The lake usually holds water for only a

few weeks after heavy rains, although springs and patches of swamp retain a

perennial water supply. Soils derived from volcanic deposits are alkaline and locally

saline because of the closed drainage. Further back the vegetation grades into

bushland or open woodland with Acacia tortilis, A. mellifera and Commiphora spp

predominating. The mean annual rainfall is 250-300 mm. The region supports a

population of 1400 elephants with the local density within the park amounting to 2-

3 elephants.km-2. These animals have become largely resident following the

suppression of former migrations by heavy poaching during the early 1970s.

Dieoffs of extensive areas of Acacia xanthophloea woodland were initially ascribed

primarily to rising salinity in the soil associated with increased rainfall (Western &

SECOND DRAFT Assessment of South African Elephant Management 2007 35

van Praet, 1973), but subsequent research has demonstrated that elephant damage

has been the primary factor in the demise of these woodlands (Western & Maitumo,

2004). The total area covered by these woodlands declined from 125 km

2 in 1950 to

merely 2 km2 by 2002, associated with an expansion in alkaline grasslands and

scrubland of Suaeda monoica and Salvadora persica (Western, 2007). Stands of

palms (Phoenix reclinata) have replaced the woodland in some localities. Exclosure

plots constructed in 1981 contained dense stands of Acacia xanthophloea which had

become 7-10 m tall by 1988 (Western & Maitumo, 2004). Acacia seedlings outside

the exclosures failed to grow and declined in abundance. Associated with the

woodland decline has been a decrease in the abundance of browsing ungulates

within the national park, although these species remain abundant outside the park.

Historical records suggested that the presence of pastoralists with their cattle had

contributed to the development of the Acacia xanthophloea stands. Woodlands

outside the park have largely recovered since the 1970s following the compression

of the elephant population within the park.

Subtropical Thicket

Research on the impacts of elephants on the plant communities of Addo has

followed a tradition of comparing elephant occupied areas with areas where

elephants have been excluded (i.e. botanical reserves). This assumed that any

difference in vegetation was due to the influence of elephants. Elephants have been

shown to reduce plant species richness, plant biomass, canopy height and volume

and density (Penzhorn et al., 1974; Barratt & Hall-Martin, 1991; Stuart-Hill, 1992;

Moolman & Cowling, 1994; Lombard et al., 2001). Stuart-Hill (1992) argued that

succulent thicket is adapted to the ‘top-down’ browsing by elephants, which

maintains thicket regeneration by protecting canopy cover at ground level. In

general, species abundance and richness of 75 special (endemic-rich geophytes and

low succulents - Johnson et al., 1999) and two indicator species (V. rotundifolium,

V. crassulae - Midgley & Joubert, 1991) declined exponentially with length of

exposure to elephant browsing, halving approximately every 7 years (Lombard et

al., 2001). An important point is that 168 plant species identified as being entirely

reliant on Addo for their conservation (Johnson et al., 1999), are potentially

vulnerable to elephant-driven extinction (Kerley & Landman, 2006).

SECOND DRAFT Assessment of South African Elephant Management 2007 36

The absence of effective density-dependence in subtropical thicket (Gough &

Kerley, 2006) is interpreted as a consequence of the aseasonal availability of high

quality forage, and it is predicted that the forage resource (and associated

biodiversity) will collapse before density-dependence emerges (Kerley & Landman,

2006).

Contrasts across biomes and ecosystems

The damage inflicted by elephants on trees may lead either to the conversion of

savanna woodland into mostly open grassland, or to the transformation of areas of

woodland into shrubland (Bell, 1981). Open grassland was more likely to develop

on clayey soils where a dense grass cover promotes hot fires. On the other hand,

trees and shrubs growing in sandy soils commonly resprout strongly from

underground parts, enabling them to persist in a shrub coppice state (Bell, 1984,

1985; McShane, 1989). The contrast in the patterns of woodland change

documented in eastern versus western parts of Kruger (Eckhardt et al., 2000) fits

this pattern, with a substantial opening of tree cover evident on basaltic soils, while

on granitic soils the overall woody plant cover did not decline although the presence

of tall trees decreased. In Masai Mara, Kenya, with basement rock-derived, but

volcanically-influenced soils, the transformation of savanna woodland into largely

open grassland was primarily the result of fire, with an increase in rainfall

promoting greater fire intensity, while elephants have secondarily suppressed tree

recovery (Dublin et al., 1990). The conversion of the Rwindi-Rutshuru plains from

savanna into grassland in Kivu National Park, Congo, where the soils are largely

volcanically derived clays, was probably promoted by fire in combination with

elephants (Bourliere, 1965). However, in Murchison Falls NP in Uganda, on similar

soils, elephant damage to trees appeared to be the primary factor in woodland

disappearance, with fire secondarily inhibiting tree regeneration, as noted above. In

Chizarira National Park in Zimbabwe, Brachystegia boehmi woodland growing on

granitically derived soils was largely eliminated by elephants concentrating in the

region following their displacement from the Zambezi Valley by the filling of Lake

Kariba and associated shifts in human settlements (Thomson, 1975). Recurrent

annual fires suppressed regrowth by the remaining saplings. Hence, rainfall (mean

SECOND DRAFT Assessment of South African Elephant Management 2007 37

700-800 mm at Chizarira) also contributes to fire intensity and hence the effect on

trees. However, in the Sengwa Research Area in Zimbabwe where Brachystegia-

Julbernadia woodland was prevalent, fire did not suppress the recovery of trees

after elephants numbers had been reduced (Guy, 1989). The subsequent recovery

took the form of a reversion to Combretum thicket, rather than the re-establishment

of the miombo tree species (Mapaure & Campbell, 2002).

Frost as well as fire contributes to topkill of small trees in Kalahari sand woodlands

of Zimbabwe and Botswana, contributing towards the persistence of a coppice

resprouting state (Holdo, 2006). Through eliminating much of the forage available

in the shrub layer, frost events may also prompt elephants to fell mature trees

(Chafota, 2007). The persistence of a shrub coppice form is also a feature of areas

where Colophospermum mopane predominates, but for this vegetation form, soil

depth as well as elephant damage are the contributory factors (Lewis, 1991). A

distinction needs to be made between the maintenance of a sapling coppice form of

trees that can potentially reach canopy height, as in the case of mopane, and the

replacement of canopy trees by shrub species, as has occurred on the alluvial terrace

border the Chobe River.

Various species of Acacia, prevalent on clayey soils or towards lower rainfall

conditions, show limited resprouting potential once mature, and are thus vulnerable

to being eliminated by elephants. However, these species generally regenerate

rapidly and profusely from seeds once provided with windows of opportunity, for

example at Lake Manyara in Tanzania (Mwalyosi, 1990), as well as at Amboseli as

described above. On the other hand Brachystegia spp as well as Burkea africana,

although not favoured by elephants appear quite highly vulnerable to being killed or

reduced to coppice by elephant felling or debarking, perhaps through being

prevalent in nutrient-poor savannas where elephants generally do not reach high

abundance (Guy, 1989; Cumming et al., 1997; Holdo, 2003, 2007). Species in these

savannas that are almost completely avoided by elephants, such as B. plurijuga,

Erythrophloem africanum and Ochna pulchra, escape these impacts. Mopane-

dominated woodlands seem fairly resistant to being converted by elephants to any

other vegetation form, apart from local stands of sapling coppice, both because the

species shows high resprouting potential and because this vegetation type covers

SECOND DRAFT Assessment of South African Elephant Management 2007 38

extensive areas. Arid savannas (e.g. Tsavo) seem no less vulnerable to being

transformed by elephants than mesic savannas (e.g. Murchison), although the

consequences may differ.

Gaps in knowledge

The studies described above have described general features of the consequences of

elephant impacts for vegetation structure and composition, for the regions or

ecosystems concerned. All areas show high spatial variability in these impacts as

well as temporal variability. It is easy photographically to contrast local devastation

with intact woodlands remaining nearby. The causes of these intense localized

damage remains unknown, although Chafota’s (2007) observations on interactions

involving fire, frost and persistence of surface water shed some light on possible

mechanisms. It is possible that the former pattern was a mosaic cycle of intense

utilization, with elephants moving elsewhere until areas previously heavily

impacted had recovered. The extent of the area required for such a spatial pattern of

utilization to be maintained is unknown. Movement studies have merely

documented opportunistic concentrations in areas where rainfall has promoted new

growth, plus dry season concentrations around remaining sources of water for

drinking. Tree populations within semi-arid environments seem also to recruit

episodically at long intervals, during rare sequences of years with high rainfall, low

fire frequency and low browsing impacts (Young & Lindsay, 1988; Walker 1989).

Little is known about the consequences of breakage and consumption of structural

components of the woody vegetation by elephants for litter decomposition and

nutrient cycling.

Rates of change

There are few studies of the rates of change brought about by elephants, the best

documented being for Addo. The elephant enclosure of Addo was enlarged on a

number of occasions providing areas with different periods of elephant occupancy.

Using these variations in elephant density and time since exposure to elephants,

Barratt & Hall-Martin (1991) showed changes in plant architecture, Lombard et al.

SECOND DRAFT Assessment of South African Elephant Management 2007 39

(2001) showed changes in the regionally rare and endemic small succulent shrubs

and geophytes, and Magobiyane (2006) estimated the rate of impact on mistletoes.

These studies in subtropical thicket show that some species respond very rapidly to

elephant impacts, while other impacts are slower.

Megaherbivore release

It may be expected that the absence of elephants may bring about changes to

ecosystems (e.g. Kerley & Landman, 2005), which is known as megaherbivore

release. This complicates the interpretation of elephant impacts as it may be argued

that where elephants have been reintroduced into an area, observed changes are a

return to the situation prior to elephant removal (Conybeare, 2004). Kamineth

(2004) showed that in the absence of megaherbivores (including areas with

historical megaherbivore records) tree Euphorbia populations were dominated by

younger plants (<100 years), with only a few adults (i.e. recruiting populations). In

the presence of megaherbivores (historical and current), however, Euphorbia

populations were characterised by individuals in younger and intermediate (100-150

years) age classes (i.e. irregular age distributions). No recruiting populations were

observed in the presence of megaherbivores. Thus, the presence of megaherbivores

has resulted in a high incidence of adult tree Euphorbia mortality, and may have

controlled tree numbers. This suggests that the local abundance of tree Euphorbias

may be an artefact of relaxation from browsing or other effects provided by

megaherbivores.

Skarpe et al., (2004) also suggest that the large populations of Acacia and

Faidherbias in the Chobe area established during periods of low herbivore biomass.

The mechanisms of megaherbivore release may extend beyond direct herbivory, as

the absence of elephants will influence a number of ecological processes (Kerley &

Landman, 2005).

SECOND DRAFT Assessment of South African Elephant Management 2007 40

Spatial perspectives 1

Elephants, like other animals, do not use the landscape in a uniform fashion and

hence vary their impacts across landscapes, producing heterogeneity in biodiversity

patterns. One of the major factors influencing space use by elephant is

topographical relief and Wall et al., (2006) showed that elephant are reluctant to

climb slopes. This is expressed in reduced elephant impact in relation to

topographic relief (Fig. 3.2). The consequences are that tree species that seem most

susceptible to elephant impacts, such as marula and baobab, tend to be prevalent in

upland regions of the landscape (Weyerhaeuser, 1985; Edkins et al., 2007).

Although Tsavo East National Park is commonly advanced as an example of the

devastation potentially brought about by elephants, less than a quarter of its 20 000

km2 extent was severely affected. Furthermore, this was largely in the lowest

rainfall region where the effect of drought conditions was most severe (Myers,

1973). Likewise, the zone of severe impact on riparian vegetation along the Chobe

River spans less than 20 km (Skarpe et al., 2004).

Elephants use vegetation types differently (e.g. Guldemond & van Aarde 2007).

Despite their reliance on grass in the diet, there is a poor understanding of their use

of grasslands, with most studies comparing woodland types, largely in terms of

impacts. In Madikwe (Govender, 2005) and Pilanesberg (Moolman, 2007),

elephants impacted Acacia woodland types significantly more than Combretum

woodland types. In Phinda, two of the top three impacted habitats were Acacia

dominated (the other was threatened sand forest), while in Mkhuze one of the top

three impacted habitats was Acacia dominated (Repton, 2007); further, some tree

species were heavily used at some sites, but the same species was not heavily used

at other sites (e.g. Madikwe - Page & Slotow, 2001; Pilanesberg – Moolman, 2007).

Impact was also heterogeneous in time, with more impact on woody vegetation in

winter months than summer months in Madikwe (Govender, 2005). In the Eastern

Cape, elephants avoided karroid shrublands in Kwandwe (Roux, 2006).

The above patterns clearly suggest that refugia from elephant impacts occur at a

variety of spatial and temporal scales, and these patterns need to be better

SECOND DRAFT Assessment of South African Elephant Management 2007 41

understood. There are two particularly important aspects of such heterogeneous

spatial patterns, firstly where elephants impact the areas around water (see

Piosphere effects below), and secondly where their impacts are confined within

small areas (see below).

Piosphere effects

Being water-dependent, elephants generally drink every 1-2 days (Owen-Smith,

1988). Thus, surface water availability limits their distribution (Western, 1975;

Belsky, 1995; Owen-Smith, 1996). In savannas that have not undergone extensive

water provision, elephants typically exhibit dry season concentrations near perennial

water (Western, 1975; Thrash et al., 1995; Owen-Smith, 1996; Leggett et al., 2003,

2004, 2006a,b; Chamaillé-James et al., 2007; Smit et al., 2007). The concentration

of elephants and other herbivores around perennial water results in zones of

attenuating impact with distance from water, i.e. a piosphere (Andrew, 1988).

Characteristics of piospheres include increases in soil nutrients, dung deposition and

trampling, decreases in trees and palatable perennial herbs, increases in annual and

unpalatable herbs and the amount of bare ground, soil compaction and increased

erosion with proximity to water (Bax & Sheldrick, 1963; Van Wyk & Fairall, 1969;

Weir, 1971; Tolsma et al., 1987; Thrash et al., 1991, 1995; Ben-Shahar, 1993;

Belsky, 1995; Owen-Smith, 1996; Thrash, 1998; James et al., 1999). Such gradients

of impact with distance from water have been documented for elephants, away from

both natural (Swanepoel & Swanepoel, 1986; Anderson & Walker, 1974) and

artificial (Ben-Shahar, 1993; Owen-Smith, 1996) sources of water.

Piospheres are manifested in woody vegetation primarily through changes to local

structural heterogeneity by elephant browsing. The effects of elephants on woody

vegetation in these piospheres includes a decrease in the density of C. mopane

shrubs and extremely high elephant impact on mopane and D. cinerea shrubs within

100-200 m of water (Fruhauf, 1997). In addition, Acacia trees (e.g. A. nigrescens, A.

erioloba) in the woodlands along the Linyanti River are apparently being

progressively eliminated by the extremely high densities of elephants that build up

there during the late dry season (Wackernagel, 1993), following the same trend as

inferred for the Chobe River front (Skarpe et al., 2004; see also de Beer et al.,

SECOND DRAFT Assessment of South African Elephant Management 2007 42

2006). Moderate elephant damage to a range of tree species has been observed

within 800 m of water sources, while lower levels of elephant damage to mopane

shrubs occur up to 1 600 m from water (Fruhauf, 1997). In contrast, Shannon et al.

(submitted) found that tree toppling increased up to 4 km from permanent water in

Kruger.

Temporary pools of water in pans and artificially provided water pumped from

boreholes or retained in dams may enable elephants to remain in areas away from

rivers through much of the dry season. In Hwange National Park, Zimbabwe, inter-

annual fluctuations in elephant distribution were related to rainfall through its effect

on surface-water availability (Chamaille-Jammes et al., 2007). In dry years,

elephants concentrated near the pumped pans, which provided the only remaining

water for drinking under these conditions.

Elephants have thus been implicated in increased impacts on herbaceous and woody

vegetation (Van Wyk & Fairall, 1969; Ben-Shahar, 1993), as well as declines in

plant species composition, density and diversity (Conybeare, 1991) in areas close to

artificial waterholes.

The spatial distribution of waterholes has also been suggested to influence the

extent of homogenization of a landscape’s vegetation through elephant impacts.

Owen-Smith (1996) predicted the vulnerability of Kruger to woodland destruction

over most of its area due to the existence of artificial water points, if elephant

population control was halted or curtailed (i.e elephant numbers were allowed to

increase). Given that elephant numbers are increasing in Kruger, this prediction

needs to be tested. Gaylard et al. (2003) suggested that the availability and

distribution of water sources can influence ecosystem structure and function at a

range of scales and organizational levels, through its influence on various processes

and feedbacks affecting both animals and plants. Specifically, the high-density

grazers (specifically buffalo, zebra and wildebeest) that occur preferentially within

4 km of water during the dry season in Kruger may benefit from the vegetation

changes brought about by elephants (Smit et al., 2007).

SECOND DRAFT Assessment of South African Elephant Management 2007 43

Impacts in confined areas/small reserves 1

Although it may be expected that elephants will utilize confined areas in a uniform

fashion, there are limited data to support this. Roux (2006) showed that for smaller

reserves (< 1000 km2) range size was a function of reserve size, but not for larger

systems, suggesting that smaller reserves would be used more comprehensively. In

Ithala (30 000 ha) about 50% of the reserve was not used by elephants because of

topography, habitat and behavior (Wiseman et al., 2004). Within Songimvelo (31

000 ha), the elephants also used a restricted part of the reserve (1 200 ha) which

meant that the local density was 2.75 elephant.km-2 (Steyn & Stalmans, 2001).

Elephants are restricted to the eastern half of Pongola Game Reserve by a railway

track bisecting the reserve (Shannon et al., 2006a), hence have an effective density

of 1 elephant.km-2. Similarly, although the entire Phinda Reserve (15 000 ha) was

used by elephant, not all parts are used with the same intensity (Druce et al., 2006).

These patterns may in part be due to the relatively short periods that elephants have

been confined in some small areas, as well as variations in density within reserves.

In contrast, elephants have been confined to Addo for over 50 years, and despite the

addition of areas, a clear pattern of homogenous impacts (i.e decline in plant

richness, taking period of occupation into account) can be seen (e.g. Lombard et al.,

2001; Magobiyane, 2006; Landman, In prep.).

Constraints to identifying elephant effects

The interpretation of elephant impacts is rarely possible to do in isolation of

possible confounding or synergistic effects (e.g. fire – Trollope et al., 1998; Bond

& Keeley, 2005; Chafota, 2007, other herbivores – Cowling & Kerley, 2002; Skarpe

et al., 2004, drought – Wiseman et al., 2004, wind toppling – Bell, 2003; frost –

Holdo, 2007 ). Specifically, in Ithala, other browsers (black rhino = 13% of

individuals; other browsers about 30%) had almost a three-fold higher effect on

woody vegetation than did elephants (16%). Of the top 20 plant species by canopy

removed, 12 were more heavily impacted by other browsers than by elephants

(Wiseman et al., 2004). Note however that these relative impacts are not expressed

in relation to browser biomass.

SECOND DRAFT Assessment of South African Elephant Management 2007 44

Furthermore, the studies on confined populations are complicated by the inability to

control for elephant density, as opposed to elephant presence (Cowling & Kerley,

2002). Bench-marking elephant impacts is also complicated by the absence of a

‘natural state’ yardstick. The measurement and interpretation of elephant impacts,

therefore, needs to be undertaken in a rigorous fashion such that confounding

effects are controlled for (Cowling & Kerley, 2002). A recently developed

experimental design is to quantify impacts on a gradient of elephant density or

period of occupation (Lombard et al., 2001; Kerley & Landman, 2006).

Furthermore, the interpretation of impacts should be based on a sound

understanding of the mechanisms of such putative impacts in order to avoid the risk

of incorrectly assigning impacts to elephants (Landman et al., In press).

Conceptual/modelling framework for contextualizing elephant effects

Caughley’s (1976b) classical model of interactive herbivore-plant systems has been

highly influential in guiding thinking about possible long term trajectories of

elephant numbers and vegetation. However, this model is abstract, and basically an

interpretation of the classical Lotka-Volterra modelling approach to predator-prey

or consumer-resource interactions. It does not accommodate heterogeneity in the

vegetation or any temporal variability in conditions, not even the seasonal cycle of

production and decay by plants. Nevertheless, this simplicity exposes a basic feature

of such interactions: lags in response to changing conditions can produce

oscillations in abundance rather than an approach to some fixed “carrying capacity”

as projected by the logistic model. In suggesting the possible relevance of this

model for elephant dynamics, Caughley (1976a) emphasised how the delayed

recovery of woodlands following their depression by elephants, coupled with the

delayed response of elephants to the woodland reduction (because of their capacity

to use grass as an alternative food source), could lead to reciprocal cycling in

abundance with a period of around 100 years. Empirical data to test this postulated

relationship between elephant population size and woodland development are still

lacking.

Duffey et al. (1999) suggested that more realistic parameter values for elephants

could lead to stability rather than cycling, by incorporating a density feedback

SECOND DRAFT Assessment of South African Elephant Management 2007 45

through basing the functional response on a consumer-resource ratio rather than

simply resource abundance. Owen-Smith (2002a) demonstrated that effective

functional heterogeneity in vegetation quality, coupled with adaptive resource

selection by herbivores, could promote stability rather than cycling, and suggested

that this finding might have some relevance for the dynamics of elephants and

woodlands (Owen-Smith, 2002b). However, of most relevance is the potential

recovery rate of tree populations.

Baxter & Getz’s (2005) model provides a foundation for contextualizing the relative

effects of elephants, fire and climatic variability on likely trends. This represented a

1 km2 cell with woody plant growth dynamics parameters specifically based on

mopane, with a relatively simple age structure of the elephant population. They

suggested that a decline in woody vegetation might occur once effective local

elephant densities exceeded 1-2 elephant.km-2. This model needs to be expanded to

take into account other woody species with different growth characteristics, as well

as seasonal and spatial variation in the local presence of elephants, and a better

elephant population model. A model developed by Holdo (2007) specifically for

Miombo woodland, indicates a likely decline in woody vegetation with elephant

densities of around 2 elephant.km-2. Most of these and other models (e.g. Wu &

Botkin, 1980; Mackey et al., 2005) failed to incorporate stochastic variation of

environmental factors. Sterk et al. (submitted) incorporated regional and temporal

variation in rainfall and studied elephant population development in a mopane

dominated areas over different age classes. Their model showed that fragmentation

of a conservation area can put elephant populations at risk.

The intermediate disturbance hypothesis, proposed by Connell (1978) to explain

species diversity in tropical forests, also has relevance for elephants. It suggests

that, without periodic disturbances from fire, wind throw or floods, plant

communities become dominated by the most competitive species, while a severe

disturbance regime leads to persistence only by those species best adapted to cope

with such disturbances. At some intermediate disturbance regime, a coexistence of

species displaying both of these adaptive syndromes leads to the greatest overall

species diversity. The problem in applying this concept in practice lies in defining

what constitutes an intermediate level, recognising that disturbances display three

SECOND DRAFT Assessment of South African Elephant Management 2007 46

aspects: their severity, frequency and extent. For example, longer intervals between

fires result in more intense fires when ignition eventually occurs. It is also important

to note that disturbance promotes diversity by creating differences between patches

in space but also changes in species abundance through time. Hence, rather than

some intermediate frequency or severity of disturbance, generated for example by

holding elephant density constant at an “intermediate” level, a range of variation in

these features, and acceptance of variation through time, might ultimately be most

beneficial. This calls for a meta-analysis in which the impact of elephants on the

tree-grass balance, and especially habitat heterogeneity and species diversity are

studied.

General assessment

Breaking and toppling

1. Moderate amount of knowledge available, but large gaps still exist.

2. We have some idea of the patterns of elephant impact. Which species and

communities are impacted, but limited spatially and temporally explicit

understanding of impact e.g. refuges vs. non-refuges on steep slopes, or the

temporal dynamics of the effects;

3. Little overall perspective e.g. although some communities may be impacted,

in many instances how widespread the impact is unknown. Is it local and

therefore creating landscape heterogeneity, thereby promoting diversity or is

it widespread and species/communities are being lost?

4. We have little understanding of the rate at which this is happening.

Plant resistance

1. Some data are known for vulnerable species e.g. LHS traits that buffer them

against impact e.g. sprouting or high levels of regeneration;

2. A few general patterns of sprouting available for southern African savannas

(Archibald & Bond, 2004; Kruger, 2005), but no taxonomic or landscape

level analyses.

SECOND DRAFT Assessment of South African Elephant Management 2007 47

3. More autecological studies of plant responses needed

Bark stripping: Little known

1. Vulnerable species should be identified and the relative risk (selection for by

elephants, bark strength and ability to re-grow bark) should be ascertained.

Furthermore, no research providing general patterns of regrowth (taxonomic,

bark type, intensity of disturbance) were found to draw upon i.e. we cannot

generalise about which species should recover following stripping.

2. Still unknown to what degree infestation by boring beetles alone might

result in tree mortality;

3. Although scientist allude to the interaction between fire and bark stripping,

few studies explicitly assess the link between elephant bark stripping and

consequent mortality due to fire. Elephant induced stripping is often fairly

high (1.5 – 3 m) off the ground & above the most intense part of the burn,

and so the relative impact might be fairly limited.

Assessment: Elephants and Biodiversity

1. The issue of elephant density effects on biodiversity is poorly understood

and needs to be explored as a matter of urgency

2. There are no instances of where elephants have directly brought about the

local loss of other large vertebrates, even though they may temporarily

outcompete some;

3. There is a need for a better understanding of the role of water (and its

management) on elephant impacts.

4. Elephants, in conjunction with fire and other browsers, are likely therefore

to have the greatest influence by changing vegetation structure;

5. No clear patterns emerge from the literature that indirect impacts of

elephants negatively or positively influence biodiversity, but few studies

exists, and this urgently needs more attention to be able to draw any

conclusions.

6. If impacts are local and small in scale, then elephants may positively

influence diversity by creating and maintaining habitat heterogeneity;

SECOND DRAFT Assessment of South African Elephant Management 2007 48

7. Large scale disturbances/changes as a consequence of elephants (if these

exist) would have significant impacts on associated diversity, but no hard

data exist to document these changes.

Overall Assessment

1. That elephants in high densities are having an impact on woodland

communities, with consequent changes in vegetation structure and species

composition, is undeniable;

2. Some plants can cope with elephant browsing, stripping or toppling,

although this can vary substantially with circumstance e.g. xeric vs mesic

savannas. Therefore, aside from a number of instances where local

extirpation has occurred, the most significant impact that elephants will have

is the changing of vegetation structure.

3. Often difficult to untangle the effects of elephants, fire and natural plant

senescence and episodic recruitment events (e.g. Skarpe et al., 2004);

4. It would seem that many plant populations will recover once the pressure of

high elephants has been released, the rate will vary between species and

landscapes;

5. Very little data on rates of change.

6. Little data about density dependent effects between elephants-resource

availability, which is a prerequisite to be able to predict future changes.

7. Whilst extensive data are available from elsewhere in Africa, but other than

extensive work done in Addo and northern KwaZulu Natal, a paucity of data

exists in SA, particularly in potentially vulnerable arid areas e.g.

Mapungubwe.

Concluding comments

We conclude that elephants are special in the nature of their feeding, and hence their

impacts, by virtue of features such as body size, the trunk and tusks. Overall, our

assessment is that while the impacts of high elephant concentrations may bring

about local changes in vegetation and associated animal species, and hence local

SECOND DRAFT Assessment of South African Elephant Management 2007 49

biodiversity, this need not be the case at the wider ecosystem level. Moreover,

unless extreme, the consumption and breakage of woody plants and uprooting of

grass tufts by elephants promotes compensatory regeneration and hence probably

enhanced ecosystem productivity, as has been demonstrated for grazing systems.

The concern is not the local severity of elephant impacts, which could be adverse

for both productivity and diversity if extreme, but rather the persistence of and

extent of such pressure on plants, and the cascading or knock-on effects of elephants

on other elements of biodiversity. The habitat transformation brought about by

elephants is restricted in extent by the spatial dispersion of perennial surface water.

This depends in turn on the extent to which water in perennial rivers and pools in

seasonal rivers is augmented by dams and boreholes elsewhere in the landscape.

The breakage of woody plants and grasses by elephants can facilitate feeding by

other large herbivore species. Adverse consequences for these species arise through

habitat transformations rather than direct competition. Prior to the large scale

changes in elephant abundance and distribution, it was recognised that elephants

impacted landscapes (Selous, 1881), but unfortunately there are no benchmarks of

elephant-landscape interactions in the absence of man. This is further complicated

by the recognition that elephant impacts varied in space and time. Defining the

severity of, and hence managing impacts, therefore will depend on management

objectives for a particular system.

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Evaluating elephant, Loxodonta africana, space-use and elephant-linked vegetation change in Liwonde National Park, Malawi

Thesis

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Apr 2024

Emma E.M. Evers

Heterogeneity, the spatio-temporal variation of abiotic and biotic factors, is a key concept that underpins many ecological phenomena and promotes biodiversity. Ecosystem engineers, such as African savanna elephants (hereafter elephant), Loxodonta africana, are organisms capable of affecting heterogeneity through the creation or modification of habitats. Thus, their impacts can have important consequences for ecosystem biodiversity, both positive and negative. Caughley’s “elephant problem” cautions that confined or compressed, growing elephant populations will inevitably lead to a loss of biodiversity. However, a shift in our understanding of elephants suggests that not all elephant impacts lead to negative biodiversity consequences, as long as there is a heterogeneous spread of elephant impacts that allows for spatio-temporal refuges promoting the persistence of both impact-tolerant and impact-intolerant species. To date, little empirical evidence is available in support of managing elephants under this paradigm and few studies are available that infer the consequences of the distribution of elephant impacts on biodiversity. In addition, most studies use parametric statistics that do not account for scale, spatial autocorrelation, or non-stationarity, leading to a misrepresentation of the underlying processes and patterns of drivers of elephant space-use and the consequences of their impacts on biodiversity. Here, I evaluate spatio-temporal patterns and drivers of elephant space-use, and how the distribution of their impacts affects biodiversity through vegetation changes, using a multi-scaled spatial approach, in Liwonde National Park, Malawi. My study demonstrates that elephant space-use in Liwonde is heterogeneous, leading to spatio-temporal variation in the distribution of their impacts, even in a small, fenced reserve. The importance of the drivers of this heterogeneous space-use varied based on the scale of analysis, water was generally important at larger scales while vegetation quality (indexed by NDVI) was more important at smaller scales. When examined using local models, my results suggest that relationships exhibit non-stationarity, what is important in one area of the park is not necessarily important in other areas. The spatio-temporal variation of the inferred impacts of elephants in Liwonde still allowed for spatio-temporal refuges to be created, no clear linear relationship was found between elephant return intervals and woody species structural and functional diversity (indexed by changes in tree cover and changes in annual regrowth using Normalized Difference Vegetation Index as a measure, respectively) throughout the park. My study provides support for adopting the heterogeneity paradigm for managing elephants and demonstrates that not all elephant impacts result in negative vegetation change. I also demonstrate the crucial implications of accounting for scale, non-stationarity, and spatial autocorrelation to evaluate how animals both respond to, and contribute to, environmental heterogeneity.

Patterns of Spatial Dynamics and Distribution of African Elephants (Loxodonta africana) in the Central Kalahari Game Reserve, Botswana

Article

Full-text available

Nov 2024

Survival trends (2008-2020) of three tree species in response to elephant impact, environmental variation, and stem wire-netting protection in an African savanna

Article

Oct 2023
FOREST ECOL MANAG

Reduced levels of the survival of large trees (≥5 m height) in Africa's savannas are a conservation concern, particularly where large trees co-occur with African elephants (Loxodonta africana). Elephants, as ecosystem engineers, can structurally modify and lesson the savanna large tree component. Wire-netting, which involves wrapping chicken-mesh around a tree's main stem, has been used as a mitigation method to increase tree survival. We assess the trends in survival of three large tree species of conservation importance, namely Lannea schweinfurthii, Senegalia nigrescens and Sclerocarya birrea, within the Associated Private Nature Reserves (APNR) on the western boundary of the Kruger National Park, South Africa. We consider survival trends linked by both elephant impact, as well as external environmental factors. We conducted four field assessments on 2,758 trees in 2008 (baseline), 2012, 2017, and 2020, where we recorded i) elephant impact levels on each tree, ii) whether the tree had wire-netting, and iii) the tree's survival status. We then modelled tree survival status as a dependent variable against multiple environmental factors. We found that tree survival was lowest when mean annual rainfall was lowest due to the drought, particularly amongst L. schweinfurthii and S. nigrescens. Wire-netting significantly increased large tree survival in comparison to control trees over the 12-year period, however, this effect decreased after four years if the wire-netting had lost its structural integrity. We illustrate how various environmental factors, in combination with elephant impact, affect large tree survival in an African savanna with a high density of artificial water points. We also provide results on the longest known study on wire-netting as a mitigation method for elephant impact on large trees and provide evidence on how a period of drought may have accelerated large tree decline in a southern African savanna.

Utilisation of Woody Plants by the Cape Porcupine in Mesic Savannas in South Africa

Article

Full-text available

Aug 2022

Herbivory plays a fundamental role in determining the structure of savannas. The impacts of small and medium-sized mammalian herbivores on trees in savannas remain poorly understood because most research attention focuses on large herbivores such as elephants whose destructive effects on trees can be pervasive at landscape scales. On the other hand, feeding activities of generalist herbivores such as Cape porcupines on woody plants can lead to tree mortality. This study investigated the utilisation of woody plants by the Cape porcupine in three mesic savanna sites in South Africa. We determined the woody plant diet of the porcupine for the early and late dry seasons at Roodeplaat Farm in Gauteng Province, and at Goss Game Farm and Bisley Valley Nature Reserve in KwaZulu-Natal Province. Thirty and twenty randomly located quadrats (30 m × 30 m) were laid at Roodeplaat and Goss, respectively, while 10 smaller quadrats (10 m × 10 m) were laid at Bisley. We measured stem diameter and the length and width of bark scars made by porcupines on stems of woody plants. We collected ten dung samples from each study site in the wet and dry seasons for quantification of woody material in porcupine diet. Porcupine foraging behaviour impacted different tree species at each site: Vachellia robusta at Roodeplaat, Spirostachys africana at Goss and Vachellia nilotica at Bisley. Each of these trees was dominant at each site. More scarring and tree mortality were recorded at Bisley with almost 70% tree sapling mortality occurring on trees that porcupine fed on. The size of bark scars was greater at Goss (P < 0.01) than at Roodeplaat and Bisley, which were similar. The area of bark damage on S. africana trees differed significantly by stem diameter size class (P = 0.007) and was greater for small stems (size class < 7.1 cm) than the larger stems (size classes 7.1-14 cm and 14.1-21). For all the study sites, dung samples revealed that woody material contributed over 80% of the porcupine diet during the dry season, but was lower at 35% during the wet season for Roodeplaat, although it was consistently high for Bisley at 79%. Porcupine foraging activities substantially contributed to tree mortality at each site. We posit that porcupine induced mortality on dominant tree species at each site may contribute to structural heterogeneity in woody plant vegetation in mesic savannas.

Standard Identification Certificate for Legal Legislation of a Unique Gene Pool of Thai Domestic Elephants Originating from a Male Elephant Contribution to Breeding Special Issue Biodiversity in Different Regions: Exploring Global Ecology Sustainability Edited by

Article

Nov 2022

first_pagesettingsOrder Article Reprints Open AccessArticle Standard Identification Certificate for Legal Legislation of a Unique Gene Pool of Thai Domestic Elephants Originating from a Male Elephant Contribution to Breeding by Nattakan Ariyaraphong 1,2,3,†,Dung Ho My Nguyen 1,2,3,†,Worapong Singchat 1,3,‡,Warong Suksavate 1,3,Thitipong Panthum 1,3,4,Warangkhana Langkaphin 5,Saran Chansitthiwet 5,Taweepoke Angkawanish 5,Arphorn Promking 6,Kantapon Kaewtip 6,Kitipong Jaisamut 1,3,Syed Farhan Ahmad 1,3,7,Suchin Trirongjitmoah 6,Narongrit Muangmai 1,3,8ORCID,Orasa Taesumrith 5,Suratchai Inwiset 5,Prateep Duengkae 1,3 andKornsorn Srikulnath 1,2,3,4,7,9,*,‡ORCID 1 Animal Genomics and Bioresources Research Unit (AGB Research Unit), Faculty of Science, Kasetsart University, 50 Ngamwongwan, Chatuchak, Bangkok 10900, Thailand 2 Laboratory of Animal Cytogenetics and Comparative Genomics (ACCG), Department of Genetics, Faculty of Science, Kasetsart University, 50 Ngamwongwan, Chatuchak, Bangkok 10900, Thailand 3 Special Research Unit for Wildlife Genomics (SRUWG), Department of Forest Biology, Faculty of Forestry, Kasetsart University, 50 Ngamwongwan, Chatuchak, Bangkok 10900, Thailand 4 Interdisciplinary Graduate Program in Bioscience, Faculty of Science, Kasetsart University, Chatuchak, Bangkok 10900, Thailand 5 National Elephant Institute, Forest Industry Organization, Lampang 52190, Thailand 6 Department of Electrical and Electronics Engineering, Faculty of Engineering, Ubon Ratchathani University, 85 Sathonlamark, Warinchamrab, Ubon Ratchathani 34190, Thailand 7 The International Undergraduate Program in Bioscience and Technology, Faculty of Science, Kasetsart University, Chatuchak, Bangkok 10900, Thailand 8 Department of Fishery Biology, Faculty of Fisheries, Kasetsart University, Chatuchak, Bangkok 10900, Thailand 9 Amphibian Research Center, Hiroshima University, Kagamiyama, Higashihiroshima 739-8526, Japan * Author to whom correspondence should be addressed. † These authors contributed equally to this work. ‡ These authors joint last author. Sustainability 2022, 14(22), 15355; https://doi.org/10.3390/su142215355 Submission received: 24 September 2022 / Revised: 1 November 2022 / Accepted: 8 November 2022 / Published: 18 November 2022 (This article belongs to the Special Issue Biodiversity in Different Regions: Exploring Global Ecology Sustainability) Downloadkeyboard_arrow_down Browse Figures Versions Notes Abstract Illegal wildlife trade is a major threat to global biodiversity. Asian elephants (Elephas maximus) are highly valued by various cultures as religious symbols and tourist attractions, which has led to a high demand for captive elephants. Owing to the unviability of captive breeding programs, several captive elephant populations are maintained by illegally obtaining wild Asian elephants. Morbidity and mortality rates among captive populations are high, whereas reproduction is low. In this study, we examined the genetic diversity among elephants using microsatellite genotyping and mitochondrial D-loop sequences of three captive elephant populations. The study results showed very low nucleotide diversity D-loop sequences and high variations in microsatellite genotyping, with an extensive variation of the gene pool estimates from different populations. This suggests that the optimal male selection during breeding could aid in maintaining the genetic diversity among captive populations. Forward genetic simulation revealed a decreasing genetic diversity in the fixed state within 50 generations. However, largely different gene pools can be effectively used to infer original elephant sources; this would facilitate the development of an identification certificate integration with machine learning and image processing to prevent illegal legislation owing to registration fraud between wild and domestic elephants. Implementing the proposed approaches and recommendations would aid in the mitigation of the illegal capture and domestic trade of wild elephants in Thailand and contribute to the success of future conservation plans in the blueprint of sustainable development goals.

Spatial point pattern of the baobab (Adansonia digitata) in semi-arid savanna, Southeast Zimbabwe

Article

Oct 2023

Species distribution modelling based on bioclimatic variables to understand habitat suitability and changes in range dominates studies on the spatial distribution of baobabs, which limits our understanding of how the small- scale plant–plant interactions influence the spatial point pattern of this keystone species in semi-arid regions of sub-Saharan Africa. Here, we investigated the spatial distribution of the baobab in two protected areas, Chipinge Safari Area (CSA) and Save Valley Conservancy (SVC) which lie in the semi-arid Southeastern lowveld of Zimbabwe. CSA was previously a sparsely human populated area before its proclamation as a protected area, has a small number of herbivores and baboons, and has no elephants, while SVC has a high density of elephants (1.5 km−2) and large number of herbivores. At each site, 1 km2 plots, SVC (n = 4) and CSA (n = 3), were established for spatial analysis. In each plot, we recorded the spatial location, elevation, height, diameter at breast height, and canopy cover of each baobab. Spatial point-pattern was assessed using both the inhomogeneous transformed L-function for Ripley’s K-function and the pair-correlation function. Baobabs in SVC were larger (height, canopy cover, and basal area) relative to those in CSA. At both sites, baobabs were clustered at small spatial scale (0–50 m), indicating that competition was insufficient to cause density-dependent thinning that can lead to even distribution as we expected. The distribution of small baobabs was independent of large baobabs, which reflects the importance of other environmental factors such as site conditions and seed dispersal rather than nurse- prot ́eg ́e on seedling establishment. The random distribution pattern of adult baobabs could be the legacy effects of these random factors and processes at establishment. Overall, our study shows that the distribution of baobabs is not dependent on local plant–plant interactions, but most likely from larger scale random pattern forming factors and processes such as seed dispersal and environmental heterogeneity

Biodiversity-based evaluation of thicket thresholds at different levels of elephant impact – Towards assessment and monitoring of thicket vegetation

Article

Jul 2023
ECOL INFORM

The Impact of Elephants (Loxodonta africana) on the Baobab (Adansonia digitata) in a Semi-arid Savanna

Article

Jun 2023

The impacts of the expanding African elephant (Loxodonta africana) population in southern Africa leads to a shift in savanna vegetation community composition and structure. However, little has been done to understand the effect of elephants on the structure of keystone tree species like the baobab. We sampled two protected areas in Southeast lowveld of Zimbabwe to quantify the impact of elephants on the baobab (Adansonia digitata L.), one area with elephants (Save Valley Conservancy: SVC) and the other without elephants (Chipinge Safari Area: CSA). Data on elephant damage, baobab density, and structural variables (tree height, stem basal area, and canopy cover) were collected in seven 1 km2 plots. Baobab damage was classed into four categories, i) new, ii) old, iii) very old, and iv) none, to have a time series interpretation. Distances of every baobab tree from spatial variables, nearest management road, perennial water source and conservancy boundary were measured. Baobabs in the absence of elephants (CSA) were taller with higher basal area and canopy cover than those where elephants were present (SVC). Although SVC baobabs had smaller structural variables compared with CSA, their density was much higher 1.69 ha-1 compared with 0.94 ha-1 for CSA. More baobabs in the smaller size classes for SVC suggests that recruitment was higher than CSA. No elephant damage was observed in the CSA although 23 % of baobabs showed signs of very old harvesting of bark by humans. All trees in SVC showed signs of elephant damage in either trunks or canopies, with most of damage classed as very old. Baobab damage decreased with distance from roads and perennial water sources while it increased with distance from conservancy boundary. Our results demonstrate that elephants have a great impact on baobab structure but not necessarily recruitment as indicated by the presence of some baobabs in smaller size classes, suggesting that other factors may be more important in determining recruitment of this keystone species.

Standard Identification Certificate for Legal Legislation of a Unique Gene Pool of Thai Domestic Elephants Originating from a Male Elephant Contribution to Breeding

Article

Full-text available

Nov 2022

Illegal wildlife trade is a major threat to global biodiversity. Asian elephants (Elephas maximus) are highly valued by various cultures as religious symbols and tourist attractions, which has led to a high demand for captive elephants. Owing to the unviability of captive breeding programs, several captive elephant populations are maintained by illegally obtaining wild Asian elephants. Morbidity and mortality rates among captive populations are high, whereas reproduction is low. In this study, we examined the genetic diversity among elephants using microsatellite genotyping and mitochondrial D-loop sequences of three captive elephant populations. The study results showed very low nucleotide diversity D-loop sequences and high variations in microsatellite genotyping, with an extensive variation of the gene pool estimates from different populations. This suggests that the optimal male selection during breeding could aid in maintaining the genetic diversity among captive populations. Forward genetic simulation revealed a decreasing genetic diversity in the fixed state within 50 generations. However, largely different gene pools can be effectively used to infer original elephant sources; this would facilitate the development of an identification certificate integration with machine learning and image processing to prevent illegal legislation owing to registration fraud between wild and domestic elephants. Implementing the proposed approaches and recommendations would aid in the mitigation of the illegal capture and domestic trade of wild elephants in Thailand and contribute to the success of future conservation plans in the blueprint of sustainable development goals.

Mapping Floristic Composition Using Sentinel-2A and a Case Study Evaluation of Its Application in Elephant Movement Ecology in Sagalla, Kenya

Article

Full-text available

Oct 2022

The quantification of vegetation structure and composition at local and global scales provides valuable information for understanding the balance of the natural and human-made environment, which is crucial for natural resource planning and management, and the sustenance of ecosystem biodiversity. In this study, we proposed using the Sentinel 2A imagery to classify vegetation cover into communities based on the floristic association of individual vegetation species. We apply traditional remote sensing techniques to process the satellite image and identify training regions of interest (ROI) which are thoroughly assessed for spectral uniqueness before using the pixel-based supervised classification algorithms for our classification. Ground truthing assessment and species dominance computations are done to determine the vegetation community composition and naming based on floristic associations. We apply the floristic compositions output in analysing elephant movement tracks in the area, to assess the potential influence the location of specific vegetation species and communities utilized by elephants has on their movement and presence, as well as on elephant bulls and family groupings. The results show that the 10 m spatial resolution Sentinel-2A is suitable for investigating and mapping vegetation species in communities for large-scale mapping operations. We determined Near-Infrared band 8 and shortwave Infrared band 11 as key for identifying and differentiating ROIs at the floristic association community vegetation mapping level. We attained an overall accuracy of 87.395%. The analysis proved the 10 m spatial resolution of Sentinel 2A to be sufficient in distinguishing vegetation communities, including those with similar dominant species but variations in other contributing species. We also found a direct connection between vegetation location and elephant movement based on the summative analysis of utilised vegetation by the different elephant groupings. Bull elephants were predominantly present in areas with Combretum, family groups in areas with Commiphora, and mixed groups with both bulls and families in areas with Commiphora, and Cissus. This study shows the value that remote-sensing scientific support can offer conservationists and governments in objective evidence-based land management, policy making and governance.

Elephant diet at the edge of the Fynbos Biome, South Africa

Article

Full-text available

Jun 2002
PACHYDERM

Antoni Milewski

Reviews observations of two forest guards who from 1990 to 2000 noted the diet and preferred foods of Knysna elephants, in the Fnybos Biome along the southern coastal region of South Africa. All plants eaten by five elephants, the last three known native animals and two introduced juveniles, were noted 'this is the first evidence that elephants routinely eat the nutrient-poor, heathy shrubs and wiry grasslike plants of the fynbos'. The native animals spent 90% of their time in the forest, but when released in 1994 the introduced juveniles only spent 2 months in this habitat. From then on they spent: 80% in fynbos and rough pasture, 10% in patchy forest, 5% in mature tree plantations, and less than 5% near vegetable/croplands which they raided. 11 species of forest trees and shrubs were eaten, Rapanea, Pterocelastrus, and Ilex seemed to be preferred. The introduced juveniles mainly ate bark when in the forest. Most of the common genera of shrubs and grasslike plants of the fynbos were eaten, but most herbaceous plants were ignored. Exotic trees in plantations were occasionally damaged for their bark and many Acacia, particularly A mearnsii were broken down, and bark, pods and leaves eaten. The animals sometimes excavated and ate tubers and rhizomes of herbaceous plants such as Iridaceae and bracken fern (Pterodium) but did not eat soil. The author notes the complementary diets elephant may have with other indigenous herbivores, and discusses the commonly held view that the Knysna habitat lacks trace elements. Observations suggest elephant could be maintained in the Fynbos Biome, and their presence in this area might be useful in controlling invasive exotic plants.

Seasonal distributions and social dynamics of elephants in the Hoanib River catchment, northwestern Namibia

Article

Full-text available

Oct 2003

Studies on the elephants of the Hoanib River catchment are limited. The most significant research undertaken during a period of drought and civil war inducing a high stress situation for the elephants. The only other reported study was undertaken at the end of the Namibian civil war and focused on elephant range and movement and did not carry out an in-depth analysis of the elephants ecology. The current study examined two distinct populations of elephants separated by an area with a high human population. The average group size of elephant herds in both the eastern and western sections of the catchment has declined steadily from the early 1980s until the present day. Average group size also appeared to be seasonally dependent, with larger group sizes observed during the cold-dry and wet season in the eastern catchment and during the wet and hot-dry season in the western catchment. The social interactions between elephants were investigated in the western section of the catchment only. Associations between different family units were only loose affiliations lacking the strong social bonds reported from other areas of Africa. Adult male group associations were shown to be transient and irregular, with small group size.

Effects of elephant damage to vegetation on the abundance of phytophagous insects

Article

Full-text available

Dec 1997

Historical incidence of the larger land mammals in the broader Eastern Cape, Second Edition

Book

Jun 2007

The book Historical mammal incidence in the Cape Province: Volume 2 - The eastern half of the Cape Province, including the Ciskei, Transkei and East Griqualand was first published in 1987, by the erstwhile Chief Directorate: Nature and Environmental Conservation of the Provincial Administration of the Cape of Good Hope, Cape Town. The author is the late C J (Jack) Skead, a legendary naturalist, scientist and historian in the Eastern Cape (see ‘The Author’). A Second Edition, titled Historical incidence of the larger land mammals in the broader Eastern Cape and including a revised, re-edited and expanded text, additional tables and maps, completely revised species distribution maps, and a number of illustrations, has now been published. This unique book brings together a huge amount of information, from a large variety of otherwise obscure sources – most notably the journals of early naturalists, travellers, hunters and farmers – on the historical distribution of the larger mammal species of the region. These include the herbivores (plant-eaters) – such as the elephant, the rhinoceros and various kinds of antelopes, and the carnivores (flesh-eaters) – such as the lion, the leopard and the hunting dog. It provides information on the status and movements of the game animals, and on the possible early human influences on their populations. It also includes chapters on interesting gaps in distribution patterns of certain species, and species exterminated in, and introduced to, the region. The book incorporates a review of the recent status of the various species. The information in the book enables a fascinating picture to be created of the larger mammals that occupied the highly diverse landscapes of the region at the time when it was being settled by Black and White pastoralists and agriculturalists, mainly from the 17th century onwards. The author provides interesting and useful interpretations of the information at hand, thereby helping us to understand the intricate relationships between the mammals and their habitats, and the possible reasons for the decrease in range and numbers of many species, and for the increase shown by others. As such, the book is of significant value to scholars, natural scientists, historians, conservation managers and environmental impact assessment practitioners. Important information for the environmentally and economically sustainable development of the burgeoning ecotourism and game-ranching industries in the broader Eastern Cape is made available. Information in the book is also useful for guiding expansion planning of extant protected areas (national and provincial parks, and local nature reserves), and the establishment of new ones, in the region.

Effects of elephant and other wildlife on vegetation along the Chobe River, Botswana /

Book