The Impact of Elephants on Large Trees

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Lisbeth
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The Impact of Elephants on Large Trees

Post by Lisbeth » Mon Sep 02, 2019 4:23 pm

August 28, 2019 3.29pm BST | Ross Harvey

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African elephant in Kruger national park, South Africa. PACO COMO/Shutterstock

Elephants are often accused of being responsible for the unsustainable loss of large trees in protected areas. This is because they strip bark and break branches. They can also have a heavier impact through uprooting trees or snapping stems. They have forage preferences too. Marula, knobthorn and red bushwillow are among their favourites.

This type of behaviour has raised concerns over the effects of elephants on large trees in protected areas such as South Africa’s Kruger National Park. As a result, elephant populations have been managed to preserve trees and the environment in a static state.

Researchers Dr Michelle Henley and Robin Cook recently set out to establish whether elephants are in fact responsible for large tree mortality.

They did this by reviewing the science and evaluating how effective past strategies have been at mitigating large tree loss, given that such loss was typically attributed to high elephant densities. These strategies usually focused on controlling elephant numbers lethally, through either culling or hunting.

Their review shows that in African savannas:

| maintaining elephant numbers at a pre-determined carrying capacity level did not prevent the loss of large trees.

The researchers conclude that the relationship between elephant populations and large trees is complex. In large ecosystems, managing elephant populations so they don’t exceed a certain threshold number is arbitrary.

What causes large tree mortality?

Large tree survival is a function of numerous historical and interacting variables.

For instance, aesthetically appealing landscapes with extensive large tree cover are probably historical anomalies. Colonially imported diseases such as rinderpest – throughout the late 19th and early 20th centuries – decimated herbivore populations. Combined with excessive recreational elephant hunting, trees of specific aged cohorts could proliferate.

The factors determining large tree mortality and distribution are complex. For example, the decline in large tree species within Botswana’s Chobe National Park has been attributed to high impala densities rather than elephants.

The authors argue that elephant management strategies should abandon the notion of carrying capacity – that landscapes can only sustain a certain threshold number of elephants per square km. Rather, managers should ensure that migratory corridors remain as open as possible.

Managers should also reduce the density of artificial water points so that elephant impact is not spread more evenly across the landscape. Intermittent natural water sources encourage seasonal movement patterns among megaherbivores. This provides important plant refugia within large, open systems, which increases overall biodiversity.

In smaller reserves, where elephant densities may be problematic for large tree survival prospects, non-lethal interventions are – from an ethical and tourism safety perspective – more desirable than culling or hunting. Contraceptive methods, pioneered by Audrey Delsink and others, lower growth rates successfully. Translocation also works, though it is traumatic and depends on space being available elsewhere.

The history and the science

The researchers reviewed the science on the interaction between elephants and large trees.

While some studies have found that elephants can have a negative influence on biodiversity, others show that they play a critical role in the propagation of large trees. For instance, mature bulls can transport seeds to a maximum distance of 65km away from their source.

Elephants modify their landscapes as ecosystem engineers, often increasing biological diversity in the process.

Large trees do have important ecosystem functions, including providing nesting sites for vultures and raptors. But the addition or reduction of large trees is not necessarily positive or negative. A reduction in large tree cover may, for instance, reveal that a degraded environment is in the process of restoration from past management practices.

Past management strategies

The second part of the paper evaluates past methods to manage elephants.

The precautionary principle is highly contested in conservation. It suggests that an action should be avoided if it is not yet scientifically established that it can prevent an undesirable outcome. Henley and Cook found that this principle had been interpreted differently in past elephant management strategies.

For instance, culling was implemented before the relationship between elephant density and large tree cover had been scientifically established. The irony is that elephants start to disperse once they reach a certain density and the population growth rate naturally starts to slow down. Culling prevents that threshold density being reached. As the paper states:

| The safety margins provided by the precautionary principle favour a static environmental state within thresholds of potential concern, which
| may not always be applicable in a dynamic ecosystem.


Culling programmes in the Kruger Park between 1967 and 1994 focused on maintaining the elephant population at one elephant per square mile – roughly 7 000 in total. The current population is over 20 000, about 3 per square mile.

The idea, embedded in the public mind, that the Kruger can only sustain 7 000 elephants, ignores the fact that, as research has pointed out, a carrying capacity of a static nature does not hold true in a complex ecological system.

The authors also stress that hunting cannot be used as a viable elephant management tool:

| Hunting is a highly selective activity, as bulls of particular age categories and with sought-after physical traits are targeted.

They have therefore not proposed it as a population reduction method as it “could result in undesirable skewed sex ratios and age structures within populations”.

Key takeaways

The key is to keep migratory corridors open – in conjunction with the natural expansion of elephants’ range in the wet season and contraction in the dry season – so that natural ecological functions occur. Minimal – and non-lethal – intervention is the optimal management strategy to maintain biological diversity in large, dynamic ecosystems.
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Re: Debunking myths about the impact of elephants on large trees

Post by Richprins » Mon Sep 02, 2019 5:41 pm

No, they do indeed not destroy many big trees.

They just don't allow any new ones to get big! 0- :-?
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Re: Debunking myths about the impact of elephants on large trees

Post by Lisbeth » Mon Sep 02, 2019 6:41 pm

The key is to keep migratory corridors open
Easier said than done O/
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Re: Debunking myths about the impact of elephants on large trees

Post by stefan9 » Tue Sep 03, 2019 9:08 pm

Excellent article. Agree with them.

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Re: The Impact of Elephants on Large Trees

Post by Lisbeth » Wed Sep 18, 2019 5:02 pm

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The management dilemma: Removing elephants to save large trees

BY MICHELLE D. HENLEY, ROBIN M. COOK - 15TH AUGUST 2019 - KOEDOE.COM

Click on the title to read the article.
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Re: The Impact of Elephants on Large Trees

Post by Lisbeth » Fri Oct 11, 2019 12:22 pm

Elephants and trees

Posted on October 9, 2019 by Africa Geographic Editorial in the DECODING SCIENCE post series.

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Mature elephant bull in the Greater Kruger © Simon Espley

DECODING SCIENCE POST by AG Editorial

“Elephant damage!” is now a common phrase in reaction to the sight of fallen trees, and landscapes bereft of trees. The apparent loss of large savanna trees such as marula and knobthorn in Africa’s protected areas is often blamed on elephants, and this perceived direct link between elephants and treefall drives many conservation authorities and strategies to focus on managing elephant numbers in order to ‘save’ trees.

And yet, there is not necessarily a direct line between elephants and the ongoing loss of large trees, as there are many layers of complexity to the situation. A recent report ‘The management dilemma: Removing elephants to save large trees’ dives into this complex, important issue and comes up with some surprising and thought-provoking conclusions.

Here follows a brief summary of this report:

THE IMPACT OF HISTORICAL PREJUDICE

The report kicks off by explaining that management practise in the mostly fenced Kruger National Park has historically sided towards managing elephants in order to achieve an ‘ideal state’ with regard to trees, which is based on a colonial perspective, tourist expectations and the pursuit of an aesthetically pleasing (treed) landscape. And yet those historical records were based on a time when elephants had been largely exterminated from South Africa, from an earlier population of about 100,000 elephants – by poaching, recreational/trophy and subsistence hunting. And, the 19th century rinderpest outbreak resulted in the crash of herbivore populations. This absence of elephants and herbivores (which eat tree seedlings) resulted in trees dominating the landscape at the time that we now refer to as having the ‘ideal landscape’.

In the post-culling era, Kruger elephant numbers have again increased, but populations are restricted to smaller areas than historically. To add to the dynamic, the ‘ideal landscape’ is now largely determined by the needs of the photographic tourism industry.

ELEPHANTS AND TREES

Elephants utilise trees such as marula, knobthorn and red bushwillow for nutrition, and may strip bark, break branches or push trees over as they forage – with large bulls pushing over more trees than cows do. Trees that are trimmed down, rather than pushed over, become vulnerable to insects and fire.

By engaging in this ‘ecosystem engineering’ behaviour, elephants benefit ecosystems by improving plant diversity – opening up woody areas to grassland. Elephants are also important dispersers and germination agents of tree seeds, often depositing those seeds in a ball of organic fertiliser (dung) up to 65 km away from the mother tree, with the seed having a higher chance of germination after being exposed to acids in the elephant’s digestive system. Elephants produce up to 150 kg of wet dung per day, further enriching the ecosystem by promoting overall biological diversity and introducing micro-habitats for insects, frogs and reptiles.

On the other hand, the dominance of elephants above a certain threshold can, in conjunction with fire, result in the removal of large trees, and resultant reduction in diversity of birds, bats and small mammals.

CARRYING CAPACITY: A POPULAR MISCONCEPTION

The Kruger National Park culling program from 1967 to 1994 was based on maintaining a population of one elephant per square mile (0,4 per km²) – about 7,000 elephants in the 1.9-million-hectare national park. This figure, which was based on outdated agricultural parameters, became entrenched in the minds of former protected area managers and some sectors of the general public, and the current elephant population of over 20,000 causes much angst and discussion amongst those sectors of society. This application of a static carrying capacity figure to a dynamic ecosystem is no longer supported by current management thinking.

FENCED-OFF AREA SHOWS SAME LOSS OF LARGE MARULA TREES

A 300-ha area in northern Kruger was fenced off to breed roan antelope, during the time of the elephant culling program, and no elephants accessed the fenced-off area. Large marula trees within the fenced-off area disappeared from that landscape at the same rate as did trees outside of that area – indicating that other factors are also at play. Also, the lack of browsers in the 300-ha roan enclosure resulted in marula seedlings growing taller than they did outside of the fence, where impala and other small herbivores predate on significant volumes of tree seedlings and saplings. This lack of a clear direct relationship between dead marula trees and elephant numbers during the culling period suggests that elephants are not solely responsible for the loss of marula trees. There is a growing body of evidence that there is a complex relationship between elephants, fire and climate change when it comes to treefall rates and bush encroachment.

TSAVO AND CHOBE COMPARISONS

Both Tsavo (Kenya) and Chobe (Botswana) National Parks have seen elephant numbers fluctuate in the last two centuries under the pressure of poaching, with resultant impact on tree cover and populations of grassland grazers versus browsers. Both protected areas are currently seeing elephant populations recover to what they were before the 19th century ivory trade period, with resultant reinstatement of a landscape with fewer large trees. Also recovering in Chobe (from the rinderpest outbreak) are impala populations, resulting in increased predation on tree seedlings and saplings, further increasing the swing back to fewer trees and more grassland than existed historically.

MITIGATION METHODS

The primary determinants of tree extirpation have been found to be elephants, fire, soil and elevation – and therefore elephant density alone does not explain the survival and recruitment rate of large trees.

That said, the report does cover various lethal and non-lethal methods for elephant population reduction, and stresses that these points are made without reference to the obvious ethical considerations. The report also emphasises that each of these methods has advantages and disadvantages.

Lethal elephant population reduction

Culling was described in the report as not effective because it results in a spike in elephant birth rates, in response to more food per head, and the inter-regional movement of elephants into culling areas. Also, culling was found to have taken place in areas that did not match the natural spatial movements of elephants. Poaching reduced elephant populations by one third in seven years across Central and East Africa, but for obvious reasons this is not a supported elephant management tool. Trophy hunting was described as non-effective because the focus on male elephants carrying large ivory results in undesirable skewed sex ratios and age structures within populations.

Non-lethal elephant population reduction

The use of contraceptives has been shown to be successful in a number of smaller reserves in South Africa, including Greater Makalali Private Game Reserve and Tembe Elephant Park. The success of elephant translocations is dependent on additional land becoming available for elephants, and the impact of successful translocations is presumed to mirror that of culling.

Elephant movement and impact on trees is regulated by the spatial availability of water resources. For example, Kruger elephant bulls make use of artificial waterholes to range further away from natural rivers than do family groups, and the Kruger management strategy now includes the closure and spatial distribution of artificial waterholes to influence elephant movement. This strategy has already resulted in the annual elephant population growth rate reducing from 6,5% to 4,2% over a 12-year period. Importantly, the closure of artificial waterholes will also reduce the populations of tree seedling predators such as impala, further improving the survival rates of trees. To date Kruger has closed two-thirds of the 365 artificial waterholes and 50 earth dams.

By comparison, the privately-owned game reserves to the west of Kruger National Park that share an unfenced border with Kruger have not reduced the number of artificial waterholes, instead choosing to protect individual trees. They are experiencing a significantly higher elephant population than was the case before Kruger started closing their artificial waterholes.

Fences are also used to influence the spatial movement of elephants. Elephants also avoid fear zones – where threats to their safety are spatially predictable, but where the timing and type of threat are unpredictable.

Protecting individual trees

Protecting individual large trees is justified as a tool to maintain both the seed banks for future generations, and the aesthetic importance of trees as landscape features. In this regard, wire-netting prevents bark-stripping, and rock-packing and honey bees keep elephants away from the trees. Artificial propagation of tree seedlings increases the density of food plants, and has been successfully applied to diminish human-elephant conflict in Thailand.


Image
Stacking rocks around the base of trees (in this case a baobab), to prevent elephants from getting to the trees © Simon Espley

Image
Wrapping wire around large trees (in this case a baobab), to protect them against bark-stripping elephants © Simon Espley

Meta-population management

Reducing the poaching threat in neighbouring protected areas such as Mozambique’s Limpopo National Park could produce benefits for South Africa’s Kruger National Park, by reducing the ‘fear zone’ implications and increasing the movements of elephants out of Kruger and between these protected areas.

CONCLUSION

The authors of this report conclude that protected area managers face difficulties in protecting biodiversity where certain objectives may be in conflict. The question “Can large trees and elephants coexist and what strategies should managers implement to optimise biodiversity goals?” is a vital one facing protected area managers.

For more information about this topic, read ‘Decoding Kruger’s Elephant Management Plan’.

Full report: Henley, M.D. & Cook, R.M. (2019). The management dilemma: Removing elephants to save large trees. Koedoe 61(1), a1564. https://doi.org/10.4102/koedoe.v61i1.1564
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Re: The Impact of Elephants on Large Trees

Post by Peter Betts » Sun Oct 13, 2019 9:30 am

Very good article

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Re: The Impact of Elephants on Large Trees

Post by Richprins » Sun Oct 13, 2019 9:32 am

CARRYING CAPACITY: A POPULAR MISCONCEPTION

The Kruger National Park culling program from 1967 to 1994 was based on maintaining a population of one elephant per square mile (0,4 per km²) – about 7,000 elephants in the 1.9-million-hectare national park. This figure, which was based on outdated agricultural parameters, became entrenched in the minds of former protected area managers and some sectors of the general public, and the current elephant population of over 20,000 causes much angst and discussion amongst those sectors of society. This application of a static carrying capacity figure to a dynamic ecosystem is no longer supported by current management thinking.


How convenient! lol

What about this part then?


On the other hand, the dominance of elephants above a certain threshold can, in conjunction with fire, result in the removal of large trees, and resultant reduction in diversity of birds, bats and small mammals.
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Re: The Impact of Elephants on Large Trees

Post by Lisbeth » Tue Jun 16, 2020 11:06 am

Of dung beetles and elephants

By Jock Orford• 15 June 2020

Image
MALELANE, SOUTH AFRICA - DECEMBER 01: A Dung Beetle rolls his collection across a hole during the first round of the Alfred Dunhill Championship at Leopard Creek Country Golf Club on December 1, 2016 in Malelane, South Africa. (Photo by Richard Heathcote/Getty Images)

Do elephants and trees have a symbiotic relationship or are the numbers and distribution of trees preordained? How do trees come to grow to their full and majestic size in the presence of elephants before they get pushed over?

Are the trees knocked over by elephants near the end of their lives, their roots loose like the roots of an old tooth? When a tree is pushed over, 90% of the wood is consumed by termites and returned to the ecosystem, for everything eats termites, including man.

But there is more to the story of the death and rebirth of trees than termites!

Marcus Byrne and Helen Lunn tell another part of this intricate story in their excellent book, Dance of the Dung Beetles (2019), in which they describe the recycling of elephant dung by the dung beetle. Dung beetles are also known as “Scarabs” and there are many thousands of species of Scarabaeidae in Africa. Ancient Egyptians, who accorded dung beetles a godlike status pertaining to “Death and Resurrection”, buried important people with replicas of Scarabs placed on their mummified bodies. Recent research has shown that some nocturnal dung beetles use the Milky Way to orientate themselves, which is vital for their survival.

Marcus and Lunn report that Malcolm Coe, a researcher from Oxford University, calculated that with 4.4 elephants per square mile in Tsavo, 27,000 piles of dung are dropped per square mile each year.

The dung beetles bury this dung, carrying both dung and the seeds of the trees eaten by the elephants into the earth.

The dung beetle, by burying the dung, improves the soil structure and fertility, increasing aeration and moisture and creates an ideal situation for the germination of new trees representing the diverse diet of the elephant. The fallen trees also open up space for the penetration of sunlight to stimulate photosynthesis in new seedlings springing up.

These authors also describe the dung beetles that fly with the herds of the annual wildebeest migration in the Serengeti. They bury 75% of the wildebeest dung as they follow the migratory pathway, with 15 to 20% of the soil in this system being made up of dung balls. This “planting” ensures the germination of the grasses suitable for wildebeest and their survival on the next migration. In 2011, 11 species of dung beetles were introduced to New Zealand, not to control flies, as in Australia, but to upgrade the composition of their soil.

It would be naïve to think that trees only grow if buried by dung beetles, but a seed buried in a dung bed, having passed through the gut of an elephant, would have a distinct advantage over a seed falling on bare ground, exposed to seed eaters and harsh weather. In a remarkable example of evolution, a single indigenous restio (a reed-like plant) in the Western Cape has adapted to produce seeds that resemble and smell like balls of antelope dung. As a result, two species of dung beetle have been duped into burying these seeds, despite getting no benefit themselves.

In Botswana, where elephants fleeing culling, hunting and poaching in adjacent countries have sought sanctuary in the northern part of the country, there is growing concern about the damage large herds might do to the trees.

Image
Photo: Robin Cook

Opinion, however, remains divided on the relationship between elephants and trees. Fearful of the loss of too many trees as a result of too many elephants, one body of opinion favours the reduction of elephant numbers by culling, a method that has always provoked as much criticism as it has advocacy.

Elephant culling has taken place in various parts of Africa and it has been widely practised in the Kruger National Park. However, in 1996 Dr Anthony Hall-Martin, the park’s then head of research, stated in a public meeting to review the management policies of Kruger, that there was no scientific evidence to support the practice.

In Namibia, the focus of concern has been different; many people are of the view that the bush itself inhibits farming. Intensive cattle and game farming have led to degradation of the veld, loss of perennial grasses, other edible plants and tree diversity, resulting in bush encroachment.

This “invasive” bush is hated and there are widespread efforts at eradication. Root and leaf poisons are used, the bush is bulldozed, small bushes are used for animal feed, and large trees are turned into charcoal – according to the Namibian newspaper, 200,000 tons of charcoal were exported last year.

Large rare trees along the Caprivi are sold by the truckload. An interesting exception is the Erindi Game Reserve, near Otjiwarongo. Initially, this Reserve was farmed but the grazing lands became degraded and the farmers turned to hunting. This further degraded the veld as the game increased in numbers and could not migrate. The farmers then turned to tourism, creating the Erindi Game Reserve of some 60,000 hectares, building a lodge, a self-catering camp and a campsite, creating jobs and paying tax. They re-introduced carnivores – lion, cheetah, wild dog. These carnivores limit the grazers’ distribution. Browsers, including around 100 elephants, were also introduced.

I suspect time will prove that elephants are opening up the bush, and the dung beetles are carrying dung and seed into the ground, thus benefiting the soil condition, thereby giving the grass and trees a chance to grow once more, returning to their former diversity.

The immense value of this rehabilitation is reflected in the price of two billion Namibian dollars paid for Erindi when it was sold last year as a going tourism concern.

The cycle of death and regeneration of the trees is part of a symbiotic circle of intimate dependence between elephants, dung beetles and the environment, which is initiated by elephants pushing down trees.

Therefore, the real question we must ask ourselves is: Are there enough elephants to ensure the survival of dung beetles and the next generation of trees? DM/ML

Dr Jock Orford is a retired Namibian medical doctor with a lifelong interest in conservation. He earned his MsC for work done in Etosha National Park, in which lionesses were successfully implanted with contraceptives to control population numbers as an alternative to culling. He is a trustee of the Namibian Cheetah Conservation Fund (https://cheetah.org)
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