Elephants & Big Trees: Evaluation of the pyramid and creosote elephant-mitigation methods in Ingwelala and N’tsiri, Umbabat

Private Nature Reserve

Report of the August 2018 Baseline Assessments

Compiled by: Mr Robin Cook (Big Trees Project Manager, Elephants Alive)

Dr Michelle Henley (Director, Elephants Alive)

Ms Tamara Eggeling (Researcher, Elephants Alive)

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Executive summary

Concerns over elephant impact on big trees have resulted in a variety of mitigation methods being

tested protect these trees. Two methods which have been applied in the Umbabat Private Nature

Reserve region of the Greater Kruger National Park are the pyramid and creosote methods. The

pyramid method involves packing rings of sharp concrete pyramids around a tree’s main stem to keep

elephants away from the tree itself, whilst the creosote method involves connecting a glass jar filled

with stones and coal-tar creosote to a tree’s main stem. Neither of these methods have been

scientifically tested. We conducted surveys on trees within the Ingwelala and N’tsiri properties of

Umbabat to set up a baseline study site for future tree assessments. Co-currently, we assessed the

effectiveness of both mitigation methods. We found great variation within the style of pyramid

packing, with no pyramids extending over 4 m away from the trees’ main stems. Pyramids were also

loosely packed at times, or scattered, allowing for elephants to reach the trees. We suggest that

pyramids need to be tightly stacked over a distance of 4-5 m from a tree’s main stem to be effective

at protecting the tree. The presence of a creosote jar in a tree did not affect its likelihood of being

impacted on by elephants in comparison to control trees, and one quarter of the surveyed creosote

jars had been broken and spilled into the environment. Due to creosote’s pollutant qualities, we

suggest that all remaining jars are removed from the site and a new mitigation method is tested in its

absence.

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1. Introduction

Whilst African elephants (Loxodonta africana) are considered to be major drivers of ecosystem change

(Coverdale et al. 2016), their impact on the surrounding environment, in particular that on big tree

species, is often considered to be negative (Helm and Witkowski 2013). Landowners and conservation

managers within the Greater Kruger National Park (Greater KNP) have expressed concern over the

loss of big trees as a consequence of elephant impact (Edge et al. 2017), with increasing elephant

numbers highlighted as a management concern (Asner et al. 2016). The survival of big tree species is

dependent on a number of ecological factors, including climate (Venter and Witkowski 2013), seed

predation (Helm et al. 2011a), seedling herbivory (Moe et al. 2009), fire-induced mortality (Jacobs and

Biggs 2001, Helm et al. 2011b), as well as elephant impact (Shannon et al. 2008, Cook et al. 2017).

However, as elephant impact on tree populations is markedly visible, most attention is focused on the

impact and how to manage it (SANParks 2012). The Greater KNP has moved away from directly

controlling elephant numbers to managing their environmental effects (SANParks 2012), primarily

through the removal of artificial water sources across the system (Ferreira et al. 2017, Robson and

Van Aarde 2017). This management approach though, is not always applicable in the private sector,

where water saturated landscapes are important for tourist revenue (Peel 2015). Therefore,

management methods have focused on directly protecting the big trees themselves. These methods

include wire-netting a tree’s main stem to prevent bark-stripping (Derham et al. 2016), as well as

hanging beehives in trees to keep elephants away in general (Cook et al. 2018). Another method which

has been tried but never scientifically analysed is the use of rings of large rocks or sharp concrete

pyramids around the main stem of a tree to prevent elephants from gaining access to the main stem

(SANParks 2012). Rocks/pyramids as a mitigation method were first introduced into the Greater KNP

in the late 1970s to protect baobab (Adansonia digitata), marula (Sclerocarya birrea), umbrella thorn

(Acacia tortilis) and ilala palms (Hyphaene coriacea) (Kruger Park Times 2017). Tol Pienaar, warden of

the KNP at the time, stated that ‘to be effective, the ring of rock had to be between four and five metres

across, to prevent elephants from reaching the tree's stem with their trunks. The elephants were

reluctant to step on the rocks, especially when they shifted underfoot, but could still topple a tree if

they could grasp it well enough with their trunks.’ (Kruger Park Times 2017). Rings of pyramids have

been placed around a number of trees in the Ingwelala and N’tsiri properties of Umbabat Private

Nature Reserve within the Greater KNP. As the location of all of these trees are known, scientifically

standard evaluation methods can be applied to each tree to assess the effectiveness of the pyramids

at preventing elephant impact.

A new method which has recently gained popularity across properties within the Greater KNP

is the use of tins or jars of coal-tar creosote nailed to the main stem of the tree (personal observation).

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It is hypothesised that the creosote scent will deter elephants. Coal-creosote is a residue produced

during the distillation of coal tar, which is a by-product of the carbonization of coal. Creosote is a thick,

oily and flammable liquid, and does not easily dissolve in water. Creosote has suspected carcinogenic

properties and the breakdown of creosote in soil can take months to years to occur (Choudhary et al.

2002). It is therefore important that assessments are carried out on creosote-containing trees before

the method is expanded across the Greater KNP.

The aim of this survey is to set up elephant impact scores on all sampled trees for future

assessments on the mitigation methods. Furthermore, we aim to provide feedback to management

on how the successfulness of the current mitigation methods and what improvements can be made

too these methods.

2. Materials and methods

2.1. Study site

The baseline assessments took place within the Ingwelala and N’tsiri properties of Umbabat

Private Nature Reserve from 13-18 August, 2018 (Figure 1). Permission was granted from John

Llewellyn (Ingwelala), Chris Mayes (Ingwelala) and Mark Griffiths (N’tsiri) to conduct assessments on

trees where mitigation methods have implemented. Wire-netted trees were thus included in the

study. These trees have been wire-netted since 2007 (Henley 2013). In order to make comparisons to

trees without protection, control trees were selected in both properties. The pyramid rings have been

around the selected trees for at least 13 years, whilst the creosote has been on the trees for 9 months.

Figure 1: Location of the selected trees within the Ingwelala and N'tsiri properties of the Umbabat Private Nature Reserve.

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Pyramids had been set up around the following trees: marula (n = 24), black monkey thorn (n

= 7), mopane (n = 7), knobthorn (n = 6), euphorbia (n = 3), schotia (n = 3), tree wisteria (n = 3), sjambok

pod (n = 1) and tamboti (n = 1). A total of 22 pyramid sites had missing trees.

Creosote jars were found on the following trees: marula (n = 63), sjambok pod (n = 20),

knobthorn (n = 5), leadwood (n = 5), schotia (n = 2), false marula (n = 1), purple pod terminalia (n = 1)

and tamboti (n = 1).

The following trees were used as controls: marula (n = 31), knobthorn (n = 21), mopane (n =

4), and sjambok pod (n = 1).

2.2. Field assessments

A total of 281 trees were assessed (Ingwelala n = 44; N’tsiri n = 246), of which 80 had pyramids,

100 had creosote, 57 were controls, and 42 were wire-netted. Standardised field assessment

procedures were applied to all selected trees. The tree’s height was measured using the VolCalc digital

photography method for measuring tree volume (Barrett and Brown 2012). The basal stem diameter

(30 cm above ground) and diameter at breast height were measured, and the tree species was

identified. Elephant impact was recorded as follows: 0 = No damage; 1: <50% of the bark around the

main stem’s circumference has been removed and/or secondary branches have been broken off; 2:

>50% of the bark around the main stem’s circumference has been removed, or one primary branch

has been broken off; 3: >50% of the bark around the main stem’s circumference has been removed

and one primary branch has been broken off, or more than one primary branch has been broken off;

4: The tree has had its main stem snapped but is coppicing or alive; and 5: Tree is dead. The presence

of ants, fungi, termites and woodborers were recorded on each tree. For rock trees, the following

additional measurements were taken: a) the distance between the tree’s main stem and the first ring

of pyramids; b) the combined length of the pyramid rings; and c) the combined lengths of ‘a’ and ‘b’,

representing the total distance between the main stem and a potential elephant.

2.3. Data analyses

All statistical analyses were performed using R statistical software (R v. 3.2.2, R Core Team,

2016) and STATISTICA v. 8. A moderately strong positive correlation existed between tree height and

BSD (Pearson’s correlation, r = 0.69, n = 213, p < 0.0001) and therefore height was used as a proxy for

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overall tree size when comparing elephant impact across size classes. Correlations were run to test for

relationships between elephant impact scores and the three measured pyramid distances. To

investigate whether creosote affected the likelihood (presence/absence) of a tree receiving any form

of elephant impact, a regression analysis through a generalised linear model with a binomial

distribution and a logit-link function was run from the ‘rcompanion’ package (Mangiafico, 2015). Tree

height and species were used as other explanatory variables. We used a Fisher’s Exact Test to further

investigate differences between the number of creosote and control trees impacted in the last 9

months.

3. Results

3.1. Pyramids

Of the 80 pyramid trees, 55 (68.75%) were alive and 25 (31.25%) were dead. 12.5% of the

trees (n = 10) were recorded as ‘scattered’, where major gaps were present for elephants to reach the

tree’s main stem (Figure 2).

Figure 2: Example of a marula tree with scattered pyramids.

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Tree to pyramid distance ranged from 0-187 cm (mean = 62.33 cm ± S.D. 61.23 cm) (Figure 2).

Actual pyramid distance ranged from 46-250 cm (mean = 147.36 cm ± S.D. 45.26 cm), whilst the sum

pyramid distance ranged from 46-383 cm (mean = 209.69 cm ± S.D. 60.25 cm) (Figure 3). No sum

pyramid distances were >400 cm in length.

Figure 3: Distance range of pyramid measurements around trees in Umbabat Private Nature Reserve.

No significant correlations were observed between elephant impact score and tree to pyramid

distance (r = -0.15, p = 0.18, n = 80) or actual pyramid distance (r = -0.06, p = 0.59, n = 80). However, a

near significant negative correlation occurred between elephant impact scores and sum pyramid

distance (i.e. increasing the sum pyramid distance decreased elephant impact scores on trees) (Figure

4).

Median

25%-75%

Min-Max

Sum

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Figure 4: Correlation between elephant impact score and sum pyramid distance in the Umbabat Private Nature Reserve.

Each pyramid cost R4.50 to produce (financial data supplied by Mark Griffiths, N’tsiri). Using

a conservative pyramid packing model of 1 m gap around the tree and 2 m radius of pyramids, a tree

would cost ± R1,700 to protect (380 pyramids). Using this formula, a tree with 3 m of pyramids and no

gap would cost ± R1,900 to protect (420 pyramids).

3.2. Creosote

Of the 100 creosote trees, 96 were still alive and 4 had been toppled by elephants. However,

23 trees had received some form of elephant impact since the creosote jars were added and 25

creosote jars had been broken. During the same time period, 29% (n = 17) control trees had received

some form of elephant impact. According to the regression analysis, the likelihood of elephant impact

could not be predicted by the presence of a mitigation method (p = 0.82), tree height (p = 0.06) or the

species of tree (p = 0.24). In a post-hoc analysis, the presence or absence of creosote on a tree did not

affect its likelihood of receiving elephant impact (Fisher’s exact test, p = 0.84).

The cost of the creosote jars were ± R5.00, as all jars and scrap materials were reused from

previous objects.

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4. Discussion

4.1. Pyramids

A total of 80 trees with pyramids surrounding them were assessed across the Ingwelala and

N’tsiri properties. There were large variations in the various pyramid distances measured, with no

pyramid ring extending beyond the 4 m mark. Furthermore, 22 trees were missing and a subsample

of trees had pyramids scattered around the main stem, having lost their tightly compacted formation.

The original ‘Kruger model’ stated that rocks around trees can only be effective when the ring

of rocks is between 4-5 m in length. Whilst the stacking of pyramids around large trees may present

on obstacle for elephants, the distance is often far too small to prevent elephants from reaching the

tree’s main stem. Furthermore, if the pyramids are not tightly packed, then elephants are able to

scatter the pyramids and reach the tree’s main stem. This process may be aided by the large gaps left

between the main stem and the pyramids, in which the elephant is able to stand. We suggest that the

ideal pyramid model should decrease the distance between the tree’s main stem and the pyramids (±

50 cm in total), with pyramids tightly stacked in rings extending to a length of 4-5 m. Whilst this will

increase the costs of protecting a single tree, both properties have spare pyramids from dead trees

which can be optimised to better protect trees which are still alive. As the pyramid model revolves

around distance between elephant and main stem, distance must be of prime focus when applying

this method.

We did note that certain pyramid sites had been used to protect seedlings. Whilst a well-

stacked ring of pyramids may be affective at mitigating elephant impact, seedling browsers such as

impala (Aepyceros melampus) or chacma baboons (Papio ursinus) may still be able to manoeuvre

through the small gaps between pyramids to access the seedlings. Chicken-mesh cages may be

additionally required for such cases.

Whilst the use of natural rocks around a tree may be a more cost-effective method versus

building concrete pyramids, caution must be given towards the effect on how the removal of large

quantities of rocks may affect the microhabitats of other organisms.

4.2. Creosote

A total of 100 trees containing creosote jars were assessed on the N’tsiri property. This is the

first known assessment on creosote effectiveness as an elephant mitigation method. Our results

suggest that the presence of creosote does not prevent elephants from impacting trees. Furthermore,

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whilst concern was taken by management to provide the creosote jars with a tin roof to ensure that

rain would not allow the creosote to overflow into the environment, this proves to be obsolete when

a jar is smashed by an elephant. The resulting consequence is both creosote and glass in the

environment. In the United States of America, spills of creosote into the environment which exceed

0.454 kg need to be reported to the Environmental Protection Agency. It is therefore a concern if

creosote is left unregulated in the Greater Kruger National Park as an elephant mitigation method,

particularly if the outcome is that trees are still not protected. Our suggestion is that the creosote jars

are removed from the trees and that alternative mitigation methods are tested. Whilst the beehive

mitigation method (Cook et al. 2018) may not be applicable on such a large scale, the use of wire-

netting for trees taller than 11 m may be a cheap and valuable mitigation method against bark-

stripping (Derham et al. 2016, Cook et al. 2017, 18). For smaller trees which are more vulnerable to

heavy elephant impact (toppling and stem snapping), the use of bio-neem oil has been suggested as a

novel mitigation method of protecting trees against elephant impact. We do, however, suggest

caution when applying a new mitigation method over a large scale, as the effect of bio-neem in the

environment is not yet fully understood. Small-scale usage in a controlled study site would be the best

option if perusing this method.

4.3. Conclusion

Whilst elephant impact on big trees is a natural phenomenon, mitigation methods can be

applied to big trees in water saturated environments to limit this impact. Our results suggest that

there is potential for stacking concrete pyramids in rings around a tree’s main stem. However, the

pyramids should extend over 4-5 m in length and be tightly packed to prevent elephants from moving

pyramids around to reach the tree. Creosote, on the other hand, did not appear to have the desired

deterrent effect, and the spillage of 25% of the creosote jars leads to concerns of creosote and glass

in the environment. We suggest that this method is replaced with a more effective method that has

less of an environmental pollutant effect.

5. Acknowledgements

We wish to thank the management of Ingwelala and N’tsiri for allowing us the opportunity to

survey their trees and for providing us with accommodation and information during the process.

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