NEWS
Debunking myths about
the impact of elephants on
large trees
Current Address: Independent Economist PhD Candidate, University of Cape Town
Reprinted From: http://bit.ly/2XgGcvC
Ross Harvey
E
lephants are often accused of be-
ing responsible for the unsustaina-
ble loss of large trees in protected
areas. This is because they strip bark
and break branches. They can also
have a heavier impact through uproot-
ing trees or snapping stems. They have
forage preferences too. Marula, knob-
thorn and red bushwillow are among
their favourites.
This type of behaviour has raised con-
cerns 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 estab-
lish whether elephants are in fact re-
sponsible for large tree mortality.
They did this by reviewing the science
and evaluating how effective past strat-
egies 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 sa-
vannas:
maintaining elephant numbers at
a pre-determined carrying capac-
ity level did not prevent the loss of
large trees.
The researchers conclude that the re-
lationship between elephant popula-
tions 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 nu-
25
merous historical and interacting vari-
ables. though it is traumatic and depends on
space being available elsewhere.
For instance, aesthetically appealing
landscapes with extensive large tree
cover are probably historical anoma-
lies. Colonially imported diseases such
as rinderpest – throughout the late
19th and early 20th centuries – deci-
mated herbivore populations. Com-
bined with excessive recreational el-
ephant hunting, trees of specific aged
cohorts could proliferate. The history and the science
The factors determining large tree
mortality and distribution are complex.
For example, the decline in large tree
species within Botswana’s Chobe Na-
tional Park has been attributed to high
impala densities rather than elephants.
The authors argue that elephant man-
agement 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 den-
sity of artificial water points so that
elephant impact is not spread more
evenly across the landscape. Intermit-
tent natural water sources encourage
seasonal movement patterns among
megaherbivores. This provides impor-
tant plant refugia within large, open
systems, which increases overall biodi-
versity.
In smaller reserves, where elephant
densities may be problematic for large
tree survival prospects, non-lethal in-
terventions are – from an ethical and
tourism safety perspective – more de-
sirable than culling or hunting. Contra-
ceptive methods, pioneered by Audrey
Delsink and others, lower growth rates
successfully. Translocation also works,
The researchers reviewed the science
on the interaction between elephants
and large trees.
While some studies have found that el-
ephants 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 dis-
tance of 65 km away from their source.
Elephants modify their landscapes as
ecosystem engineers, often increasing
biological diversity in the process.
Large trees do have important eco-
system functions, including providing
nesting sites for vultures and raptors.
But the addition or reduction of large
trees is not necessarily positive or neg-
ative. A reduction in large tree cover
may, for instance, reveal that a de-
graded 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 princi-
ple had been interpreted differently in
past elephant management strategies.
For instance, culling was implemented
before the relationship between el-
ephant density and large tree cover
had been scientifically established. The
Grassroots
Vol 19
No 4
November 2019