NEWS
7 Consequences of replacing
wildlife with livestock
Reprinted From: http://bit.ly/32Mp2qM
Africa Geographic Editorial
A
frica has the largest remaining
area of untransformed (unculti-
vated) land on Earth, but research
suggests that the combined impact of
increasing human populations and the
decimation of native species over the
last few centuries by colonial hunters,
means that livestock populations now
vastly outnumber wildlife.
Do livestock species restore ecological
processes, by serving as comparable re-
placements for native herbivores?
A fascinating study has been published
about the impact on ecological pro-
cesses and ecosystems of the ongoing
extinction of native African herbivore
species and the increase in livestock
populations. This report compares cur-
rent data with estimates of herbivore
biomass since the Pleistocene period
(11,700 years ago).
Here are 7 interesting findings:
1. Herbivore biomass change
Total herbivore biomass has decreased
across Africa, mainly due to the remov-
al of elephants by hunters. Only arid
regions have experienced increases,
largely due to the use of artificial water
points and forage for livestock.
Relatively speaking, livestock biomass
now surpasses native herbivore species
biomass.
2. Herbivore functional diversity
African rangelands are now dominated
by three species – cattle, goats and
sheep – which account for 90% of cur-
rent herbivore biomass. In other words,
Africa has undergone a vast contraction
in herbivore diversity. The removal of
elephants has had a particularly pro-
nounced impact, due to their beneficial
impact on density and diversity of forest
saplings and on seed dispersal – but the
removal of other specialist browsers and
frugivores has also been felt. The result
has been an increase in bush encroach-
ment and reduction in seed dispersal.
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Figure 1: Cattle and herder in a drought-stricken region in Africa
3. Fires versus grazers
Fire is a significant alternative consum-
er of vegetation to herbivores and the
balance between the two shapes eco-
systems. Conceptually, grazers can sup-
press fires when they consume so much
grassy material in the wet season that
there is insufficient fuel to carry fires in
the dry season. Fewer grazers therefore
means more fire, and vice versa – all of
which is subject to rainfall levels.
4. Woody cover
Herbivores directly and indirectly affect
woody cover. The report predicts that
the increasing dominance of livestock
over native herbivore species will en-
hance woody cover in African savannas,
in addition to other factors such as car-
bon dioxide levels.
The substantial contraction of elephant
distribution ranges and populations
has and will result in more woody cover
as fewer trees are toppled. Moreover,
the increase in grazer densities (live-
stock) has reduced fire across much of
the continent, thereby also increasing
woody cover. However, mitigating this
to a degree is the increase in small-
stock browser farming and subsequent
increase in consumption of woody cov-
er.
5. Greenhouse gas emissions
Carbon is stored above and below
ground. The increase of woody cover
increases the above-ground carbon
stocks and therefore influences the car-
bon cycle – but the exact extent is not
known. More easily measured is the
methane emissions of herbivores. Meth-
ane has 28 times the warming potential
of carbon dioxide. Ruminants (mam-
mals that first partly digest food in one
stomach, then regurgitate it and chew
it further before re-ingesting it) such as
Grassroots
Vol 19
No 4
November 2019