Blind,
starving cheetahs: the new symbol of climate change?
Thorny
plants have begun to smother grasslands, transforming rangeland into
impenetrable thicket – bad news for the big cats
21
June, 2013
The
world's fastest land animal is in trouble. The cheetah, formerly
found across much of Africa, the Middle East and the Indian
subcontinent, has been extirpated from at least 27 countries and is
now on the Red List of threatened species.
Namibia
holds by far the largest remaining population of the speedy cat.
Between 3,500 and 5,000 cheetahs roam national parks, communal
rangelands and private commercial ranches of this vast, arid country
in south-western Africa, where they face threats like gun-toting
livestock farmers and woody plants.
Yes,
woody plants. Namibia is under invasion by multiplying armies of
thorny trees and bushes, which are spreading across its landscape and
smothering its grasslands.
So-called
bush encroachment has transformed millions of hectares of Namibia's
open rangeland into nearly impenetrable thicket and hammered its
cattle industry. Beef output is down between 50 and 70% compared with
the 1950s, causing losses of up to $170m a year to the country's
small economy.
Bush
encroachment can also be bad news for cheetahs, which evolved to use
bursts of extreme speed to run down prey in open areas. Low-slung
thorns and the locked-open eyes of predators in "kill mode"
are a nasty combination. Conservationists have found starving
cheetahs that lost their sight after streaking through bush
encroached habitats in pursuit of fleet footed food.
Farmers
and researchers recognised bush encroachment as a serious problem in
many parts of southern Africa by the 1980s, and it has long been
thought to be caused by poor land management, including overgrazing.
But, as I recently reported in Yale e360, an emerging body of science
indicates that rapidly increasing atmospheric carbon dioxide may be
boosting the onrushing waves of woody vegetation.
Savanna
ecosystems, such as those that cover much of Africa, can be seen as
battlegrounds between trees and grasses, each trying to take
territory from the other. The outcomes of these battles are
determined by many factors including periodic fire, an integral part
of African savannas.
In
simple terms, fire kills small trees and therefore helps
fire-resilient grasses occupy territory. Trees have to have a
long-enough break from fire to grow to
a
sufficient size — about four metres high — to be fireproof and
establish themselves in the landscape. The faster trees grow, the
more likely they are to reach four metres before the next fire.
Lab
research shows that many savanna trees grow significantly faster as
atmospheric CO2 rises, and a new analysis of satellite images
indicates that so-called 'CO2 fertilisation' has caused a large
increase in plant growth in warm, arid areas worldwide.
Although
poor land management is undoubtedly partly to blame for bush
encroachment, increased atmospheric CO2 seems to be upsetting many
savanna ecosystems' vegetal balance of power in favour of trees and
shrubs.
If
increasing atmospheric carbon dioxide is causing climate change and
also driving bush encroachment that results in blind cheetahs, should
blind, starving cheetahs be a new symbol of climate change, to join
polar bears whose Arctic sea ice hunting grounds are melting?
Conservationists
have noted cheetahs with severe eye injuries since the 1990s, but, as
specialist eye vet Dr. Gary Bauer told me, no research has been done
to figure out how common these injuries are in the wild population or
to confirm the assumption that cheetahs living in bush-encroached
areas suffer more eye injuries than cheetahs in open habitats.
There's no hard proof that eye injuries are an immediate threat to
the species' survival, or if they're any worse in bush-encroached
areas.
Research
has confirmed that cheetah prey species change as a landscape becomes
more thickly wooded. Plains game animals like wildebeest, springbok
and red hartebeest are squeezed out and replaced by bush-tolerant
species like kudu. This changeover in game species is by itself not a
disaster for cheetahs, which can hunt even in fairly wooded habitat
as long as they have enough space to exploit their extraordinary
acceleration, speed and agility. But if bush becomes so dense that
it's difficult for cheetahs to move through (as happens in severe
cases of encroachment) then cheetahs will disappear.
"It's
cheaper to buy a hectare than to clean and repair a hectare" of
bush-encroached land, said Donna Hanssen of the AfriCat Foundation, a
big cat conservation group based in Namibia, underscoring the
challenge faced by landowners wanting to rid themselves of the thorny
scourge, but, she reminded me, "the biggest killer of cheetah in
this country is man. Farmers."
Farmers
shoot and trap large numbers of cheetahs, which they blame for
killing cattle, sheep and goats. As Namibia's population expands,
more cattle are being herded deeper into natural areas, bringing men
with guns and poison into previously safe wildernesses.
Organisations
like AfriCat and the Cheetah Conservation Fund are working hard —
with some apparent success — to educate farmers about cheetahs and
help them live with big cats instead of killing them. They're also
pioneering methods of dealing with bush encroachment like turning
invading trees into biomass fuel blocks, although it remains to be
seen if these methods can be economically scaled up to deal with the
literally millions of hectares of expanding encroacher bush.
In
summary: Are thorn-inflicted eye injuries currently a threat to the
cheetah's survival as a species? Probably not.
Is
increasing atmospheric CO2 driving bush encroachment in African
savannas? Probably, although savannas are complex ecosystems,
influenced by many drivers, and the scientific understanding of CO2
fertilisation in these systems is incomplete.
Is
uncontrolled bush encroachment severely impacting plains game and
could it ultimately drive cheetahs out? Is it a real conservation
problem? Almost certainly.
Are
blind, starving cheetahs useful symbols of climate change? You
decide.
No comments:
Post a Comment
Note: only a member of this blog may post a comment.