THE devastating weather system El Niño may have a benevolent side.
Researchers in Holland say it could be harnessed to recover land that has been
degraded by overgrazing and desertification.
Ecologists Marten Scheffer and Milena Holmgren of Wageningen University in
the Netherlands say some arid areas are so badly degraded that they cannot
recover by themselves, even when grazing animals are removed. But doing this
when El Niño arrives—which happens about once every 3 to 6 years
and leads to a dramatic increase in rainfall in some normally dry
regions—could provide the impetus to make these areas fertile again.
They point out that for many ecosystems, different stable states or
“equilibria” may exist for the same set of environmental conditions. Each state,
such as woody, herbaceous or bare soil, is relatively stable and can withstand
fluctuations in the weather.
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But a dramatic shift in environmental conditions, such as the amount of
grazing or rainfall, can push each system over a threshold into a different
state, where it remains even if conditions return to what they were before. This
is bad news for farmers who overgraze their land, but it could also provide a
way to recover desertified areas. “You don’t realise you are coming close to a
crash. That is the bad part,” says Scheffer. “The good part is that sometimes
you can give a little push and you jump up to the other state.”
Scheffer and Holmgren believe that landowners could harness the power of El
Niño to shock their lands into recovery. If farmers removed animals from
their land for just one season during El Niño, the combined effect of
increased rainfall and reduced grazing could be enough to flip the land into a
new, stable, recovered state, and grazers could be gradually reintroduced.
The researchers are testing their ideas on arid lands in northern Chile. “We
want to find out whether in the far past El Niño has facilitated recovery
of the forest,” says Scheffer. They will check tree rings to see how the climate
has changed, and test plots of land with and without herbivores and water, to
try to pinpoint the critical thresholds.
Ecologist Mohan Wali of Ohio State University in Columbus says the idea is
good in theory, but he’s not sure how it would work in practice. One problem is
that El Niño is unpredictable. “You may only get a few weeks’ warning.
What could you do in that time? We are talking about vast areas of land,” he
says.
Mary Cablk, an ecologist at the Desert Research Institute in Nevada, agrees
that implementing the strategy would be a huge challenge. “You have to go up
against the cattle grazing industry,” she says. “They are likely to be unwilling
to remove grazers unless the land is so badly degraded that it is of no worth to
ٳ.”
Scheffer and Holmgren are collaborating with sociologists to try and
determine the best ways to work with local people. “We think it is feasible in
many situations,” Scheffer says.
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More at:
Ecosystems (vol 4, p 151)
