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THE devastating weather system El Ni帽o 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 Ni帽o arrives鈥攚hich happens about once every 3 to 6 years
and leads to a dramatic increase in rainfall in some normally dry
regions鈥攃ould provide the impetus to make these areas fertile again.

They point out that for many ecosystems, different stable states or
鈥渆quilibria鈥� 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.

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. 鈥淵ou don鈥檛 realise you are coming close to a
crash. That is the bad part,鈥� says Scheffer. 鈥淭he good part is that sometimes
you can give a little push and you jump up to the other state.鈥�

Scheffer and Holmgren believe that landowners could harness the power of El
Ni帽o to shock their lands into recovery. If farmers removed animals from
their land for just one season during El Ni帽o, 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. 鈥淲e
want to find out whether in the far past El Ni帽o has facilitated recovery
of the forest,鈥� 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鈥檚 not sure how it would work in practice. One problem is
that El Ni帽o is unpredictable. 鈥淵ou may only get a few weeks鈥� warning.
What could you do in that time? We are talking about vast areas of land,鈥� he
says.

Mary Cablk, an ecologist at the Desert Research Institute in Nevada, agrees
that implementing the strategy would be a huge challenge. 鈥淵ou have to go up
against the cattle grazing industry,鈥� she says. 鈥淭hey are likely to be unwilling
to remove grazers unless the land is so badly degraded that it is of no worth to
迟丑别尘.鈥�

Scheffer and Holmgren are collaborating with sociologists to try and
determine the best ways to work with local people. 鈥淲e think it is feasible in
many situations,鈥� Scheffer says.