Planting trees may create deserts

New Scientist Breaking News ^ | 7/29/2005 | Fred Pearce

[sionnsar]

Planting trees can create deserts, lower water tables and drain rivers, rather than filling them, claims a new report supported by the UK government.

The findings - which may come as heresy to tree-lovers and most environmentalists - is an emerging new consensus among forest and water professionals.

“Common but misguided views about water management,” says the report, are resulting in the waste of tens of millions of pounds every year across the world. Forests planted with the intention of trapping moisture are instead depleting reservoirs and drying out soils.

The report summarises studies commissioned over the past four years by the Forestry Research Programme, funded by the UK government’s Department for International Development.

It agrees that, in some places, the environmental nostrum works: trees trap moisture from the air and bind soils that prevent floods, store water and nourish the environment. But it says that in other places, trees suck up moisture from the soil, evaporate water from their leaves, lower water tables, empty rivers and create deserts.

This matters especially when trees are planted specifically to protect water supplies, says chief author John Palmer of the Natural Resources Institute at the University of Greenwich, London, UK. Often, he says, “projects intended to improve water conditions in developing countries may be wasting massive amounts of money”.

Steady flow

Panama is currently seeking hundreds of millions of dollars from the World Bank to plant trees to increase water flow into the reservoirs that feed the Panama Canal. There is, Palmer says, no scientific justification for this plan.

But not everyone agrees. Robert Stallard, a hydrologist at the Smithsonian Tropical Research Institute in Panama backs reforesting the canal’s watershed. He says forested watersheds may deliver less water, but they deliver it in a steadier flow.

Forests are not always bad, the authors concede. “We’re not saying they never produce water benefits or that they don’t have an important role in the ecosystem,” says Ian Calder from the University of Newcastle. “But if we are trying to manage water resources effectively, the simple view that more trees are always better is bad policy.”

Hurting not helping

The studies found that in the Indian states of Himachal Pradesh and Madhya Pradesh, when fields were converted to forests to provide more water for reservoirs, they actually reduced water yields from the land, by 16% and 26% respectively.

In South Africa, the spread of foreign pine and eucalyptus trees across the country has cut river flow by an estimated 3%. The country is currently employing some 40,000 people to uproot many foreign trees. And it taxes plantation owners for their hydrological damage.

High in the mountains of Costa Rica, researchers found that forests do not harvest moisture from the clouds, as previously supposed. Chopping them down in many places barely alters rainfall, according to Sampurno Bruijnzeel from the Free University of Amsterdam, who contributed to the project.

[barkeep]

As long as the Gov't is spending money researching the sex life of obscure toads and such, I think a results oriented project could be justified researching how tornados form aluminum magnets. From news reports, it seems a tornado will back up in its course to feed on a trailer park. If it is the aluminum that attracts them, think of the commercial uses for such a device!

[GreenFreeper]

they say man has destroyed all the wet lands... when the fact is that theirs only one natural lake in texas.

While that maybe true, lakes aren't the primary concern when we talk about protecting wetlands. It's the ephemeral wetlands, the bogs, the marshes, etc. that people are concerned about losing. People like lakes. Most people don't like the mosquito haven small wetlands.