Can planting trees, …

Can planting trees, in some cases, lower water reserves? Apparently so.

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.

This is not, by any means, a blanket statement. However, the study shows that the opposite is also not a blanket statement. The idea that planting forests always conserves the water resources is flat-out false. Here are some examples:

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.

There is no one-size-fits-all solution; more trees is not always the best way to go. But environmentalists, I bet, will not let go of that thought easily.

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