The Right Tree for a Dry Place

Increasing water scarcity in many regions of the world has triggered a heated debate: Will planting trees ease water shortages or make them worse?

Last year, in an article in the Economist, researchers from the University of Newcastle, in Britain, and the Free University, in Amsterdam, argued that planting trees can exacerbate droughts.

Scientists at the World Agroforestry Centre (ICRAF) beg to differ. "Trees are not bad, but it has to be the right tree in the right place," explains Prof. Chin Ong, the Centre's principal scientist.

According to ICRAF studies of the Kenyan drylands over the past 20 years, integrating trees into agricultural systems can increase water use efficiency. However, there is one caveat ¾ fast-growing evergreen trees intensify water shortages.

ICRAF scientists found that plantations of Eucalyptus or pine trees, which consume a lot of water, should be avoided in water-scarce areas. Deciduous trees are an attractive alternative because they consume less water, shed their leaves during the dry season, and produce timber, fruits, fodder and other valuable products.

The scientists also addressed the problem of competition for water between crops and trees. Field studies show that coppicing and root pruning reduces trees' water requirements, giving crops an added advantage.

These are important lessons for the future, the scientists say, when the effects of climate change and expected declines in rainfall will make the water balance effects of trees critical to the management of agricultural landscapes across Africa.