Strategic tree planting could save water in dry areas

Some trees, like this eucalyptus, are more 'thirsty' than others Copyright: FAO

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Researchers say that planting trees in dry regions of the world could make better use of scarce water resources increasingly threatened by climate change.

They warn, however, that although planting the right species in the right areas could improve water efficiency, other species could make the problem much worse.

The World Agroforestry Centre (ICRAF) findings, based on 20 years of research in Kenya, were announced at the World Water Week meeting in Stockholm on 22 August.

Many African countries have large plantations of pines or eucalyptus. But ICRAF scientists advise against planting these fast-growing evergreen trees because they need a lot of water.

Instead, they recommend planting deciduous trees in integrated ‘tree-crop’ systems, in which agriculture and forestry are practised on a single piece of land.

Such trees shed their leaves for up to six months of the year, nearly halving the amount of water they need. This enables them to cope with long dry spells and also means they won’t compete with crops for water.

ICRAF recommends tree species for specific regions.

A relative of mahogany called Melia volkensii, which produces high-value timber, would benefit semi-arid areas such as those in East Africa, for example.

Water-catchment areas in Central and West Africa, meanwhile, would suit Cordia africana. Small-scale honey producers value the tree because its flowers are highly attractive to honey bees.

Chin Ong, a plant physiologist at ICRAF who led the research, said climate change has made rainfall in southern and western Africa unpredictable and variable — causing many rivers to dry up for months at a time.

“Trees are not able to adapt quickly over such a short period,” he told SciDev.Net, “We must select trees that are more efficient in their use of water and that can cope with the changing rainfall.” He said that without action, 70 per cent of rivers would dry up.

ICRAF is trying to encourage policymakers and communities who continue to plant evergreen trees — as sources of pine resin or pulp for paper production, for example — to change their practices.