Green Wall

China built its famous Great Wall to keep out marauders. Now, millennia later, a "Great Green Wall" may rise in Africa to deter another, equally relentless invader: sand.

The proposed wall of trees would stretch from Senegal to Djibouti as part of a plan to thwart the southward spread of the Sahara, Senegalese officials said earlier this month at the UN's Copenhagen climate conference...


Trees are almost always formidable foes against encroaching deserts, said Patrick Gonzalez of the University of California, Berkeley's Center for Forestry.

That's because stands of trees act as natural windbreaks against sandstorms, and their roots improve soil health—especially by preventing erosion. ...

Nigerian President Olusegun Obasanjo first proposed the idea of a desert-blocking wall in 2005, and it was approved by the African Union in 2007.

All 11 countries that would house the Great Green Wall have pledged to help fund the project.

But the wall has been slow to break ground: Of the 4,350 miles (7,000 kilometers) it needs to cover, only about 326 miles (525 kilometers) have been planted so far, all within Senegal.

In Copenhagen, President Wade emphasized that he has made the wall a priority, and he has already asked scientists working on the project to choose species hardy enough to survive in arid conditions without maintenance. ..

More than 70 percent of Africa's poor depends on farming, according to the IPCC.

But drought, desertification, and other climate-related disasters are forcing many farmers to abandon their lands, spurring a heavier flow of immigrants out of central and North Africa.

The 9.3-mile-wide (15-kilometer-wide) wall of trees would improve the surrounding, now-degraded soils, allowing farmers to again grow crops and more easily raise livestock in the region.

Senegal also plans to dig rainwater reservoirs along its portion of the wall—virtual lifesavers in a region where rain falls only three months out of the year, supporters say....

The gigantic tree barrier would also trap some atmospheric carbon dioxide, a potent greenhouse gas, and produce a refuge for native animals and plants.

Some of the trees themselves may become valuable crops.

The native acacia senegal tree, which is to be a staple plant in the Great Green Wall, produces gum arabic, a main ingredient in consumer products such as cosmetics and soft drinks.

Farmers could collect the sap and even sustainably harvest some of the wood to make tools or produce charcoal, Senegalese environment advisor Djeng said.

A solution to many problems at once. I love these. [nationalgeographic.com]