Old people in Widou Thiengoly say they can remember when there were so many trees that you couldn’t see the sky. Now, miles of reddish-brown sand surround this village in northwestern Senegal, dotted with occasional bushes and trees. Driedanimal dung is scattered everywhere, but hardly any dried grass is. Overgrazing and climate change are the major causes of the Sahara’s advance, said GillesBoetsch, an anthropologist who directs a team of French scientists working with Senegalese researchers in the region.“The local Peul people are herders, of tennomadic. But the pressure of the herds on the land has become too great,” Mr.Boetsch said in an interview. “The vegetation can’t regenerate itself.” Since 2008,however, Senegal has been fighting back against the encroaching desert. Each year it has planted some two million seedling trees along a 545-kilometer, or 340-mile, ribbon of land that is the country’s segment of a major pan-Africanregeneration project, the Great Green Wall.First proposed in 2005, the programlinks Senegal and 10 other Saharan states in an alliance to plant a 15kilometer-wide, 7,100-kilometer-long green belt to fend off the desert. Whilemany countries have still to start on their sections of the barrier, Senegalhas taken the lead, with the creation of a National Agency for the Great GreenWall. “This semi-arid region is becomingless and less habitable. We want to make it possible for people to continue tolive here,” Col. Pap Sarr, the agency’s technical director, said in aninterview here. Colonel Sarr has forged working alliances between Senegaleseresearchers and the French team headed by Mr. Boetsch, in fields as varied assoil microbiology, ecology, medicine and anthropology. “In Senegal we hope toexperiment with different ways of doing things that will benefit the other countriesas they become more active,” the colonel said. Each year since 2008, from Mayto June, about 400 people are employed in eight nurseries, choosing and overseeing germination of seeds and tending the seedlings until they are readyfor planting. In August, 1,000 people are mobilized to plant out rows ofseedlings, about 2 million plants, allowing them a full two months of the rainyseason to take root before the long, dry season sets in. After their first dry season, the saplings look dead, brown twigs sticking out of holes inthe ground, but 80 percent survive. Six years on, trees planted in 2008 are upto three meters, or 10 feet, tall. So far, 30,000 hectares, or about 75,000acres, have been planted, including 4,000 hectares this summer.