WEST AFRICAN REFORESTATION PROJECTS, Senegal, 1985 - Almost completely deserted villages, like this one in northern Senegal, still survive as patches of green vegetation among the white and ochre dunes of sand waiting to engulf them. Their trees are carefully tended, and new ones planted, by the remaining villagers, mostly the older generation. Man is now believed to be the primary cause of the desert's advance across the Sahel region in Africa - because of his indiscriminate acts of deforestation. Even the tropical, humid countries south of the Sahel are beginning to show the effects of the encroaching desert. All these countries have begun huge reforestation operations in their depleted areas. The Food and Agriculture Organisation of the United Nations (FAO) has joined in this battle against desertification and is cooperating closely with governments and other national and international agencies in their fight to save the land.