Leafless, dead trees cast little shade on the sere earth below. In time, they will crumble into dry dust, blowing over the baked soil of northern Senegal. Meanwhile, the average annual temperature continues to rise and the rains to decrease. - - West African Reforestation Projects. 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 th