The semi-desert plains of the Sahel stretch across large portions of the North African nation of Senegal on the edge of the Sahara. Uncontrolled grazing and overcutting of trees have caused environmental stress throughout Africa south of the Sahara. In Senegal, desertification is an especially serious problem in northern regions outside the reach of the Sénégal River. The combination of environmental damage, drought, and severe dust-and-sand storms has rendered much of the Sahel worthless for agriculture.