Between the Sahara to the north and the savannas to the south is the Sahel, a thin semi-arid region.
Flat, arid plains stretch 5,400 kilometres (3,300 miles) across Africa from Senegal to Sudan.
Africa's longest river, the Niger, flows through the Sahel's rich delta.
Drought, deforestation, and intensive agriculture are turning the Sahel into desert.
The Sahel's animal groups are always searching for water and vegetation.
During the wet season, farmers and animals quickly exploit the Sahel's verdant flora.
Baobabs are drought- and fire-resistant trees with 15-meter (50-foot) trunks (85 feet).