savanna or savannah, tropical or subtropical grassland lying on the margin of the trade wind belts. The climate of a savanna is characterized by a rainy period during the summer when the area is covered by grasses, and by a dry winter when the grasses wither. Savannas near the equatorial belt, e.g., in Nigeria, support clumps of trees. The most extensive savannas—all important pasture lands—are in Africa; others include the llanos and the campos of South America.