The southern part of Côte d’Ivoire is characterized by broad plains, dissected by three main rivers, the Sassandra, the Bandama, and the Komoé. These plains and their productive soils were once forested, but are now heavily used for agriculture and plantations. The center of the country is a transition zone between forest and savanna. Most of the savannas are being encroached upon by rainfed agriculture, especially in the north, along the borders with Mali and Burkina Faso. In northwestern Côte d’Ivoire, several highlands rise from the surrounding plateau. This mountainous region is part of the Guinean Highlands that extend from the southern Fouta Djallon through southeastern Guinea, northern Sierra Leone and Liberia, and adjacent areas of Côte d’Ivoire.