The Sahel lies between the Sahara of northern Africa and grasslands to the south, and assumes characteristics of both landscapes. Michael A. Mares, author of "The Desert Encyclopedia," notes that while 1,200 species of plants grow in the Sahel, fewer than 40 of these species are native. "Habitats of the World" states that rainfall in the north can average between 3 and 5.5 inches each year, while regions in the south may receive between 43 and 58 inches of rain per year. These conditions, as well as the region's deep, sandy soil, mean that plants must be hardy in order to survive.
Most species of grass in the Sahel are annuals. Mares lists Cenchrus biflorus, Aristida stipoides and Tragus racemosus as species that grow throughout the Sahel, and Panicum turgidum and Stipagrostis pungens as species that grow mostly in the north. Most of these grasses have evolved ways to live in a tough environment. Cencrus biflorus, Aristida stipoides, and Tragus racemosus may only be used for grazing when they are very young; as they age, they develop spikes or thorns. In certain regions, the seeds of Cencrus biflorus are used as a grain to make porridge or bread.
Mares lists the most common woody plants of the Sahel as "species of Acacia (Leguminosae), Balanites (Balanitaceae) and Boscia (Capparidaceae)." According to G.E. Wickens, author of the article "Role of Acacia species in the rural economy of dry Africa and the Near East," over 80 per cent of woody species in the Sahel are of the acacia family. The species Acacia Senegal yields gum Arabic, which is a major crop of Sudan.
Between the sandy soil, high temperatures and variable rainfall, the farmers of the Sahel must always remain conscious of the environmental conditions that confront them. According to the report "Agroforestry in the West African Sahel," "many of the traditionally important grain crops in the region, such as sorghum and millet, are C4-pathway crops, which are capable of converting very highlight intensities more efficiently than is possible in . . . crops such as wheat and rice." Important export crops from the Sahel include groundnuts and cotton.
The Sahel bears the mark of centuries of human activity. Because of deforestation, particularly intense since the 1970s, woody plants are often scarce. The absence of roots leads to more soil erosion, which contributes to drought, producing a cycle of negative effects on the ecosystem. Overgrazing of cattle has also done its part to deplete the soil. Plants die as a result of overgrazing. Their roots loosen, leading, again, to erosion. The Sahel experienced drought beginning in 1968, throughout the 70s and a particularly harsh period between 1983 and 1985. Since then, the population of the Sahel has largely recognised the value of existing vegetation and, with the help of some international organisations, put tree and water conservation measures into place.