 The northern section of West Africa (narrowly defined to exclude the western Maghreb) is composed of semi-arid terrain known as Sahel, a transitional zone between the Sahara and the savannahs of the western Sudan.Forests form a belt between the savannas and the southern coast, ranging from 160 km to 240 km in width.The northwest African region of Mauritania periodically suffers country-wide plagues of locusts which consume water, salt and crops on which the human population relies.