<P> Historically, the western part of the Sahel was sometimes known as the Sudan region . This belt was roughly located between the Sahara and the coastal areas of West Africa . </P> <P> The Sahel spans 5,400 km (3,360 mi) from the Atlantic Ocean in the west to the Red Sea in the east, in a belt that varies from several hundred to a thousand kilometers (c. 600 miles) in width, covering an area of 3,053,200 square kilometers (1,178,850 sq mi). It is a transitional ecoregion of semi-arid grasslands, savannas, steppes, and thorn shrublands lying between the wooded Sudanian Savanna to the south and the Sahara to the north . </P> <P> The topography of the Sahel is mainly flat; most of the region lies between 200 and 400 meters (660 and 1,310 ft) in elevation . Several isolated plateaus and mountain ranges rise from the Sahel, but are designated as separate ecoregions because their flora and fauna are distinct from the surrounding lowlands . Annual rainfall varies from around 100--200 mm (4--8 in) in the north of the Sahel to around 600 mm (24 in) in the south . </P> <P> The Sahel is mostly covered in grassland and savanna, with areas of woodland and shrubland . Grass cover is fairly continuous across the region, dominated by annual grass species such as Cenchrus biflorus, Schoenefeldia gracilis and Aristida stipoides . Species of acacia are the dominant trees, with Acacia tortilis the most common, along with Acacia senegal and Acacia laeta . Other tree species include Commiphora africana, Balanites aegyptiaca, Faidherbia albida, and Boscia senegalensis . In the northern part of the Sahel, areas of desert shrub, including Panicum turgidum and Aristida sieberana, alternate with areas of grassland and savanna . During the long dry season, many trees lose their leaves and the predominantly annual grasses die . </P>

What is sahel and where is it located