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Crops of the West African Semi -Ar id Tropics

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RA 00016.pdf1.51 MB
Kassam, A.H.
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International Crops Research Institute for the Semi-Arid Tropics ; Patancheru, Andhra Pradesh, India
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In West Africa the area between the humid equatorial High Forest and the desert bio-climates of Trans-Saharian Africa comprises of a variety of semi-arid tropical regions which have in common a number of physical and biological features. The natural vegetation in these regions is dominated by grassland with varying densities of scattered  trees or shrubs. Ecologically, the varied assemblages of vegetation within these regions are described as Savanna. Differentiated by variables of climatic gradients but particularly by a easonal amount and distribution of rainfall, resulting i n water regimes with marked rainy and dry seasons of varied duration and intensity, these regions carry their own characteristic vegetation. Because the dominant climatic factors and elements affecting the distribution of Savanna vegetation have very pronounced gradients along the north-south axis, the area of the West African  avanna is in consequence a strip of territory lying nearly parallel with the equator (Cocheme and Franquin, 1967). The area extends from the Atlantic Ocean in the west to Central Sudan in the east. The uniformity of the pattern is broken further east by the influence of the Ethiopian mountains and the Red Sea. The southern limit of the Savanna area successional to the humid High Forest cannot be sharply defined. However, from the vegetation maps of the Savanna regions (Phillips, 1959) the approximate limit of the southern boundary in respect of latitudinal (LA) and longitudinal (LO)1 position may be described by the equation, LA = 8.2 - LO/11.9. Thus, for example, at LO = 0, the southern boundary is approximately at 8.2°N latitude.
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