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InWest Africa, theDahomey Gap refers to the portion of theGuinean forest-savanna mosaic that extends all the way to the coast inBenin,Togo, andGhana, thus separating theforest zone that covers much of the south of the region into two separate parts. The forest region west of the gap is called theUpper Guinean forests or Guinean forest zone, and the portion east of the gap is called theLower Guinean forests, Lower Guinean-Congolian forests, or Congolian Forest Zone.
The major cities in the Gap areAccra,Lomé,Cotonou andPorto-Novo. Several other cities, such asKumasi, exist on the fringe of the Gap.
The dryness of the Dahomey Gap is unusual, given that it lies surrounded by a very wetmonsoon belt on all sides, without mountains to block moisture. Yet, Accra, which is in the heart of the Gap, receives only 720 mm (28 in) of rainfall per year — less than half the amount needed to sustain tropical rainforest (which would be expected at a latitude of6° N).
The cause of the dryness of the Dahomey Gap can simply be explained thus:
Evidence from biogeography suggests that the Dahomey Gap has had significance for up to 90 million years. Murphy and Collier, in their analysis of twoaplocheiloid fish genera, show a split in the African species which they attribute to the presence of anepicontinental sea between the lateCenomanian and earlyEocene.[2] This discontinuity had earlier been noted in plant species byWhite[3] and is supported by an analysis of theCoffea clade by Maurin et al.[4]
The Dahomey Gap has existed in its present form for only about four thousand years.[5] For most of theQuaternary, dry conditions due to a much colderAtlantic Ocean (aided by extensive cold currents from ice sheets inEurope andNorth America) have meant that the present-day forest zone has supported very little or no rainforest.[6] Ininterglacial periods, however, rainfall throughout West Africa has often been so heavy that theGap has become wet enough to support rainforest, thus eliminating the savanna.[6][7]
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