Aspects of Nigerian coastal vegetation in the Holocene: some recent insights

A palynological study of an 11m terrestrial core from the Badagry area in coastal South- Western Nigeria was undertaken as part of an international project: “The Dahomey Gap: vegetation history and archaeobotany of the forest/savanna boundary in Bénin and South- Western Nigeria.” The project is the joint effort of a team comprising an archaeobotanist (German), a botanist (Béninois), and four palynologists (Béninoise, German, Moroccan, and Nigerian). The Dahomey Gap is an unusual portion of the Guinean-Congolian forest zone, comprising a mosaic of savanna and the drier type lowland rain-forest. This Gap today stretches from the western-most part of Southern Nigeria through Bénin (formerly Dahomey) and Togo to the eastern-most part of Ghana. It effectively partitions the forest zone into western and eastern blocks (Plate 2).

As reviewed by Hamilton (1976), Martin (1990) and Maley (1996), biogeographers, studying the African tropical forest biota, plants, mammals, birds, insects, butterflies and molluscs, were the first to recognise centres of endemism in West and Central Africa. These centres, which “showa considerably higher species diversity than surrounding forest areas” (Martin 1990) are believed to have been refuges during the arid phases of the Pleistocene when the rain-forest was drastically reduced and fragmented. The issue of exactly where the refuges were is as yet not completely resolved. In the most current reconstruction, based on the work of several authors, these refuges during the peak of the last major arid phase are believed to have been in Liberia, Southwest Ghana and Southeast Côte d’Ivoire in the west, and South Cameroon, Gabon and Congo-Zaïre basin in the east.