The origin of the Dahomey Gap

The savanna corridor of the Dahomey Gap, separating the African rainforest into the western Guinea zone and the Central African Congo zone, reaches the Atlantic coast in Togo and Benin. To answer the question when and why the savanna corridor developed, sediment cores from the coastal areas of SW Nigeria and S Benin and from Lac Sélé  (7° 9'N, 2° 26'E) in the southern savanna zone of Benin were studied for pollen and geochemistry.

The results show that the rain forest only opened at the beginning of the Late Holocene, and that the determining factors were climatic and not anthropogenic. In the area of Lac Sélé semi-evergreen forests were thriving in the Middle Holocene. Around 4500 years BP they were substituted by open savannas due to a climatically induced aridification. In the period between 3300 and 1100 BP precipitation increased and forest elements expanded, but the closed rainforest could not re-establish. Instead, the Dahomey Gap was covered by a forest-savanna mosaic including many pioneer forest trees, such as the oil palm Elaeis guineensis, the expansion of which was favoured by climatic factors.

Publications

Salzmann, U. & P. Hoelzmann (2005): The Dahomey Gap: an abrupt climatically induced rain forest fragmentation in West Africa during the late Holocene. The Holocene15(2): 190-199.

Sowunmi, M.A. (2004): Aspects of Nigerian coastal vegetation in the Holocene: Some recent insights. In: Battarbee R.W., F. Gasse & C.E. Stickley (eds), Past Climate Variability through Europe and Africa. Kluwer Academic Publishers, Dordrecht, the Netherlands.

Ballouche, A., A. Akoègninou, K. Neumann, U. Salzmann & M.A. Sowunmi (2000): Le projet "Dahomey Gap" : une contribution à l'histoire de la végétation au Sud-Bénin et Sud-ouest du Nigéria. - Berichte des Sonderforschungsbereichs 268, Bd. 14: 237 - 251; Frankfurt a. M. pdf

Ballouche, A. (1999): Premiers éléments de l'histoire des mangroves et des paysages végétaux holocènes du Sud-Bénin. 124° Congrès des Soc. historiques et scientifiques, Nantes: 98-99.

Dissertation

Tossou, M. (2002): Recherche palynologique sur la vegetation Holocène du Sud-Bénin (Afrique de l'Ouest). Unpublished doctoral thesis, Université de Lome, Faculté des Sciences, 133 pp + Annexures.