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The Dahomey Gap: an abrupt climatically induced rain forest fragmentation in West Africa during the late HoloceneJ W. Goeth Universität, Seminar für Vor- und Friihgeschichte, Archäologie und Archäobotanik Afrikas, Grüneburgplatz 1, 60323 Frankfurt/M., Germany; Center for Tropical Marine Ecology (ZMT), Fahrenheitstr. 6, 28359 Bremen, Germanyulrich.salzmann{at}zmt.uni-bremen.de
Max-Planck-Institut für Biogeochemie, PO Box 100164, 07701 Jena, Germany; LECO Instrumente GmbH, Marie Bernays Ring 31, 41199 Mönchengladbach, Germanyphilipp.hoelzmann{at}leco.de The Dahomey Gap, a savanna corridor interrupting the zonal West African rain forest, did not exist during the mid-Holocene. The pollen diagram from Lac Sélé (7°9'N, 2°26'E) indicates that in southern Benin a semi-evergreen rainforest prevailed between c. 8400 and 4500 cal. yr BP. The mid-Holocene marine transgression caused a spread of mangrove forest along the inland lagoons. Pollen analysis and geochemistry indicate that the Dahomey Gap became established at the onset of the late Holocene due to an abrupt climatic change between c. 4500 and 3400 cal. yr BP. Drier climatic conditions led to a rapid deterioration of the rain forest and subsequent spread of Sudano-Guinean savannas. A return to wetter climatic conditions between c. 3300 and 1100 cal. yr BP resulted in a rise in the lake level and a renewed spread of forests into the savanna. During this time the Dahomey Gap consisted of a forest-savanna mosaic with a high number of pioneer tree taxa including the oil palm Elaeis guineensis After c. 1100 cal. yr BP the lake level dropped again and the Lac Sélé profile indicates drier environmental conditions resulting in the establishment of an open savanna which persists until present. The palaeorecord from Lac Sélé suggests that the role of humans in shaping the West African savannas has been overestimated. The opening of the Dahomey Gap and spread of the oil palm E. guineensis can now be confidentially attributed to climatic change and was not initiated by humans.
Key Words: Pollen • vegetation history • geochemistry • savanna • rainforest • Dahomey Gap • sea-level change • Elaeis guineensis • Holocene • human impact
The Holocene, Vol. 15, No. 2,
190-199 (2005) This article has been cited by other articles:
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