Late quaternary vegetation and climate of the Sahel
Résumé
Pollen and phytogeographic evidence provides a vegetational history of the Sahel for the period 0-18,000 yr B.P. The zonal vegetation fluctuated latitudinally and its most extreme positions occurred at 18,000 and 8500 yr B.P. The first involved a southward shift of the Sahelian wooded grassland to 10"N under the arid conditions of the last glacial maximum. The second change shows a rapid northward migration of humid vegetation: Guinean elements reach 16°N and Sahelo- Sudanian elements extend to the southern margin of the modem Sahara (21°N) when the Atlantic monsoon flux increased. In the middle Holocene the extensive spread of Sudanian elements into the modem Sahelian zone suggests the appearance of a markedly dry season. The modem Sahelian semiarid conditions appeared abruptly at 2000 yr B.P.