Vegetation change in equatorial West Africa: time-slices for the last 150 ka

Abstract

Drawing on marine and terrestrial palynological data, vegetation maps of equatorial West Africa are presented for eleven time slices over the last 150,000 years. Long marine records are used as a basis for the regional picture and provide a chronology for the last glacial cycle. Much shorter terrestrial records help fill in the picture for the most recent periods and facilitate interpretation of regional patterns for the longer timescale. Temporal and spatial variation is revealed in relation to global patterns of climate change. Rain forest was widespread during Oxygen Isotope Stages 1 and 5, but strongly reduced during Stages 3 and 4 and especially during Stages 2 and 6 when open, grass-rich vegetation prevailed. Glacial rain forest refuges are found in the southwest of the Guinean mountains and along the eastern coast of the Gulf of Guinea. Miombo woodland of the Zambezian vegetation zone expanded during Stage 5, especially during the first half. Podocarpus forest had its largest expansion during Substages 5d (115 to 105 ka) and 5b (95 to 85 ka). The last occurrence of Podocarpus in the Guinean mountains is during Stage 5a. The distribution of mangrove swamps was extremely reduced during glacial times. During Stage 6, savanna and open dry forest covered large areas along the northern coast of the Gulf of Guinea. The southern Saharan desert reached far to the south and the Namib desert far to the north. The area of rain forest was restricted, mangrove swamps were strongly reduced, and the area of Podocarpus forest fluctuated. During Stage 5 large changes in the area of Afromontane forest, rain forest, dry open forest and savanna occurred. Rain forest was widespread and mangroves were extensive along the coast during the last interglacial (Substage 5e). Podocarpus forest area strongly extended during Substages 5d and 5b. In Substages 5c and 5a, rain forest reclaimed areas it had lost in the previous substages (5d and 5b, respectively). Mangrove swamps were less widespread in the later substages of Stage 5 than during Substage 5e. During Stage 4, the rain forest area was again strongly reduced, and recovered only slightly during the following Stage 3. Also the mangrove swamp area was reduced except along the Ivory Coast and along the northwestern coast of the Gulf of Guinea. Podocarpus forest only occurred in Angola and may be in Congo during Stage 4. Again forest was much reduced during Stage 2 and open vegetation types covered large parts of equatorial West Africa. Mangrove swamps must have been rare. At the beginning of the Holocene, mangrove swamps had recovered and reached their largest extension. Also the rain forests area increased in the early Holocene and Guinean and Congolian rain forests were probably not separated by a savanna corridor now existing in Togo and Benin.