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

Drawing on marine and terrestrial palynological data, vegetation maps of eq uatorial 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 pictur e and provide a chronology for the last glacial cycle. Much shorter terrest rial records help fill in the picture for the most recent periods and facil itate interpretation of regional patterns for the longer timescale. Tempora l and spatial variation is revealed in relation to global patterns of clima te 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 refug es are found in the southwest of the Guinean mountains and along the easter n 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 reduc ed during glacial times. During Stage 6, savanna and open dry forest covere d 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 nor th. The area of rain forest was restricted, mangrove swamps were strongly r educed, 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 fore st area strongly extended during Substages 5d and 5b. In Substages 5e and 5 a, rain forest reclaimed areas it had lost in the previous substages (5d an d 5b, respectively). Mangrove swamps were less widespread in the later subs tages of Stage 5 than during Substage 5e. During Stage 4, the rain forest a rea was again strongly reduced, and recovered only slightly during the foll owing Stage 3. Also the mangrove swamp area was reduced except along the Iv ory Coast and along the northwestern coast of the Gulf of Guinea. Podocarpu s 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 la rge parts of equatorial West Africa. Mangrove swamps must have been rare. A t 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. (C) 2000 Elsevier Sc ience B.V. All rights reserved.