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Seasonality change and the third millennium BP rainforest crisis in southern Cameroon (Central Africa)

Published online by Cambridge University Press:  20 January 2017

Alfred Ngomanda ,
Katharina Neumann ,
Astrid Schweizer  and
Jean Maley
Alfred Ngomanda*
Affiliation:
J.W. Goethe-Universität, Institut für Archäologische Wissenschaften, Abteilung Vor- und Frühgeschichte, Grüneburgplatz 1, D-60323 Frankfurt am Main, Germany Institut des Recherche en Ecologie Tropicale, (IRET/CENAREST) BP 13545 Libreville, Gabon
Katharina Neumann*
Affiliation:
J.W. Goethe-Universität, Institut für Archäologische Wissenschaften, Abteilung Vor- und Frühgeschichte, Grüneburgplatz 1, D-60323 Frankfurt am Main, Germany
Astrid Schweizer
Affiliation:
J.W. Goethe-Universität, Institut für Archäologische Wissenschaften, Abteilung Vor- und Frühgeschichte, Grüneburgplatz 1, D-60323 Frankfurt am Main, Germany
Jean Maley
Affiliation:
Institut des Sciences de l'Evolution de Montpellier, UMR 5554, Université de Montpellier II, Place Eugène Bataillon, cc 61, 34095 Montpellier Cedex 5, France
*
*Corresponding authors. Email Address:ngomanda@em.uni-frankfurt.de, ngomanda@yahoo.fr, k.neumann@em.uni-frankfurt.de
*Corresponding authors. Email Address:ngomanda@em.uni-frankfurt.de, ngomanda@yahoo.fr, k.neumann@em.uni-frankfurt.de
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Abstract

The third millennium BP crisis of the central African rainforest is not sufficiently understood. The low resolution of most pollen profiles and a large plateau of the calibration curve aggravate the exact dating of the event, and its causal climatic parameters are debated. We present a high-resolution pollen profile from the swamp site Nyabessan in the southern Cameroonian rainforest, covering the period 3100-2300 cal yr BP. Between 3100 and 2500 cal yr BP, the climate was favourable for a regional evergreen forest with Caesalpiniaceae and Lophira and a local Raphia swamp forest. Around 2500/2400 cal yr BP, a significant decrease of mature forest and swamp forest taxa and an increase of pioneers indicate that the rain forest was seriously disturbed and replaced by secondary formations. The dominance of Trema orientalis, a pioneer well adapted to seasonal desiccation, points to a much more accentuated seasonality after 2500 cal yr BP, which seems to be linked to a southwards shift of the ITCZ during the northern hemisphere winter months. We propose that the rain forest crisis between 2500 and 2200 cal BP created favourable conditions for farming and paved the way for a major expansion of Bantu speaking populations.

Keywords

Climatic changeSeasonalityITCZpioneer forestTrema orientalisBantu expansion
Type
Articles
Information
Quaternary Research , Volume 71 , Issue 3 , May 2009 , pp. 307 - 318
Copyright
University of Washington

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