Abrupt changes and permanence of rainforests from Atlantic central Africa during the Holocene
by
Fabienne Marret
School of Ocean Sciences, University of Wales Bangor, UK
Coauthors: J. Maley (ENSAM, Montpellier), H. Elenga (Univ. Marien Ngouabi, Brazzaville, Congo), A. Vincens (CNRS/CEREGE, Aix-en-Provence), P. Brenac (BSI, Palyno. Consultant, N.Wales, UK), I. Farrera (ENSAM, Montpellier)

Review of vegetation records from the equatorial central Africa document the dynamics of the lowland rainforest in relation to climate changes during the Holocene. The expansion of the lowland rainforest that started around 14 ka BP was at its greatest around between 9.5 and 4-3 ka BP. From 4 ka BP, an increase of semi-deciduous and heliophilous forest taxa is recorded in the southern part of the Congolese sector, indicating drier conditions. In opposition, at the same time, an increase of evergreen rain forest taxa in west and south Cameroon is observed. This dichotomy can be explained by a contrasted evolution of the monsoon system in relation to sea-surface conditions in the equatorial Atlantic. Cooler conditions of sea surface waters recorded around 4 ka BP may have induced the production of non-rainy clouds over the western Congo. In contrast, evergreen rainforest development in western Cameroon suggests the establishment of rainy nimbostratus types of clouds.

Another major change in the vegetation is registered between 3 and 2 ka BP, with a rapid increase of herbaceous vegetation all over the Atlantic central Africa. This general regression of the forest is probably linked to deterioration of climate rather than anthropogenic influence. However, this opening of the vegetation may have initiate human population movements. The last 2000 years record a general dynamism of the forest ecosystem towards a new expansion of the rainforest despite human activities.

Date received: July 18, 2002