Actualité scientifique
N° 416
November 2012
It is a much debated
question: why did Central
African forests become
partially fragmented
between 2,500 and
2,000 years ago, leaving
room for more open forest
landscapes and savannah?
Recently, a publication
attempted to explain that it
was the farming Bantu
peoples who were
responsible for this, through
the large-scale clearing
that they undertook. But
several IRD experts and
their partners1 contest this
argument in Science
magazine. The fragmentation
of the Central African forest
was the result of drastic
climate change. In fact,
during this period a phase of
general desiccation spread
from the equatorial region
right to the edges of the
Sahel. Numerous data show
that it was only 500 years
later, in other words some
2,000 years ago, that Bantu
colonisation became
widespread. The first Bantu
populations therefore merely
took advantage of the
opening up of the forest to
enter these areas and start
growing their crops.
Actualidad cientifica
Who deforested Central Africa:
Man or climate?
© IRD / Y. Boulvert
Scientific news
The dense forests of Africa (here in the Central African Republic) shrank considerably some 2,500 years ago.
Did the first Bantu farmers who colonised the
forests of Central Africa 2,500 years ago, also
clear the land on a large scale, as was recently
put forth? Or did they simply take advantage of a
drastic climate change that fragmented the
forests and made it easier for them to enter these
parts? Several IRD experts and their partners 1,
archaeologists, paleo-environmentalists and
palynologists 2 , defend the climate theory in
Science magazine.
A semi-nomadic lifestyle
The ancestors of the Bantu star ted settling
4,000 years ago from the northern edge of the
forest down to the coastal grasslands of Gabon.
They practiced pottery and stone polishing, and
cleared small parts of the forest fringe for slashand-burn farming. But there were few of them
and their impact was slight. When the major fragmentation of forests started 2,500 years ago, the
Bantu had only just learnt to use iron: it was the
beginning of the Iron Age.
A boom period for the Bantu
The concentration and spreading of archaeological records – more than 500 radiocarbon dates
established on pottery, stone or iron tools – show
that the massive colonisation of the Congo Basin
by Bantu farmers started only 2,000 years ago,
and that it reached a peak between 1,900 and
1,600 years ago. At the same time, all the available paleo-environmental data indicate a new
phase of forest expansion that also started about
2,000 years ago depending on the regions, proving
that growing Bantu settlement did not prevent the
vegetation from flourishing. The young civilisation
simply took advantage from the opening up of the
forest to enter it more easily.
The extent of forests has varied
greatly over the past 11,000 years
During the early and mid-Holocene, in other
words between 11,000 and 4,000 ago, much
more of the earth was covered by forests than
today. During this period, monsoons brought
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abundant, well distributed rainfall throughout the
year. But according to various geological and
palynological data, a first significant reduction of
forest areas began some 4,000 years ago,
making place for savannah. This phenomenon
was caused by a sudden decrease in monsoon
rains which paleoclimatologists attribute to a
drop in water surface temperatures in the Gulf of
Guinea3. However, the reduction in rainfall did not
affect the heart of the great forests.
New fragmentation 2,500 years ago
Sediment and pollen records as well as the
analysis of plant remains found on archaeological sites show that another disturbance
occurred 2,500 years ago. Much more significant
than the previous one, it had a strong impact on
Central African forests, with the spreading of
pioneer trees and herbaceous plants that are
typical of degraded forests and the appearance
of savannah. The strong erosion associated with
this phenomenon indicates that it was caused by
dominant storm rainfalls and a shortened wet
season. Due to the erosion caused by this type of
rainfall over several centuries, many ancient soils
were laid bare and “washed out”. Sediments
carried away by the Congo River became very
rich in aluminium and potassium as a result. It
was the discovery of this high concentration in
submarine deposits of the Congo River that led
to the erroneous theory of “anthropological”
intervention as an explanation for deforestation
in Central Africa.
Contacts
Jean MALEY, research director at IRD
jmaley@univ-montp2.fr
UMR Institut des sciences de l’évolution
de Montpellier – ISEM (IRD / CNRS /
université Montpellier 2)
Address
Université Montpellier 2
Place Eugène-Bataillon
Case 065
34095 Montpellier cedex 5
Present-day human activities often have a devastating impact on the environment, due to the
strong geographic expansion of populations.
However, in past ages, such activities cannot
necessarily bare the blame for something like the
major ecological disruption that affected forests
in Central Africa between 2,500 and 2,000 years
ago. Research by archaeologists and paleontologists in fact shows that the extent of Bantu settlement was very small during this period and
could therefore not have caused such a major
disturbance. Only a profound change in the
climate pattern of the entire sub-region could
bring about such a change in the landscape.
Richard Oslisly, researcher at IRD
Tel: + (237) 96 03 69 65
richard.oslisly@ird.fr
UMR Patrimoine locaux – Paloc
(IRD / MNHN)
Address
IRD
BP 1857
Yaoundé
Cameroun
References
MaleyJean,GiresseP.,DoumengeC.,Favier
C. Comment on «Intensifying weathering
and land use in iron age Central Africa».
Science, 2012, 337 (6098), ISSN 00368075. fdi:010057115
Neumann K., Eggert M.K.H., Oslisly
Richard, Clist B., Denham T., Maret P.
de, Ozainne S., Hildebrand E., Bostoen
K., Salzmann U., Schwartz D., Eichhorn
B., Tchiengué B., Höhn A. Comment on
«intensifying weathering and land use in
iron age Central Africa». Science, 2012,
337, p. 1040-c. fdi:010056928
Oslisly R., 2011. Changements
climatiques et changements culturels
depuis 5000 ans (Cameroun et Gabon).
In : Ngounou Ngatcha B., Sebag D.,
Diedhiou A., Durand A.& Servat E. (Eds.).
Colloque international : sciences de l’eau,
du climat et de l’environnement pour un
développement durable de l’Afrique : livre
des résumés. 2011/12/21-25
By Jean Maley
and Gaëlle Courcoux (DIC)
1. From CNRS, Cirad, the Universities of Montpellier, Perpignan and Strasbourg in France, Frankfurt and Tübingen in Germany, Gent and Brussels in
Belgium, Melbourne in Australia, Geneva in Suisse, Stony Brook in the USA, Newcastle in the United Kingdom, and Herbier National in Cameroun, and
various research institutes in Cameroun and Gabon.
Keywords
Deforestation, Bantu, climate,
Central Africa
2. Palynologists study fossilised pollens found in sediment deposits.
3. Associated with the start of the rain season.
Coordination
Gaëlle Courcoux
Information and Culture Department
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Indigo, IRD Photo Library
Daina RECHNER
Tel: +33 (0)4 91 99 94 81
indigo@ird.fr
IRD photographs on this topic, free for media
reproduction without additional permission:
www.indigo.ird.fr
Archaeological excavations (here in Cameroun) have shown that the Bantu civilisation started to colonise the sub-region much later than when the forest was replaced
by savannah (between savannah and forest in the middle of the Central African Republic). On the right, slash-and-burn in a forest in Gabon.
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