Coforchange

In order to reconstruct the vegetation dynamics in Central Africa over the past 3000 years, pollen analyses were collected from a number of sedimentary sequences spread over the Congolian forest domain  (Figure 1 ), from the Atlantic side (South Cameroon, Gabon, Western Congo) to the eastern side of the Congo Basin region and the surroundings of Victoria Lake (Maley & Brenac, 1998 ).

These records indicate that a significant change in the vegetation occurred throughout the region between 2500 and 2000 BP, wrought by a major disturbance which destroyed or strongly modified the forests. In addition, this disturbance still exerts a major influence on present vegetation formations (Maley, 2001, 2002 ). In several sites on the western and eastern sides of Congo (e.g. Barombi-Mbo and Mayombe or Osokari and Epulu), a short period of savanna extension was triggered by this event (Figure 2 ).

Then, very rapidly, forests started to re-establish (Ngomanda & al., 2005), with a flush of pioneer taxa  appearing in many sites, and in particular the oil palm (Maley, 1999 ; Maley & Chepstow-Lusty, 2001 ), as was observed in the south of the Central African
Republic (CAR) (Figure 3 ).

These pioneer forests persisted until 1000 – 800 years BP, then the forest recovery continued until the present day, accompanied by an increasing importance of more shade-tolerant taxa.
A core was recently collected in Mopo Swamp, located in Congo near the southern frontier of the CAR, close to the centre of the CoForChange study area (Brncic, Willis & al., 2009 ).

The dominant pollen taxa found in this record spanning the last 2500 years BP have revealed a vegetation history very similar to that previously outlined from the other sites, with a brief savanna extension episode dated 2500 years BP (Figure 4 ). This record confirms that there has been a greater spatial extension of the savanna vegetation during this interval in time as previously thought.

Research undertaken in the CoForChange project shall try to validate the hypothesis, proposed by Letouzey in 1968, then precised in 1985, and formalised and dated by Maley in 2001 and 2002 (Figure 5 ), that a large savanna corridor once opened up across the Central African forests and linked the Northern Sudanian savannas to the Southern Batéké savannas.

References

BRNCIC, T.M., WILLIS, K.J., HARRIS, D.J., TELFER, M.W., BAILEY, R.M. 2009 . Fire and climate change impacts on lowland forest composition in northern Congo during the last 2580 years from palaeoecological analyses of a seasonally flooded swamp. The Holocene, 19 : 79-89.
LETOUZEY, R. 1968 . Etude phytogéographique du Cameroun. Encyclopédie Biologique, 69, 508 p. (p. 227-233)
LETOUZEY, R. 1985 . Notice de la carte phytogéographique du Cameroun au 1/500.000è. Inst. Carte Intern. Végétation, Toulouse, et Inst. Rech. Agron., Yaoundé. (p. 80-81)
MALEY, J. & BRENAC, P. 1998 . Vegetation dynamics, palaeoenvironments and climatic changes in the forests of West Cameroon during the last 28,000 years. Rev. Palaeobot. & Palyno., 99: 157-188.
MALEY, J. 1999 . L'expansion du palmier à huile (Elaeis guineensis) en Afrique centrale au cours des trois derniers millénaires : nouvelles données et interprétations. In S.Bahuchet & al. (eds) L'Homme et la Forêt Tropicale. 237-254. Trav. Soc. Ecologie Humaine, Paris.
MALEY, J. et CHEPSTOW-LUSTY, A. 2001 . Elaeis guineensis Jacq. (oil palm) fluctuations in central Africa during the late Holocene : climate or human driving forces for this pioneering species? Veget. Hist. Archaeobot., 10: 117-120.
MALEY, J. 2001 . La destruction catastrophique des forêts d’Afrique centrale survenue il y a environ 2500 ans exerce encore une influence majeure sur la répartition actuelle des formations végétales. Syst. & Geogr. Plants, 71: 777-796.
MALEY, J. 2002 . A catastrophic destruction of African forests about 2,500 years ago still exerts a major influence on present vegetation formations. Bulletin Inst. Development Studies, 33, 13-30, Brighton Univ.
NGOMANDA, A., K. NEUMANN, A. SCHWEIZER, J. MALEY. 2009 . Seasonality change and the third millenium BP rainforest crisis in southern Cameroon (central Africa). Quat. Res., 71: 307-318.