Forest response to climate changes in Atlantic Equatorial Africa during the last 4000 years BP and inheritance on the modern landscapes

This review paper synthesizes the recent published palaeoecological results obtained in Atlantic Equatorial Africa (ECOFIT program) on the history of forest ecosystems and inferred climate changes during the past 4000 years. Evidence are mainly provided by pollen analysis carried out at nine sites f rom Congo, Cameroon and Ghana, locally supported by macroflora remains, phy toliths, diatoms, delta(13)C and mineralogical data. At all the sites, except Lake Bosumtwi (Ghana), following a large expansion of rain and mesophilous forests until 3000 years sp, a major change is reg istered, affecting floristic composition, structure and geographical distri bution. According to the hydrological sensitivity of the different sites, l ocal openings of the forests with development of heliophilous formations an d/or isolated enclosed savannas are observed at the most humid sites; compl ete disappearance of forested formations at the driest. The agreement betwe en pollen records, hydrological and hydrobiological data definitely demonst rates that an arid event has been the primary driving factor of this change and is responsable for the main features of the modern landscapes in Atlan tic Equatorial Africa. Moreover, the most recent palaeoecological data obta ined in Congo (Lake Sinnda), indicate that this Late Holocene increasing ar idity was of longer duration, from 4000 to 1300 years sp, and more progress ive than previously inferred. A new expansion of forests is locally detecte d c. 900-600 BF despite increased human impact.