ANALYSIS OF THE HISTORY OF FORESTS AND ASSOCIATED CLIMATES

Previously, dense tropical forests were considered to be the most stable ecosystems on the planet, and their exceptional richness has often been associated specifically with their resistance to past climate changes. Because of recent advances in paleoecology, however, it has been shown that dense forests, such as those in Africa and in Amazonia, have in fact undergone profound changes in response to global climatic changes.

The history of dense forests and their dynamics can be reconstructed by the study of fossils such as pollens or – much rarer – wood or carbon, within specific disciplines such as palynology, paleo-botany or anthracology. Reconstitution of paleo-vegetation is one method, among others, of reconstructing the paleo-climates of past eras. Nevertheless, even though there has been much progress in studying the history of intertropical forests and their associated climates, several problems remain, linked mainly to the small amount of data available. This introduces subjectivity in describing the succession of paleo-environments.

Nearly all trees in dense tropical forests are angiosperms. It would be logical to begin the history of these forests at the time when angiosperms evolved, i.e. during the lower Cretaceous era through to the Barremian and the Aptian eras, around 120 million BP (Maley, 1996a). Up until then, gymnosperms were the dominant plant form but by the end of the Cretaceous, dense tropical forests had become made up almost entirely of angiosperms.