First European meeting on phytolith research : the state of the art of phytoliths in soils and plants

The reconstitution of African tropical grassland history during the late Holocene can be carried out using phytolith analysis. Fossil phytolith assemblages from the lake Guiers, in the sahelian region of Senegal, and from the lake Sinnda, in the guineo-congolian region of Congo are investigated. The phytolith data are compared to pollen data previously obtained on the same sites. Samples of soil surfaces from the sahelian, sudanian and guineo-congolian regions are analysed for reference. The phytolith data emphasizes that the driest phase of the Late Holocene, around the lake Sinnda, occurred between 4000 and 1200 yr BP, ensued by the opening of the rainforest and its replacement by a short grass savanna. After 1200 yr BP, wetter climatic conditions development are evidenced by the setting of modern shrub and tall grass savanna up to now. In the sahelian zone around the lake Guiers, a dry phase occurred after about 2000 yr BP and has not been ensued by climatic improvement. It is evidenced by the progressive replacement of a tall grass savanna woodland by a shrub and short grass savanna which occurs until today. This study has been supported by the french programs PEGI and ECOFIT. (Résumé d'auteur