Late Holocene rainforest disturbance in French Guiana

Palm swamp forest sediments collected in French Guiana provide new data abo ut late Holocene rainforest. Two cores were collected in 'Les Nouragues' ec ological station (40 degrees5 'N, 52 degrees 40 'W). The lithology shows tw o different types of sediment, organic peat in the upper part and oxidized clay with low organic content and lacking pollen in the lower part, both se parated by a gravel horizon. Radiocarbon dates show that this gravel horizo n could have been deposited between 4500 and 3000 yr BP. Pollen analysis ca rried out on the organic sediments record rainforest disturbances between c a 1520-1380 and 1060-860 cal yr BP suggested by the presence of the pioneer tree species Cecropia together with other shade intolerant genera. Cecropi a is recorded for a period that lasts between 660 and 320 years. This abnor mal duration for presence of a pioneer species in rainforest is explained b y brief and repeated changes in the composition of the canopy asssociated t o perturbations of the palm swamp. (C) 2001 Elsevier Science B.V. All right s reserved.