DYNAMIC HISTORY OF A TROPICAL SWAMP - POLLEN EVIDENCE FROM NDURUMU, BURUNDI

This paper presents the results of the pollen analysis of two cores taken in a papyrus swamp of the Ndurumu Valley, north of Burundi (2-degrees-43'S, 29-degrees-58'E) at 1367 m of altitude. The zonation of the pollen record and the interpretation of pollen data are controlled by multivariate statistical studies such as the diversity index, factorial and cluster analysis. At the bottom of the core, dated around 6400 yr BP, the pollen assemblages document the installation of a pioneer forest including Macaranga and abundant ferns. Between 2800 and 1600 yr BP, the valley was occupied by a swamp forest dominated by Syzygium and Phoenix. The establishment of a papyrus swamp dates from 1250 yr BP when the forest disappeared. The abrupt disappearance of the forest is interpreted as the result of a rising water table rather than an effect of human deforestation, although a syncbronous appearance of the cultivated Ricinus communis is registered at the same time.