Numerical interpretation of a high resolution Holocene pollen record from Burundi

Abstract

The Holocene history of the tropical montane forest is reconstructed using a high resolution pollen record from a valley swamp (3°35′S, 29°41′E), at 2000 m elevation. The post-glacial establishment of the montane rain forest is evidenced at ca. 10,600 yr B.P. Numerical analysis combines the Correspondence Analysis with the Cluster Analysis of both 38 modern and 101 fossil pollen spectra including 125 identified pollen taxa. Four distinct successionnal stages of forest development have been identified. The past vegetation recorded during the early Holocene period (10,600–3800 yr B.P.) was more closely related to modern pollen spectra from secondary forest rather than to primary forest samples from Burundi. At 3800 yr B.P., a sharp decrease of arboreal pollen percentages and a noticeable increase of Celtis, a semi-decidous tree indicate the opening of montane forest due to a drier climatic event. The beginning of the anthropogenic impact evidenced after at 3500 yr B.P., contemporaneously with the Early Iron Age in Burundi, follows the late Holocene climatic shift.