Late Quaternary vegetation change in the Tari Basin, Papua New Guinea

Abstract

The changes in Late Quaternary vegetation at two sites in the Tari Basin, central highlands of New Guinea, are presented. Haeapugua basin (1650 m altitude) and Tugupugua basin (2300 m altitude) lie within the lower montane forest belt, where the climate is characterised by high relative humidity and low seasonality. Pollen analysis, mineral magnetics, carbonised particle analysis, and dating by radiocarbon and thermoluminescence techniques are employed to reconstruct the vegetation and sediment history. The sequences include fragmentary interglacial/interstadial records from before 50,000 yr B.P. and a continuous record from at least 28,000 yr B.P. to the present. The study shows that, prior to 21,000 yr B.P., vegetation in the basin was dominated by fluctuating proportions of tree taxa indicative of a forested environment. The montane forest taxon, Nothofagus, is important throughout the record, although other tree taxa, including Castanopsis, Myrtaceae, Dacrydium and Pandanus, attain dominance at different times under the influence of a range of environmental factors. The creation of an open environment around 21,000 yr B.P. is considered to be a consequence of the arrival of humans in the region. The late glacial transition, between 14,500 and 8500 yr B.P., is a period of climatic instability with landscape and vegetation adjustments proceeding at different rates across the highlands. Vegetational adjustments match modern ranges by about 8500 yr B.P., when swamp forest developed across the sites. At the lower altitude site there are indications of anthropogenic forest disturbance, associated with swamp forest clearance, commencing around 1700 yr B.P. and intensifying through to the present. Forest clearance is recorded only after 700 yr B.P. at the higher site, where agriculture was probably only sustainable after the introduction of sweet potato (Ipomoea batatas).