Sago production, human impacts, climate change, and ecological dynamics at Lake Kutubu: A new palaeoeoclogical record from the humid tropics of southern Papua New Guinea

The Sago palm (Metroxylon) is an important food (starch) source across its range from Southeast Asia, New Guinea and the Pacific Islands. In Papua New Guinea Metroxylon sagu is cultivated in lowland tropical rainforests and freshwater swamps, where it is a major staple food for around 10% of rural villages. The economic and cultural significance of sago in lowland PNG is immense, but the extent to which human populations have managed sago in the past is poorly understood. Here I present a new palaeoecological record from Lake Kutubu, the largest freshwater lake in Papua New Guinea, and a modern centre for sago production in the region. The evidence shows that Metroxylon sagu in association with lowland swamp forest disturbance (fire related) is evident only in the last 1500 yr BP, and it appears to undergo expansion in area planted and intensification of use after ~800 yr BP. The multi-proxy approach to reconstructing past landscape and climate change at Lake Kutubu is beginning to suggest a link between climate change (monsoon/ENSO), aquatic ecosystems dynamics and human exploitation of resources in the humid tropics over the last few millennia. I discuss the evidence for long-term socio-ecological change across the region and suggest that the timing and intensification of sago production may have been, at least in part, driven by a weakening of the monsoon between 2500-800 yr BP resulting in a regionally drier climate and the need for more intensively managed food production systems.