Late Quaternary environmental change and the impact of Melanesian colonisation in New Caledonia

Relatively little is known of the long term environmental history of tropical south Pacificislands. In addition there is some debate as to whether pollen evidence for vegetationdisturbance in the late Holocene is an appropriate proxy for human presence and whethersuch evidence can contribute to debates concerning island colonisation in the south Pacific.This thesis reports the results of vegetation history analyses carried out in New Caledonia.Three lowland sites from the main island (all below 10 m asl) were investigated usingpollen and spore counts, charcoal counts and stratigraphic analysis. Plum Swamp on theleeward coast of New Caledonia provides a continuous record from the last glacialmaximum (LGM) to the present, while the sediments analysed from Lac Saint Louis andCanala Swamp are mid to late Holocene in age.The results of the study are:1) Littoral forest and lowland rainforest in the Plum River Valley did not undergodramatic change during the last glacial maximum. The valley remained forested.2) Vegetation disturbance associated with fire occurred between 16- 12,000 yr BP,but the composition of the vegetation did not change significantly.3) Present day climatic conditions appear to have been in place around 12,000 yr BP.4) A dramatic vegetation shift from littoral forest and lowland rainforest to aMelaleuca woodland and open shrubland occurred around 3000 yr BP, coincidingwith the commencement of the archaeological record for the island.Plum is one of only two truly lowland sites in the tropics to record persistent rainforestcover during the LGM. This suggests that reduction of precipitation during the LGM intropical islands may not be as great as generally thought. Given the lack of data fromPacific islands, this has important implications for global reconstructions of LGM climate.While vegetation disturbance caused by fire has a long history in the New Caledonianenvironment, it is the arrival of people at around 3000 yr BP that has had the most dramaticimpact on the island's vegetation since the LGM. The pollen records suggest that thevegetation surrounding the sites has changed little over the last 3000 years