A late Quaternary record of environmental change and human impact from New Caledonia

A late Quaternary vegetation record is presented from a lowland site on the leeward southwest coast of New Caledonia. Plum Swamp is a backswamp on the Plum River at around 10 m a.s.l., just within the ultramafic terrain that dominates the southern third of New Caledonia. Pollen analysis, charcoal analysis, radiocarbon dating and stratigraphic analysis are employed to reconstruct the vegetation and sedimentary history of the valley. The vegetation record commences at around 20,000 yr BP and shows that from this time up until the late Holocene the valley was forested. The greater representation of taxa more prevalent at higher altitudes during the late glacial suggests a response to cooling and an enrichment of the lowland forest with more montane elements. The late glacial transition between 14,000 and 9000 yr BP is a period of instability within the valley when vegetation is disturbed by fire. Forest recovers after this and there is increasing stability until the arrival of people in the late Holocene at around 3000 yr BP. The initial colonisers of New Caledonia had a profound effect upon the vegetation of the valley, converting the lowland forest to a stunted and species poor maquis on the ultramafic sediments and Melaleuca woodland on the non-ultramafic substrates. However, sedimentary processes are relatively unchanged during this time. Dramatic geomorphic change does occur in the catchment though, during the latter part of the 20th Century as a consequence of mining.