A late-Holocene record of human impact from the southwest coast of New Caledonia

A late-Holocene vegetation record is presented from the southwest coast of New Caledonia. Lac Saint Louis is a freshwater swamp at 3m a.s.l. adjacent to the River Coulee delta. Pollen analysis, charcoal analysis, radiocarbon dating and stratigraphic analyses have been used to reconstruct the vegetation and sedimentary history of the swamp. The sediment record commences at 6000 BP and reflects rapid floodplain development associated with postglacial sea-level rise. This rapid accumulation of sediment ceased around 5500 BP and the site became a freshwater swamp. From 5500 to 3000 BP the pollen record reflects several aspects of this coastal landscape; coastal forest, the swamp surface and the adjacent mangrove zone. At 3000 BP charcoal levels increase significantly in conjunction with abrupt changes in the pollen record. Mangrove pollen declines and pollen indicative of coastal forest is replaced by pollen indicative of coastal savanna. These changes coincide with the commencement of the archaeological record in New Caledonia and mirror similar changes in other late-Holocene records elsewhere on the island, and are interpreted as representing human impact. Yam terraces surrounding Lac Saint Louis may have been built around 2000 BP based on mineral magnetic measurements and charcoal accumulation. The decline in mangrove vegetation adjacent to site may be the result of a late-Holocene fall in sea level. Increased sediment accumulation along the coastal foreshore as a result of forest clearance in the River Coulee’s catchment, however, is also considered.