Holocene vegetational and climatic history, Sponge Swamp, Haast, south-western New Zealand

Palynological studies from most of the drier eastern and southern parts of the South Island, New Zealand, suggest that the climate regime switched from prevailing northerly airflows to dominant south-westerly airflows during the mid to late Holocene. To substantiate the tenet, a South Westland mire site with little historic disturbance was selected for vegetation reconstruction and comparison with the regional environmental history. Pollen concentrations were dated to provide better age control. Lowland podocarp/hardwood forest persisted under a warm and moist climate from about 7700 BP after the formation of the fen. The climate became slightly warmer and drier around 6800 BP, which was responsible for the loss of mire flora, the suppression of Dacrydium cupressinum and a subsequent large increase of Ascarina lucida. From ca. 6800 BP, a Substantial cool interval started with a sudden decline in stands of A. lucida in conjunction with expansion or establishment of some cold tolerant taxa, in particular Nothofagus menziesii. This period lasted nearly 3000 years and was most pronounced at ca. 3500 BP. A significant dry episode from ca. 3700 BP was shown by gradual replacement of tree ferns and swamp forest taxa with forest taxa which are tolerant of drought. The reduction of rainfall is also supported by evidence from the substantial positive excursion of delta C-13 values around 3230 BP in coastal northwest South Island sites. Vegetation and climate history reconstructed from this site coincided well with the regional vegetation and climate history. The climate trend derived from this site, e.g. from warm and moist to cold and dry conditions, is most likely to be caused by the reduction of the humid northerlies and intensification of the cold and dry south-westerlies. (c) 2007 Elsevier Ltd and INQUA. All rights reserved.