Vegetation history from the Kaihinu (last) interglacial to the present, West Coast, South Island, New Zealand

Abstract

An outline of the vegetation history of Hokitika-Westport area, West Coast, South Island, since the beginning of the Kaihinu Interglacial, is based on pollen analytical data from 20 sites. Interpretation of the pollen diagrams is constrained by the geology of the sites and by the unreliability of radiocarbon dates caused by widespread sample contamination by modern carbon. Accumulation of the pollen-bearing materials took place within the framework of deposition and erosion resulting from Kaihinu (last) Interglacial and Aranui Postglacial high sea levels and intervening glacier advances of the Otira (last) Glaciation. The principal groups of sites are associated with (1) high sea level deposits, (2) fluvial deposits, (3) loessic terrace cover deposits and (4) wet hollows. Together with spot samples, mostly previously described from late Otiran full glacial sites, the sites exemplify a wide variety of vegetation types and climatic environments ranging from warm temperate podocarp rain forest, through beech ( Nothofagus) forest and shrubland, to full glacial grassland. Based on the patterns of climatic change and geological events, tentative correlations are made with deep-sea Oxygen Isotope Stages of late Stage 6, through the substages of Stage 5, followed by Stages 4 to 1. Forest prevailed throughout the Kaihinu Interglacial (Stage 5), being initially dominated by the podocarp Dacrvdium cupressinum and then by Nothofagus. Individual sites cover estimated time ranges up to ca. 35,000 years in apparently unbroken sequences. In the terrace coverbeds, none more than 2 m thick, severe mixing of pollen is at least partly related to breaks in the sequences. A widespread early Aranuian break (latest Stage 2) and another in the mid-Otiran interstadial (Stage 3), are both in transitional periods between fully glacial and fully interglacial conditions, and probably required periods of seasonally dry and windy conditions to strip the loessic deposits from wide areas.