A 30,000 Year Pollen, Vegetation and Climate Record from Otakairangi (Hikurangi), Northland, New Zealand

Abstract

A long pollen profile from Otakairangi (Hikurangi), mid-Northland, New Zealand, extending from c. 30,000 years to 2000 years ago, provides new perspectives into the vegetation history of this region. A phase of Nothofagus Blume forest dominance, during which fires were extensive, is dated to the late glacial, although the radiocarbon chronology is problematical and a 'last glacial maximum' age seems more likely. At other times the vegetation cover was primarily warm temperate conifer-angiosperm forest, which probably persisted up to the human era. Thus, although the composition of forest changed significantly at times, there is no evidence for substantial loss of forest. Similarly, conclusive evidence is lacking for any taxa extending their present latitudinal ranges during the last glacial, assuming the Halocarpus Quinn and Nothofagus Blume pollen identified are from the Northland species of these genera. The palaeoclimatic implications are that the last glacial temperature depression in Northland may have been less than in the rest of New Zealand, although the 'last glacial maximum' was probably very dry. Nothofagusfusca type pollen is tentatively assigned to N. truncata Ckn. on the basis of aperture counts as well as ecological and biogeographical considerations. Its expansion, evidently in association with fire, and its postglacial contraction, are consistent with its scattered distribution in Northland today. It may possibly have survived in the region as an opportunist species responding to periodic disturbances in the predominantly conifer-angiosperm forest cover. Agathis australis Salisb. was prominent in Northland for most of the last 30,000 years, except during the period of Nothofagus dominance (the 'last glacial maximum'?). Its postglacial history at this site and at others from Northland indicate expanding populations after around 8000 years ago, with no major contraction until the human era. A. australis appears to have been especially susceptible to both natural and anthropogenic fires.