Aranuian (post-glacial) pollen diagrams from the Tongariro region, North Island, New Zealand

Abstract

Retreat of glaciers on the Tongariro Volcanoes began before 14 000 yr B.P. By 14 000 yr B.P., podocarp-hardwood forest had begun replacing the previous scrub and grassland communities. We recognise three major post-glacial pollen zones. (i) 14 000–10 000 yr B.P. Podocarpus spicatus forest was dominant. Annual temperatures may have been only 2–3°C lower than present, but the climate was substantially drier. (ii) 10 000–5 000 yr B.P. Docrydium cupressinum forest was dominant and the climate much wetter and milder than present. (iii) 5 000 yr B.P.-present. Return of Podocarpus spicatus-dominant forest, increase or Nothofagus, and a general trend away from the mild climates of (ii) to a more drought- and frost-prone climate. The present pattern of Nothofagus forest on the Volcanic Plateau originated during the last glacial maximum when forest was confined to small relict areas. The development of milder climates, and the post-glacial expansion of podocarp-hardwood forests kept the Nothofagus forest confined to small, scattered localities. Only in the last 5 000 years has there been significant expansion of Nothofagus forest, but the large rhyolitic eruptions of the last 3 500 years have tended to delay this spread.