Palynology of Pohehe Swamp, northwest Wairarapa, New Zealand: a study of climatic and vegetation changes during the last 41,000 years

Abstract

In Pohehe Swamp, adjacent to the eastern edge of the Northern Tararua Range, sediments up to 4.5 m thick yielded abundant palynomorphs. They were present through most of the sequence but fewer at depths between 1.2 m and 1.6 m. Dating controls were provided by Aokautere Ash at 22.6 ±.0.23 ka bp, 1.9 m below the surface; a radiocarbon date of ≥. 36 ka bp on wood, 3.7 m below the surface; and the superposition of the swamp deposits on Eketahuna Gravels ( c . 70 ka bp). The palynological sequence indicates four distinct floras in chronological sequence. (1) Between 41 ka and 24 ka bp, a regional Nothofagus menziesii (silver beech) forest with grassland in exposed areas, an estimated timber line at c. 500 m and a cool climate; (2) between 24 ka and 13 ka bp, grassland with shrubs in a cold climate; (3) between 13 ka and 10 ka bp a podocarp forest with a variable distribution of grass and shrubs during fairly rapid warming of climate; (4) Between 10 ka and 5 ka bp a well developed podocarp broadleaf forest growing in the climatic maximum. Nothofagus menziesii , now absent in the beech gap extending from the northern Tararua Range to the central Ruahine Range, started to decline in quantity at c. 24 ka bp and disappeared from the region around Pohehe swamp by c. 19 ka bp.