AbstractsGeography &GIS

Late Quaternary palynological investigations into the history of vegetation and climate in northern New Zealand

by Rewi M. (Rewi Munro) Newnham

Institution: University of Auckland
Year: 1990
Record ID: 1299406
Full text PDF: http://hdl.handle.net/2292/2253


This thesis describes the vegetation and climatic changes over the past 20,000 years from pollen records at eight northern New Zealand lowland peat and lake sites, ranging from Taranaki to the Far North. The sites investigated are Umutekai Swamp (Taranaki), Lakes Rotomanuka, Rotokauri, and Okoroire (Waikato), Kopouatai Bog (Hauraki Plains), Lake Waiatarua (Auckland), Otakairangi Swamp (mid-Northland), and Trig Road Swamp (Far North). At sites from Auckland southwards, dating and correlation of the pollen records were enhanced by the occurrence of multiple tephra layers within the pollen-bearing sediments. The clearest picture of regional vegetation history and tightest chronologic control were obtained from the tephra-rich organic lake sediments of the Waikato lowlands. Holocene vegetation changes were broadly consistent throughout this northern New Zealand region and indicate climates, which were initially moist, mild and equable, but became increasingly variable and probably drier overall during the late Holocene. Podocarpangiosperm forest was always prominent and Agathis australis forest expanded throughout the region north of latitude 38?? S during the last 6,000 years. Kauri was especially prominent in the Waikato region during the 1000 years or so following the Taupo eruption of c.1800 years ago. At pollen sites from Waikato, Hauraki Plains, and Auckland, palynological evidence suggests that people began clearing forests as early as 800 years ago, but probably not much earlier. Pollen records for the last glacial show less regional uniformity. South of Auckland, scattered tracts of Nothofagus or Libocedrus forest within a shrubland/grassland mosaic were succeeded, between c.14.5 and 10 ka by the regional expansion of podocarp-angiosperm forest, with Prumnopitys taxifolia initially prominent. North of Auckland, the pre-Holocene vegetation history is complicated by uncertain chronologies. Conifer-angiosperm forest with prominent A. austalis grew in the Far North during the last glacial, while in mid-Northland, a substantial period of Nothofagus forest, shrub and grassland communities may correspond to either the entire last glacial or to the late glacial. Local variations in vegetation cover were maintained to some extent independently of regional climate, influenced by site specific factors including edaphic controls, hydroseral succession, and local hydrological changes caused by, e.g., lahar or lava flow, fluvial activity and sea level change. The influence of these local factors is most evident for the late glacial, during which period podocarp-angiosperm forest spread throughout northern New Zealand generally, but with considerable variation in timing even between nearby sites. Fire appears to have been an important factor in vegetation change throughout the period investigated, not just during the human deforestation era; peat swamp communities show a long history of association with fire, while in dryland vegetation, Agathis australis appears to have been especially affected by burning. No unequivocal…