A postglacial vegetation history of the southern-central uplands of North Island, New Zealand

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Abstract
Bogs at 1000–1400 m altitude in Moawhango Ecological Region in the central North Island provide a pollen record of vegetation change spanning the last 11,000 years. Bogs have developed on the greywacke summits of the southern Kaimanawa Mountains and on marine sediment plateaus and greywacke summits of the northern Ruahine Range. Andesitic and rhyolitic tephras from the Taupo volcanic zone provide a tephrochronology where they are interbedded in the peat bogs. Topogenous or basin peats commenced accumulation in the late glacial, while higher altitude ombrogenous or capping peats date from the mid-Holocene. The persistence of mild, dry winters in the early Holocene prevented growth of ombrogenous bogs, but with a change to colder, wetter winters in the late Holocene, peat accumulated at high altitudes. By 11,000 yr BP post-glacial forests of podocarps and Nothofagus were well established in lower montane and sheltered upper montane sites. Just after 11,000 yr BP on exposed plateau surfaces, late glacial shrubland-low forest of first Halocarpus then Phyllocladus was replaced by Libocedrus bidwillii forest. While Nothofagus expanded asynchronously throughout the Holocene in the greywacke mountains, Libocedrus continued to dominate on sedimentary plateaus. Although there has been a slow inexorable spread of Nothofagus from refugia throughout the Holocene, a late Holocene shift to sunnier, less cloudy summers increased the momentum of spread. Pre-human fires initiated deforestation in the southern Kaimanawa Mountains c. 3000 years ago. The rhyolitic Taupo Pumice eruption also destroyed vegetation in the same region, and there was little recovery before the widespread destruction of forests throughout the Moawhango by human fires. Of the andesitic ash showers only the Mangarnate Formation (9700–9780 yr BP) damaged Nothofagus forests of the Kaimanawa foothills adjacent to the Tongariro volcanoes. The rejuvenated pavements arising from individual ash falls have generally been exploited by podocarps at the expense of Nothofagus.

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