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A vegetational history and palaeoclimatic changes are established for the last 25,000 yr by pollen analysis of two peat cores from Kaitaia Bog, far northern New Zealand. Twelve AMS radiocarbon dates provide a chronology covering the Last Glacial Maximum to the late Holocene, ca. 2500 yr ago. Prior to 22,000 yr B.P. a tall, complex, conifer-beech-hardwood forest dominated by podocarp trees covered the region. The most abundant of these was Dacrydium cupressinum. Nothofagus (N. cf. truncata) was also an important element. Other common emergent trees included Podocarpus, Prumnopitys ferruginea, P. taxifolia, Dacrycarpus dacrydioides, Libocedrus and Metrosideros. From 22,000 to ca. 14,000 yr B.P. regional forest was dominated by Nothofagus cf. truncata, and warm, moist elements such as Ascarina lucida and Agathis australis were scarce. This Last Glacial Maximum forest cover contrasts with the open grass and shrub communities which dominated landscapes south of Auckland. Cool climate species such as Nothofagus cf. truncata began to decline towards the end of the Lateglacial, and from ca. 11,300 yr B.P. Ascarina lucida started to increase rapidly. Replacement of conifer-beech-hardwood forest with a conifer-hardwood association proceeded rapidly in the Postglacial as Nothofagus cf. truncata retracted sharply and Dacrydium cupressinum increased in abundance. The regional expansion of Agathis australis followed rapidly. Regional forest in the mid- to late Holocene consisted of a conifer-hardwood association dominated by Dacrydium cupressinum, Podocarpus, Phyllocladus and Agathis australis. A mid-Holocene decline for Ascarina lucida and coincident increased abundance of Prumnopitys taxifolia suggest somewhat cooler conditions prevailed from this time. Nothofagus cf. truncata, though still present, assumed only a minor role as more favourable conditions allowed other species a competitive advantage. |
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