Late Holocene environmental history in the Kaikoura area (1976)
AuthorsDavidson, G. D.show all
Three pollen diagrams were prepared to study Late Holocene vegetation change in the Kaikoura area. The vegetation on the Kahutara Hills has passed through a succession of formations; Leptospermum scrubland, Podocarp-mixed hardwood forest, pteridium fernland, and European grassland) over an undated time period. However, the Nothofagus element at Lake Rotoiti has remained relatively static and thus could imply that the core post dates the southward Nothofagus migration and spans about 6000 years. Fire throughout has been a constant feature of the environment, but correlates with the vegetation fonnations, suggesting that it may be responsible for the changes. The highest frequencies of fire correlate with the pteridium fernland and lowest frequencies with the Podocarp-mixed hardwood forest. Most of the fires were probably natural, however man has been at least partly responsible in the last 1000 years. The vegetation on the Kaikoura Peninsula, determined from dated pollen diagrams from Wairepo Lagoon and Mudstone Bay show that the vegetation has remained unaltered for 400 years. There is no record of the Podocarp-mixed hardwood forest recorded by Moar, (in Duckmanton, 1974), supposedly destroyed at about 300 years B.P. High charcoal frequencies, derived from Polynesian fires, could explain the lack of vegetation change. The environmental change of barrier beach building recorded by Duckmanton (1974), can be attributed to fire caused cliff instability and to Polynesian burning in the Kowhai and Hapuku Catchments. A coincidental tectonic uplift caused the barrier beaches to move and to enclose areas of shore platform behind which lagoons developed, slope deposits covering lagoonal peats (Duckmanton, 1974) are considered to be due to Maori Pa building. Sedimentation in European Times varied considerably. Silting at Lake Rotoiti, 4.5cms/10 years, was very rapid. On the Peninsula the effect of the European varied, from no effect at Wairepo Lagoon to a marked increase at Mudstone Bay. The pollen analysis however records no significant effect of the European on vegetation structure other than the change to introduced grassland.