Studies on the pollen of New Zealand gymnosperms
Degree GrantorUniversity of Canterbury
Degree NameDoctor of Philosophy
This thesis has been particularly concerned with the interpretation of gymnosperm pollen percentages in modern and fossil pollen spectra in New Zealand. The morphology of the pollen of the indigenous gymnosperms was first studied to enable a correct identification of those types present in a sample to be made. Dacrydium pollen can be identified specifically except for D. bidwillii and D. biforme which are inseparable; Podocarpus pollen is readily separated into groups but further identification, especially within the P. totara complex, is difficult; the three species of Phyllocladus possess small pollen grains making specific identification impossible, especially with the light microscope; and Libocedrus plumosa and L. bidwillii are similar in all characters and thus inseparable. A new term, region of 'weakness', has been introduced for a feature previously not recognised in gymnosperm pollen. This region is adjacent to the dorsal roots of the bladders at the lateral margins of the cap and may have a function in harmomegathy. Modern pollen rain has been studied quantitatively in South Westland where pollen percentages in moss cushions were compared to a quantitative assessment of the local vegetation surrounding the sampling sites; qualitatively at various localities in the South Island and Stewart Island; and qualitatively and quantitatively at Lady Lake, North Westland, where surface lake sediments and moss cushions were analysed for their pollen content. Representation of pollen in surface samples is shown to be related to the pollination mechanism of each species present, the size of the plant and the structure of the local vegetation. Gymnosperm pollen is usually well represented because all species are anemophilous and thus produce large quantities of pollen. Most are trees (except Dacrydium laxifolium and Podocarpus nivalis) and their pollen is therefore released into the atmosphere above the vegetation from where it is effectively dispersed. The Aranuian vegetation at Lady Lake was studied and for the last 5700 radiocarbon years has been broadly similar to that of the present day. The pollen analysis provides evidence for complexity in the development of Aranuian vegetation in Westland and also suggests that, locally, fluctuations in lake level have been responsible for subtle changes in the vegetation.