Aspects of the ecology of Desmoschoenus spiralis (A. Rich.) Hook. f
Degree GrantorUniversity of Canterbury
Degree NameMaster of Science
The taxonomy and a general description of Desmoschoenus spiralis (pingao) is given. The distribution of Desmoschoenus in New Zealand is mapped and discussed. Although pingao is still widespread throughout New Zealand, only remnant populations now exist in most of their former localities, and their numbers are still declining due to various human activities. The germination of the seeds of pingao and the dispersal mechanisms of the fruits of pingao are investigated. Of the germination treatments none were successful above 10%. Pericarp scarification was most successful in promoting germination. Seeds were capable of germination after 50 days floatation in seawater. Transport of fruit by sea is put forward as a means of long distance dispersal while wind is responsible for short distance dispersal. Fieldwork on aspects of the ecology of pingao was undertaken at Kaitorete Spit Scientific Reserve, Canterbury, New Zealand. Descriptions of the physical and climatic features of the Spit, its dune system, and the study area are made. Seedling studies include monitoring leaf production and mortality of new seedlings, and of older seedlings with respect to browsing. Selected measurements and counts of plants of pingao of the foredune zone and the reardune-grassland zones were made. These include tuft dispersion, percentage cover, habit type, vegetative and inflorescence measurements and counts, density counts and biomass estimates. Plants of each zone were also monitored for leaf production, leaf dieback, rhizome growth, and new tuft and inflorescence development. Differences between the foredune and reardune- grassland zones were found for most of these results. By monitoring selected environmental factors of the foredune and reardune-grassland zones, it was found that sand was slowly accumulating around plants of the foredune but not around plants of the other zones. Water is more limiting to reardune-grassland plants than to foredune plants. Plants of the grassland zone on which sand was deposited for a year developed characteristics similar to plants of the foredune zone. It is concluded that pingao requires a regular influx of sand to sustain vigour and survival by keeping the rooting zone far enough below the sand surface so that new roots are able to grow into moist sand. If sand influx ceases, as pingao plants grow, their rhizome changes its orientation from vertical to horizontal and spreads along the sand surface. New roots grow into the top few centimetres of sand which, due to its very low water content, is limiting to the growth of pingao.