Autecological Aspects of Phyllocladus Alpinus Hook.f.(Mountain Toatoa, Celery Pine) in New Zealand

Abstract

Phyllocladus alpinus (Hook.f; Podocarpaceae) is a widespread species, with the apparent ability to invade tussock grasslands. Most literature on this species is mainly descriptive and, in general, confined to forest communities, although several authors have noted its distinctive ecological characteristics. This thesis, therefore, researches autecological aspects of this species and attempts to fulfil the following aims: 1) To describe and quantify the communities in which Phyllocladus alpinus is found at present. To compare the ecology of the taxon in tussockland, tussock-shrubland and forest. 2) To describe and quantify the regeneration ecology of Phyllocladus alpinus. To determine whether the taxon shows different demographic structures in response to different environmental conditions; to establish a relationship (if any) with the presence of other species. 3) To initiate studies, and if possible, determine whether ecotypes in Phyllocladus alpinus are present. Study sites were selected to represent a wide range of environments in which Phyllocladus alpinus grows. Microclimatic conditions were determined and soil investigations carried out at the study sites. The vegetation at the different study sites were classified into community groups and related to environmental factors at the sites. Demographic studies in the different community groups were carried out, while studies were also done on seedling survival and seed germination. The frost resistance of Phyllocladus alpinus and several other species was determined and related to successional changes in tussocklands. From these investigations, it was concluded that Phyllocladus alpinus is a species with low competitive capabilities, but with the ability to withstand adverse climatic and soil conditions. This species is therefore most prominent in environments where adverse conditions limit the presence of other species, or after disturbance has occurred. It was further concluded that Phyllocladus alpinus is able to migrate into human-induced tussocklands. In natural tussocklands (above the tree line), a narrow margin of Phyllocladus alpinus is often present, but climatic conditions here limit further migration of the species.Shrublands and woodlands represent, in general, an established stage of Phyllocladus alpinus. Where climatic and/or soil conditions are suitable for other forest species, these species will ultimately outgrow Phyllocladus alpinus and a forest will establish. In forests, Phyllocladus alpinus is often widespread, but at low density, ready to increase its numbers once disturbance occurs. Where disturbance has not occurred for a long time, the species needs to retreat into niche sites from which it can migrate again once disturbance does occur. Morphological characteristics of Phyllocladus alpinus of herbarium specimens were used to divide the species into 17 groups, using a compact clustering technique. Cuttings from different environments were grown in a single location, to determine whether the plants would show different growth rates. Growth of cuttings showed that plants with long-wide phylloclades, collected from low altitudes show, in general, higher growth rates than plants with smaller phylloclades. These low-altitude plants separated out in the clustering at the third level of division, so that division into 17 groups was partly justified. Further taxonomic studies are required to investigate the genetic variability within Phyllocladus alpinus.