On the Ecology and Restoration of Podocarpus cunninghamii in the Eastern South Island High Country
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Podocarpus cunninghamii is an endemic New Zealand conifer that, in pre-human times, formed extensive forest communities across the eastern South Island high country. Anthropogenic disturbances have reduced the distribution of Podocarpus cunninghamii communities such that they now exist mainly as small and isolated remnants within a highly modified, predominantly pastoral landscape. Very little is known of the ecology of high country Podocarpus cunninghamii communities, and without this information it is not possible to develop an ecological basis for their restoration. This thesis explores the ecology of Podocarpus cunninghamii in the eastern South Island high country, investigating factors that potentially affect the restoration of Podocarpus cunninghamii within this environment, with special attention paid to the role of arbuscular mycorrhizal fungi (AMF).
Field investigations of Podocarpus cunninghamii communities showed that they contain a high degree of floristic and structural variation determined by soil and climatic variables. Analysis of age and size class distributions suggest that Podocarpus cunninghamii has more than one regeneration strategy, and can regenerate within intact forest following the opening of small canopy gaps or can undergo large-scale recruitment following catastrophic disturbance. Field and glasshouse experiments investigating growth and nutrient responses of Podocarpus cunninghamii to different AMF inoculants found that Podocarpus cunninghamii responses are dependent on both AMF type and grass competition. Finally, investigation of Podocarpus cunninghamii carbon stocks showed that they are less than that of other New Zealand forest types, but are greater than that of grazed pastures.
Successful restoration of high country Podocarpus cunninghamii communities will require the incorporation of associated species based on local environmental conditions, and will also need to allow for disturbance processes. AMF may have an important role to play in restoration by reducing seedling production times and by increasing the competitiveness of Podocarpus cunninghamii when in competition with exotic grasses.