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Restoration of three indigenous forest types in Tauranga City, New Zealand

This research examined the current state and developmental trajectory of forest restoration projects in Tauranga City with the aim of establishing whether they will eventually develop into functioning forest ecosystems similar to their natural counterparts. Three forest types historically present in Tauranga were studied: coastal Metrosideros excelsa forest, semi-coastal broadleaved forest, and semi-coastal Dacrycarpus dacrydioides swamp forest. Forty-five variable-area plots were established in thirteen categories comprising at least two planted sites of different ages for each forest type, naturally regenerating sites within the city, and old-growth reference forests outside of the city. Vegetation parameters including tree diameters, numbers of saplings and seedlings, cover abundance and groundcover were measured or recorded. Site characteristics such as aspect and slope were also recorded. Soil samples were taken in each of the thirteen forest categories and microclimate conditions were recorded over a period of eight months using micro data loggers. Data were analysed by comparing species population structures along with diversity and naturalness in each forest category. Non-metric Multidimensional Scaling and Multi-Response Permutation Procedures were used to examine the relationships between restoration sites and reference sites in each forest type and across all three forest types. Environmental data were compared using ANOVA and relationships between physical, environmental, and vegetation characteristics were examined using Spearman rank correlations. Results from the planted restoration sites were compared with the naturally regenerating forests and the reference forests. Coastal forest restoration sites were found to be developing into Metrosideros excelsa forest but recruitment of mid- and late-successional species was failing, probably due to browse from exotic animals and isolation from seed sources. This was the case even in mature Metrosideros excelsa forest on Mauao. Restricted regeneration of canopy species was evident in the semi-coastal broadleaved reference sites but the reason for this was not clear. Naturally regenerating sites were being invaded by Prunus campanulata which has the potential to dominate the vegetation. The understorey in the restoration sites was developing through regeneration and colonisation of species that had not been planted, indicating that the vital ecosystem function of seed dispersal has been restored. However, successional canopy species were failing to recruit. Old-growth Dacrycarpus dacrydioides forest at White Pine Bush was found to be on a trajectory towards Beilschmiedia tawa-dominated forest. Naturally regenerating swamp forest in Kopurererua Valley was dominated by Salix cinerea and had almost no regeneration of native species. Planted restoration sites in Kopurererua Valley and Te Maunga are likely to become Dacrycarpus-dominated stands but with lower stem densities than natural stands. The Dacrycarpus dacrydioides in the older restoration sites at Te Maunga were beginning to naturally regenerate but seedlings are only likely to survive where there is sufficient light and reduced competition. Across all forest types the proportion of exotic species decreased from an average of 50% in the youngest restoration sites to just 1.5% in the reference forests. Microclimate conditions generally became more similar to reference forest conditions with increasing stand age. While younger sites had similar average temperatures and relative humidity to reference sites, the fluctuations in temperature and humidity significantly decreased with stand age from an average range of 28.6 °C and 76.7% RH in the youngest restoration sites, to an average range of 19.9 °C and 48.9% RH in the reference sites. Recommendations relevant to the management of existing and future restoration plantings in each of the three forest types are provided.
Type of thesis
Dean, H. A. (2013). Restoration of three indigenous forest types in Tauranga City, New Zealand (Thesis, Master of Science (MSc)). University of Waikato, Hamilton, New Zealand. Retrieved from https://hdl.handle.net/10289/7898
University of Waikato
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