A stratified GIS-based model to identify optimal locations for establishing new permanent sample plots for Eucalyptus bosistoana and Eucalyptus globoidea in New Zealand
Degree GrantorUniversity of Canterbury
Degree NameMaster of Forestry Science
As part of an effort to develop a forest industry based on durable hardwood eucalypts in New Zealand, the New Zealand Dryland Forests Initiative (NZDFI) have considered Eucalyptus bosistoana and Eucalyptus globoidea as two candidate species. There have been 158 permanent sample plots (PSPs) of the two species established in seven trial sites across the two main islands of the country. The network of these PSPs has provided information for the NZDFI’s research program, especially for growth and yield modelling for the target species to examine the relationship between trial sites and the species (i.e. site-species matching). However, the existing PSPs do not cover the entire range of environmental conditions in New Zealand, nor do they cover the range of conditions the species are capable of growing in. Hence, the PSP network could be strategically expanded into new areas. This thesis describes a methodology, which combines habitat modelling and stratified random sampling approaches with the capability of geographic information systems (GIS), to build a GIS-based habitat model for a strategic expansion of the current PSP network.
The method applied in this study consisted of three main stages. In the first stage, the study selected 17 model variables in three categories (i.e. topography, climate, and soil), defined their importance, and tested them for multicollinearity. For each model variable, data were collected for three geographic zones: (1) the native habitat of the species, (2) all of New Zealand, and (3) the existing PSPs. The second stage was to process data to build the model. The third stage applied variable restriction and stratification analyses to calculate a priority index for the complete study area. This index represented the priority for establishing new PSPs in the study area, based on under-represented environmental characteristics.
The result chapter presents available areas for the expansion of the PSP network after the restriction process as the potential habitat for the target species. Besides excluded areas (i.e. not suitable for plantations of E. bosistoana and E. globoidea in the study area), by assessing the priority index in the available areas, the result map highlighted: (1) over-represented areas (i.e. high environmental similarity, where the environmental conditions have been described by many PSPs in the existing network), and (2) under-represented areas (i.e. high environmental dissimilarity, where the environmental conditions have been described by no or few PSPs in the existing network). The results suggest that new PSPs for the two species should be established in Rangitikei District and Taupo District. Other high-priority areas include Northland and Auckland regions, the east coast of the Gisborne region, and southeast-facing hillsides of the mountain chains in the central South Island.
Overall, the study built a stratified GIS-based habitat model that successfully determined locations for strategic expansion of the PSP networks of two different species, E. bosistoana and E. globoidea, in New Zealand. With the strengths of GIS and the availability of global GIS data, the methodology in this thesis has high potential to be applied more broadly for different species, different PSP networks, and different study areas.