Mapping projective forest cover in Western Australia´s Goldfields region. Investigation of the effect of soil backgrounds

The Department of Conservation and Land Management in Western Australia recently carried out the GOLDFOR project in the Western Australia Goldfields. The work was designed to rapidly collect information on Projective Forest Cover (PFC) as part of the National Forest Inventory (NFI). This region is dominated by scrubland that has only recently been brought within the definition of Forest by a change to that definition. The method used for mapping PFC uses indices based on selected bands of Landsat TM imagery, assisted by ground truthing in the form of colour air photography and site visits. The indices are developed after stratification of the imagery using the Interim Biogeographic Regionalisation for Australia (IBRA). The purpose of this study was to investigate the effect on forest cover estimates of using soil type as an alternative stratification tool. The reflectance spectra of soil samples collected over a study zone in the Southern Goldfields, were measured using a GER IRIS spectrometer. Sufficient clustering in the spectral response was evident to allow partitioning of the area into two zones that corresponded to broad soil zones identified from the Atlas of Australian Soils. New vegetation indices were then developed for each of the soil types, using optimal band combinations derived using principal component analysis. Some differences were observed that indicate that the method of mapping vegetation cover without taking into account the soil background may overestimate the vegetation cover. Further investigation of the new indices is ongoing.