Determining the distribution and abundance of a regional koala population in south-east Queensland for conservation management
Dique, DS, Preece, HJ, Thompson, J & de Villiers, DL 2004, Wildlife Research, vol. 31, pp. 109-117.
Integrating strip-transect surveys and landcover classification, this study identifies the distribution and abundance of a regionally threatened koala population in the Koala Coast, south-east Queensland. Koala densities were found to be greatest in remnant patches and large areas of eucalypt bushland, especially towards the region’s centre. Urban areas possessed lower, but significant densities.
Within the study area, a landcover classification system was developed using GIS and remote sensing to identify patches of potential koala habitat. Following this, koala habitat was stratified into four strata (urban, remnant bushland, bushland and other), with density surveys taking place at sites within each stratum. As preliminary results showed that survey sites located closer to the region’s centre possessed higher koala densities, remnant bushland and bushland strata were further classified as either low-density or high-density. High-density remnant bushland strata possessed the greatest mean densities (0.41-1.26 koalas/ha), with high-density bushland sites exhibiting lower densities (0.2-0.57 koalas/ha-1). Density estimates from urban survey sites show that there remain substantial populations in residential areas (0.157-0.183 koalas/ha), at higher mean densities than low-density bushland stratum (0.02-0.19 koalas/ha). Based on four habitat strata, the koala population of Koala Coast was estimated to be 7230 initially and 6246 when including low and high-density remnant and bushland strata.
While both population estimates indicate that there exists a considerable distribution of koalas throughout Koala Coast, the lower estimate of 6246 was considered more reliable, taking into account the higher densities found towards the region’s centre and thus reducing within-strata variation. In recognising these higher density areas, the study emphasises the importance of large tracts of bushland for koala conservation as it was shown to provide habitat for the majority of koalas in the region. In view of this, bushland within the region’s centre was targeted as an area of high conservation significance and as such, measures should be put in place to prevent loss and fragmentation of habitat. Establishing regional koala distribution using a novel method of koala surveys and landcover classification is arguably more accurate in its identification of high-value habitat than other described models. Where most studies assess habitat quality based on a measure of preferred tree species, the present model uses actual koala abundance as a foundation for identifying significant conservation areas. Importantly, no assumption is made of an association between habitat quality and floral composition as this is unlikely to apply to broad geographic areas.
The Koala Coast harbours a large, essentially closed population of koalas that is highly vulnerable to expanding urbanisation. Accordingly, conservation of high-value bushland located within the region’s centre is essential in maintaining this population and must be incorporated into existing management and monitoring programs. The results of this study show that loss of high-density bushland and remnant bushland would likely lead to significant population decline in this region.
Summarised by Julian Radford-Smith
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