Remote sensing shows south-east Queensland koalas (Phascolarctos cinereus) prefer areas of higher tree canopy height within their home ranges

Abstract

Context. Home range studies allow investigation of faunal habitat use within a well-defined area, and for some species, the concept of 'core' and 'non-core' home ranges provides the means to examine how resource use varies within home ranges. Taking this approach, we investigated whether koalas preferentially used areas of taller forest canopy within home ranges. After an extensive examination of data quality and home range estimation methods, we used remote sensing techniques to provide canopy height information at high resolution. Aims. In many areas, koalas prefer taller individual trees at the plot scale; our aim was to investigate whether koalas prefer forest areas with higher canopy height within their home ranges. Methods. In our southeast Queensland study area, we developed a canopy height model (CHM) from airborne LiDAR (Light Detection and Ranging) data. Existing radio telemetry and GPS data from 135 koalas were used to generate home ranges using 95% kernel density estimators, and 50% kernels represented core home ranges. Some home ranges occupied more than one forest type (Regional Ecosystem -RE); we treated each RE as an individual patch, and used 225 patches in our analysis. We intersected the 95% kernels with the CHM, and used hierarchical spatial clustering to derive four categorical canopy height classes within each patch. We then compared differences in height class area proportions between core and non-core areas for each patch. Key results. The highest of the four canopy height classes comprised a significantly higher proportion of core areas (42.3%) than non-core areas (30.7%). Classes 2 and 3 were evenly distributed, and the proportion of Class 4 (lowest canopy height) was 20.3% of non-core areas and 11.0% in core areas. Results were similar for REs grouped by Land Zone and individual REs. Conclusions and implications. We conclude that areas of higher canopy are an important habitat resource for koalas. We have, for the first time, examined resource variability within entire koala home ranges using remote sensing, and our methods demonstrate an avenue for further research using other forms of remote sensing. Classified canopy height models could also be used for strategic conservation planning, and at population-level koala habitat management when combined with other relevant habitat factors.

GPS tracking reveals koalas Phascolarctos cinereus use mosaics of different forest ages after environmentally regulated timber harvesting

“…Our results differ from those of a recent study that also assessed tree use by koalas using GPS‐tracking data and a canopy height model (Mitchell et al., 2023). Koala core home ranges in the peri‐urban landscapes of south‐east Queensland were comprised of a significantly higher proportion of the highest height class (28 m median) than non‐core areas, highlighting regular use of areas with higher canopies in this landscape.…”

“…Core areas in our study represented 23%–29% of 95% AKDE home ranges, which is similar to that found by Mitchell et al. (2023) in south‐east Queensland.…”

“…data), both of which are indicative of medium-quality habitat for NSW. Core areas in our study represented 23%-29% of 95% AKDE home ranges, which is similar to that found by Mitchell et al (2023) in south-east Queensland.…”

“…Koala home ranges are also known to vary substantially with habitat quality and the size of our estimated home ranges suggests the habitat was of medium quality. Our home ranges (male -64 ha; females 21 ha) are moderately large compared to other studies including peri-urban south-east Queensland (13.9 ha; Mitchell et al, 2023), more productive blackbutt forest in northern NSW (7-34 ha; Radford Miller, 2012), dry woodland in the Pilliga (10 ha; Kavanagh et al, 2007) and blue gum plantations in Victoria (<1 ha; Ashman et al, 2020). But they are similar to koalas near Port Stephens (Matthews et al, 2016) and are considerably smaller than koalas on infertile sandstone (Ward, 2002) and fragmented farmland (Kavanagh & Stanton, 2012).…”

“…GPS devices are increasingly used to provide a detailed picture of an animal's home range and selection of habitat because of the vast quantity of high-resolution fixes that can be collected (Kie et al, 2010;Seidel et al, 2018). Such detailed depictions of an individual's home range can also be overlaid with remote-sensing data to capture high-resolution vegetation structures over large areas and assess how these are used by an individual (Mitchell et al, 2023). This is particularly relevant to the koala Phascolarctos cinereus, an arboreal folivore, listed as an endangered species in Australia.…”