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Predictive Koala Habitat Model

Koala Habitat Model

The Predictive Koala Habitat Model (PDF 4.2MB) (the model) was developed in partnership with the Department of Industry (DoI) – Forest Science Unit.

The model is the final stage of the EPA's koala mapping program, which has delivered a series of important habitat mapping products and research findings.

The model produces two fine-scale maps (250 metre grid cell) of koala habitat suitability for forests in north-eastern NSW. One map is set for elevations above 500m and the other is for areas below 500m. The categories of habitat suitability are based on the modelled relationship between koala records and environmental variables that have been shown to be reliable predictors of koala habitat.

Unlike the mapping approaches trialled in the pilot project which rely on vegetation, the model accounts for the influence of multiple environmental variables, including existing vegetation mapping, soil type and climate. The field validation work undertaken as part of the development and refinement of the model showed that the model output positively correlated with site habitat quality and likelihood of koala occupancy.

The EPA will use the outputs of the koala mapping program, including the model, to inform improvements to koala identification and protection requirements on both public and private land.

View the map

The predictive habitat model can be viewed online. For instructions on how to use the map viewer, see the Native Forestry Map Viewer Guide .

To download the spatial datasets, please visit our open data portal and search using the keyword 'Koala'.

Koala map

Map of koala habitat suitability in north-east NSW (red is lowest habitat suitability, yellow and green are moderate suitability and blue is highest habitat suitability).

Frequently asked questions

Why is a predictive koala habitat model useful?

Koalas can be difficult animals to detect. They are well camouflaged, with large home ranges and they occur at low densities outside of the best quality habitat. Koala pellet surveys have been shown to be unreliable indicators of koala occupancy, due to variations in how easy they are to detect and the rates the pellets decay.

A predictive model, which uses a suite of environmental variables that influence habitat suitability and extrapolates to areas not previously surveyed, is an important resource to help guide the management of koalas.

How well does the model predict quality of habitat?

The field validation showed that the model is a reliable predictor of both koala occupancy and habitat quality. Field validation of the model output demonstrated a linear increase in estimated koala occupancy with higher model output values. Similarly, the model output was correlated positively with the site-based habitat quality index.

The model output also provided a better fit to estimated koala occupancy than the site-based habitat quality index, probably because the model considers many environmental variables simultaneously, rather than just browse species.

What are the variables used in the model and how were they chosen?

The model uses 14 predictor variables that reflect vegetation productivity, soils, forest type, topography, climate and frequency of wildfire. These variables were chosen for their potential influence on koala habitat suitability, as well as their robustness as data-layers for modelling. The full list of variables is in the report (PDF 4.2MB).

Why have some layers been excluded?

A total of 30 variables were considered for their potential influence on koala habitat suitability. Some variables were ultimately removed because either they were highly correlated with other variables (e.g. an index of primary productivity (NDVI) was correlated with Foliage Projective Cover, so NDVI was removed to avoid bias), or because they did not make ecological sense (e.g. areas with greater Total Nitrogen were indicated as poorer quality habitat. This is counter-intuitive and most likely due to the effect of agricultural land being excluded from the model).

Why do the pilot maps and model show differences in habitat quality for the same site?

The koala mapping program explored different approaches to mapping koala habitat. Due to the difference in aims, methodologies and scales of the two approaches, variations in the model output and the pilot maps are not unexpected.

The pilot project mapped habitat classes, based on likely proportion of koala feed trees, using only vegetation mapping (Plant Community Type undertaken specifically for this project). The Model maps predicted habitat suitability using a range of environmental variables which have been shown to influence habitat suitability, in addition to vegetation mapping. The range of variables used in the model were shown to be significantly correlated with koala occupancy and are available for the entire study area.

Why does the model say a particular area is low quality habitat, when I have seen koalas there?

Koala home ranges vary from five to 50 hectares, depending on habitat quality and the presence of other dominant adult koalas. Koalas also wander over very large distances (up to 20 kilometres) and can sometimes be seen in areas of low quality habitat. Low quality habitat is less likely to support resident koala populations, but can be important for movement and dispersal between areas of high quality habitat. High quality habitat is expected to be more important for supporting breeding koalas.

How was the model validated?

The model was field validated in two ways using ground-truth data collected at 65 sites across NSW north coast (this is a statistically significant sample size).

First, the model was validated using koala occupancy data that was collected using koala pellet searches and a novel approach involving acoustic recording devices. From this extensive field work (comprising more than 400 nights of recordings), a 'probability of koala occupancy' was calculated and found to positively correlate with modelled koala habitat quality (i.e. koalas were more likely to be found in modelled high habitat quality areas).

Secondly, the model was validated using a site habitat quality index which was based on the size and diversity of koala browse trees present at each ground-truth site. The validation showed that a positive correlation between site habitat quality and the model outputs (i.e. areas that were identified as high quality in the field were also modelled as high quality).

In addition, the model was validated across the entire study area using over 3000 koala records held in the NSW BioNet, which had not been used in the production of the model. This process showed a high concentration of Koala records in areas the model predicted as high quality and very few records in areas the model predicted to be poor quality.

Has the model been reviewed by koala experts?

The model was developed and validated by a team of ecologists and modellers in the Department of Industry (DoI) - Lands Forest Science Unit with assistance from external consultants. Floristic associations in the vegetation layer was coded for koala suitability by Forestry Corporation of NSW and reviewed by the Office of Environment and Heritage (OEH). The model was reviewed at a number of stages by koala experts and forest ecologists from NSW EPA, OEH, DoI as well as independent experts.

How will the model be used?

The EPA will use the outputs of the koala mapping program, including the model, to inform the development of improved koala identification and protection requirements in both the new coastal Integrated Forestry Operations Approvals and the review of the Private Native Forestry Code of Practice.

Page last updated: 03 May 2017