The Natural Resources Commission commissioned the project to strengthen the evidence base for modelling and managing hollow‑bearing trees in NSW State forests. The project is referenced in the Forest health - Coastal IFOA Monitoring Program.
Project overview
Researchers at the Australian National University, led by Professor Philip Gibbons, delivered research and recommendations to improve hollow‑simulation modelling for State forests. This modelling predicts how many trees with hollows are perpetuated under current Coastal IFOA conditions.
Working with modellers at Forestry Corporation of NSW (FCNSW), the researchers used the Forest Resource and Management Evaluation System (FRAMES) and a hollow suitability model to predict how hollow‑bearing trees persist and recruit under a range of scenarios. That research recommended a pilot study to collect more field data and check how well the broad, landscape predictions match what is observed at local sites.
Field surveys in 2025 collected more data to test the predictions. Professor Gibbons’ methods paper explains how FRAMES was used for modelling hollow persistence, and his 2026 report compares predictions with field observations.
Key documents
- Research note - Field testing of hollow-bearing tree models (PDF 532.73KB) (June 2026)
- Report - Modelling hollow-bearing trees (PDF 783KB) (May 2026)
Modelling how many hollow-bearing trees occur and how many are suitable for hollow-dependent fauna under the Coastal IFOA. A pilot study in the Coffs Harbour Timber Supply Zone. - Research note - New method to model hollow-bearing trees in coastal NSW forests (PDF 713.75KB) (December 2024)
- Report - Perpetuating trees with hollows under the CIFOA (PDF 776.05KB) (February 2024)
- Report - Predicting trees containing hollows suitable for vertebrate fauna in NSW forests (PDF 409.35KB) (March 2023)
Key findings
Professor Gibbons recommends revising the Coastal IFOA hollow-bearing tree definition so that retained trees are more likely to provide suitable habitat for fauna. He also advised that tree models should be further developed before they can confidently be used to predict how hollow bearing trees retained during harvesting operations persist in the long-term.
The research found:
- The current Coastal IFOA definition does not reliably identify the trees that provide the best habitat for hollow‑dependent fauna
- A revised definition based on simple indicators - such as species, diameter at breast height and visible hollows - would be clearer and easier to apply in the field
- Around 50% of trees with hollows visible from the ground contain hollows suitable for vertebrate fauna.
- Hollow‑bearing trees kept in the net harvest area (outside retention clumps) make up about 35% of all trees with visible hollows across the pilot study area.
- Improved tree models are needed to better predict the number of hollow‑bearing trees and the number of trees with hollows suitable for occupancy.
- In the Coffs Harbour pilot area, the number of hollow-bearing trees identified in the field did not match what existing models predicted. The models overpredicted the number of hollow-bearing trees in harvested areas and underpredicted the number in harvesting exclusions.
Recommendations being implemented
Several recommendations from the research have been implemented by the monitoring program:
- Professor Gibbons collected more tree‑hollow data in the Coffs Harbour Timber Zone pilot area and compared field observations with model predictions.
- The University of Melbourne developed models that predict fire impacts on hollow‑bearing trees in coastal NSW State forests.
- FCNSW has modified forest inventory procedures to collect additional hollow data in inventory plots.
The findings from this study could be considered by the Environment Protection Authority and Forestry Corporation of NSW as part of ongoing improvements to the Coastal IFOA.