The Natural Resources Commission commissioned and oversaw the project to strengthen independent evidence on how forestry practices affect tree species composition and habitat values in NSW coastal State forests.
This project is referenced in the Forest health - Coastal IFOA Monitoring Program
Project overview
Researchers from the Forest Science Unit at the Department of Primary Industries and Regional Development assessed how tree species composition has changed over time in coastal State forests. Timber harvesting can change the abundance of different tree species, which can then affect habitat quality and food availability for wildlife that depend on them.
The researchers analysed permanent growth plot data collected by Forestry Corporation of NSW between 1979 and 2023. The work also assessed changes in key feed trees for koalas, greater gliders and yellow‑bellied gliders—such as tallowwood, grey gum and manna/ribbon gum—and important commercial species, including blackbutt and spotted gum.
Publications
- Research note: Investigating the effect of disturbance on tree species composition in coastal state forests (PDF 191.48KB) (July 2025)
- Technical report: The effect of timber harvesting and fire on tree species composition in eucalypt forests with a focus on arboreal marsupial feed trees (PDF 2.75MB) (May 2025)
Key findings
The research found that timber harvesting or fire alone generally have minor and short‑lived effects on tree species composition when measured by basal area.
Lower‑intensity, selective harvesting has less impact than more intensive harvesting or repeated disturbances.
The researchers found
- Timber harvesting or fire alone cause small and temporary changes in tree species composition (based on basal area).
- Many key feed tree species show similar short‑term responses, although the size and direction of change varies by species, region and harvest intensity.
- Harvesting does not significantly increase basal area for preferred commercial species.
- The changes observed are unlikely to pose a severe risk to arboreal marsupials, based on this study and the wider body of research on their habitat requirements.
Note: Data considerations
The researchers note several limitations that affect interpretation of the results:
- limited historic disturbance records
- limited measurements for some tree species
- changes in plot size over time
- fewer monitored plots outside the North Coast
- fewer plots remeasured after 2020
They recommend further work to improve understanding of habitat recovery and the influence of other disturbances and climate on long‑term tree species composition.