What the evidence says about bushfire risk in Australia’s forests.
Concerns that timber harvesting makes native forests more flammable, and more prone to bushfire, have become prominent in media and policy debate. The evidence behind these claims is contested.
The studies most often cited examined one forest type, in one part of the country, and measured one thing — fire severity. Their findings are often communicated as though they apply to all forests. They do not.
This means a claim drawn from a small, specific set of studies is being applied far more widely than the evidence allows.
Why the words we use matter
Much of the confusion stems from terminology. Five terms are often used as if they mean the same thing. They do not — and each requires a different method to study.
- Bushfire-prone – a planning term used to zone land that can burn. It covers all native forests, whether or not harvesting occurs. It is a policy label, not a measure of how a forest behaves.
- Fire intensity – the heat released along a fire front. It rises with the amount, dryness and arrangement of fuel.
- Forest flammability – how easily vegetation ignites, and how readily and fiercely it burns.
- Fire severity – the effect of a fire on the landscape, measured by how much vegetation is consumed or canopy killed.
- Fire risk – the likelihood of a fire starting and spreading, and the consequences if it does.
The studies claiming that timber harvesting raises flammability and landscape fire risk did not measure flammability, intensity or risk. They measured fire severity. The terms are not interchangeable.
The evidence comes from one forest type
- The research behind these claims studied clearfelling in tall, wet eucalypt forests in south-eastern Australia and Tasmania.
- That forest type makes up less than 2% of Australia’s forested area.
- The relationships between forest age, management history and fire severity do not hold consistently from one forest type to the next.
Different forms of harvesting produce very different outcomes on the ground. Reducing that to a single rule — that harvesting always increases fire risk — is not supported by the evidence.
- At a single site, recently harvested or regrowth forest can burn at higher severity than nearby mature forest, because the trees are shorter and denser and flames reach the canopy more easily.
- This pattern does not always hold. One study found that clear-felled, regrowing areas had a lower probability of bushfire for 20 years and a lower risk of high-severity fire for several decades because fuel built up slowly.
Site-level severity and landscape-wide fire risk are not the same thing. There is no clear evidence that higher severity at a harvested site translates into higher fire risk across a landscape.
When fire weather turns extreme, severity is governed by weather far more than by fuel or forest age.
- In Victoria’s 2003 alpine fires, severity and extent were driven almost entirely by weather, slope, aspect, fuel, atmospheric stability and the scale of the fire.
- In the 2019–20 fires across south-east Australia, extreme weather and topography were the dominant drivers. Past disturbance — whether harvesting or earlier burning — was of low importance.
- After the 2009 Victorian fires, analysis found no evidence that post-logging mountain ash regrowth burned more severely than forest more than 70 years old.
Across multiple severe fires, the pattern holds: weather and topography set the scale and severity of the burn, not the management history of the forest.
State and Commonwealth inquiries after the 2019–20 fires looked for a link between timber harvesting and the severity of those fires. They did not find one at the landscape scale.
- In New South Wales, a greater share of protected National Park burned at high severity than State forest available for timber production. There was no clear sign that 35 years of harvesting had shaped severity at a landscape scale.
- In Victoria, the proportion of forest burned at high severity was essentially the same in State Forest open to harvesting and in National Park, where harvesting is excluded.
Where harvested and conservation tenures burned side by side in the same fires, the difference in high-severity fire between them was minor or absent.
It is often said that old-growth forests rarely burn at high severity. Large areas of it have.
- In 1939, fire killed 70% of the old-growth wet forests in Melbourne’s water catchments, where harvesting is not allowed, converting them to young regrowth.
- In the 2019–20 Victorian fires, about 40,800 hectares of old-growth forest burned at high severity — around two-thirds of it inside conservation reserves where harvesting is excluded.
Fire effects across forests of different ages come down to many factors. They are not explained by a simple split in which regrowth is flammable and old forest is not.
There is no clear evidence that it does.
- During the 2019–20 NSW fires, 60% of the largest fires started in National Parks, where harvesting does not occur. Just 6% started in State Forest, where it may.
- Tasmania’s 2019 Riveaux Road fire began inside a World Heritage Area before spreading east into multiple-use forest.
Harvesting roads can create chances for human ignition. Yet across the 2019–20 fires, lightning-caused fires burned six times the area of fires started by people.
Why it matters
At the landscape scale, fire weather and topography are the main drivers of high-severity fire. Harvesting, stand age and land tenure have comparatively minor effects. At a site scale, young forest can burn more severely than adjacent mature forest, mainly because it is shorter and denser. But large areas of old forest, including forest inside conservation reserves, are also being severely burned.
The claim that timber harvesting increases the flammability of Australia’s forests is misleading. It rests on incorrect use of fire terminology, and on selective use of site-scale severity data that does not match the findings of landscape-wide studies.
For Australia, consistent use of fire terminology, careful reading of the evidence, and clear distinctions between site-scale and landscape-scale findings are vital to ensure debate is grounded in what the science actually shows.