Scientists hope the belated listing of fires as a threat to forest species can stop the destructive use of hazard-reduction burning. By Karen Middleton.
The case against prescribed burning to fight bushfires
For 15 years, as bushfires ravaged Australia’s summers, scientists urged successive federal governments to officially acknowledge fire as a key threat to the plants and animals living in the nation’s forests.
But in all that time, even after Victoria’s 2009 Black Saturday disaster and the catastrophic fires of 2019-20 in New South Wales, which a 2020 University of Sydney study found harmed three billion animals, ministers have not done so – until this year.
A month before the May federal election, the then federal Environment minister Sussan Ley added fires that damage biodiversity to the “key threatening processes” listed under federal environmental law.
Ley’s decision means fire joins 21 other listed processes under the Environment Protection and Biodiversity Conservation Act, which include land-clearing, predation, and losses due to invasive species. A process qualifies if it threatens multiple species. The fire threat is linked to the impact of climate change and the threat from introduced species that can then invade. It was the first such listing in eight years.
The listing is not restricted to bushfires. It covers any fires that harm biodiversity – including those lit trying to stop bushfires in the first place.
Listing precedes an optional national threat abatement plan, which new Environment Minister Tanya Plibersek would need to authorise in conjunction with the states and territories, requiring that fire management strategies don’t jeopardise biodiversity.
Some fire scientists hope this amplifies the alarm they have sounded for years: that the most widely accepted prevention tool – hazard-reduction burning – is rarely helping and often making things worse.
“We’ve been undermining the natural processes that made forest resistant to fire,” says fire behaviour scientist Philip Zylstra, an adjunct associate professor at both Curtin University and the University of Wollongong. “We’ve kind of been breaking the system.”
Zylstra and his colleagues have found that hazard-reduction burning, also known as prescribed burning, is only effective in limited circumstances and for a relatively short time.
In peer-reviewed research published internationally, Zylstra has established that much large-scale burning is achieving the opposite of its intent. Rather than lessening the likelihood of future infernos, it is making forests more flammable and increasing the risk.
The scientists have found that while prescribed burning can have a positive short-term, suppressive effect, in some cases for up to seven years, that is not always the case, and the risk increases dramatically for the next few decades, before decreasing again over time.
In other words, the oldest, most undisturbed forests are least likely to burn.
Zylstra says fire prevention strategies need to abandon the accepted wisdom around large-scale prescribed burning and instead catch and attack fires when they are small: “It requires a change in thinking.”
He warns that the approach requires switching budgetary focus from lighting fires to fighting them. It also requires leaving forests alone. “It’s very emotive because burning feels like you’re doing something and you can see results straight after, rather than saying ‘just wait another decade and it will self-thin’.”
Zylstra says living plants determine fire spread. Whether plants accelerate or slow fire depends on the kinds of plants and the gaps between them. Burning encourages plants to grow back thicker initially because fire stimulates germination, light accesses the soil surface and ash adds nutrients. A thinned canopy lets in the wind and the foliage thickens closer to the ground, igniting more easily. New growth still burns. In fact, because it’s thicker and lower, with less overhead, it burns faster.
But public inquiries held in the wake of bushfires have largely ignored his and others’ findings. “There’s equal weight given to the opinion of a random angry person, instead of someone who’s gone out and actually measured things,” Zylstra says. “We have a mindset that we have to step in and change the country to what we want. It means that anybody who says ‘no, no, just leave it alone’, even if they’ve got evidence on their side, gets ignored.”
Zylstra conveyed his findings to the NSW Bushfire Inquiry in 2020. His submission noted that more prescribed burning had occurred during the previous decade in NSW national parks than in any decade before, and more than double the rate of burning in the preceding 10 years.
“It is apparent that the most extreme fire season coincided with the greatest amount of prescribed burning,” Zylstra wrote.
He noted that the notorious Gospers Mountain fire, north-west of Sydney, had covered an area burnt six years earlier, and the Werri Berri fire near Bemboka had “passed unhindered” through an area burnt in the winter of 2018, in a prescribed burn that escaped and destroyed homes.
“An analysis of fire severity for NSW found that wildfires burned through almost all recent prescribed burns in the state,” Zylstra wrote, “indicating that for the vast majority of cases, these provided no material assistance in containing fires.”
Rural Fire Service firefighters also reported areas burning again. “Our members have referred to numerous instances of fires burning, at a pace that made their control impossible, through areas that had been burnt no less than 12 months prior,” the Rural Fire Service Association wrote in its submission to the inquiry. “This was common both in areas that had been treated by hazard reduction burns and also those burnt by bushfires during the previous season.”
Zylstra published further research in the Environmental Research Letters journal earlier this year, with ecophysiologist Professor Don Bradshaw of the University of Western Australia and forest ecologist Professor David Lindenmayer of the Australian National University.
Lindenmayer says the burning orthodoxy is not always based on peer-reviewed science. “Prescribed burning is one of those things that has surprisingly little robust information to support it,” he says.
He argues that fire managers are often more focused on per-hectare burning targets than whether they help to preserve life and property.
Some research has found prescribed burning can be effective for a short time, on urban fringes close to property. But he says this is often not what’s being done.
“Here you’re burning to hit a target,” he says. “So you burn remote places that are far away when, to have an effect, you’ve got to burn very close. The forest then regenerates, and it comes into that high-flammability stage.”
He says burning frequently becomes crucial to keep the forest in its early stage and reduce risk.
Indigenous burning practices, often described as “cool burning”, are more effective and different to mass-area hazard reduction.
Wiradjuri man and Indigenous ambassador for the Invasive Species Council, Richard Swain, who is based in the NSW Monaro region, says much of the traditional Indigenous knowledge – involving burning in small areas more lightly and frequently, highly contingent on weather conditions and other circumstances – has been lost in southern Australia.
“I believe that the landscape has modified to the point where cool burning may be appropriate in some areas,” Swain says. “But it also needs to go hand in hand with the best of regenerative science and monitoring what we are doing.”
Swain would like to see as much effort put into bringing water back into the landscape as into fire prevention.
David Lindenmayer and colleagues at ANU have designed an integrated system to reduce fire risk by leaving the forests to age and self-thin, while attacking bushfires early, using satellite technology to pinpoint outbreaks and drones to assess and then drop water on them.
The proponents estimate it would cost $40 million to develop the system, a fraction of what insurance costs in fire-prone areas, which could also be marketed to other countries. They say with wildfires driven extensively by climate and weather, prescribed burning may not work and early, urgent suppression is required.
But when the proposal was put to the previous government, it got nowhere.
Lindenmayer warns that prescribed burning is “now an industry”.
“It’s lots of people in uniforms and hats out there burning in these areas,” he says. “We need to make sure our prescribed burning moves quickly with the new science.”
Another of Zylstra’s collaborators, botanist Professor Kingsley Dixon of Western Australia’s Curtin University, shares that view. “The mantra is burn or be burnt,” Dixon says. “Clearly, it’s not that simple.”
Dixon is a member of the independent Threatened Species Scientific Committee, which prepares listing advice for the minister. After so many of her predecessors left the 2007 fire nomination for a “key threatening process” unresolved, he acknowledges Sussan Ley’s decision to sign it upon receiving updated advice. “It is critical,” he says of its confirmation that burning must be done the right way. “Without that approach, species and ecosystems will be lost.”
Sussan Ley says the 2019-20 bushfires prompted her to complete the stalled process. “I am very proud I was able to finalise what I consider to be an important scientific assessment,” she tells The Saturday Paper. “I made sure it was finalised in 18 months, which was something that five previous Environment ministers were unable to do.”
But the listing itself will have little impact without a threat abatement plan. New minister Tanya Plibersek has not yet committed to producing one.
A spokesperson for Plibersek says the recent string of catastrophic bushfires has put a severe toll on the environment, on human life and on property.
“The minister will be working with other ministers to consider the best way to collaboratively manage the risks of future disaster events, across all levels of government.”
Although there is a growing body of research challenging prescribed burning, the work of these scientists has enraged some in the firefighting and fire-science community, who argue that reducing fuel loads must logically reduce flammability.
“That’s the thing about science,” Zylstra says. “To do things better, you’ve got to say that what we’re doing is not working.”
Zylstra traces what he calls the “myth-making” to events such as the Dwellingup fire in Western Australia in the 1960s, the narrative around which overlooked that it covered recently deliberately burnt ground.
Before that, it had been accepted that forest “disturbance” through fire, logging, land-clearing and other methods of artificially thinning the undergrowth was part of the problem.
In his report on Victoria’s 1939 bushfires, royal commissioner Leonard Stretton noted the difference in flammability before settlement and after. He said that since colonisation burning practices to clear scrub had broken down “the balance of nature” and began a “cycle of destruction which cannot be arrested in our day”.
Stretton expressed in 1939 what 21st century science confirms.
“The scrub grew and flourished,” he wrote. “Fire was used to clear it. The scrub grew faster and thicker. Bushfires caused by the careless or designing hand of man ravaged the forests; the canopy was impaired, more scrub grew and prospered, and again the cleansing agent, fire, was used. And so today, in places where our forefathers rode, driving their herds and flocks before them, the wombat and the wallaby are hard put to it, to find passage through the bush.”
Eighty-three years on, the countless creatures exposed to fires are not just struggling for passage, they are battling to survive at all.
This article was first published in the print edition of The Saturday Paper on July 16, 2022 as "Fighting fire".
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