More than 80 people gathered at the Mechanics Hall in Lakes Entrance last Saturday afternoon to hear fire behaviour scientist Dr Philip Zylstra challenge one of the most repeated ideas in Australian fire management: that the weight of leaf litter on the forest floor is what makes a bushfire dangerous.
Dr Zylstra, an Adjunct Associate Professor at Curtin University and a former remote area firefighter, told the audience the concept of “fuel load” did not originate from Australian science.
It came from United States pine forestry in the 1950s, where the primary objective was to clear undergrowth to harvest timber crops. It reached Australia through a forestry leaflet that was never peer-reviewed.
“He just gave us nine dots drawn in this leaflet, fitted a line to it and said that… if you double the amount of fuel, the weight of fuel on the ground, you double the rate of spread of a fire,” he said.
“You are not allowed on a fireground unless you can recite that scripture: double the fuel load, double the rate of spread.”
Dr Zylstra said that when researchers later attempted to verify the relationship, they could not find it.
“In the 1990s, Neil Burrows in WA very, very carefully replicated those experiments with the same type of leaf litter and everything, both in the lab and in the field. And he found there was no relationship at all. It didn’t matter what the fuel load was,” he said.
He noted that the state’s own field guide inadvertently makes the point.
“They’ve shown here, just with a really simple experiment, that if you crumple up a bit of newspaper you get a bigger flame than if it’s lying flat, because it’s not about the weight of the fuel, it’s about the structure. They’re aware of that.”
The same conclusion, he said, emerged from Australia’s largest experimental burn program.
“Project Vesta is the biggest set of experimental burns that have been done in Australia… the latest publication in 2022 laid it out very, very simply. It’s the height and the cover of the understorey,” Dr Zylstra said.
“That’s the state-of-the-art empirical fire behaviour model that all of the agencies pay lip service to. Nothing to do with the weight of leaf litter.”
Dead leaves produce small flames. Shrubs and dense regrowth produce the flames that carry fire into the treetops. In the Black Summer fires, Dr Zylstra told the audience, only 12 per cent of the burnt area experienced crown fire.
While a burn strips the ground bare and lowers fire risk for a short period, the forest responds with dense regrowth.
“This is not a layer of dead leaves. This is a forest composed of lives wanting to survive, and they fight back,” he said.
“Straight after they’ve been hit like that, you get this massive flush of dense growth, and as that shrub layer gets taller and denser, that flammability keeps going up and up and up, until you get to this sort of peak where even the shrub layer can ignite the trees. And that’s when you can get the crown fires.”
He said that regrowth acts as a ladder carrying fire into the canopy, persisting for decades until the understorey grows tall enough to thin itself naturally. Burning a forest does not leave it safer; it resets it to its most flammable stage.
Dr Zylstra pointed to a grazing family at Wulgulmerang in East Gippsland who kept records of nearly a century of burning their own country.
“Their conclusion was, yeah, we kind of stuffed that up. You can’t get through there anymore, it’s so dense,” he said.
“We made it dense by burning it. It doesn’t make it open, it makes it dense.”
He tested the pattern against mapped historical records, breaking every bushfire across more than one million hectares into one-hectare cells and analysing 65 million points. Fire risk is low immediately following a fire, rises steeply as the regrowth thickens, then falls away as the forest matures.
“The timing’s different, the intensity of that curve is different, but it’s always that same trend,” he said.
“We may be the cause of the problem, not the cure.”
HISTORICAL POLICY AND
MODERN RESPONSE
Dr Zylstra said his experience as a remote area firefighter first pushed him toward the research, because official models were sending crews to the wrong locations.
“It was telling us that this fire here was safe to get into and you could send fire crews in there because the fuel load was really low, and this place over here you’d have to stay away from… And so often it was exactly the wrong way around,” he said.
“So you’d miss an opportunity to put that fire out and contain it, and you’d put your fire crews at risk putting them in front of that fire.”
He traced current policy back to Judge Leonard Stretton’s 1939 Royal Commission into the Black Friday fires, which concluded that burning had begun a cycle of destruction that could not be arrested “in our day”.
“In our day. 1939. It’s not 1939 anymore,” Dr Zylstra said.
A Goongerah Environment Centre (GECO) spokesperson said that was the core message local residents took away from the session.
“Victoria has detection and suppression capability that did not exist in 1939. Catching a fire in the first hours is what stops it becoming a disaster, and that takes trained crews on standby, aircraft and eyes on the ground,” they said.
“The best available research on Australian house loss found that what most reliably protects a home is the vegetation within 40 metres of it. Beyond about three kilometres, burning made no measurable difference. So put the money where the houses are, and put the rest into rapid response.”
Agencies plan to burn 428,575 hectares across 260 planned burns in the DEECA Gippsland region between 2025 and 2028.
GECO is encouraging community members to join the Victorians for Nature campaign ahead of the state election, calling for an end to years of underinvestment in nature across Victoria.
“The science is not the bottleneck. The funding and the political will are,” the spokesperson said.
