Hazard-reduction burning can make some ecosystems more "combustible" in future, experts have told the bushfire royal commission.
After an incendiary debate over whether a lack of prescribed burning had contributed to the fires which burnt more than 18 million hectares across Australia last summer, the Royal Commission into National Natural Disaster Arrangements heard while burns could help protect certain assets, they were not a one-size-fits-all solution.
University of Tasmania Professor of Environmental Change Biology, David Bowman said all fuel management approaches should be seen as "giant experiments that we're still evaluating".
"We can see benefits of fuel treatments, not only prescribed burning but also vegetation manipulation, defendable space around houses in close proximity to where people live," Professor Bowman said.
However the outcomes heavily depended on the environment.
"The sort of outcomes you get from prescribed burning in a tropical savanna are very different to the sort of outcome you would get in the southern forests of Tasmania where prescribed burning is extraordinarily limited and basically restricted to treeless swamps because the vegetation is too thick," Professor Bowman said.
Director of the University of Wollongong's Centre for Environmental Risk Management of Bushfires, Ross Bradstock said there was also a "window of effectiveness" for prescribed burns.
"Generally speaking it's around five to 10 years, [but] it is highly contingent on the weather conditions at the time in which a wildfire moves through a fuel-reduced area," Professor Bradstock said.
"So under the most dire weather conditions, such as a catastrophic fire danger index, the window of effectiveness of antecedent treatment may be extremely short, a year or so in terms of reducing some measurable level of reduction in fire intensity.
"Under benign weather conditions, it may be more of the order of five to 10 years. So we need to understand that effectiveness is contingent upon the circumstances when a fire - a bushfire or a wildfire encounters a fuel-reduced area."
Associate Professor Kevin Tolhurst from the University of Melbourne's Department of Forest and Ecosystem Science said in the case of the 2003 Canberra fires, a firebreak of kilometres worth of grazed paddocks was no match for the fire that came down from the mountains.
"I guess the elephant in the room still is the scale that fires can get to in the back country," Associate Professor Tolhurst said.
Professor Bowman also said doing burns in inappropriate areas could make them more "combustible" in future.
"As you manipulate or modify an environment to change fire behaviour ... one of the consequences of that can be that you change the fuel types, and therefore you change the risk profile. And that's - that can in some cases be a perverse outcome," Professor Bowman said.
"Inappropriate management could drive a system to become more combustible because for instance there is more fine fuel mass such as grass.
"That's why fire management is so complicated."
Professor Bowman said it people should avoid falling into the "trap" of assuming fuel management meant prescribed burning.
It could also mean thinning vegetation or creating defendable space near assets, he said.
Professor Bowman also shot down the idea of blanket hazard-reduction targets.
"Using simulation modelling in Tasmania, we're able to show that you get a much better benefit if you concentrate your fuel management around where your assets are," he said.
The commission also heard evidence of how unusual last fire season was.
The number of so-called "black swan" events where pyrocumulonimbus clouds developed during the fires, creating a fire storm, doubled last summer when compared to records stretching back over 30 years.
"Something happened this last summer which is truly extraordinary because what we would call statistically a black swan event, we saw a flock of black swans. That just shouldn't have happened," Professor Bowman said
Professor Bradstock said some of the areas that burnt over the summer were wet forests that ordinarily would not burn but had dried out due to the drought.
These areas burnt at "phenomenal intensities, potentially some of the highest intensities ever recorded on earth", Professor Bradstock said.
The royal commission continues on Wednesday, with NSW Rural Fire Chief Rob Rogers and ACT Emergency Services Commissioner Georgeina Whelan set to appear.