Australian researchers have found hazard reduction burns and logging can make forests up to seven times more flammable.
Research from the Australian National University and Curtin University calls for a rethink of fire prevention strategies and forest management.
But some fire and forest authorities have expressed concerns and say planned burns are a proven tool when it comes to managing fires.
ANU Professor David Lindenmayer led the new study, which reviewed existing analyses of fire behaviour during Victoria's 2009 Black Saturday blazes, and the Black Summer fires that ravaged the east coast in 2019/20.
The study also looked at the fire histories of plantations and forests in other countries like Brazil, the USA and Spain.
"We found that places that had been long unburnt were the ones where fire severity was the lowest," says lead researcher David Lindenmayer, from ANU.
The scientists concluded the risk of high-severity fires can increase where forests are thinned, logged or where hazard reduction burns have been carried out.
"In some places that (hazard reduction) makes it up to seven times worse in terms of the risk of increased flammability."
In Australian eucalypt forests, the risk continued for several decades.
"Peak flammability often occurs in forests between 10 and 70 years after disturbance by logging or burning," the paper says.
"The things that we do in the forest now are still having effects decades and decades ahead," Prof Lindenmayer adds.
"Forests recovering from fire in the previous 10 to 32 years were three times more likely to experience full canopy scorch or crown burn than forests that had not experienced fire for at least 75 years," the paper says.
Prof Lindenmayer, who is considered a world expert in forest ecology, has previously come under fire from the logging industry over research that found logging elevates the risk of bushfires.
He's a published author and has contributed to 925 peer-reviewed international papers on forest ecology over the past 30 years.
Prof Lindenmayer says a rethink of broad-scale intervention is needed.
"We don't throw away prescribed burning, but we need to be much, much smarter about where we do it and why we're doing it and the kinds of vegetation that we're doing it in," he says.
Co-author Associate Professor Philip Zylstra, from Curtin University, says current thinking divorces fire behaviour from forest ecology.
“We know that old forests tend to be cooler, more moist and more sheltered. By limiting disturbance, forests can reach an appropriate age where they can be better protected from the increased frequency and severity of Australian bushfires.”
But NSW Rural Fire Service Commissioner Rob Rogers says the level of hazard reduction burning is already low, and reducing it would make little difference.
He says the Black Summer fires tore across 5.5 million hectares but in a busy year NSW authorities only deliberately burn about 200,000 hectares.
"We get thousands of fires every year - there's accidental escape, there's arson, there's lightning. Most of the fires are not hazard reductions, they are other factors.
"Hazard reduction compared to the whole landscape is just not that big. I can't see that making all these changes, I just don't think it's practicable."
Forestry Australia dismissed the findings, saying the consensus among bushfire scientists confirms prescribed burning is a key tool in managing bushfires.
"Reduced fuel levels in forests will reduce the severity of bushfires in all bar the most catastrophic fire weather conditions," says Tony Bartlett, the organisation's science policy advisor.
“Criticising prescribed burning is like dismissing the value of seat belts in cars because people still die in car accidents."
The peer reviewed research is published in the journal Biological Reviews.
