For at least 11,000 years, and likely for much longer, Indigenous Australians deliberately burned forest understories, lowering the risk of catastrophic fire. The arrival of Europeans in the late 18th century brought an end to that age-old practice, and as a result, forests are now ripe for “mega-fires,” new research claims.
“These high-intensity fires were not a thing during the time of Indigenous occupation of Australia but became a thing afterwards.”
The study, led by Michela Mariani of the University of Nottingham and published in Science, sought to understand why the fires of the 2019–2020 “Black Summer,” during which more than 24 million hectares of Australia’s forests burned, were so devastating.
“There is evidence that these high-intensity fires were not a thing during the time of Indigenous occupation of Australia but became a thing afterwards,” Mariani said.
Core Values
The team analyzed core samples from lake beds and wetlands throughout southeastern Australia. These cores held pollen grains and evidence of a changing climate over a 130,000-year period.
When analyzing pollen, the team focused on shrub species that form a forest understory. These plants provide “ladder” fuel, allowing fires to climb into the canopy. This is a relatively new approach, said study coauthor Haidee Cadd of the University of Wollongong.
“A lot of Australian shrub species don’t preserve the pollen that well in record,” she said. “So often it’s been overlooked, and we’ve missed that connection that exists between the shrub layer and high fire danger.”
For tens of thousands of years, the density of shrubs fluctuated in response to climate, the team found.
“Clearly it’s not climate alone that’s driving those changes.”
Then, about 6,000 years ago, a decoupling occurred. After a wet peak, the climate returned to dry, stable conditions, yet the vegetation didn’t return to its previous level. Instead, for the rest of the Holocene epoch, shrub cover steadily declined.
“Clearly it’s not climate alone that’s driving those changes,” Mariani said. It was around this time that human occupation of the area rose.
Also contained in the core samples were charcoal remains from ancient forest fires. The abundance of these pieces dwindled after 6,000 years ago, suggesting that fires throughout this period were of lower intensity.
The results indicate sustained, deliberate burning by humans living in the area, Cadd said. “It’s one of the first times that we’ve actually been able to show with empirical data that Indigenous Australians were able to manage large-scale fire events.”
Deadly Impact
Pyrogeographer David Bowman of the University of Tasmania, a coauthor of the study, called analyzing ladder fuel “a really seminal idea.” The findings put colonization in the spotlight, he said. “What happened when we blew up a sustainable fire management system 250 years ago?”
The research builds on a 2022 study, also led by Mariani, that showed how shrub density skyrocketed during the postcolonial period.
After Europeans arrived, large areas of forest were cleared for farmland. Fearing fire, colonists actively suppressed it. This is the reason Australia’s forests are now tinderboxes primed to ignite, Mariana and her colleague argued.
Ecologist David Lindenmayer of Australian National University, who was not involved in the study, said that though the team’s evidence was “compelling…I think the mechanism they’re talking about is wrong.”
Rather than fire suppression, Lindenmayer countered, it might have been postcolonial forest clearing and disturbance that promoted the growth of flammable shrubs, a phenomenon he terms “disturbance-stimulated flammability.”
He also said that Aboriginal cultural burning was likely not as widespread in southeastern Australia as the research suggests. First Nations people burned forest undergrowth to promote plant growth and to clear paths for movement. “All of those kinds of fire are actually very limited in their extent,” he said, adding, “there were substantial areas that weren’t burned.”
A Global Story
The study took “a good approach to identify how Indigenous regimes of burning have shaped vegetation communities globally,” said Don Hankins, a Plains Miwok fire researcher at California State University Chico who works with Indigenous groups in both North America and northern Australia.
Kira Hoffman, a fire ecologist with the University of British Columbia, said she was “not surprised” by the study’s findings because they mirror the North American experience. “Our society has a deep fear of fire,” she said, “because we have been really successful with Smokey Bear campaigns and telling kids that fire is dangerous.”
Heavy fuel loads in British Columbia forests, she said, have led to catastrophic fires. Neither Hoffman nor Hankins was involved in the Australian study.
Mariani and her colleagues advocate for a “wide-scale” return of traditional burning techniques. Geochemist Michael Bird of James Cook University agreed that the findings suggest a need to reimplement traditional fire management, although he cautioned that that “requires a significant change to vegetation structure that is likely to take a while to establish.” Bird was not involved in the study.
Lindenmayer said he has “really deep concerns” about promoting a return to cultural burning without fully understanding its complexities. Many animal species, he said, depend on the forest undergrowth for their survival. “I think we need to be fairly careful about simple recipes that could be wrong in some of these really important areas.”
- Please Note: This story was originally published by Bill Morris, (2025), Six thousand years of controlled burning, up in smoke?, Eos, 106, https://doi.org/10.1029/2025EO250006. Wood Central has shared the story under a Creative Commons Licence. CC BY-NC-ND 3.0. Except where otherwise noted, images are subject to copyright. Any reuse without express permission from the copyright owner is prohibited.
