a century before human-driven climate change began
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Six researchers carried coring equipment through recently burnt forest to reach Purghagoolah, a lake in Croajingolong National Park.
The park in East Gippsland ranks among south-eastern Australia's most fire-prone forests.
The team set out to reconstruct vegetation, fire and erosion across the past 1,000 years.[4]
The 2019-20 Black Summer fires burnt more than 1.5 million hectares in Victoria and killed five people.
That season prompted the study.
Researchers worked with several Aboriginal communities, focusing on wetlands, lakes and forests.[5]
Purghagoolah, or Lake Elusive, covers about 40 hectares and reaches 21 metres deep. The lake sits in Gippsland, Victoria, on Gunaikurnai Country. Researchers took the core from the lake's deepest point.[6]
The team extracted a sediment core, a cylinder of lake-bed mud, on 9 February 2021. Each layer records one slice of time. Dating with lead-210 and radiocarbon places the core between about 844 and 2021 CE.[6]
Pollen grains reveal which plants grew near the lake. Charcoal particles record fire regimes, the pattern of how often and how intensely fires burn. Together these proxies, indirect measures that sediment retains, trace vegetation and fire through time.[1]
Infrared analysis of the charcoal added fire temperature to the record. Researchers matched chemical signatures that plants leave at different burning temperatures against the sediment. Cool cultural fires gave way to hot wildfires after colonisation, with high-temperature charcoal rising from the mid-nineteenth century.[3][7]
The Gunaikurnai Land and Waters Aboriginal Corporation represents traditional owners of the area. Researchers worked with the corporation to reconstruct 1,000 years of vegetation and fire history. Lead author Michael-Shawn Fletcher describes the pre-colonial landscape as cared for and managed.[1]
The corporation co-authored the paper and provided cultural authority for research on Gunaikurnai Country. It contributed knowledge of Country that shaped the study design and the reading of the record. It also reviewed and approved the manuscript before publication.[2]
Gunaikurnai elder Uncle Russell Mullett says his ancestors lived with towera, meaning fire, as part of daily life. Country turns extremely dangerous for people, animals and plants once towera stops, he says. The study supplies firm scientific evidence to support towera land management initiatives, in his view.[5]
Change-point analysis, a statistical method that detects abrupt shifts in a time series, tested when the landscape changed. Across 5,000 reconstructions, the mean break in eucalypt cover sits at 1867 CE. That timing lies within the period of colonial frontier violence that removed the Gunaikurnai from Country.[2]
Historical evidence shows the Gunaikurnai regularly burnt the land until the British removed them violently in the mid-nineteenth century. For 800 years before that, the record shows open woodland of grasses and few trees. Woody shrubs then spread across the area.[7]
Fletcher says the removal of the Gunaikurnai changed the balance of trees and shrubs and drove more fires. He dates the shift to a land use change that preceded climate change by more than a century. Hot fires then triggered eucalypt recruitment, the establishment of new seedlings, and the eucalypts drove further fire.[1]
Eucalypt cover rose fourfold, and open woodland became forest. Fire temperatures climbed and soil erosion increased as the landscape changed. Those changes preceded human-caused warming, so land use set the stage for the climate-driven fires.[2]
Researchers call this cycle a catastrophic wildfire loop. Each hot fire produces dense regrowth that primes the next blaze. Fletcher says climate now largely drives the loop, though the initial change came from land use.[1][5]
First Nations people practise cultural burning, using low-temperature fire to keep land safe and productive. Communities still apply it in parts of Australia today.[1]
Practitioners follow a responsive right time, right place approach. Government agencies run prescribed hazard reduction burns, planned fires that cut fuel, and those methods differ. The research gives scientific evidence for the value of cultural burning, Fletcher says.[1]
The paper concludes that restoring cultural burning and supporting Traditional Owners is essential to mitigating wildfire risk. Croajingolong has long carried a pristine wilderness label, yet it is among south-eastern Australia's most repeatedly burnt areas. Fletcher says the forest people protect there is a product of colonisation, and that legacy now imperils its survival.[3]
Fletcher hopes the findings open a conversation about possibilities for a new future. In that future, communities could start getting control of the catastrophic fire problem. Integrating Indigenous knowledge into modern fire management underpins that prospect, he says.[1]
University of Tasmania fire scientist David Bowman, who sits outside the author team, calls the research significant. He says the research adds to a growing realisation about the legacy of lost Indigenous fire management. He calls long-term records critically important for tracing how fire regimes respond to climate.[1]
One big question in wildfire science, Bowman says, is how unprecedented current fire events are. Introduced animals and, in places, introduced plants have worsened the changes, though lost traditional fire management remains very significant. He calls the research a pipe opener for a conversation about managing landscapes as the fire crisis worsens.[1]
Bowman calls the evidence very convincing that the loss of Indigenous fire management drove drastic changes in fire regimes. He wants trials of thinning for overgrown forests and cultural burning, with substantial ongoing government investment. Professor Trent Penman of the University of Melbourne says fire predictions have underestimated human influences.[4]
Victoria's pre-1750 vegetation map models potential natural vegetation from climate and soils, then adds historical records and explorer accounts. At Purghagoolah that map and the 2005 map look effectively identical, although pollen shows open woodland. The authors say the national baseline wrongly treats post-colonial vegetation as the natural reference condition.[2]
The Purghagoolah record shows colonial land use loaded south-east Australian forests with fuel long before warming began. Climate change now amplifies a vulnerability that official baselines treat as natural.
Vegetation baselines and the wilderness label for Croajingolong rest on assumptions that this evidence challenges. Agencies that manage these forests carry responsibility for testing those assumptions against the sediment record.
Traditional Owners hold knowledge that kept this landscape stable for centuries. Governments now face the task of funding Traditional Owner-led fire management, a step that scientists such as Bowman consider urgent. Accountability for the fire crisis therefore extends beyond emissions to the land management decisions that shaped these forests.
1. ‘Catastrophic wildfire loop’ created after colonisation left parts of Australia more at risk from bushfires, study finds. Guardian Australia report on the Nature study, with comments from lead author Michael-Shawn Fletcher and fire scientist David Bowman.
2. Australia’s current wildfire crisis linked to colonial land-use change. Peer-reviewed Nature paper by Fletcher and colleagues, including the Gunaikurnai Land and Waters Aboriginal Corporation, reconstructing 1,000 years of vegetation and fire at Purghagoolah.
3. Australia’s bushfire crisis linked to colonial land-use change. University of Melbourne media release summarising the sediment findings, the fourfold eucalypt surge and the infrared charcoal analysis.
4. BRIEFING ALERT: Australia’s current bushfire crisis linked to British colonisation. Australian Science Media Centre briefing with expert reaction from Professor David Bowman and Professor Trent Penman.
5. Indigenous cultural burning could break catastrophic bushfire cycle, study finds. Australian Associated Press report, republished by Dubbo Photo News, quoting Fletcher and Gunaikurnai elder Uncle Russell Mullett on the study and towera.
6. Multiproxy palaeoecological record from Purghagoolah (Lake Elusive), Gippsland, southeastern Australia. PANGAEA dataset by Fletcher and Romano documenting the core site, collection date and age range.
7. Australia’s bush fires got worse after British colonization: this is why. Nature news report explaining the pollen and charcoal reconstruction and the loss of Indigenous burning.
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