Tame the Flame

Many believe that cultural burning practices were being carried out by indigenous Australians to control the landscape long before European occupation. But there hasn’t been much hard evidence to support the idea. That is until researchers in Australia analyzed charcoal sediment from Lake Couridjah using infrared (FTIR) spectroscopy. By applying chemometrics and combining the results with local archaeological records, they found that cultural burning has been taking place in Australia for at least 10,000 years. 

“This was an exciting finding,” says Mark Constantine, Paleoecologist and Researcher at the Earth and Sustainability Science Research Centre in Sydney Australia, lead author of this study.

The research showed that fire intensity in the current interglacial period is significantly lower than it was in the one previous, despite having similar climate conditions and vegetation characteristics. The only difference was the presence of people during the present interglacial – suggesting that indigenous people were influencing the timing and frequency of bushfires. 

The researchers believe the findings about that past could help with developing mitigation strategies that could reduce the intensity of bushfires in the modern day too.

The study was the first in Australia to use chemometrics to assess changes in fire intensity over time. “If used more broadly, this method could model how bushfires are affected by climate change – allowing us to stay ahead of the field in fire management strategies,” says Constantine. 

Constantine prepared the charcoal samples without using oxidants, such as hydrogen peroxide, after discovering that those commonly used methods removed a significant proportion of charcoal formed at lower temperatures (below about 450°C). “This is important when considering all fires – including so-called ‘cool’ fires, which are thought to have been used by Indigenous peoples to reduce large bushfires,” he says. 

The samples were scanned with FTIR spectroscopy, and the spectra were compared with a lab-produced reference library using statistical modeling to identify and compare their chemical characteristics. Next, a charing intensity value is assigned to the data, which is a combination of maximum heat influx and time of exposure that formed the charcoal.

“There was a steep learning curve when applying chemometrics to this project,” says Constantine. “I decided to look at FTIR spectroscopy and chemometrics as application tools without complete understanding of their constituent parts. With further use and some very patient chemists at UNSW Chemistry, I gained greater understanding of their backgrounds and other application uses, which proved beneficial for this research.”

“I’d gladly jump at the chance to continue working with FTIR spectroscopy, especially with so few published studies covering this method of analysis,” says Constantine. “The next step for the research would be to focus on improving and expanding the model by using charcoal that has been produced through more advanced methods to better approximate bushfire conditions.” 

Constantine ends with a tempting invitation: “I’d like to welcome other analytical scientists who are interested in extending this research further to collaborate!”