‘Catastrophic wildfire loop’ created after colonisation left parts of Australia more at risk from bushfires, study finds

The colonization of Australia led to a significant increase in wildfire danger, according to a study analyzing 1,000 years of lake sediment. The transformation of the landscape into forests with high density of gum trees was a direct result of colonization and land-use change, not just climate change, says Michael-Shawn Fletcher from the University of Melbourne in Australia.

The arrival of the British in 200 years ago caused a sudden shift in sediment deposition in Purghagoolah Lake, located in Croajingolong National Park in southeastern Australia. Prior to colonization, Indigenous GunaiKurnai people managed the landscape through cultural burning practices for thousands of years, maintaining open woodland vegetation with a tree cover of around 10%.

However, after the arrival of the British and the removal of Indigenous people and their cultural burning practices, shrub species rapidly took over and bushfires became hotter. This led to an increase in eucalypt cover to around 40% and a loop of hot, catastrophic fires. Analysis from other sites in southeastern Australia shows similar trends, with up to six times more eucalyptus trees in the modern period compared to the past.

Increasing tree density creates conditions where flames can spread more easily, while shrub growth on the forest floor allows fire to "ladder" up to the crown of the forest. Fletcher argues that the "cult of the tree" is causing economic loss and national trauma, and that dense forests don't hold carbon securely due to their high ignition risk.

He suggests that returning to a regime of widespread cultural burning could help reduce the intensity and impact of wildfires.