The colonisation of Australia transformed much of its landscape into forests with a high density of gum trees, and this led to the country’s cycles of dangerous wildfires, an analysis of 1000 years’ worth of lake sediment reveals. He and his colleagues extracted a metre-long core, representing a millennium of sediment deposition, from the bed of Purghagoolah, also known as Lake Elusive, in Croajingolong National Park in south-eastern Australia. The lake is surrounded by forest and has a catchment area of around 10,000 square kilometres.
It is an area where people are largely excluded and nature is unimpeded by active management. The researchers examined the core at 0.5-centimetre intervals and found that the sediment deposition suddenly changed 200 years ago. Prior to the arrival of the British, the local Indigenous community, the GunaiKurnai, had managed the landscape, primarily through cultural burning practices, for thousands of years.
Pollen falling into the lake was reflective of open woodland vegetation, with a tree cover of around 10 per cent for 800 years, right up until the local colonisation. But between 1830 and 1860, European settlers massacred and forcibly removed the Indigenous population and cultural burning ceased. Early settlers to the region reported being able to easily move herds of cattle through the area, which was then much more open woodland.
Shrub species swiftly moved in and, as charcoal evidence demonstrated, bushfires became hotter, which in turn led to thicker regeneration of eucalypt species and tree cover increased to around 40 per cent. When tree density increases, the canopy begins to connect, creating conditions where flames can spread more easily, while shrub growth on the forest floor means fire can “ladder” up to the crown of the forest. Although climate change will continue to drive wildfires, a return to a regime of widespread cultural burning would help to reduce their intensity and impact, says Fletcher.
He argues that the “cult of the tree” is having devastating consequences in terms of economic loss and national trauma. Also, these much denser forests don’t hold carbon securely because they are so much more prone to igniting. Australia is getting free electricity – will other countries follow?
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