Analysis of sediment cores taken from ancient lakes shows that Australia's indigenous peoples have been using fire to manage their environment for at least 11,000 years.

michael bird Researchers at James Cook University in Cairns, Australia, say their findings suggest that returning to indigenous regimes of more frequent but smaller fires could reduce the risk of catastrophic wildfires. This suggests that environmental management could be improved.

It has long been known that Australia's first people, who are thought to have lived on the continent for 65,000 years, carefully managed the landscape, using fire to make it easier to move around and hunt prey. . They also realized that this benefits some of the plants and animals they like and reduces the risk of more dangerous fires.

But how long this has been going on is difficult to establish, Bird said. That's because most waterways dry up completely during the annual dry season, destroying carbon in the sediment.

Girraween Lagoon, near Darwin in the Northern Territory, is a huge sinkhole that covers an area of ​​about 1 hectare and has remained permanently wet for at least 150,000 years. As the climate changed over the millennia, so did the vegetation around the sinkhole. “Girraween Lagoon has 150,000 years worth of sediment that has never dried out,” says Bird.

Bird and his colleagues were able to study three important indicators by analyzing sediment cores from the lagoon floor. It is a measure of the accumulation of fine charcoal particles, the proportion of burnt material in charred vegetation material, and the amount of different types of charcoal. Carbon that remains after combustion.

The first two indicators allow researchers to estimate the intensity of the fire, and the third indicates whether the fire was cold enough to leave traces of grass.

Before the arrival of humans, natural fires in the savanna of northern Australia were ignited by lightning strikes at the end of the dry season, when the vegetation and landscape were almost completely dry. This type of more intense fire burns biomass more completely, especially fine fuels such as grass and trash, leaving less grass uncharted.

Indigenous fires, on the other hand, burn more frequently, but with much lower heat, and their impact is confined to smaller areas and to the ground layer, promoting a mosaic of vegetation and helping to protect biodiversity.

Byrd said recent layers of the core show more frequent fires and clear evidence of grass that hasn't completely burned, indicating the fires are cooler. . This type of fire is very different from traditional natural fire patterns and is evidence of indigenous fire management, he says.

This signal can be seen in sediments that are at least 11,000 years old, but the study found that metrics for the proportion of grass and tree debris before that point have become difficult to study. Bird said there are signs of human fire starting 40,000 years ago, but the evidence is less clear.

“This means that savannahs have been growing alongside humans for at least 11,000 years,” he says. “Biodiversity has grown with that fire policy. When you remove this kind of burnout, you start to see serious problems with biodiversity.”

david bowman Researchers from Australia's University of Tasmania say the paper highlights the twin importance of climate and humans in shaping fire regimes.

“Decoupling climate from anthropogenic and, importantly, indigenous fire management is a very important topic,” he says. “As we fight to combat climate-induced wildfires around the world, a long-term perspective like this will be an invaluable addition to current research and development in sustainable fire management. .”