Ancient Charcoal Reveals Past Fire Patterns and Risks in Australia

Fire is a vital element of the Australian landscape, but it can also pose serious threats to life and property.

Understanding how fire has shaped the ecology and history of Australia is crucial for managing the risks and benefits of fire in the future.

However, most of the existing fire records are derived from organic sediments, such as lakes and swamps, which are limited in their spatial distribution and temporal resolution.

A new study by researchers from the Desert Research Institute and The University of Queensland has discovered a novel source of fire records that can overcome these limitations: sand dunes.

How sand dunes preserve fire records

(Photo : HERIKA MARTINEZ/AFP via Getty Images)

Sand dunes are not an obvious place to look for fire records, as they are often disturbed by ant activity and wind erosion.

However, the researchers found that the foot slopes of dune front walls (the leading edge of a dune) can preserve undisturbed layers of sediment that contain charcoal fragments from past fires, as per Phys.org.

These charcoal fragments can be used to reconstruct the frequency and intensity of fires over time, as well as the type and amount of vegetation that burned.

The researchers collected charcoal samples from four sand dunes in South-East Queensland, ranging in age from 10,000 to 30,000 years old.

They used radiocarbon dating to determine the age of each charcoal layer and analyzed the size and shape of the charcoal pieces to infer the characteristics of the fires that produced them.

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What sand dunes reveal about fire history

The results showed that fire activity in South-East Queensland varied significantly over time, depending on changes in climate and vegetation.

The researchers identified four distinct periods of fire history:

•  The Last Glacial Maximum (LGM), 30,000-18,000 years ago: This was a cold and dry period, with sparse vegetation and low fire activity. The fires that occurred were mostly low-intensity surface fires that burned grasses and shrubs.
•  The Late Glacial (LG), 18,000-12,000 years ago: This was a transitional period, with increasing temperature and moisture, and expanding vegetation cover. Fire activity increased as well, with more frequent and intense fires that burned trees and woody plants.
•  The Early Holocene (EH), 12,000-8,000 years ago: This was a warm and wet period, with dense vegetation and high fire activity. The fires were mostly high-intensity crown fires that consumed large amounts of biomass.
•  The Late Holocene (LH), 8,000 years ago-present: This was a cooler and drier period, with reduced vegetation and fire activity. The fires were mostly low-intensity surface fires that burned grasses and shrubs.

The researchers compared their fire records from sand dunes with those from other sources, such as lakes and swamps, and found that they matched well in terms of timing and magnitude of fire events.

This suggested that sand dunes can provide reliable and consistent fire records that complement other sources.

Why sand dunes matter for fire management

The discovery of fire records in sand dunes has important implications for fire management in Australia and beyond, as per Down to Earth.

Sand dunes are widely distributed across dryland regions of the world, which cover about 40% of the Earth's land surface.

These regions are often underrepresented in global fire databases due to the scarcity of organic sediments.

Sand dunes can fill this gap by providing long-term fire records that can help us understand how fire regimes have changed over time in response to climate and vegetation shifts.

By comparing fire records from different regions and sources, we can identify patterns and trends of fire behavior at local, regional, and global scales.

This can help us assess the risks and opportunities of fire in different ecosystems, and inform strategies for fire prevention, mitigation, and adaptation.

Sand dunes are not only fascinating geological features but also valuable archives of fire history.

By unlocking their secrets, we can gain a bigger picture of the role of fire in shaping our planet.

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