Australian bushfires – have they always burned so hot?

The austral summer of 2019/2020 saw the largest and most devastating bushfires in recorded history in Australia: the Black Summer Fires in southeast Australia. Australia is no stranger to fire, but have they always burned so hot?

The biota of this vast, dry and nutrient depleted continent is finely attuned to fire. A relationship honed over millions of years of fire-biota feedbacks. In southeast Australia, forests are dominated by highly flammable Eucalyptus trees (sclerophyll forests).

Aboriginal and Torres Strait Islanders – Australia’s First Peoples – recognised the key role that fire plays in Australian ecosystem dynamics and they have used fire to manage, manipulate and create Australian vegetation landscapes since arriving more than 68,000 years ago.

Southeast Australia was owned and occupied by a diverse number of Traditional Owner groups  who managed their Country with fire using small-scale, high frequency and low intensity burning – Cultural Burning. Cultural burning brings life to Country and keeps it open, clean and healthy.

Now, much of the southeast forest estate is managed with a fire-suppression mindset using hazard reduction burning around selected assets.

Around 250 years ago, the British invaded the lands of Australia’s First Peoples. This marked the beginning of a continuing attempt to remove Aboriginal and Torres Strait Islanders from their Country and impose European-style land management regimes.

This attempt has largely failed. The climate and geology is largely inhospitable to imported crops and livestock. The dependence on fertilisers and irrigation have exacted a significant toll on the Australian environment.

The European attitude toward fire (characterised by fear) and “nature” have also had a major impact on the Australian environment.

The attempt to remove Aboriginal and Torres Strait Islanders from Country and deny their skill and agency in shaping and managing Country with fire has caused widespread changes in vegetation across the continent.

Further, the futile attempt to suppress and fight fires on this continent has deprived ecosystems of essential disturbance, increased fuel loads and produced sick Country.

More recently, climate change has caused an increase in extreme weather events (heatwaves, droughts and floods), adding to the pressure Australian environment faces.

These three key factors (removal of traditional management, importation of inappropriate methods and attitudes and climate change) have resulted in Australia experiencing the fastest rate of biodiversity loss on Earth.

The Black Summer Fires were concentrated in southeast Australia. Southeast Australia experienced the first recorded catastrophic bushfire in 1850 (nearly a century after the British Invasion) and there has been a marked increase in the occurrence of large and devastating catastrophic bushfires toward the present day.

This project brings together a unique team of experts in Indigenous knowledge and practice, fire ecology, palaeoecology and ecological modelling to understand how fires and fuels have changed over the past 500 years in southeast Australia – a period that spans Aboriginal management through the British Invasion to the present climate change world.

PF-FIRE is composed of a team of international scientists seeking to understand how fire has changes in frequency and intensity in space and in time. We specialise in time, using the fossil and sub-fossil record to reconstruct changes in fire and fuels (vegetation) across the Earth.

Has it always burned so hot? Fuel and fire changes in southeast Australian forests

An Australian Research Council funded Indigenous Discovery Project (IN21010005)

This project brings together classical Palaeoecology and cutting edge modelling and scientific methods. We will employ 4 key methodologies to address our 4 research questions:

Project summary

Indigenous cultural burning has been raised as a way of mitigating against climate-driven catastrophic bushfires in southeast Australian forests. It is argued that returning an Indigenous style fire regime will keep landscape fuel loads low, thus reducing the frequency and intensity of bushfires and mitigating against large catastrophic bushfires.

To explore this further and advocate for policy change, this project aims to bring together the enormous reservoirs of traditional fire knowledge in Indigenous communities with data-driven science by empirically testing how fuel loads, fuel type, fire frequency and fire intensity have changed in southeast Australian forests during the transition from Indigenous to British management over the past 500 years

Cutting-edge pollen-vegetation modelling

QUESTION 1 – FUEL LOADS: Have fuel-loads increased since the removal of Aboriginal management?

APPROACH: In this project, we will apply well-founded methods of estimating biomass change from subfossil pollen stored in wetland sediments. This procedure involves detailed mapping of forest inventories surrounding target wetland sites using a distance-weighted approach that involves direct biomass measurements and remote sensing. These contemporary forest inventories are calibrated against pollen accumulation identified from a fine-scale analysis of wetland sediments that have a robust radiometric age-control (such as those developed from the analysis of a combination of isotopic Lead, Caesium, Radium and Carbon within the wetland sediments). This calibration data can then be used to hind-cast forest biomass (at the level of individual plant taxa or community groups).  The assembled research team, particularly CIs Mariani, Connor and Fletcher, have a well-developed skillset in developing and implementing calibrations between pollen and distance-weighted vegetation sampling in Tasmania, mainland Australia and elsewhere. This phase of the project will require intensive field sampling of forest inventories and collection of wetland sediments targeted within southeast Australian forests systems.

We will develop pollen accumulation rate-plant biomass calibrations for plant species/pollen types ranging between low biomass (e.g. grassland, low heath) through to high biomass (tall forest). The number of sites is based on the literature underpinning these methods and the experience within the research team. The calibration will then be applied to pollen data analysed from sediment cores across the southeast Australian forest region.

HYPOTHESIS:   If cultural burning maintained a lower landscape-scale fuel loads in southeast Australian forests, our biomass reconstructions will show a systematic increase in woody biomass following the British Invasion and subsequent removal of cultural burning.

Classical Palaeoecology

QUESTION 2 – FUEL TYPE: Has the composition of fuels changed since the cessation of Aboriginal cultural burning?

APPROACH: In this project, we will apply novel modelling techniques to quantify past vegetation (i.e. fuel) cover, similarly to previous applications by the research team (Mariani, Connor, Fletcher) in Tasmania.  Pollen is the key proxy to track past vegetation changes, but pollen spectra suffer from some important biases (taphonomy, pollen productivity, dispersal capability). Pollen records are often dominated by pollen from a few high pollen-producing plant taxa (e.g. wind-pollinated plants), which mask the less producing taxa (e.g. animal-pollinated plants). In effect, there is a non-linear relationship between pollen percentages and plant cover. Estimating past vegetation cover from sedimentary pollen composition then requires to correct for productivity and dispersal biases using empirical-based models. Such models for quantitative vegetation reconstruction (e.g. REVEALS) have yet been mostly applied in the Northern Hemisphere in the last 10 years and can now be used in Australia thanks to the work conducted by the research team. By using this approach on newly developed pollen records, we will be able to quantitatively assess past fuel composition changes across SE Australia.

We will develop land cover-pollen calibration data for the same pollen taxa/plant species targeted for the biomass calibration. The calibration will then be applied to pollen data analysed from 10sediment cores across the southeast Australian forest region.

HYPOTHESIS:   If cultural burning maintained a more open (i.e. low near surface and elevated fine fuel)landscape in SE Australia, our land-cover reconstructions will show an increase in tree cover following British Invasion after the removal of Aboriginal management.

Palaeofire analysis

QUESTION 3:    Have fires become more frequent since the removal of Aboriginal management?

APPROACH: Our approach to reconstructing fire frequency involves two complementary approaches.  The first is founded on the well-established technique of charcoal peak analysis, which has been used in hundreds of fire history studies from around the world.  Peak analysis is performed using CharAnalysis software, which applies a robust lowess smoother to charcoal accumulation rates and then uses statistical thresholds to isolate individual fire ‘peaks’ from the ‘background’ charcoal produced by biomass burned on a regional scale. As part of this project, we will improve peak detection techniques to incorporate counting errors for the first time.  This improved technique will be coded in R and released for use by other researchers. We will compare peak detection results to a second approach, regime-shift analysis or change-point analysis, a novel technique for detecting rapid shifts in fire regime from sedimentary charcoal records. Both approaches to fire frequency reconstruction will be compared to historically documented catastrophic fires to: 1) provide a robust test of the fidelity of charcoal records from different sedimentary contexts and 2) calibrate the sedimentary signal to fire characteristics such as spatial extent, severity and frequency. This will constitute the first test of charcoal record fidelity in the Australian context.

The fire frequency analysis will be applied to charcoal data analysed from sediment cores across the southeast Australian forest region.

HYPOTHESIS:   Catastrophic fires have increased in frequency since British invasion due rapid accumulation of flammable biomass and ground fires, characteristic of cultural burning, have decreased in frequency since the suppression of Aboriginal management.

Fourier Transformed Infrared Spectroscopy

QUESTION 4 – FIRE INTENSITY: Have fires become more intense since the removal of Aboriginal management?

APPROACH: We will apply a state-of-the-art technique to reconstruct past fire intensity from fossil charcoal. The temperature of burning organic material results in a unique combination of combustion products which is captured in the chemical signature of charcoal. Fourier Transformed Infrared Spectroscopy (FTIR) will be used to analyse chemical spectra in fossil charcoal as a proxy for past fire combustion temperatures (fire intensity). The FTIR spectral absorbance of fossil charcoal fragments (>125 μm) will be recorded and the statistical analysis of FTIR spectra will be analysed in R studio using the Mclust and Chemospec to identify significant clusters of chemical spectra. These data will be compared with the reference database using a best-fit modelling to estimate fire intensity of fossil charcoal fragments. PI Maezumi has helped developed the protocol for analysing and calibrating fire intensity from fossil charcoal in the Amazon. This phase of the project will require lab analysis time that will be conducted at the University of Amsterdam.

The fire intensity analysis will be applied to charcoal data analysed from sediment cores across the southeast Australian forest region.

HYPOTHESIS:   If cultural burning maintained a lower landscape-scale fuel loads in southeast Australian forests, fire intensity will show lower fire intensities associated with cultural burning prior to the British Invasion.

Project leaders

Associate Professor Michael-Shawn Fletcher

School of Geography, University of Melbourne

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I am a descendent of the Wiradjuri. I am interested in the long-term interactions between humans, climate, disturbance and vegetation at local, regional and global scales. My current work involves developing and integrating high-resolution palaeoenvironmental records from across the Southern Hemisphere using multiple proxies, including microfossil, charcoal, geochemical and isotopic analyses to provide comprehensive reconstructions of environmental change.

Dr Simon Connor

Archaeology and Natural History, Australian National University

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I am a geographer researching the long-term dynamics and diversity of terrestrial ecosystems. My research interest is in how plants and people migrated following the last glacial period, and how they interacted with climate change in the Caucasus, Mediterranean, Macaronesian and Australasian regions. I’m also passionate about environmental education and its role in creating more sustainable, forward-thinking societies.

Dr Michela Mariani

School of Geography, University of Nottingham

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I am an early-career researcher in the fields of Quaternary science, Palaeoclimatology and Biogeography, but I prefer to call myself a pollen lover, a palaeo nerd and a tireless time traveller. I am currently Assistant Professor at the School of Geography of the University of Nottingham (UK). Previously, I completed my PhD at the School of Geography at the University of Melbourne (Australia; 2015-2018) and I worked as a teaching/post-doc fellow for the same institution. My research lines fit within the broad scheme of studies about climate change and environmental impacts of climate change. I specifically focus on the climate-fire-vegetation interactions over timescales varying from millennia to decades, mostly across the Australian continent. I believe knowing the past climate variability, fire regimes and ecosystem responses are key to sustainably manage our planet under the impending pressures brought by climate change.

Dr Yoshi Maezumi

Institute for Biodiversity and Ecosystem Dynamics, University of Amsterdam

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I am a Paleoecologist specializing in the legacy of human land use and fire management in modern ecosystems. I am currently a Marie Curie Fellow at the University of Amsterdam. My project FIRE: Fire Intensity in Rainforest Ecotones examines the role of fire in shaping Amazon rainforest-savanna ecotones.

Project Staff

Anthony Romano

School of Geography, University of Melbourne

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I am a Research Assistant in Palaeoecology and I am interested in human societies and cultures, fire regimes, terrestrial ecosystems, climate and the interactions and changes within these over millennial to decadal timescales across Australia. Previously, I completed an undergraduate in Archaeology at La Trobe University, Bundoora, and an Honours at the School of Geography at the University of Melbourne, which focused on environmental variability in response to human population growth during the late-Holocene in northwest Tasmania. Amid the Climate Crisis, it is fundamental that we understand how people both influence and are influenced by their environments across various timescales. This is particularly important for invaded and colonised landscapes such as Australia, in which imported landscape management paradigms have resulted in widespread environmental degradation. I believe integrated studies of archaeology and palaeoecology allow for greater understanding of human-environment interactions and as such has the potential to provide important tangible insights into the historical legacy of humans in Australia that can then generate sustainable management policies of landscapes.

William Henriquez

School of Geography, University of Melbourne

Researchgate

I am a biologist with interests in paleoecology and paleoclimatology. I just completed my PhD at the School of Geography, Environment and Earth Sciences at Victoria University of Wellington in New Zealand. My research focused on reconstructing and understating past environmental and climate change in Chilean Patagonia and New Zealand’s southwestern South Island using detailed chronologies of fossil pollen, charcoal and chironomids preserved in lake sediments.

Student researchers

Harriet Magee

School of Geography, University of Melbourne

I am currently studying a Masters in Geography, with interest in the relationships between humans and landscape change over time. Pyrogeography is a major interest of mine, with its ability to delve into the past and predict future landscapes. The PF-FIRE project will help me learn to better understand landscape evolution and future land care needs.

Caitlin O’Shea

School of Geography, University of Melbourne

I am a Master of Environment student with a background in ecology and marine biology, and I’m thrilled to be diving (no pun intended) into a field that is new and exciting to me with the PF-FIRE team. My research is around vegetation composition and fire regime change in eastern Victoria pre- and post-British invasion. I’ll be analysing a core taken from Lake Elusive in East Gippsland, looking for changes in pollen and charcoal deposits throughout the subfossil record. I’m particularly interested in land and fire management and how indigenous cultural burning practices can work to influence landscape-scale fuel loads while also maintaining biodiversity and fostering connections to Country.

Alice Laming

School of Geography, University of Melbourne

I am currently studying a Masters of Environment, interested in land management practices and policies in Australia. In particular, fire activity and its history; how it was once utilised to shape and care for the land compared to the now severe bushfires we experience and how this has evolved. I look forward to partaking in the PF-Fire project, in order to better understand exactly how fire activity has changed over time and what we can learn from this.

Callum Simpson

School of Geography, University of Melbourne

I am currently completing a Masters of Environment specialising in water catchment management and before that I studied undergraduate geology. I am passionate about natural history and past environmental changes. My research project is focussed on the sedimentology and geochemistry of a sediment core from the Bolin Bolin Billabong in Melbourne’s east. My aim is to reconstruct the historical flood regimes and past environments at the site. This work will complement the work of others in the lab in developing a history of fire and human-environment interactions along the Birrarung (Yarra river) and around current-day Melbourne, especially from before and after European colonisation of the lands of the Wurundjeri people.

For questions regarding this project, contact:

Associate Professor Michael-Shawn Fletcher
Assistant Dean (Indigenous) | Faculty of Science
Director (Research Capability) | Indigenous Knowledge Institute
Associate Investigator | Centre of Excellence for Australian Biodiversity and Heritage (CABAH)

p. +61 3 90353048 | e. michael.fletcher@unimelb.edu.au | tw. @theotheroad @Melb_Palaeo

School of Geography | The University of Melbourne
Room 2.09, Level 2, 221 Bouverie Street, Parkville VIC 3010