Under climate change, winter will be the best time for bush burn-offs – and that could be bad news for public health


Giovanni Di Virgilio, UNSW; Annette Hirsch, UNSW; Hamish Clarke, University of Wollongong; Jason Evans, UNSW; Jason Sharples, UNSW, and Melissa Hart, UNSW

At the height of last summer’s fires, some commentators claimed “greenies” were preventing hazard reduction burns – also known as prescribed burns – in cooler months. They argued that such burns would have reduced the bushfire intensity.

Fire experts repeatedly dismissed these claims. As then NSW Rural Fire Service Commissioner Shane Fitzsimmons noted in January this year, the number of available days to carry out prescribed burns had reduced because climate change was altering the weather and causing longer fire seasons.




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How does bushfire smoke affect our health? 6 things you need to know


This public conversation led our research team to ask: if climate change continues at its current rate, how will this change the days suitable for prescribed burning?

Our results, published today, were unexpected. Climate change may actually increase the number of burn days in some places, but the windows of opportunity will shift towards winter months. The bad news is that burning during these months potentially increases the public health impacts of smoke.

A hot debate

Hazard reduction involves removing vegetation that could otherwise fuel a fire, including burning under controlled conditions. But its effectiveness to subdue or prevent fires is often debated in the scientific community.

Commissioner Fitzsimmons weighs in on a national debate about hazard-reduction burns.

Those with experience on fire grounds, including Fitzsimmons, say it’s an important factor in fire management, but “not a pancea”.

Despite the debate, it’s clear hazard reduction burning will continue to be an important part of bushfire risk management in coming decades.




Read more:
The burn legacy: why the science on hazard reduction is contested


Modelling future weather

Before conducting prescribed burns, firefighting agencies consider factors such as vegetation type, proximity to property, desired rate of spread and possible smoke dispersal over populated areas. But we wanted to distil our investigation down to daily weather factors.

We reduced those factors to five key components. These were maximum temperature, relative humidity, wind speed, fuel moisture and the McArthur forest fire danger index (the index used to forecast fire danger in southeast Australia).

We looked at these elements on prescribed burning days between 2004-2015. We then used climate models to simulate how the conditions would change with global warming over southeast Australia, relative to a baseline historical 20-year period for 1990-2009.

To make a valid 20-year comparison, we compared the historical period to a modelled period from 2060-2079, assuming emissions continue to rise at their current pace.

A controlled burn in bushland, with small flames and lots of smoke.
Under global warming, suitable conditions for prescribed burns will be shifted to late winter and early spring in many places.
Shutterstock

Surprisingly, we found, with one regional exception, the number of days suitable for prescribed burning did not change. And in many places, the number increased.

As the fire season lengthened under a warming climate, the number of days suitable for burning just shifted from autumn to winter.

Shifting seasons

Our research indicated that by 2060 there’ll be fewer prescribed burning days during March, April and May. These are the months when most burning happens now.

But there will be significantly more opportunities for burning days from June to October. This is because the conditions that make for a good day for prescribed burning – such as mild and still days – start to shift to winter. Today, weather in these months is unsuitable for conducting burns.

Interestingly, these results aren’t uniform across southeast Australia. For example, much of the Australian east coast and South Australia would see seasonal shifts in burning windows, with around 50% fewer burning days in March to May.

Much of Victoria and in particular the southern regions saw an increase in burning windows during April to May and, in some parts of the state, through September and October as well.

Only the east Queensland coast would see a total reduction in prescribed burn days from April to October.

The smoke trap

This may be good news for firefighters and those agencies who depend on prescribed burning as a key tool in bushfire prevention. But, as so often is the case with climate change, it’s not that simple.

A byproduct of prescribed burning is smoke, and it’s a very significant health issue.

Last year, research showed global warming will strengthen an atmospheric layer that traps pollution close to the land surface, known as the “inversion layer”. This will happen in the years 2060-79, relative to 1990-2009 – especially during winter.




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Unfortunately, the conditions that create inversion layers – including cool, still air – correspond with conditions suitable for prescribed burning.

For asthmatics and those sensitive to air pollution, smokier burn days could make winter months more difficult and add further stress to the health system.

It also creates an additional challenge for firefighting agencies, which must already consider whether smoke will linger close to the surface and potentially drift into populated regions during prescribed burns.

This is just one factor our firefighting agencies will need to face in the future as bushfire risk management becomes more complex and challenging under climate change.




Read more:
How does bushfire smoke affect our health? 6 things you need to know


The Conversation


Giovanni Di Virgilio, Research associate, UNSW; Annette Hirsch, Post Doctoral Research Fellow, UNSW; Hamish Clarke, Research Fellow, University of Wollongong; Jason Evans, Professor, UNSW; Jason Sharples, Professor of Bushfire Dynamics, School of Science, UNSW Canberra, UNSW, and Melissa Hart, Graduate Director, ARC Centre of Excellence for Climate Extremes, UNSW

This article is republished from The Conversation under a Creative Commons license. Read the original article.

The mystery of the Top End’s vanishing wildlife, and the unexpected culprits



A brush-tailed rabbit-rat, one of the small mammals disappearing in northern Australia.
Cara Penton, Author provided

Alyson Stobo-Wilson, Charles Darwin University; Brett Murphy, Charles Darwin University; Graeme Gillespie, University of Melbourne; Jaana Dielenberg, The University of Queensland, and John Woinarski, Charles Darwin University

Only a few decades ago, encountering a bandicoot or quoll around your campsite in the evening was a common and delightful experience across the Top End. Sadly, our campsites are now far less lively.

Northern Australia’s vast uncleared savannas were once considered a crucial safe haven for many species that have suffered severe declines elsewhere. But over the last 30 years, small native mammals (weighing up to five kilograms) have been mysteriously vanishing across the region.




Read more:
Scientists and national park managers are failing northern Australia’s vanishing mammals


The reason why the Top End’s mammals have declined so severely has long been unknown, leaving scientists and conservation managers at a loss as to how to stop and reverse this tragic trend.

The author smiles at an adorable glider in a little blanket she's holding.
Alyson Stobo-Wilson with a savanna glider. Gliders are among the mammals rapidly declining in northern Australia.
Alyson Stobo-Wilson, Author provided

Our major new study helps unravel this longstanding mystery. We found that the collective influence of feral livestock — such as buffaloes, horses, cattle and donkeys — has been largely underestimated. Even at quite low numbers, feral livestock can have a big impact on our high-value conservation areas and the wildlife they support.

The race for solutions

In 2010, Kakadu National Park conducted a pivotal study on Top End mammals. It found that between 1996 and 2009, the number of native mammal species at survey sites had halved, and the number of individual animals dropped by more than two-thirds. Similar trends have since been observed elsewhere across the Top End.

Given the scale and speed of the mammal declines, the need to find effective solutions is increasingly urgent. It has become a key focus of conservation managers and scientists alike.

The list of potential causes includes inappropriate fire regimes, feral cats, cane toads, feral livestock, and invasive weeds.

Many small and medium-sized mammals are in rapid decline in northern Australia.

With limited resources, it’s essential to know which threats to focus on. This is where our study has delivered a major breakthrough.

We looked for patterns of where species have been lost and where they are hanging on. With the help of helicopters to reach many remote areas, we used more than 1,500 “camera traps” (motion-sensor cameras to record mammals) and almost 7,500 animal traps (such as caged traps) to survey 300 sites across the national parks, private conservation reserves and Indigenous lands of the Top End.

A new spotlight on feral livestock

We found most parts of the Top End have very few native mammals left. The isolated areas where mammals are persisting have retained good-quality habitat, with a greater variety of plant species and dense shrubs and grasses.

This habitat provides more shelter and food for native mammals, and has fewer cats and dingoes, which hunt more efficiently in open areas. In contrast, sites with degraded habitat have much less food and shelter available, and native mammals are more exposed to predators.

Six dark coloured horses roam among sparse trees in the Top End.
Feral horses can overgraze and trample over habitat, making it far less suitable for small native mammals.
Jaana Dielenberg, Author provided

Across northern Australia, habitat quality is primarily driven by two factors: bushfires and introduced livestock, either farmed or feral.

Our surveys revealed that areas with more feral livestock have fewer native mammals. This highlights that the role of feral livestock in the Top End’s mammal declines has previously been underestimated.

Even at relatively low densities, feral livestock are detrimental to small mammals. Through overgrazing and trampling, they degrade habitat and reduce the availability of food and shelter for native mammals.




Read more:
The world’s best fire management system is in northern Australia, and it’s led by Indigenous land managers


Frequent, intense fires also play a big role. Australia’s tropical savannas are among the most fire-prone on Earth, but fires that are too frequent, too hot and too extensive remove critical food and shelter.

Yet, even if land managers can manage fires to protect biodiversity, for example by reducing the occurrence of large, intense fires, the presence of feral livestock will continue to impede native mammal recovery.

A wild buffalo walks over grass, in front of trees.
Even small numbers of feral livestock can play a big role in native mammal declines.
Northern Territory Government, Author provided

A new way to manage cats

Cats have helped drive more than 20 Australian mammals to extinction. So it’s not surprising we found fewer native mammals at our sample sites where there were more cats.

However, our results suggest the best way to manage the impact of cats in this region may not be to simply kill cats, which is notoriously difficult across vast, remote landscapes. Instead, it may be more effective to manage habitat better, tipping the balance in favour of native mammals and away from their predators.

A striped, ginger cat with shining eyes looks at the camera at night.
A feral cat at one of the study sites. Cats have helped cause more than 20 native mammal extinctions.
Northern Territory Government, Author provided

The combination of prescribed burning to protect food and shelter resources, and culling feral livestock, might be all that’s needed to support native mammals and reduce the impact of feral cats.

What about dingoes?

Many scientists have suggested dingoes could also be part of the solution to reducing cat impacts — as cats are believed to avoid dingoes. With this in mind, we explored the relationship between the two predators in this study.

A brownish motion detection camera trap strapped to a tree.
One of more than 1,000 motion detection cameras used in this study.
Jaana Dielenberg, Author provided

We found no evidence dingoes influenced the distribution of feral cats. In fact, survey sites with more dingoes had fewer native small mammals, suggesting a negative impact by dingoes.

But, unlike cats, culling dingoes is not an option because they provide other important ecological roles, and are culturally significant for Indigenous (and non-Indigenous) Australians.

Controlling herbivores, not predators

Our study suggests an effective way to halt and reverse Top End mammal losses is to protect and restore habitat. For example, by improving fire management and controlling feral livestock through culling.




Read more:
EcoCheck: Australia’s vast, majestic northern savannas need more care


It is also very important to conserve the environments that still have high-quality habitat and healthy mammal communities, such as the high-rainfall areas along the northern Australian coast. These areas provide refuge for many of our most vulnerable mammal species.

A photo from a camera trap showing a black-footed tree-rat on its hind legs.
The native black-footed tree-rat has had major declines across northern Australia. It’s vulnerable to cats and is now restricted to areas that still have good quality habitat, fewer herbivores and less frequent fire.
Hugh Davies, Author provided

The tropical savannas of northern Australia are the largest remaining tract of tropical savanna on Earth and new species are still being discovered.

While there’s more research to be done, it’s crucial we start managing habitat better, before we lose more of our precious mammal species.


The authors would like to gratefully acknowledge the support from many Indigenous ranger groups, land managers and Traditional Owners. This includes the Warddeken, Bawinanga, Wardaman and Tiwi rangers, the Traditional Owners and land managers of Kakadu, Garig Gunak Barlu, Judbarra/Gregory, Litchfield and Nitmiluk National Parks, Djelk, Warddeken and Wardaman Indigenous Protected Areas, and Fish River Station and was facilitated by the Northern, Tiwi and Anindilyakwa Land Councils.The Conversation

Alyson Stobo-Wilson, Postdoctoral Research Associate, Charles Darwin University; Brett Murphy, Associate Professor / ARC Future Fellow, Charles Darwin University; Graeme Gillespie, Honorary Research Fellow, University of Melbourne; Jaana Dielenberg, Science Communication Manager, The University of Queensland, and John Woinarski, Professor (conservation biology), Charles Darwin University

This article is republished from The Conversation under a Creative Commons license. Read the original article.