Climate change is testing the resilience of native plants to fire, from ash forests to gymea lilies

One year following the 2019/20 fires, this forest has been slow to recover.
Rachael Nolan, CC BY-NC-ND

Rachael Helene Nolan, Western Sydney University; Andrea Leigh, University of Technology Sydney; Mark Ooi, UNSW; Ross Bradstock, University of Wollongong; Tim Curran, Lincoln University, New Zealand; Tom Fairman, The University of Melbourne, and Víctor Resco de Dios, Universitat de LleidaGreen shoots emerging from black tree trunks is an iconic image in the days following bushfires, thanks to the remarkable ability of many native plants to survive even the most intense flames.

But in recent years, the length, frequency and intensity of Australian bushfire seasons have increased, and will worsen further under climate change. Droughts and heatwaves are also projected to increase, and climate change may also affect the incidence of pest insect outbreaks, although this is difficult to predict.

How will our ecosystems cope with this combination of threats? In our recently published paper, we looked to answer this exact question — and the news isn’t good.

We found while many plants are really good at withstanding certain types of fire, the combination of drought, heatwaves and pest insects may push many fire-adapted plants to the brink in the future. The devastating Black Summer fires gave us a taste of this future.

Examples of fire-adapted plants: prolific flowering of pink flannel flowers (upper left), new foliage resprouting on geebung (upper right), seed release from a banksia cone (lower left), and an old man banksia seedling (lower right).
Rachael Nolan

What happens when fires become more frequent?

Ash forests are one of the most iconic in Australia, home to some of the tallest flowering plants on Earth. When severe fire occurs in these forests, the mature trees are killed and the forest regenerates entirely from the seed that falls from the dead canopy.

These regrowing trees, however, do not produce seed reliably until they’re 15 years old. This means if fire occurs again during this period, the trees will not regenerate, and the ash forest will collapse.

This would have serious consequences for the carbon stored in these trees, and the habitat these forests provide for animals.

Southeast Australia has experienced multiple fires since 2003, which means there’s a large area of regrowing ash forests across the landscape, especially in Victoria.

The Black Summer bushfires burned parts of these young forests, and nearly 10,000 football fields of ash forest was at risk of collapse. Thankfully, approximately half of this area was recovered through an artificial seeding program.

Ash to ashes: On the left, unburned ash forest in the Central Highlands of Victoria; on the right, ash forest which has been burned by a number of high severity bushfires in Alpine National Park. Without intervention, this area will no longer be dominated by ash and will transition to shrub or grassland.
T Fairman

What happens when fire seasons get longer?

Longer fire seasons means there’s a greater chance species will burn at a time of year that’s outside the historical norm. This can have devastating consequences for plant populations.

For example, out-of-season fires, such as in winter, can delay maturation of the Woronora beard-heath compared to summer fires, because of their seasonal requirements for releasing and germinating seeds. This means the species needs longer fire-free intervals when fires occur out of season.

The iconic gymea lily, a post-fire flowering species, is another plant under similar threat. New research showed when fires occur outside summer, the gymea lily didn’t flower as much and changed its seed chemistry.

While this resprouting species might persist in the short term, consistent out-of-season fires could have long-term impacts by reducing its reproduction and, therefore, population size.

Out-of-season fires could have long-term impacts on gymea lilies.
Shutterstock

When drought and heatwaves get more severe

In the lead up to the Black Summer fires, eastern Australia experienced the hottest and driest year on record. The drought and associated heatwaves triggered widespread canopy die-off.

Extremes of drought and heat can directly kill plants. And this increase in dead vegetation may increase the intensity of fires.

Another problem is that by coping with drought and heat stress, plants may deplete their stored energy reserves, which are vital for resprouting new leaves following fire. Depletion of energy reserves may result in a phenomenon called “resprouting exhaustion syndrome”, where fire-adapted plants no longer have the reserves to regenerate new leaves after fire.

Therefore, fire can deliver the final blow to resprouting plants already suffering from drought and heat stress.

Drought stressed eucalypt forest in 2019.
Rachael Nolan

Drought and heatwaves could also be a big problem for seeds. Many species rely on fire-triggered seed germination to survive following fire, such as many species of wattles, banksias and some eucalypts.

But drought and heat stress may reduce the number of seeds that get released, because they limit flowering and seed development in the lead up to bushfires, or trigger plants to release seeds prematurely.

For example, in Australian fire-prone ecosystems, temperatures between 40℃ and 100℃ are required to break the dormancy of seeds stored in soil and trigger germination. But during heatwaves, soil temperatures can be high enough to break these temperature thresholds. This means seeds could be released before the fire, and they won’t be available to germinate after the fire hits.

Heatwaves can also reduce the quality of seeds by deforming their DNA. This could reduce the success of seed germination after fire.

Burnt banksia — Many native plants, such as banksia, rely on fire to germinate their seeds.
Shutterstock

What about insects? The growth of new foliage following fire or drought is tasty to insects. If pest insect outbreaks occur after fire, they may remove all the leaves of recovering plants. This additional stress may push plants over their limit, resulting in their death.

This phenomenon has more typically been obverved in eucalypts following drought, where repeated defoliation (leaf loss) by pest insects triggered dieback in recovering trees.

When threats pile up

We expect many vegetation communities will remain resilient in the short-term, including most eucalpyt species.

But even in these resilient forests, we expect to see some changes in the types of species present in certain areas and changes to the structure of vegetation (such as the size of trees).

Resprouting eucalypts, one year on following the 2019-2020 bushfires.
Rachael Nolan

As climate change progresses, many fire-prone ecosystems will be pushed beyond their historical limits. Our new research is only the beginning — how plants will respond is still highly uncertain, and more research is needed to untangle the interacting effects of fire, drought, heatwaves and pest insects.

We need to rapidly reduce carbon emissions before testing the limits of our ecosystems to recover from fire.

Rachael Helene Nolan, Postdoctoral research fellow, Western Sydney University; Andrea Leigh, Associate Professor, Faculty of Science, University of Technology Sydney; Mark Ooi, Senior Research Fellow, UNSW; Ross Bradstock, Emeritus professor, University of Wollongong; Tim Curran, Associate Professor of Ecology, Lincoln University, New Zealand; Tom Fairman, Future Fire Risk Analyst, The University of Melbourne, and Víctor Resco de Dios, Profesor de Incendios y Cambio Global en PVCF-Agrotecnio, Universitat de Lleida

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

Pest plants and animals cost Australia around $25 billion a year – and it will get worse

Corey J. A. Bradshaw, Flinders University and Andrew Hoskins, CSIRO

Shamefully, Australia has one of the highest extinction rates in the world.
And the number one threat to our species is invasive or “alien” plants and animals.

But invasive species don’t just cause extinctions and biodiversity loss – they also create a serious economic burden. Our research, published today, reveals invasive species have cost the Australian economy at least A$390 billion in the last 60 years alone.

Our paper – the most detailed assessment of its type ever published in this country – also reveals feral cats are the worst invasive species in terms of total costs, followed by rabbits and fire ants.

Without urgent action, Australia will continue to lose billions of dollars every year on invasive species.

Feral cats are Australia’s costliest invasive species.
Adobe Stock/240188862

Huge economic burden

Invasive species are those not native to a particular ecosystem. They are introduced either by accident or on purpose and become pests.

Some costs involve direct damage to agriculture, such as insects or fungi destroying fruit. Other examples include measures to control invasive species like feral cats and cane toads, such as paying field staff and buying fuel, ammunition, traps and poisons.

Our previous research put the global cost of invasive species at A$1.7 trillion. But this is most certainly a gross underestimate because so many data are missing.

As a wealthy nation, Australia has accumulated more reliable cost data than most other regions. These costs have increased exponentially over time – up to sixfold each decade since the 1970s.

We found invasive species now cost Australia around A$24.5 billion a year, or an average 1.26% of the nation’s gross domestic product. The costs total at least A$390 billion in the past 60 years.

Increase in annual costs of invasive species in Australia from 1960 to 2020. The predicted range for 2020 is shown in the upper left quadrant. Note the logarithmic scale of the vertical axis.
CJA Bradshaw

Worst of the worst

Our analysis found feral cats have been the most economically costly species since 1960. Their A$18.7 billion bill is mainly associated with attempts to control their abundance and access, such as fencing, trapping, baiting and shooting.

Feral cats are a main driver of extinctions in Australia, and so perhaps investment to limit their damage is worth the price tag.

Tasmania’s bane — ragwort (*Senecio jacobaea*)
Adobe Stock/157770032

As a group, the management and control of invasive plants proved the worst of all, collectively costing about A$200 billion. Of these, annual ryegrass, parthenium and ragwort were the costliest culprits because of the great effort needed to eradicate them from croplands.

Invasive mammals were the next biggest burdens, costing Australia A$63 billion.

The 10 costliest invasive species in Australia.
CJA Bradshaw

Variation across regions

For costs that can be attributed to particular states or territories, New South Wales had the highest costs, followed by Western Australia then Victoria.

Red imported fire ants are the costliest species in Queensland, and ragwort is the economic bane of Tasmania.

The common heliotrope is the costliest species in both South Australia and Victoria, and annual ryegrass tops the list in WA.

In the Northern Territory, the dothideomycete fungus that causes banana freckle disease brings the greatest economic burden, whereas cats and foxes are the costliest species in the ACT and NSW.

The three costliest species by Australian state/territory.
CJA Bradshaw

Better assessments needed

Our study is one of 19 region-specific analyses released today. Because the message about invasive species must get out to as many people as possible, our article’s abstract was translated into 24 languages.

This includes Pitjantjatjara, a widely spoken Indigenous language.

Even the massive costs we reported are an underestimate. This is because of we haven’t yet surveyed all the places these species occur, and there is a lack of standardised reporting by management authorities and other agencies.

For example, our database lists several fungal plant pathogens. But no cost data exist for some of the worst offenders, such as the widespread Phytophthora cinnamomi pathogen that causes major crop losses and damage to biodiversity.

Developing better methods to estimate the environmental impacts of invasive species, and the benefit of management actions, will allow us to use limited resources more efficiently.

*Phytophthora cinnamomi*, a widespread, but largely uncosted, fungal pathogen.
Adobe Stock/272252666

A constant threat

Fall armyworm, a major crop pest.
Adobe Stock/335450066

Many species damaging to agriculture and the environment are yet to make it to our shores.

The recent arrival in Australia of fall armyworm, a major agriculture pest, reminds us how invasive species will continue their spread here and elsewhere.

As well as the economic damage, invasive species also bring intangible costs we have yet to measure adequately. These include the true extent of ecological damage, human health consequences, erosion of ecosystem services and the loss of cultural values.

Without better data, increased investment, a stronger biosecurity system and interventions such as animal culls, invasive species will continue to wreak havoc across Australia.

The authors acknowledge the Traditional Owners of the lands on which they did this research.

Ngadlu tampinthi yalaka ngadlu Kaurna yartangka inparrinthi. Ngadludlu tampinthi, parnaku tuwila yartangka.

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

Australia needs construction waste recycling plants — but locals first need to be won over

Salman Shooshtarian, RMIT University and Tayyab Maqsood, RMIT UniversityStrong community opposition to a proposed waste facility in regional New South Wales made headlines earlier this year. The A$3.9 million facility would occupy 2.7 hectares of Gunnedah’s industrial estate. It’s intended to process up to 250,000 tonnes a year of waste materials from Sydney.

Much of this is construction waste that can be used in road building after processing. Construction of the plant will employ 62 people and its operation will create 30 jobs. Yet every one of the 86 public submissions to the planning review objected to the project.

Residents raised various concerns, which received widespread local media coverage. They were concerned about water management, air quality, noise, the impact of hazardous waste, traffic and transport, fire safety and soil and water. For instance, a submission by a local businessman and veterinary surgeon stated:

“The proposed facility is too close to town, residences and other businesses […] Gunnedah is growing and this proposed development will be uncomfortably close to town in years to come.”

Map showing location of the proposed waste recycling facility in Gunnedah — The location of the proposed waste recycling facility in Gunnedah.
Source: Google Maps (2021), Author provided

The general manager of the applicant said descriptions such as “toxic waste dump” were far from accurate.

“It’s not a dump […] Its prime focus is to reclaim, reuse and recycle.”

He added: “[At present] the majority of this stuff goes to landfill. What we’re proposing is very beneficial to the environment, which is taking these resources and putting them back into recirculation. The reality is the population is growing, more waste is going to get generated and the upside is we’re much better processing and claiming out of it than sending it to landfill.”

Why are these facilities needed?

According to the latest data in the National Waste Report 2020, Australia generated 27 million tonnes of waste (44% of all waste) from the construction and demolition (C&D) sector in 2018-19. That’s a 61% increase since 2006-07. This waste stream is the largest source of managed waste in Australia and 76% of it is recycled.

However, recycling rates and processing capacities still need to increase massively. The environmental impact statement for the Gunnedah project notes Sydney “is already facing pressure” to dispose of its growing construction waste. Most state and national policies – including the NSW Waste Avoidance and Resource Recovery Strategy 2014-2021, NSW Waste and Resource Recovery Infrastructure Strategy and 2018 National Waste Policy – highlight the need to develop infrastructure to effectively manage this waste.

Why, then, do people oppose these facilities?

Public opposition to new infrastructure in local neighbourhoods, the Not-in-My-Back-Yard (NIMBY) attitude, is a global phenomenon. Australia is no exception. We have seen previous public protests against waste facilities being established in local areas.

The academic literature reports the root causes of this resistance are stench and other air pollution, and concerns about impacts on property values and health. Factors that influence individuals’ perceptions include education level, past experience of stench and proximity to housing.

Protesters march behind a sign reading 'We demand fair development'. — Local communities around the world have protested against local waste management plants that they see as a threat to their health.
United Workers/Flickr, CC BY

What are the other challenges of recycling?

Our research team at RMIT University explore ways to effectively manage construction and demolition waste, with a focus on developing a circular economy. Our research shows this goal depends heavily on the development of end markets for recycled products. Operators then have the confidence to invest in recycling construction and demolition waste, knowing it will produce a reasonable return.

A consistent supply of recycled material is needed too. We believe more recycling infrastructure needs to be developed all around Australia. Regional areas are the most suitable for this purpose because they have the space and a need for local job creation.

To achieve nationwide waste recycling, however, everyone must play their part. By everyone, we mean suppliers, waste producers, waste operators, governments and the community.

Today we are facing new challenges such as massive urbanisation, shortage of virgin materials, increasing greenhouse gas emissions and bans on the export of waste. These challenges warrant new solutions, which include sharing responsibility for the waste we all generate.

What can be done to resolve public concerns?

Government has a key role to play in educating the public about the many benefits of recycling construction and demolition waste. These benefits include environmental protection, more efficient resource use, reduced construction costs, and job creation.

Government must also ensure communities are adequately consulted. A local news report reflected Gunnedah residents’ concern that the recycling facility’s proponent had not contacted them. They initiated the contact. One local said:

“I do understand the short-term financial gains a development like this will bring to the community, but also know the financial and environmental burden they will cause.”

Feedback from residents triggered a series of consultation sessions involving all parties.

A robust framework for consulting the community, engaging stakeholders and providing information should be developed to accompany any such development. Community education programs should be based on research.

For instance, research indicates that, unlike municipal waste recycling facilities, construction and demolition waste management facilities have negligible to manageable impact on the environment and residents’ health and well-being. This is due to the non-combustible nature of most construction materials, such as masonrt.

Such evidence needs to be communicated effectively to change negative community attitudes towards construction and demolition waste recycling facilities. At RMIT, through our National Construction & Demolition Waste Research and Industry Portal, we continue to play our part in increasing public awareness of the benefits.

Salman Shooshtarian, Research Fellow, RMIT University and Tayyab Maqsood, Associate Dean and Head of of Project Management, RMIT University

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

About 500,000 Australian species are undiscovered – and scientists are on a 25-year mission to finish the job

Kevin Thiele, The University of Western Australia and Jane Melville, Museums VictoriaHere are two quiz questions for you. How many species of animals, plants, fungi, fish, insects and other organisms live in Australia? And how many of these have been discovered and named?

To the first, the answer is we don’t really know. But the best guess of taxonomists – the scientists who discover, name, classify and document species – is that Australia’s lands, rivers, coasts and oceans probably house more than 700,000 distinct species.

On the second, taxonomists estimate almost 200,000 species have been scientifically named since Europeans first began exploring, collecting and classifying Australia’s remarkable fauna and flora.

Together, these estimates are disturbing. After more than 300 years of effort, scientists have documented fewer than one-third of Australia’s species. The remaining 70% are unknown, and essentially invisible, to science.

Taxonomists in Australia name an average 1,000 new species each year. At that rate, it will take at least 400 years to complete even a first-pass stocktake of Australia’s biodiversity.

This poor knowledge is a serious threat to Australia’s environment. And a first-of-its kind report released today shows it’s also a huge missed economic opportunity. That’s why today, Australia’s taxonomists are calling on governments, industry and the community to support an important mission: discovering and documenting all Australian species within 25 years.

Australia: a biodiversity hotspot

Biologically, Australia is one of the richest and most diverse nations on Earth – between 7% and 10% of all species on Earth occur here. It also has among the world’s highest rates of species discovery. But our understanding of biodiversity is still very, very incomplete.

Of course, First Nations peoples discovered, named and classified many species within their knowledge systems long before Europeans arrived. But we have no ready way yet to compare their knowledge with Western taxonomy.

Finding new species in Australia is not hard – there are almost certainly unnamed species of insects, spiders, mites and fungi in your backyard. Any time you take a bush holiday you’ll drive past hundreds of undiscovered species. The problem is recognising the species as new and finding the time and resources to deal with them all.

Taxonomists describe and name new species only after very careful due diligence. Every specimen must be compared with all known named species and with close relatives to ensure it is truly a new species. This often involves detailed microscopic studies and gene sequencing.

More fieldwork is often needed to collect specimens and study other species. Specimens in museums and herbaria all over the world sometimes need to be checked. After a great deal of work, new species are described in scientific papers for others to assess and review.

So why do so many species remain undiscovered? One reason is a shortage of taxonomists trained to the level needed. Another is that technologies to substantially speed up the task have only been developed in the past decade or so. And both these, of course, need appropriate levels of funding.

Of course, some groups of organisms are better known than others. In general, noticeable species – mammals, birds, plants, butterflies and the like – are fairly well documented. Most less noticeable groups – many insects, fungi, mites, spiders and marine invertebrates – remain poorly known. But even inconspicuous species are important.

Fungi, for example, are essential for maintaining our natural ecosystems and agriculture. They fertilise soils, control pests, break down litter and recycle nutrients. Without fungi, the world would literally grind to a halt. Yet, more than 90% of Australian fungi are believed to be unknown.

fungi on log — Fungi plays an essential ecosystem role.
Shutterstock

Mind the knowledge gap

So why does all this matter?

First, Australia’s biodiversity is under severe and increasing threat. To manage and conserve our living organisms, we must first discover and name them.

At present, it’s likely many undocumented species are becoming extinct, invisibly, before we know they exist. Or, perhaps worse, they will be discovered and named from dead specimens in our museums long after they have gone extinct in nature.

Second, many undiscovered species are crucial in maintaining a sustainable environment for us all. Others may emerge as pests and threats in future; most species are rarely noticed until something goes wrong. Knowing so little about them is a huge risk.

Third, enormous benefits are to be gained from these invisible species, once they are known and documented. A report released today
by Deloitte Access Economics, commissioned by Taxonomy Australia, estimates a benefit to the national economy of between A$3.7 billion and A$28.9 billion if all remaining Australian species are documented.

Benefits will be greatest in biosecurity, medicine, conservation and agriculture. The report found every $1 invested in discovering all remaining Australian species will bring up to $35 of economic benefits. Such a cost-benefit analysis has never before been conducted in Australia.

The investment would cover, among other things, research infrastructure, an expanded grants program, a national effort to collect specimens of all species and new facilities for gene sequencing.

Two scientists walk through wetlands holding boxes — Discovering new species often involves lots of field work.
Shutterstock

Mission possible

Australian taxonomists – in museums, herbaria, universities, at the CSIRO and in
government departments – have spent the last few years planning an ambitious mission to discover and document all remaining Australian species within a generation.

So, is this ambitious goal achievable, or even imaginable? Fortunately, yes.

It will involve deploying new and emerging technologies, including high-throughput robotic DNA sequencing, artificial intelligence and supercomputing. This will vastly speed up the process from collecting specimens to naming new species, while ensuring rigour and care in the science.

A national meeting of Australian taxonomists, including the young early career researchers needed to carry the mission through, was held last year. The meeting confirmed that with the right technologies and more keen and bright minds trained for the task, the rate of species discovery in Australia could be sped up by the necessary 16-fold – reducing 400 years of effort to 25 years.

With the right people, technologies and investment, we could discover all Australian species. By 2050 Australia could be the world’s first biologically mega-rich nation to have documented all our species, for the direct benefit of this and future generations.

Kevin Thiele, Adjunct Assoc. Professor, The University of Western Australia and Jane Melville, Senior Curator, Terrestrial Vertebrates, Museums Victoria

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

Social plants: in the wild, staghorn ferns grow in colonies to improve water storage for all members

Kevin Burns, Te Herenga Waka — Victoria University of WellingtonSocial colonies are nothing new in the animal kingdom. We know bees, ants and termites live in large colonies, divide labour and co-operate to take care of offspring produced by a single queen.

This behaviour, known as eusociality, has evolved independently in insects, crustaceans (certain species of shrimp) and even some mammals (naked mole rats), but it has never been observed in plants. This suggested plants were somehow less complex than animals.

Our study, published this week, turns our understanding of the evolution of biological complexity on its head. It documents the life history of a remarkable species of fern that grows in the tops of rainforest trees on Lord Howe Island, a small volcanic island in the north Tasman Sea.

Rather than growing as individual ferns in the treetops, the staghorn fern (Platycerium bifurcatum) lives in colonies, in an adaptation to its harsh habitat high above the water and nutrients stored in the soil below.

Individuals differ markedly in size, shape and texture. But they always grow side-by-side within colonies, fitting together like puzzle pieces to form a bucket-like store of water and nutrients available to all colony members.

Many individuals forgo reproduction and instead focus on capturing or storing water to the benefit of other colony members.

Life in the tree tops

Staghorn ferns belong to a group of tree-dwelling plants known as epiphytes. Tree canopies are a challenging environment for plants to grow. Without access to soil, epiphytes are regularly exposed to severe water and nutrient stress.

Epiphytes have evolved several ways to mediate the lack of access to water and nutrients. Bromeliads grow cup-shaped leaves, while orchids have specialised root tissues. But staghorn ferns have developed a colony lifestyle to overcome the problem.

Panorama taken on Lord Howe Island — On Lord Howe Island, staghorn ferns grow in colonies.
Author provided

Staghorn ferns can be bought at many garden stores and will grow like any other pot plant. But in the wild on Lord Howe Island, we discovered individual plants collaborate, specialising in different tasks in the construction of the communal water and nutrient store, often at the cost of their own reproduction — just like social insects.

This radically changes our understanding of biological complexity. It suggests major evolutionary transitions towards eusociality can occur in both plants and animals. Plants and beehives aren’t as different as they might seem.

For decades, scientists interested in eusociality argued for a strict definition — many felt the term should be reserved for only a select group of highly co-operative insects.

This perspective led to widespread scepticism about its occurrence in the natural world. Perhaps this is why it was overlooked for so long in one of horticulture’s most popular pot plants.

Evolution of biological complexity

Four billion years ago, life began as simple, self-replicating molecules. Today’s diversity arose from these simple origins towards increasingly complex organisms.

Evolutionary biologists think that biological complexity developed in abrupt, major evolutionary transitions, rather than slow and continuous changes. Such transitions occur when independent entities begin to collaborate, forming new, more complex life forms — such as, for example, when single-celled organisms evolved into multi-cellular organisms.

A microcopic image of one of the first complex multi-cellular plants, algae known as Volvox — Early in the evolution of plants, single-celled algae joined to form more complex structures.
Shutterstock/Lebendkulturen.de

Another example is the transition from unspecialised bacterial (prokaryotic) cells to cells with an enclosed nucleus and specialised organelles that perform particular functions, known as eukaryotic cells.

Co-operation underpins the evolutionary origins of organelles — they likely evolved from free-living ancestors that gave up their independence to live safely within the walls of another cell.

There are eight commonly recognised major evolutionary transitions — and eusociality is the most recent. Eusocial animals differ from others in three fundamental ways:

they live in colonies comprised of different generations of adults
they subdivide labour into reproductive and non-reproductive groups
they care for offspring co-operatively.

Our observations over the past two years on Lord Howe Island found staghorn ferns meet these criteria.

In highly eusocial species, caste membership is permanent and unchanging. But in primitively eusocial species, individuals can alter their behaviour to suit many roles required by the colony. Staghorn ferns probably fit under the latter category.

Our ongoing research will determine the staghorn’s position along this continuum of eusociality. But, for now, we know plants and animals share a similar evolutionary pathway towards greater biological complexity.

Kevin Burns, Professor, Te Herenga Waka — Victoria University of Wellington

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

The 50 beautiful Australian plants at greatest risk of extinction — and how to save them

Caley’s grevillea (*Grevillea caleyi*) occurs in Sydney. It needs fire to germinate but burns are hard to carry out near urban areas.
Tony Auld, Author provided

Jennifer Silcock, The University of Queensland; Jaana Dielenberg, Charles Darwin University; Roderick John Fensham, The University of Queensland, and Teghan Collingwood, The University of QueenslandAs far as odds go, things don’t look promising for the slender-nerved acacia (Acacia leptoneura), a spiky plant with classic yellow-ball wattle flowers. With most of its habitat in Western Australia’s wheat belt cleared for agriculture, it was considered extinct for more than 160 years.

Now, just two plants are known in the world, and they’re not even in the same place. This species is among many Australian plants that have come perilously close to extinction.

To help prevent the loss of any native plant species, we’ve assembled a massive evidence base for more than 750 plants listed as critically endangered or endangered. Of these, we’ve identified the 50 at greatest risk of extinction.

The good news is for most of these imperilled plants, we already have the knowledge and techniques needed to conserve them. We’ve devised an action plan that’s relatively easy to implement, but requires long-term funding and commitment.

What’s driving the loss?

There are 1,384 plant species and subspecies listed as threatened at a national level. Twelve Australian plant species are considered probably extinct and a further 21 species possibly extinct, while 206 are officially listed as critically endangered.

Yellow wattle — Two known plants of slender nerved acacia (*Acacia leptoneura*) remain, about 1 kilometre apart. Propagation attempts have been unsuccessful and the genetic diversity is probably very low.
Joel Collins, Author provided

Australian plants were used, managed and celebrated by Australia’s First Nations people for at least 60,000 years, but since European colonisation, they’ve been beset by a range of threats.

Land clearing, the introduction of alien plants, animals, diseases, and interruptions to ecological processes such as fire patterns and flooding have taken a heavy toll on many species. This is particularly the case in the more densely populated eastern and southern parts of the continent.

Close-up of yellow flower — Ironstone pixie mop (*Petrophile latericola*) occurs on a soil type that’s been heavily cleared for agriculture, and is suspected to be susceptible to an introduced root-rot fungus. In 2020 fewer than 200 plants remained, in poor condition.
Andrew Crawford, Author provided

Things aren’t improving. Scientists recently compiled long-term monitoring of more than 100 threatened plant species at 600 sites nationally. And they found populations had declined on average by 72% between 1995 and 2017.

This is a very steep rate of decline, much greater than for threatened mammal or bird populations.

On the brink

Many species listed as threatened aren’t receiving targeted conservation action or even baseline monitoring, so an important first step in preventing extinctions was identifying the species at greatest risk.

To find the top 50, we looked at the evidence: all available published and unpublished information and expert surveys of over 120 botanists and land managers.
They’re targeted by our Action Plan for Australia’s Imperilled Plants.

Action Plan for Australia’s Imperilled Plants.

Thirty of the species in the plan have fewer than 50 mature individual plants remaining.

And 33 are known only from a single location, such as the Grampians pincushion-lily (Borya mirabilis), which occurs on one rocky outcrop in Victoria. This means the entire population could be destroyed by a single event, such as a major bushfire.

A dead-looking gum tree on agricultural land — About 2,000 Morrisby’s gums were growing in the early 1990s, but by 2016 fewer than 50 remained. Climate change and damage from insects and animals threaten those left. Protecting trees with fencing has led to new seedlings.
Magali Wright, Author provided

Fewer than 10 lax leek-orchids (*Prasophyllum laxum*) remain. Declines are ongoing due to drought and wildfire, and the South Australian species only occurs on private property not managed for conservation. Proposed recovery actions include habitat protection and establishing the orchid and its mycorrhizal fungi in conservation reserves.
Shane Graves, Author provided

Fewer than 15 woods well spyridium (*Spyridium fontis-woodii*) shrubs remain on a single roadside in South Australia. Research into threats and germination requirements is urgently needed, plus translocation to conservation reserves.
Daniel Duval/South Australian Seed Conservation Centre, Author provided

So how can we protect them?

Some of the common management actions we’ve proposed include:

preventing further loss of species’ habitat. This is the most important action required at a national scale
regularly monitoring populations to better understand how species respond to threats and management actions
safely trialling appropriate fire management regimes, such as burning in areas where fires have been suppressed
investing in disease research and management, to combat the threat of phytophthora (root-rot fungus) and myrtle rust, which damages leaves
propagating and moving species to establish plants at new sites, to boost the size of wild populations, or to increase genetic diversity
protecting plants from grazing and browsing animals, such as feral goats and rabbits, and sometimes from native animals such as kangaroos.

Once common, the dwarf spider-orchid (*Caladenia pumila*) wasn’t seen for over 80 years until two individual plants were found. Despite intensive management, no natural recruitment has occurred. Propagation attempts have successfully produced 100 seedlings and 11 mature plants from seed. This photo shows botanist Marc Freestone hand-pollinating dwarf spider-orchids.
Marc Freestone, Author provided

Only 21 mature plants of Gillingarra grevillea (*Grevillea sp. Gillingarra*) remain on a disturbed, weedy rail reserve in southwestern WA. Half the population was destroyed in 2011 due to railway maintenance and flooding. Habitat protection and restoration, and translocations to conservation reserves are needed to ensure its survival.
Andrew Crawford, Author provided

Another common issue is lack of recruitment, meaning there’s no young plants coming up to replace the old ones when they die. Sometimes this is because the processes that triggered these plants to flower, release seed or germinate are no longer occurring. This can include things like fire of a particular intensity or the right season.

Unfortunately, for some plants we don’t yet know what triggers are required, and further research is essential to establish this.

Now we need the political will

Our plan is for anyone involved in threatened flora management, including federal, state, territory and local government groups, First Nations, environment and community conservation groups, and anyone with one of these plants on their land.

The Border Ranges lined fern (*Antrophyum austroqueenslandicum*) and its habitat are exceedingly rare. It’s threatened by drought and climate change, and fewer than 50 plants remain in NSW. If the threat of illegal collection can be controlled, the species would benefit from re-introduction to Queensland’s Lamington National Park.
Lui Weber, Author provided

Plants make Australian landscapes unique — over 90% of our plant species are found nowhere else in the world. They’re also the backbone of our ecosystems, creating the rich and varied habitats for our iconic fauna to live in. Plants underpin and enrich our lives every day.

Now we have an effective plan to conserve the Australian plants at the greatest risk of extinction. What’s needed is the political will and resourcing to act in time.

Jennifer Silcock, Post-doctoral research fellow, The University of Queensland; Jaana Dielenberg, University Fellow, Charles Darwin University; Roderick John Fensham, Associate Professor of Biological Sciences, The University of Queensland, and Teghan Collingwood, Research Technician, The University of Queensland

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

Scientists are more likely to study bold and beautiful blooms, but ugly flowers matter too

*Myricaria germanica* is a rare and endangered species hit hard by climate change, but little research is undertaken to help save it.
Martino Adamo, Author provided

Kingsley Dixon, Curtin UniversityWe all love gardens with beautiful flowers and leafy plants, choosing colourful species to plant in and around our homes. Plant scientists, however, may have fallen for the same trick in what they choose to research.

Our research, published today in Nature Plants, found there’s a clear bias among scientists toward visually striking plants. This means they’re more likely chosen for scientific study and conservation efforts, regardless of their ecological or evolutionary significance.

To our surprise, colour played a major role skewing researcher bias. White, red and pink flowers were more likely to feature in research literature than those with dull, or green and brown flowers. Blue plants — the rarest colour in nature — received most research attention.

But does this bias matter? Plants worldwide are facing mass extinction due to environmental threats such as climate change. Now, more than ever, the human-induced tide of extinction means scientists need to be more fair-handed in ensuring all species have a fighting chance at survival.

Hidden plants in carpets of wildflowers

I was part of an international team that sifted through 280 research papers from 1975 to 2020, and analysed 113 plant species found in the southwestern Alps in Europe.

The Alps is a global biodiversity hotspot and the subject of almost 200 years of intensive plant science. But climate change is now creating hotter conditions, threatening many of its rarest species.

White flower with mountains in background — Edelweiss is a charismatic plant of the Alps that heralds spring.
Shutterstock

Carpeted in snow for much of the year, the brief yet explosive flowering of Europe’s alpine flora following the thaw is a joy to behold. Who was not bewitched when Julie Andrews danced in an alpine meadow in its full spring wildflower livery in The Sound of Music? Or when she sung “edelweiss”, one of the charismatic plants of the Alps that heralds spring?

Hidden in these carpets of bright blue gentians and Delphiniums, vibrant daisies and orchids, are tiny or dull plants. This includes small sedges (Carex species), lady’s mantle (Alchemilla species) or the snake lily (Fritillaria) with its sanguine drooping flowers on thin stems.

Many of these “uncharismatic plants” are also rare or important ecological species, yet garner little attention from scientists and the public.

Close-up of a blue flower — Bellflowers (*Campanula*) are conspicuous and prominent in the Alps.
Martino Adamo, Author provided

The plants scientists prefer

The study asked if scientists were impartial to good-looking plants. We tested whether there was a relationship between research focus on plant species and characteristics, such as the colour, shape and prominence of species.

Along with a bias towards colourful flowers, we found accessible and conspicuous flowers were among those most studied (outside of plants required for human food or medicine).

Blue flowers — Bold and beautiful flowers in alpine meadows win scientific attention.
Martino Adamo, Author provided

This includes tall, prominent Delphinium and larkspurs, both well-known garden delights with well-displayed, vibrant flowers that often verge on fluorescent. Stem height also contributed to how readily a plant was researched, as it determines a plant’s ability to stand out among others. This includes tall bellflowers (Campanula species) and orchids.

But interestingly, a plant’s rarity didn’t significantly influence research attention. Charismatic orchids, for example, figured prominently despite rarer, less obvious species growing nearby, such as tiny sedges (Cypreaceae) and grass species.

The consequences of plant favouritism

This bias may steer conservation efforts away from plants that, while less visually pleasing, are more important to the health of the overall ecosystem or in need of urgent conservation.

In this time of urgent conservation, controlling our bias in plant science is critical. While the world list of threatened species (the IUCN RED List) should be the basis for guiding global plant conservation, the practice is often far from science based.

Mat rush with brown flowers — Mat rushes are home for rare native sun moths.
Shutterstock

We often don’t know how important a species is until it’s thoroughly researched, and losing an unnoticed species could mean the loss of a keystone plant.

In Australia, for example, milkweeds (Asclepiadaceae) are an important food source for butterflies and caterpillars, while grassy mat rushes (dull-flowered Lomandra species) are now known to be the home for rare native sun moths. From habitats to food, these plants provide foundational ecological services, yet many milkweed and mat rush species are rare, and largely neglected in conservation research.

Likewise, we can count on one hand the number of scientists who work on creepy fungal-like organisms called “slime molds”, compared to the platoons of scientists who work on the most glamorous of plants: the orchids.

Yet, slime molds, with their extraordinary ability to live without cell walls and to float their nuclei in a pulsating jelly of cytoplasm, could hold keys to all sorts of remarkable scientific discoveries.

Yellow slime on tree trunk — Slime molds could hold the key to many scientific discoveries, but the organisms are understudied.
Shutterstock

We need to love our boring plants

Our study shows the need to take aesthetic biases more explicitly into consideration in science and in the choice of species studied, for the best conservation and ecological outcomes.

While our study didn’t venture into Australia, the principle holds true: we should be more vigilant in all parts of the conservation process, from the science to listing species for protection under the law. (Attractiveness bias may affect public interest here, too.)

So next time you go for a bushwalk, think about the plants you may have trodden on because they weren’t worth a second glance. They may be important to native insects, improve soil health or critical for a healthy bushland.

Kingsley Dixon, John Curtin Distinguished Professor, Curtin University

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

Rainforest giants with rare autumn displays: there’s a lot more to Australia’s red cedar than timber

Gregory Moore, The University of MelbourneNative deciduous trees are rare in Australia, which means many of the red, yellow and brown leaves we associate with autumn come from introduced species, such as maples, oaks and elms.

One native tree, however, stands out for its leaves with soft autumnal hues that drop in March and April: Australia’s red cedar. Don’t be fooled by its common name — red cedar is not a cedar at all, but naturally grows in rainforests throughout Southeast Asia and Australia.

You may be more familiar with its timber, which I’ve been acquainted with all of my life. My grandmothers had cedar chests of drawers they had inherited from their mothers or grandmothers, and I had assumed they were made from one of the Northern hemisphere cedar species. The wood still smelled of cedar after all this time in family homes – a scent I associate with grandparents and country homes.

By the time I was given one of these chests to restore, I knew much more about the tree and valued the chest of drawers all the more. So, with autumn putting a spotlight on Australian red cedars, let’s look at this species in more detail.

Majestic giants of the rainforest

I first encountered red cedar trees in the sub-tropical rainforests of Queensland and New South Wales in the 1980s. Then, its scientific name was called Cedrela toona and later Toona australis. Now, it’s recognised as Toona ciliata.

The various names reflect a taxonomic history in which the Australian species was once regarded as being separate from its Asian relatives, but all are now considered one.

Two red cedars in a rainforest — Native red cedar trees can grow up to 60m tall.
Shutterstock

The trees are awe-inspiring. Under the right conditions, it can grow to 60 metres tall (occasionally more) with a trunk diameter of up to 7m.

After losing its foliage in autumn, the new foliage in spring often has an attractive reddish tinge. In late spring it has small (5 milimetres) white or pale pink flowers, but they usually go unnoticed in the rainforest because of their height or the density of other tree canopies growing beneath.

Older red cedars have wonderful buttresses at the base of their trunk, a characteristic shared by many tall tropical trees. These buttresses have long been considered an advantage for species that can emerge above the canopy of a rainforest where winds are much stronger, with the buttresses and expanded root systems providing greater strength and resistance to the wind.

These buttresses also greatly increase the surface area of the base of the trees exposed to air, which facilitates the uptake of extra oxygen as the activity of micro-organisms in the soil can leave it oxygen-depleted.

White flowers against the leaves of red cedar — Tiny white flowers are hard to see from the ground in a rainforest.
Forest and Kim Starr/Wikimedia, CC BY-SA

Logged to near extinction

With a wide distribution throughout Asia and Australia, its uses in ancient times were many and varied. In traditional medicine, bark was used or digestive remedies as well as wound dressing and its resin was used for treating skin conditions.

Dyes, oils and tannins used for preparing leather could also be extracted by boiling various plant parts. Today the wood is used for culturing shiitake mushrooms, which are much in demand in restaurants.

But the recent history of red cedar is a typically sad colonial tale. The species belongs to the same family as mahogany (Meliaceae) and, not surprisingly, was exploited for its timber from the early days of colonisation.

Red cedar bannister — You can find red cedar timber in many public buildings across Australia.
denisbin/Flickr, CC BY-ND

The timber is durable, lightweight and suitable for naval use and so was very heavily logged, right along the east coast of Australia from the early 1800s until the early 20th century.

The rich deep red colour of its timber and the fact it was soft and easily worked meant it was used for furniture, ornate carvings in public buildings, town halls and parliaments, such as the State Library in Melbourne. It was also used for implements and handles, and for sailing and racing boats.

You’ve probably had a close encounter with the lovely red banisters on some of these old buildings that were made of red cedar, often darkened under the patina of so many hands.

The once common and widespread species was logged almost to extinction along the east coast by the mid-1900s, and to the point of practical commercial extinction with little timber available to industry by the 1960s.

So valued was the timber that in the late 1970s, a plan was hatched to remove red cedar from Queensland National Park rainforests using helicopters. Luckily, the idea did not fly and so some great trees persist. The species has a conservation status of concern, but is not considered to be endangered at present.

Leaves of the Toona ciliata — The leaves of red cedar begin to fall in late March.
Peter Woodard/Wikimedia

A terrible pest

The fact they are deciduous makes them potentially very interesting and useful for horticultural use, but that potential remains largely unrealised. And given the value and quality of its timber, you may be wondering why it’s not being grown in plantations across the continent.

The reason is a native moth called the cedar tip moth (Hypsipyla robusta), which lays its eggs on the main growing shoot of the tree. When the eggs hatch the larvae bore down the shoot, which not only results in shoot dieback but also causes the trees to develop multiple stems and branches which reduce its timber value.

Despite this, they are still planted as a quick-growing ornamental tree for their shade in other parts of the world, such Hawaii and Zimbabwe.

The moths are attracted to the scent of the tree, so they’re very difficult to control. The moth does not attack the tree in South America, for instance, because the moth has not established there, so there are large plantations of red cedar in Brazil.

It’s an interesting reminder: often it’s the little things in ecology that can affect success, or failure. When we humans meddle without knowledge, things don’t necessarily go to plan, usually to our cost.

Gregory Moore, Doctor of Botany, The University of Melbourne

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

Attack of the alien invaders: pest plants and animals leave a frightening $1.7 trillion bill

Corey J. A. Bradshaw, Flinders University; Boris Leroy, Muséum national d’histoire naturelle (MNHN); Camille Bernery, Université Paris-Saclay; Christophe Diagne, Université Paris-Saclay, and Franck Courchamp, Université Paris-SaclayThey’re one of the most damaging environmental forces on Earth. They’ve colonised pretty much every place humans have set foot on the planet. Yet you might not even know they exist.

We’re talking about alien species. Not little green extraterrestrials, but invasive plants and animals not native to an ecosystem and which become pests. They might be plants from South America, starfish from Africa, insects from Europe or birds from Asia.

These species can threaten the health of plants and animals, including humans. And they cause huge economic harm. Our research, recently published in the journal Nature, puts a figure on that damage. We found that globally, invasive species cost US$1.3 trillion (A$1.7 trillion) in money lost or spent between 1970 and 2017.

The cost is increasing exponentially over time. And troublingly, most of the cost relates to the damage and losses invasive species cause. Meanwhile, far cheaper control and prevention measures are often ignored.

Yellow crazy ants attacking a gecko — Yellow crazy ants, such as these attacking a gecko, are among thousands of invasive species causing ecological and economic havoc.
Dinakarr, CC0, Wikimedia Commons

An expansive toll

Invasive species have been invading foreign territories for centuries. They hail from habitats as diverse as tropical forests, dry savannas, temperate lakes and cold oceans.

They arrived because we brought them — as pets, ornamental plants or as stowaways on our holidays or via commercial trade.

The problems they cause can be:

ecological, such as causing the extinction of native species
human health-related, such as causing allergies and spreading disease
economic, such as reducing crop yields or destroying human-built infrastructure.

In Australia, invasive species are one of our most serious environmental problems – and the biggest cause of extinctions.

Feral animals such as rabbits, goats, cattle, pigs and horses can degrade grazing areas and compact soil, damaging farm production. Feral rabbits take over the burrows of native animals, while feral cats and foxes hunt and kill native animals.

Wetlands in the Northern Territory damaged by invasive swamp buffalo (*Bubalus bubalis*)
Warren White

Introduced insects, such as yellow crazy ants on Christmas Island, pose a serious threat to a native species. Across Australia, feral honeybees compete with native animals for nectar, pollen and habitat.

Invasive fish compete with native species, disturb aquatic vegetation and introduce disease. Some, such as plague minnows, prey on the eggs and tadpoles of frogs and attack native fish.

Environmental weeds and invasive fungi and parasites also cause major damage.

Of course, the problem is global – and examples abound. In Africa’s Lake Victoria, the huge, carnivorous Nile perch — introduced to boost fisheries – has wiped out more than 200 of the 300 known species of cichlid fish — prized by aquarium enthusiasts the world over.

And in the Florida Everglades, thousands of five metre-long Burmese pythons have gobbled up small, native mammals at alarming rates.

In Africa, numbers of the beautiful cichlid fish have been decimated by Nile perch.
Shutterstock

Money talks

Despite the serious threat biological invasions pose, the problem receives little political, media or public attention.

Our research sought to reframe the problem of invasive species in terms of economic cost. But this was not an easy task.

The costs are diverse and not easily compared. Our analysis involved thousands of cost estimates, compiled and analysed over several years in our still-growing InvaCost database. Economists and ecologists helped fine-tune the data.

The results were staggering. We discovered invasive species have cost the world US$1.3 trillion (A$1.7 trillion) lost or spent between 1970 and 2017. The cost largely involves damages and losses; the cost of preventing or controlling the invasions were ten to 100 times lower.

Clearly, getting on top of control and prevention would have helped avoid the massive damage bill.

Average costs have been increasing exponentially over time — trebling each decade since 1970. For 2017 alone, the estimated cost of invasive species was more than US$163 billion. That’s more than 20 times higher than the combined budgets of the World Health Organisation and the United Nations in the same year.

Perhaps more alarming, this massive cost is a conservative estimate and likely represents only the tip of the iceberg, for several reasons:

we analysed only the most robust available data; had we included all published data, the cost figure would have been 33 times higher for the estimate in 2017
some damage caused by invasive species cannot be measured in dollars, such as carbon uptake and the loss of ecosystem services such as pollination
most of the impacts have not been properly estimated
most countries have little to no relevant data.

A bucket by a lake with a sign reading 'Biosecurity station. Please dip your feet and nets' — Prevention strategies, such as biosecurity controls, are a relatively cheap way to deal with invasive species.
Shutterstock

Prevention is better than cure

National regulations for dealing with invasive species are patently insufficient. And because alien species do not respect borders, the problem also requires a global approach.

International cooperation must include financial assistance for developing countries where invasions are expected to increase substantially in the coming decades, and where regulations and management are most lacking.

Proactive measures to prevent invasion must become a priority. As the old saying goes, an ounce of prevention is better than a pound of cure. And this must happen early – if we miss the start of an invasion, control in many cases is impossible.

More and better research on the economic costs of biological invasions is essential. Our current knowledge is fragmented, hampering our understanding of patterns and trends, and our capacity to manage the problem efficiently.

We hope quantifying the economic impacts of invasive species will mean political leaders start to take notice. Certainly, confirmation of a A$1.7 trillion bill should be enough to get the ball rolling.

Corey J. A. Bradshaw, Matthew Flinders Professor of Global Ecology and Models Theme Leader for the ARC Centre of Excellence for Australian Biodiversity and Heritage, Flinders University; Boris Leroy, Maître de conférences en écologie et biogéographie, Muséum national d’histoire naturelle (MNHN); Camille Bernery, Doctorante en écologie des invasions, Université Paris-Saclay; Christophe Diagne, Chercheur post-doctorant en écologie des invasions, Université Paris-Saclay, and Franck Courchamp, Directeur de recherche CNRS, Université Paris-Saclay

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

How the size and shape of dried leaves can turn small flames into colossal bushfires

Jamie Burton, University of Melbourne; Alexander Filkov, University of Melbourne, and Jane Cawson, University of Melbourne

The 2020-21 fire season is well underway, and we’ve watched in horror as places like K’gari (Fraser Island) burn uncontrollably, threatening people and their homes and devastating the environment.

To lessen the impact of fires, we need to know when they are likely to burn and how intensely. Central to this is the flammability of litter beds — the layer of dead leaves, needles, twigs and bark on the forest floor.

Every large fire begins as a small fire, igniting and initially spreading through the litter bed, but what makes some litter beds more flammable than others?

Aerated litter beds fuel bigger fires

Over the past few years, fire scientists across the world have been busy tackling this burning question. In tropical forests in the Amazon, oak forests in North America and eucalypt woodlands in Australia, they have been collecting leaf litter beds and burning them in the laboratory to understand why litter beds from some plant species burn differently to others.

Each of these studies focused on leaf litter beds made up of a single species, and each identified a range of drivers of flammability. These drivers relate to both the characteristics of the individual litter particle (leaf, needle or branch) and the litter bed itself.

Our new research sought to consolidate these studies to find the common drivers of flammability between different single-species litter beds from different parts of the world.

From our meta-analysis, we found “litter packing” and “litter bulk density” were key factors in litter bed flammability.

Litter packing is a measure of how many gaps are between the dried leaves, needles and branches, and is important for determining how much air is available for burning. Likewise, litter bulk density is a measure of how much litter there is, and is important for determining how quickly and how long litter burns.

Oak tree litter bed — The litter bed from oak trees. The curly leaves create air gaps throughout the litter bed, which lead to bigger fires.
Jamie Burton, Author provided

We found loosely packed litter beds spread fire faster, burned for shorter periods of time and were more consumed by the flames. Importantly, we found this was universal across different types of litter beds.

We also identified the characteristics of leaves, needles and branches that cause variations in litter packing and litter bulk density.

For example, if the litter particles are “curly” and have a high surface area to volume ratio, then they’ll form litter beds with low packing ratios which burn faster and have higher consumption. Examples include leaves from some oak (Quercus) species.

At the opposite end, small and less curly leaves form densely packed litter beds which are less aerated. Examples include coast tea tree (Leptospermum laevigatum) and conifers with small needles such as Larix and Picea. This results in slower moving fires, which do not consume all the litter.

For eucalypt litter beds, things are a little more complicated. Some species have thick and flat leaves which pack densely, so fire spreads more slowly and less litter is consumed. Other species, such as the southern blue gum (Eucalyptus globulus), have larger leaves which tend to pack less densely, so fires burn more quickly with taller flames.

Eucalyptus litter bed — The litter bed of eucalyptus trees.
Jamie Burton, Author provided

How can this information help us manage fires?

Of course, under extreme fire weather conditions, any litter bed will burn. However, at the beginning of a fire or under mild conditions, differences in litter characteristics may strongly influence how that fire spreads. Research on this can be useful for many aspects of fire management and planning.

For example, if we know which plants produce less flammable litter, we can select them for planting around houses, landscaping in fire-prone areas and also use them as green firebreaks to reduce the risk to people and homes. If a fire was to start, it may spread less quickly and be less intense, making it easier to contain and put out.

_Allocasuarina_ needle litter — *Allocasuarina* species with long thin needles tend to pack loosely, leading to faster flame spread and shorter burning times.
Jamie Burton, Author provided

But also it may not be that straightforward. When deciding which species to plant, the flammability of living plants needs to be considered, as well. Some plants that have less flammable litter may actually be highly flammable as a living plant. For example, although coast tea tree may form densely packed litter beds, the high oil content in the leaves makes it highly flammable as a living plant.

Our findings could also be used for predicting fire behaviour. For example, our results could be integrated into fire behaviour models, such as the Forest Flammability Model, which uses information on the composition and structure of the plant community to predict fire behaviour.

Next steps

Our study provides information on what leaf and litter characteristics affect flammability in litter beds composed of a single species. But in many forests, litter beds are made up of a variety of plant species, and more research is needed to understand what happens to litter packing and flammability in these multi-species litter beds.

Besides different species, litter beds also contain different components such as twigs and bark. For example, in a mature wet eucalypt forest, bark and twigs can make up to 44% of the litter bed.

And for some eucalypt species, we already know bark burns differently to leaves. For example, the flaky bark of the Sydney red gum (Angophora costata) tends to take longer to ignite, but burns for a longer time compared to its leaves.

With fires becoming more frequent and fire seasons becoming longer, research into litter bed flammability has never been more needed.

Jamie Burton, PhD Candidate, University of Melbourne; Alexander Filkov, Senior research fellow, University of Melbourne, and Jane Cawson, Research Fellow in Bushfire Behaviour and Management, University of Melbourne

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

What happens when fires become more frequent?

What happens when fire seasons get longer?

When drought and heatwaves get more severe

When threats pile up

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Huge economic burden

Worst of the worst

Variation across regions

Better assessments needed

A constant threat

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Why are these facilities needed?

Why, then, do people oppose these facilities?

What are the other challenges of recycling?

What can be done to resolve public concerns?

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Australia: a biodiversity hotspot

Mind the knowledge gap

Mission possible

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Life in the tree tops

Evolution of biological complexity

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What’s driving the loss?

On the brink

So how can we protect them?

Now we need the political will

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Hidden plants in carpets of wildflowers

The plants scientists prefer

The consequences of plant favouritism

We need to love our boring plants

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Majestic giants of the rainforest

Logged to near extinction

A terrible pest

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An expansive toll

Money talks

Prevention is better than cure

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Aerated litter beds fuel bigger fires

How can this information help us manage fires?

Next steps

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