The summer bushfires you didn’t hear about, and the invasive species fuelling them



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Fire has burned through a swathe of the Tjoritja National Park.
Author provided

Christine Schlesinger, Charles Darwin University and Barry Judd, Charles Darwin University

In January 2019, fires burned across a 100-kilometre length of the iconic Tjoritja National Park in the West MacDonnell Ranges, from Ormiston Gorge nearly to the edge of Alice Springs.

These fires affected an area comparable to the recent Tasmanian fires, but attracted relatively little national attention. This is partly because the fires in Tasmania were so unusual – but we believe the fires in central Australia were just as unexpected.




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Dry lightning has set Tasmania ablaze, and climate change makes it more likely to happen again


In the past, fires of this magnitude have tended to come after heavy rain that powers the growth of native grasses, providing fuel for intense and widespread fires. But our research highlights the new danger posed by buffel grass, a highly invasive foreigner sweeping across inland Australia and able to grow fast without much water.

Far from being pristine, Tjoritja and the Western MacDonnell Ranges are now an invaded landscape under serious threat. Our changing climate and this tenacious invader have transformed fire risk in central Australia, meaning once-rare fires may occur far more often.

Buffel grass in Australia

Buffel grass is tough and fast-growing. First introduced to Australia in the 1870s by Afghan cameleers, the grass was extensively planted in central Australia in the 1960s during a prolonged drought.

Introductions of the drought-resistant plant for cattle feed and dust suppression have continued, and in recent decades buffel grass has become a ubiquitous feature of central Australian landscapes, including Tjoritja.

Buffel grass has now invaded extensive areas in the Northern Territory, Queensland, Western Australia and South Australia and is spreading into New South Wales and Victoria. It was legally recognised as a key threat in 2014, but so far only South Australia has prohibited its sale and created statewide zoning to enforce control or destruction.

Buffel grass crowds out other plants, creating effective “monocultures” – landscapes dominated by a single species. In central Australia, where Aboriginal groups retain direct, active and enduring links to Country, buffel grass makes it hard or impossible to carry out important cultural activities like hunt game species, harvest native plant materials or visit significant sites.

Buffel grass impacts on Anangu Pitjantjatjara Yankunytjatjara communities in central Australia.

But buffel grass isn’t only a threat to biodiversity and Indigenous cultural practices. In January the Tjoritja fires spread along dry river beds choked with buffel, incinerating many large old-growth trees. Much like the alpine forests of Tasmania, the flora of inland river systems has not adapted to frequent and intense fires.

We believe the ability of the fires to spread through these systems, and their increased intensity and size, can be directly attributed to buffel grass.

Fire and buffel grass

Because of the low average rainfall, widespread fires in central Australia have been rare in the recorded past, only following unusual and exceptionally high rainfall.

This extreme rain promoted significant growth of native grasses, which then provided fuel for large fires. There could be decades between these flood and fire cycles. However, since the Tjoritja (previously West MacDonnell Ranges) National Park was established in the 1990s, there have been three large-scale fires in 2001, 2011 and 2019.

What has changed? The 2001-02 and 2011-12 fires both came after heavy rainfall years. In fact, 2011 saw one of the biggest La Niña events on record.

Climate change predictions suggest that central Australia will experience longer and more frequent heatwaves. And although total annual rainfall may stay the same, it’s predicted to fall in fewer days. In other words, we’ll see heavy storms and rainfall followed by long heatwaves: perfect conditions for grass to grow and then dry, creating abundant fuel for intense fires.

The remains of a corkwood tree after an unplanned bushfire in an area heavily invaded by buffel grass near Simpsons Gap. Very few large old corkwood trees now remain in this area.
Author provided

If central Australia, and Tjoritja National Park in particular, were still dominated by a wide variety of native grasses and plants, this might not be such a problem. But buffel grass was introduced because it grows quickly, even without heavy rain.

The fires this year were extraordinary because there was no unusually high rainfall in the preceding months. They are a portent of the new future of fire in these ecosystems, as native desert plant communities are being transformed into dense near-monocultures of introduced grass.

The fuel that buffel grass creates is far more than native plant communities, and after the fire buffel grass can regenerate more quickly than many native species.

So we now have a situation in which fuel loads can accumulate over much shorter times. This makes the risk of fire in invaded areas so high that bushfire might now be considered a perpetual threat.

Changing fire threat

In spinifex grasslands, traditional Aboriginal burning regimes have been used for millennia to renew the landscape and promote growth while effectively breaking up the landscape so old growth areas are protected and large fires are prevented. Current fire management within Tjoritja “combines traditional and scientific practices”.

However, these fire management regimes do not easily translate to river environments invaded by buffel grass. These environments have, to our knowledge, never been targeted for burning by Aboriginal peoples. Since the arrival of buffel grass, there is now an extremely high risk that control burns can spread and become out-of-control bushfires.

Even when control burns are successful, the rapid regrowth of buffel grass means firebreaks may only be effective for a short time before risky follow-up burning is required. And there may no longer be a good time of year to burn.




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Our research suggests that in areas invaded by buffel grass, slow cool winter burns – typical for control burning – can be just as, or more, damaging for trees than fires in hot, windy conditions that often cause fires to spread.

Without more effective management plans and strategies to manage the changing fire threat in central Australia, we face the prospect of a future Tjoritja in which no old-growth trees will remain. This will have a devastating impact on the unique desert mountain ranges.

We need to acknowledge that invasive buffel grass and a changing climate have changed the face of fire risk in central Australia. We need a coordinated response from Australia’s federal and state governments, or it will be too late to stop the ecological catastrophe unfolding before us.


The authors acknowledge the contribution of Shane Muldoon, Sarah White, Erin Westerhuis, CDU Environmental Science and Management students, and NT Parks and Wildlife staff to the research at experimental sites and ongoing tree monitoring in central Australia.The Conversation

Christine Schlesinger, Senior Lecturer in Environmental Science and Ecology, Charles Darwin University and Barry Judd, Professor, Indigenous Social Research, Charles Darwin University

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

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How we wiped out the invasive African big-headed ant from Lord Howe Island



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Not welcome: the African big headed ant might be small but it can be a pest if it gets in your home.
CSIRO, Author provided

Ben Hoffman, CSIRO

The invasive African big-headed ant (Pheidole megacephala) was found on Lord Howe Island in 2003 following complaints from residents about large numbers of ants in buildings.

But we’ve managed to eradicate the ant completely from the island using a targeted mapping and baiting technique than can be used against other invasive species.

Up to 15% of Lord Howe Island was thought to be infested with the ant.
CSIRO, Author provided

A major pest

The African big-headed ant is one of the world’s worst invasive species because of its ability to displace some native plants and wildlife, and adversely affect agricultural production.




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It’s also a serious domestic nuisance. People can become overwhelmed by the large number of ants living in their buildings – you can’t leave a bit of food lying around, especially pet food, or it will be covered in ants.

It remains unclear how long the ant had been on Lord Howe Island, in the Tasman Sea about 770 km northeast of Sydney, before being found. But it is likely to have been present for at least a decade.

Because of the significant threat this ant posed to the conservation integrity of the island, an eradication program was started. But on-ground work done from 2003 to 2011 had many failings and was not working.

In 2011, I was brought in to oversee the program. The last ant colony was killed in 2016, but it is only now, two years later, that we are declaring Lord Howe Island free from the ants.

No African big-headed ants have been seen on the island for two years.
CSIRO, Author provided

A super colony

The ability to eradicate this ant is largely due to its relatively unique social organisation. The queens don’t fly to new locations to start new nests – instead, they form interconnected colonies that can extend over large areas.

This makes the ant’s distribution easy to map and treat. The ant requires human assistance for long-distance transport, so the ant will only be found in predictable locations where it can be accidentally transported by people.

From 2012 to 2015, all locations on the island where the ant was likely to be present were formally inspected. Priority was given to places where an infestation was previously recorded or considered likely. The populations were mapped, and then treated using a granular bait available at shops.

In the latter years we found 16 populations covering 30 hectares. Limited by poor mapping in the early years, we estimate that the ant originally covered up to 55 hectares, roughly 15% of the island.

Stopping the spread

The widespread distribution of the ant through the populated area of the island is thought to have been aided by the movement of infested mulch and other materials from the island’s Waste Management Facility.

To prevent any more spread of the ant, movement restrictions were imposed in 2003 on the collection of green waste, building materials and other high risk items from the facility.

The baiting program used a product that contains a very low dose of insecticide that has an extremely low toxicity to terrestrial vertebrates such as pet cats and dogs, birds, lizard etc. The toxicant rapidly breaks down into harmless chemicals after exposure to light.

No negative impacts were recorded on any of the native wildlife on the island.

Importantly, the African ant usually kills most other ants and other invertebrates where it is present, so there are few invertebrates present to be affected by the bait.

Ecological recovery of the infested areas was rapid following baiting and the eradication of the African ant.

Another ant invader

One of the main challenges was getting the ground crew to correctly identify the ant.

It turns out there was a second (un-named) big-headed ant species present, also not native to the island, that created a lot of unnecessary work being conducted where the African ant wasn’t present.

CSIRO and Lord Howe Island Board team tackling the African big headed ant problem.
CSIRO, Author provided

Like numerous other exotic ant species present, this second species was of no environmental or social concern, so there are no plans to manage or eradicate it.

The protocols used in this program are essentially the same that are being used in other eradication programs against Electric ant in Cairns and Browsing ant in Darwin and Perth, because those two species also create supercolonies.




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It is highly likely that those programs will also achieve eradication of their respective species, the first instance where an ant species has been eradicated entirely from Australia.

The fire ant program in Brisbane has many similarities, but there are distinct differences in that the ants there don’t form supercolonies that are so easy to map, and the area involved is far greater.The Conversation

Ben Hoffman, Principal research scientist, CSIRO

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

A numbers game: killing rabbits to conserve native mammals



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Controlling rabbit populations has a key role in conserving Australia’s native plants and animals
William Booth

Euan Ritchie, Deakin University; Damien Fordham, University of Adelaide, and Miguel Lurgi, Centre national de la recherche scientifique (CNRS)

Invasive species have a devastating effect on biodiversity. In Australia, introduced red foxes and feral cats have been implicated in the majority of the extinctions of the native mammal fauna, which has been decimated since European arrival.

But there’s a herbivore that also causes eco-catastrophe. Rabbits both compete with native animals for food and shelter and act as easy prey for abundant populations of cats and foxes. By over-grazing vegetation and reducing habitat complexity, they make hunting easier for introduced predators.




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Invasive predators are eating the world’s animals to extinction – and the worst is close to home


Food webs are complex. Because of this, once an invasive species is embedded in a food web, simply eradicating them without considering the potential knock-on effects to other species they interact with, could cause unintended and undesirable consequences. We modelled different rates of rabbit population reduction to assess what level of control might be best for aiding the conservation of native mammals and not causing negative outcomes.

Rabbit numbers boom and crash

Rabbits, famously, reproduce rapidly and can cope with a relatively high predation rate. This can cause “hyper-predation”, where rabbit-inflated cat and fox populations indirectly increase the predation pressure on native mammals. This is especially so when rabbit populations intermittently crash due to, for example, extreme environmental events (like severe and prolonged droughts) or disease. This causes predators to switch their diet and eat more native mammals.

Threatened species such as the greater bilby are likely to benefit from rabbit control.
Jasmine Vink

This logically suggests that reducing rabbit numbers might thus help reduce cat and fox populations, by removing their abundant prey. Collectively this should benefit native plants and animals, including many threatened mammal species. However, ecosystem and pest management is a complex game.

When controlling rabbits we need to look beyond one or two species. We should consider the potential consequences for the entire ecological community, which ultimately depend on how changes in one species percolate through the network of ecological interactions between them.

Our new research, recently published in the Journal of Applied Ecology, set out to examine these questions in more detail. We consider other key players in Australia’s arid regions, such as kangaroos and dingoes, when looking at the effects of rabbit control on small native mammals. Our aim was to provide a better understanding of how changes in rabbit populations might affect other species via the food web.

We developed a multi-species ecological network model to describe and quantify how changing rabbit abundance can affect species on different feeding levels. In addition to rabbits, small native mammals, and mesopredators (cats and foxes), our model also considers apex predators (dingo) and large herbivores (kangaroo) as part of the Australian arid food web. This model allowed us to examine changes in predator-prey interactions (including potential prey switching and hyper-predation) and how these could affect the survival of native prey through time.

Our model of an Australian arid ecosystem food web.
Author provided

We found that removing rabbits at rates between 30-40% appeared to benefit small mammals. This is approximately the rate at which rabbits are currently managed in Australia using biocontrol agents (introduced diseases).

Rabbit control in Australia typically involves a “press and pulse” approach. Rabbit populations are suppressed via biocontrol (press) and periods of warren destruction and poisoning (pulse). Finding that reducing rabbit populations by around 40% seems most beneficial to small mammals is important, as it informs how and when we combine these strategies.

The 40% rate corresponds well with the disease-induced (press) mortality rate in rabbit populations due to rabbit haemorrhagic disease and myxomatosis. These are the primary biocontrol agents used in arid Australia to control rabbit populations.

Our study supports rabbit-reduction strategies that involve sustained “press” control, that kill a moderate portion of a rabbit population, with less frequent removal at higher proportions of the population.

To effectively manage invasive species, it’s important to focus on entire communities. Targeting single species might not be enough – every animal exists within a complex web of interactions.




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Mourn our lost mammals, while helping the survivors battle back


There has been much focus by the current government on controlling feral cats, as a way to conserve many of Australia’s unique and threatened mammal species.

The ConversationHowever, more focus could be devoted to protecting habitat cover and complexity, by reducing the land clearing and over-grazing that makes hunting easier. We can also manage rabbits sensibly to reduce competition for resources, and indirectly control cats and foxes.

Euan Ritchie, Associate Professor in Wildlife Ecology and Conservation, Centre for Integrative Ecology, School of Life & Environmental Sciences, Deakin University; Damien Fordham, , University of Adelaide, and Miguel Lurgi, Postdoctoral research fellow, Centre national de la recherche scientifique (CNRS)

This article was originally published on The Conversation. Read the original article.

Tandem virus cocktail kills pest rabbits more effectively



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Tagged European rabbit kitten infected with myxoma virus, but that died from rabbit haemorrhagic virus disease (RHDV).
Photo by David Peacock, Biosecurity South Australia, CC BY-NC-SA

Corey Bradshaw, Flinders University; Louise Barnett, Flinders University, and Thomas Prowse, University of Adelaide

Farmers, landowners and conservationists across Australia are benefiting from an unexpected, combined effect of two biological controls that target feral populations of European rabbits (Oryctolagus cuniculus), according to our research, published in the Journal of Applied Ecology.




Read more:
Explainer: how ‘biocontrol’ fights invasive species


Pest rabbits cost the Australian economy over A$200 million each year in lost production, and millions more in pest control. They compete with livestock for food and cause enormous environmental damage.

Rabbits previously reached plague numbers in much of agricultural and outback Australia, until the introduction of two rabbit-specific viruses and insect vectors.

Myxoma virus was first introduced in 1950, followed by European rabbit fleas in the 1960s to help spread the virus, and then Spanish rabbit fleas in the 1990s to increase spread into arid areas.

Then, in 1995, rabbit haemorrhagic disease virus (RHDV) escaped from quarantine, before an official release in 1996. These biocontrols have reduced rabbit numbers by an estimated 75-80% (see references in our paper) in South Australia alone since the 1950s.

Rabbits around a waterhole at the myxomatosis trial enclosure on Wardang Island in 1938.
National Archives of Australia/Wikimedia Commons

Together, myxoma virus and RHDV saved the Australian economy an estimated A$70 billion by 2011.

But managing rabbits’ growing immunity to these virus biocontrol agents is now presenting new challenges for Australian land managers.




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Controlling rabbits: let’s not get addicted to viral solutions


This is why our new discovery of a positive interaction between the two main viruses is great news for the Australian environment and economy.

Our study represents the first solid evidence that a combination of these two rabbit diseases is more effective in reducing rabbits’ abundance, providing agencies and landowners with more bang for their buck during rabbit control programs.

Our findings were made possible by one of the longest-running monitoring programs in disease ecology: the 21-year (and ongoing) Turretfield Rabbit Research Project north of Adelaide.

Roughly every two months for more than two decades, PIRSA Biosecurity South Australia has counted, tagged, virus-tested, and released rabbits of all ages from the isolated sentinel rabbit population.

Analysing this unrivalled dataset, we discovered that the probability of dying from rabbit haemorrhagic disease was 10% higher than expected when an individual rabbit had previously been exposed to myxoma virus. These means that rabbits that are now immune to the myxoma virus (Australia’s first rabbit biocontrol) are nevertheless more susceptible to RHDV (Australia’s second rabbit biocontrol).

In other words, the two diseases (a poxvirus and a calicivirus) interacted to give a population-level effect that resulted in more rabbit deaths overall.

Such an interaction between biocontrol agents is rare; in fact, it is the first discovery of its kind in the world.

Tagged rabbit from Turretfield (photo taken September 8, 2014). This individual had no antibodies against RHDV or myxoma virus, but was found dead from haemorrhagic disease two hours later.
David Peacock/Biosecurity SA

The knowledge that the two viruses combine as a potent weapon against rabbits has major implications for land owners and farmers around the world who battle pest rabbits. Disease outbreaks could potentially be timed to ensure that the death rate of pest rabbits is as high as possible.

In Australia, rabbits are a dietary mainstay for two other damaging invasive species: feral cats and red foxes. A large rabbit population can keep the two predator species at high densities, thus promoting their high predation rates on native wildlife.




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Invasive predators are eating the world’s animals to extinction – and the worst is close to home


Keeping rabbit numbers low can therefore benefit our environment. In fact, the rate of native vegetation cover has increased since RHDV began to spread in 1995, and there have been documented increases in the numbers of small native mammal species since that time.

Ecologically informed biocontrol is therefore just another smart way to manage invasive species.

Our discovery also has implications right across the world. European rabbits cause environmental and agricultural damage in places as diverse as the United Kingdom, New Zealand, and in parts of South America.

The ConversationOur findings will also help researchers and conservationists to safeguard the rabbit in its natural range in Europe, and support Australia’s search for other biocontrols in the future.

Corey Bradshaw, Matthew Flinders Fellow in Global Ecology, Flinders University; Louise Barnett, Adjunct researcher, Flinders University, and Thomas Prowse, Postdoctoral research fellow, School of Mathematical Sciences, University of Adelaide

This article was originally published on The Conversation. Read the original article.

The future is fenced for Australian animals



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Mala, also known as rufous hare-wallabies, will be protected behind an enormous cat-proof fence.
Donald Hobern/Flickr, CC BY-SA

Michael Bode, The University of Queensland

Many of Australia’s mammals spend their entire lives imprisoned, glimpsing the outside world through tall chain-link fences and high-voltage wires. There are dozens of these enclosures across Australia. Many are remote, standing alone in the endless expanse of inland Australia, but others are on the outskirts of our largest cities – Melbourne, Perth, Canberra.

Every year there are more of them, the imprisoned population growing, while the wild populations outside dwindle. These are Australia’s conservation fences.




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The captives within our conservation fences are adorable – floppy-eared bilbies, tiny hare-wallabies, long-tongued numbats – and they all share an extreme susceptibility to introduced predators. At least 68 native mammal species cannot exist in the wild if either foxes or cats are present. Many of these species once numbered in the millions, ranging from the woodlands of Queensland to the deserts of Western Australia, but predation has driven them to the brink of extinction.

Fences offer these species a future in the wild, and conservation groups have risen to the challenge. Last week, the Australian Wildlife Conservancy completed a new cat-proof fence in their Newhaven Sanctuary, the largest conservation fence ever constructed.

Fences are extraordinarily successful

Make no mistake, these conservation fences work. Species that wilt at the sight of a fox, that have been exterminated from every corner of the Australian mainland, will explode in numbers behind fences. Along with offshore islands, inside these fences are the only places in Australia where these species can prosper – a few hundred square kilometres of safety, surrounded by 7.6 million lethal square kilometres.

Environmentalists have never particularly liked fences. Rather than hide behind walls, they repeatedly took the fight to the cats and foxes on the outside.

Their tactics have been diverse, innovative and brutal. Managers have rained bullets from helicopters and poison baits from planes. They have set cunning snares and traps, mimicked the smell and sound of their enemies, and have turned landscapes to ash with wildfire.

Nothing has worked for the most threatened marsupials. Some of the largest and most expensive management campaigns in Australian conservation history have ended in exhaustion and stalemate, and with a retreat back behind the fences.

Fences were once a source of vehement debate in conservation circles. Should they be permanent? Are fenced populations wild or captive? Should they contribute to species’ conservation status?

These arguments have effectively been abandoned. Scientific studies and painful experience has proven fences and offshore islands to be the only reliable method of protecting predator-threatened species http://www.wildliferesearchmanagement.com.au/Final%20Report_0609.pdf. In place of these debates, conservation organisations and governments have turned to more practical questions of fence height, electric wire voltage and skirt depth.

So now, on average, Australians are building a new fence every year, some of them truly enormous. The just-completed fence at Newhaven encloses a staggering 10,000 hectares of red sand and spinifex. By the time the project is complete, this fence will be home to 11 different threatened mammal species.

And Australia is not alone: around the world, from New Zealand to Hawaii to South Africa, an archipelago of fences is emerging from an ocean of predators. It is one of the great achievements of modern conservation and has already averted the extinction of critically endangered species. Although it’s much smaller than our network of protected areas, it offers refuge to species that are long-gone from our national parks and wilderness areas.

Red foxes have been extraordinarily successful in Australia.
Harley Kingston/Flickr, CC BY

A troubling pattern

However, in recent years a concerning pattern has begun to emerge. While the number and size of fences continue to increase, the number of new species being protected has stalled. In fact, the last five fences haven’t included any new species – they have only offered additional protection to species that were already protected behind existing fences https://www.nature.com/articles/s41559-017-0456-4.

As an example, the first two marsupials planned for introduction behind the Newhaven fence will be the mala (Lagorchestes hirsutus) and the burrowing bettong (Bettongia lesueur). These two species undeniably deserve more protection. Both are highly susceptible to foxes and cats and will derive tremendous benefit from the protection of this enormous fence. However, both species are already found elsewhere behind fences (four different fences for burrowing bettongs). Meanwhile, yet-to-be-published research from the National Environmental Science Program has found 41 other species that are desperately vulnerable to introduced predators are not protected by any fence.

This problem is not new to conservation. In the 1990s, Australian researchers suddenly realised that our national park system was failing to protect the full range of Australian ecosystems. Despite our best efforts, we had created a system of reserves that was biased towards mountainous landscapes and deserts, and away from the fertile valley floors. The solution was to create new national parks using systematic and mathematical methods.

This discovery – the theory of systematic conservation planning – revolutionised global conservation. In 2018, conservation fences need their own systematic revolution.

Unfortunately, the national park system had natural advantages that fences lack. The vast majority of Australia’s protected areas belong to the state and federal governments. The centralised nature of the protected area network is perfect for systematic thinking and top-down optimisation – picture the Soviet Union’s Politburo. In contrast, the conservation fencing sector is diverse and decentralised – picture the third day of Woodstock.




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All cost, little benefit: WA’s barrier fence is bad news for biodiversity



Fences are built by governments at the state, federal and municipal levels, by multimillion-dollar NGOs like the Australia Wildlife Conservancy, by tiny local environmentalist groups and by profit-making corporations. This diversity is a fundamental strength of the fence network, giving it access to a spectrum of funding and ideas. But it makes it almost impossible to plan in a systematic manner. You can’t tell a small bilby conservation group in western Queensland that they should protect the central Australian rock-rat instead (Zyzomys pedunculatus). It doesn’t necessarily matter to them that bilbies are already protected behind four different fences and the rock-rat has none.

While conservation science tries to work this problem out, new and larger fences will continue to be built at an accelerating rate into the foreseeable future. True, the absence of coordination will make mathematicians break their slide rules, but each fence will do its job. The furry denizens will hop, and scurry, and bounce around, heedless of their precarious safety.

The ConversationAnd for us, from the outside looking in, these fences will help us forget the parlous state of Australian marsupial conservation. It will be possible to forget our record-breaking rate of extinctions, to forget the empty forests and deserts, and to imagine what a bushwalk might have been like before Europeans unleashed foxes and cats onto Australia.

Michael Bode, Associate Professor of Mathematics, The University of Queensland

This article was originally published on The Conversation. Read the original article.

South Africa should sort out the bad from the really bad on its invasive species list



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Managing trout is a contentious issue with conflicting views about whether they pose a risk, or are beneficial.
Shutterstock

Tsungai Zengeya, South African National Biodiversity Institute

This article is the third in a series The Conversation Africa is running on invasive species.

Alien species have been introduced to Africa for a variety of reasons. They provide food, raw materials for industry, ornamental plants, recreation in the form of sport fishing, hunting and pets. Some that are highly valued have been moved around widely. And in some areas they now form prominent components of societies and ecosystems like the domestic cat for example.

Many alien species bring considerable benefits. But some have become invasive, causing a loss of biodiversity, changes to ecosystems, economic losses and, in some cases, even affecting people’s health.

The shrub Prosopis or mesquite is an example. It was introduced to South Africa to provide fodder, firewood and shade in arid parts of the country. But it’s also a major water user. And two trout species (S. trutta and O. mykiss) are used for recreational angling and commercial aquaculture. But they’ve also been implicated in having a negative effect on the environment.

Managing invasive species is therefore critical. In South Africa the movement and use of 552 listed invasive species are managed under the Biodiversity Act and regulations attached to it. But not all the species on the list are equally harmful. Several may in fact be relatively harmless.

All the listed species under these regulations require management. Given that the capacity is limited, regulations should arguably focus on priority species because not all are necessarily harmful to the extent that would justify spending large amounts of time and effort on keeping them under control.

The question then is: are there some species that could be removed from the list? In our recent study we set out to answer this question by classifying species as inconsequential, beneficial, destructive or conflict generating species. This was done by assessing the relative degree of benefit they brought and their negative effects.

Beneficial and harmful species

The classification was done by using a simple scoring system. It had two categories for the negatives (ecological and socio-economic) and two for the benefits (economic and intrinsic).

  1. Inconsequential species: these make up 55% of the species listed under the act and in the regulations. They were associated with relatively low costs and low benefits to society. Species in this group had limited distribution or no known impact and were largely introduced as ornamentals or pets. Some examples include the eastern grey squirrel (Sciurus carolinensis), European perch (Perca fluviatilis), and the Père David’s Deer (Elaphurus davidianus).

  2. Destructive species: these make up 29% of the list. They don’t bring substantial benefits to society or the environment, but they have a highly negative impact. Many were introduced accidentally and are regarded largely as pests and weeds. Examples include invasive rodents like the black rat (Rattus rattus) which causes damage to infrastructure and transmission of zoonotic diseases and pitch canker (Fusarium circinatum) a growing threat to pine plantations and forests worldwide.

The jacaranda is an iconic tree species in the city of Pretoria where it’s regarded as part of the identity.
Shutterstock
  1. Beneficial species: they make up 10% of the list and have clear social or environmental benefits. For example the jacaranda (Jacaranda mimosifolia) is an iconic tree species in the city of Pretoria where the species is regarded as part of the identity and “sense of place” of the city. Active management is not necessary or should only be done in particular cases.

  2. Conflict-generating organisms: these can be either beneficial or destructive, depending on one’s perspective or what value is placed on them. They make up only 6% of the list. There’s huge disagreement about whether these species should be controlled, or how they should be controlled. Examples include woody plants introduced for forestry, erosion control, sand dune stabilisation, agriculture and as ornamentals. Acacias and pines are examples. Animal examples include species like the Himalayan tahr which was introduced to the Table Mountain National Park. The goat has been the focus of eradication attempts, despite strong opposition. It also includes species introduced for aquaculture like maroon and brown trout. Managing trout has been highly contentious with conflicting views about whether they pose a risk, or deliver a benefit. This has led to them being listed and delisted. The trout fraternity refuse to acknowledge that trout are invasive species and highlight the lack of scientific evidence of the risks they pose.

Finding common ground

We need to keep sight of the fact that there is general agreement on 94% of listed species. By identifying the small number that are generating the greatest tension, it’s more likely discussions can be held to reach common ground on regulation.

Most countries in Africa don’t have invasive species regulations. But there’s growing recognition that they’re needed. South Africa offers useful lessons on how this could be done.

The control of species listed under the country’s biodiversity act is compulsory. This means that plans to manage them have to be drawn up and implemented. But this doesn’t seem sensible given that not all are equally harmful and resources are limited. Our study suggests that some of the species currently regulated could be removed from the list.

Countries wanting to set up a system of managing invasive species could start by classifying a prospective list of candidates. Policymakers could then quickly bring out legislation against the most damaging and destructive ones. At the same time, discussions could be had on the ones that generate conflict with the aim of reaching consensus.

The ConversationThis would allow managers and regulators to focus on the most destructive species – as well as those that are at the centre of fierce disagreement.

Tsungai Zengeya, Researcher at the South African National Biodiversity Institute, South African National Biodiversity Institute

This article was originally published on The Conversation. Read the original article.