introduced species

An(other) Accidental Invasion

This is a guest post by Emily De Stigter.

Gazing across a north-eastern Victorian landscape, you might notice some unusually fluorescent shades of green mixed into the otherwise earthy tones of Eucalypt forests. Generally, the brightness in hue indicates a species that did not originate in Australia, and if the lime colour appears alongside a riverbank, what you are likely looking at is some form of invasive willow. Since the first species was introduced to Australia in the 1930s, dozens of different willow species now cover hundreds of kilometres of river bed in Victoria, visibly altering the look (and function) of the landscape. So how did these non-native trees end up here?

We put them there, of course! Willows hail from Europe and were brought in at the suggestion of natural resource managers to provide river bank stability in paddocks and shading for cattle. Certainly, at the time this was a reasonable recommendation based on what managers knew of willows: they have thick, matted root systems that excel at holding soil in place. Unfortunately, the managers responsible for introducing the willows did not anticipate the massive problem the shrubs would cause in years to come.

Willows growing into Yarrabula Creek in northeastern Victoria.  Image: Emily De Stigter

Willows growing into Yarrabula Creek in northeastern Victoria. Image: Emily De Stigter

At first, after planting the willows all seemed well. Seedlings grew to trees and the willows were successfully doing their job in stabilising riverbanks. Unfortunately, as time went by river managers and farmers began to slowly recognise the turmoil that the willows were causing. Their fine, dense roots were so successful at holding soil together that instead of stopping erosion, they began causing it. As willows grow larger, their finger-like root systems extend toward the centre of the river, grab onto the soil and pull it upwards, eventually forcing the river bed to shallow.

Then, since the river has less depth, the displaced water is diverted around the willows, widening the river. Over time, this results in islands of willows in the middle of the altered rivers and a patchwork of willows within and along entire river catchments. This pattern is detrimental to the surrounding ecosystems (and avid Victorian fishermen) because shallow rivers cannot house large populations of native fish. Additionally, many willow species form dense, single species stands with shady underbellies where no native species are able to grow due to the lack of light.

Mature, foliating willow at high elevation, near Mount Hotham, Victoria.  Image: Emily De Stigter

Mature, foliating willow at high elevation, near Mount Hotham, Victoria. Image: Emily De Stigter

Grey sallow willows ( S. cinerea ) along the Buckland River, somewhat askew from a recent flood.  Image: Emily De Stigter

Grey sallow willows (S. cinerea) along the Buckland River, somewhat askew from a recent flood. Image: Emily De Stigter

With such dire consequences, it may seem like a massive oversight of the managers to introduce these trees, but it was seemingly done with good managerial intentions and minimal public opposition. In fact, this sort of accidental, human-mediated invasion happens all the time and in many different forms across Australia and the world. Within Australia, the most famous accidental invasion story is that of the cane toads that were introduced in 1935 in the hopes that they would eat up the cane beetles that were destroying sugar crops in Queensland.

The fairly significant misstep in the toad story is that cane toads did not actually eat the cane beetles, one of the reasons being that the toads are generalists, happy to gobble down many different types of insects that happen to cross their paths. So, unfortunately, the cane beetles weren’t eaten, the sugar cane was still being eaten, and the cane toads became a new problem, spreading from coastal Queensland all across the northern coast of Australia to the west coast, eating every insect in sight (except the cane beetles).

Cane toads ( Bufo marinas ) are another example of a species intentionally introduced to Australia by humans.  Image: Wikimedia Commons

Cane toads (Bufo marinas) are another example of a species intentionally introduced to Australia by humans. Image: Wikimedia Commons

The cane toad and the willows are examples of intentional human-mediated introduction, leading to accidental invasions. However, very often species will be introduced without humans even realising that they themselves were the cause until much later. For example, it is thought that many non-native plant species are introduced by seeds becoming stuck to boots of unconcerned passengers travelling abroad. The plants can then seed in a new, pest-free location.

Another way that species can become invasive is through human interference in gardens. Green thumbs relish in their unique spread of trans-continental herbs while accidentally introducing them to a new, potentially idyllic habitat. Animals are capable of utilising humans to inhabit faraway locations as well: certain lizards have attached themselves to the undersides of planes and jumped off in a newly discovered home. One of the most successful invaders of all time, the black rat is famous for hitching a ride on ships travelling from Asia to Europe as long ago as the First Century A.D, and now inhabits nearly every continent.

So when you’re glancing around Victorian landscapes and notice some species that don’t quite appear to belong… you’re probably right! Victoria is home to hundreds of species of non-native flora and fauna, most of which have arrived in this country as a result of our recent and ancient human relatives. Perhaps with this information you’ll now feel a bit more patient with airport security when they ask to see the fruits you’re trying to carry across international borders!

Emily De Stigter

Emily moved from the redwoods of northern California where her passion for botany bloomed. Here in Melbourne she is working on her PhD in plant ecology at Monash University, studying the flowering patterns of invasive willows in northeastern Victoria. 

Banner image of developing female willow catkins courtesy of Emily De Stigter.

Fantasy, Rabbits & Conservation: Watership Down & the Importance of Environmental Fiction

Yes, it’s a story about rabbits - and Australia hates rabbits. What possible relevance could a book written in 1970s England, set in the British countryside, and explicating the plight of a few lost bunnies have to Australia’s present day environmental predicaments (to put habitat destruction, climate change and species endangerment extremely lightly)?

Well the answer is, more than you’d think. Considered one of the most famous environmental allegories in the history of English Literature, Richard Adams’ Watership Down may only have begun as a simple fantasy story told to his own children. However, it has since transformed into a symbol of pro-conservation and environmentalism, capturing the empathetic hearts and minds of readers through the story of a group of rabbits whose burrow is destroyed by humans.

The amazing potential of many fantasy and science fiction writers to seemingly ‘predict the future’, especially in terms of environmental effects and technological advancement, has become more and more evident in contemporary writing. It is now difficult for many writers to discuss global issues through fiction without humans’ destruction of nature and its species coming into play. Now at the forefront of so much scientific attention, it should be difficult for just about anyone, let alone writers, to ignore such issues.

The destruction of the rabbits’ home too clearly represents what occurs, and has occurred, in Australia and more locally Victoria for over 200 years. The devastation of so many natural habitats in Melbourne and surrounding areas means that, although not rabbits, Australia’s native animals are being forced to seek alternative habitats or otherwise survive in the ones that humans have altered.

All of this might seem blaringly obvious to some, but it is clear that more action needs to be taken to prevent further habitat destruction and species endangerment, or to relieve the damage that has already been done. Although millions of dollars have so far been spent to protect threatened species, federal government action has only resulted in one animal being removed from Australia’s threatened species list – the saltwater crocodile (a patch of clear blue in the midst of a dismally rainy day).

Many governmental and private sustainability organisations are indeed working towards protecting species and lessening the effects of habitat destruction, but it is clear that a broader input from the public is vital for action to be effective. Although on the odd occasion publicity regarding native animals and habitat devastation appears, the amount of times such stories actually surface does not correlate with the real significance of the problem. In other words, one story on a new native animal at the zoo does not correspond to the many hundreds of issues surrounding the plight of Victoria’s natural environments.

At this point in time, many adults are probably more likely to read or watch fictional stories, if just with their children, than will actively seek out scientific information on environmental issues. More people will better understand and even relate to the plight of animals whose homes have been destroyed if it is described in such a way that anthropomorphises them. Although perhaps a sad reality, many elements of literature provide effective ways of encouraging empathy towards animals other than humans. A recent study showed that reading literary fiction can actually enhance a person’s understanding of another’s mental state (Kidd & Castano 2013), suggesting that fiction is much more capable of influencing human social relationships than has been assumed. Perhaps it also has the power to increase our understanding of other elements of human life. It has been said that fiction can reveal the truth that reality obscures. I think environmentalist fiction can do this, if at least for those currently unable to see the truth in an already blatant reality.

Reading is definitely not for everyone though, and it is true that many non-environmentalists are probably not very likely to read literature that is known for its positive take on conservation. However, simply by writing and publicising such stories, authors and journalists may slowly be able to turn around at least a few inquisitive minds that previously found it difficult to empathise with native fauna.  

As well as personifying the rabbits, Adams makes sure to emphasise the downfall of those few creatures that become too alike to humans. When leader Hazel and the other traveling rabbits come across a burrow that reluctantly takes them in, it isn’t long before they realise that something about this unusual new home isn’t quite right. It is eventually discovered that the pessimistic attitude of this newly found colony of rabbits is due to their acceptance that some must be sacrificed to the rabbit traps placed around their burrow by the local farmer. This human intrusion has caused them to become ‘different from other rabbits’; more human in themselves and more sacrificial of other creatures in order to survive. Although death and survival are of course natural parts of any animal’s life, the development of a morally based choice to sacrifice the newcomers to the traps is distinctly human.

Just as in Orwell’s Animal Farm, it is strange how frightening it can be to envision a world where other animals have taken on a human persona, mirroring in particular the characteristics of humanity that most of us like to pretend we don’t possess - greed, betrayal, selfishness and xenophobia, to name but a few. Although in terms of survival many of these traits are evident in certain other animals, humanity’s ‘speciesist’ decision to forsake the lives of what have been deemed lesser beings for the expansion of the human population is one that is made in the light of intelligence and responsibility – a responsibility to protect those animals that cannot combat the effects of environmental destruction on their own. As Adams explains, ‘Animals don’t behave like men…If they have to fight, they fight; and if they have to kill, they kill. But they don’t sit down and set their wits to work to devise ways of spoiling other creatures’ lives and hurting them.’

Much like E.M. Forster predicts the popular use of video communication in 'The Machine Stops', and similarly to H.G. Wells and 'The Time Machine' describing the possible consequences of industrialisation, Adams comments on (and somewhat foretells) the worldwide issue of mass species extinction and the destruction of nature. Expanding on this, many contemporary novels also seem careful to focus on environmental catastrophe when it comes to the end of the world. Once it was the plague, more recently nuclear war, but climate change has now stolen the spotlight for the apocalyptic fear of the 21st Century, and with good reason. So the next time you’re looking for a book to read, pick up Watership Down. It is not only an entertaining, sometimes humorous, and heartfelt story about some of nature’s creatures, but is also a novel that inspires both empathy and fear – empathy for those animals whose lives are so dangerously affected by humans, and fear for what we as humans may destroy if changes are not made. 

Already read and enjoyed Watership Down? Check out the booklist below for similar fiction and non-fiction titles.  



Children’s Fiction

The Lorax – Dr Seuss

The Animals of Farthing Wood – Colin Damn

The Wind in the Willows – Kenneth Grahame

Red Wall – Brian Jacques

Mrs Frisby and the Rats of Nimh – Robert C. O’Brien

The Amazing Maurice and his Educated Rodents – Terry Pratchett

General Fiction

Animal Farm – George Orwell

Oryx and Crake – Margaret Atwood

The Machine Stops – E.M. Forster



The End of Nature – Bill McKibben

The Weather Makers – Tim Flannery

After the Future: Australia’s New Extinction Crisis – Tim Flannery

Walking – Henry David Thoreau