Billions spent on Murray-Darling water infrastructure: here’s the result


Q J Wang, University of Melbourne and Avril Horne, University of Melbourne

Earlier this year, researchers suggested the amount of water returned to the Murray Darling Basin under a federal program has been “grossly exaggerated”, to the tune of hundreds of billions of litres.

The report argued that government investment in irrigation improvements might even result in a net loss of water for the environment.




Read more:
The Darling River is simply not supposed to dry out, even in drought


To investigate these claims, the Murray Darling Basin Authority commissioned us to undertake an independent review to examine the best available data for every irrigation efficiency project funded across the basin.

We found the government investment into irrigation efficiency projects has achieved 85% of the 750 gigalitres per year target. The remaining 15% of the target may be affected by unintended side-effects.

This result highlights the need for continued review of risks to the basin plan, as Australia grapples with the management of an extraordinary complex natural system.

How is water for the environment recovered?

The Water Act 2007 introduced significant reforms aimed at setting aside more water for the environment. At the time, record high levels of surface water were being consumed. Aiming to save 2,750 gigalitres of surface water (water flowing in the open air, rather than underground) the federal government began buying back water rights and investing in more efficient infrastructure.

The Commonwealth is providing A$3.1 billion to buy these water rights, of which A$2.5 billion has been spent. It is also providing more than A$8 billion for modernising infrastructure and water efficiency improvements, of which more than A$4 billion has so far been spent.

These projects aim to improve water delivery – reducing leaks and evaporation – and make irrigation more efficient. The water saving generated from these projects is shared between the governments for environmental use, and irrigators.

Mass fish deaths earlier in the year raised serious concerns about the health of the Murray-Darling system.
DEAN LEWINS/AAP

What are “return flows”?

To understand why the government investment in irrigation efficiency projects have not achieved 100% of the original target, we need to talk about return flows.

When water is diverted from the river for irrigation, not all of it gets consumed by the plants. Some water will make its way back to the river. This is called return flow. A large part of the return flow is through groundwater to the rivers, and this part is extremely difficult to measure. More efficient infrastructure and irrigation generally means less return flow to the river.

If these reductions are not considered when calculating the water savings, it is possible there will be implications for irrigators, the environment and other water users downstream, that previously benefited from return flows.

What we tried to determine is how much the efficiency projects reduced return flow.




Read more:
We wrote the report for the minister on fish deaths in the lower Darling – here’s why it could happen again


Are the water savings real?

For the first time, we attempted to bring together data on individual projects in order to assess return flows across the basin. We developed a framework for calculating return flows, which took into account water in the rivers, groundwater, and efficiency projects.

This is the first attempt to bring together the existing data on individual projects to assess return flows in the basin at a detailed level. A large portion of the data used in this study was collated for the first time and not previously available in a readily accessible format.

We found a reduction in return flow of 121 gigalitres per year as a result of the government funded projects. This is comparable to 16% of the recovery transferred to environmental entitlements.

What does this mean for the Basin Plan?

There are several important details that must be considered to assess the importance of the return flow volume for the environment and Basin Plan objectives. We do not attempt here to quantify the outcomes, but instead to raise a number of important considerations beyond simply “volume”.

1. Recovered water should be legally protected

Return flows are good for the environment, but are essentially accidental. As irrigation becomes more efficient, inevitably they will diminish.

On the other hand, formally allocated environmental water entitlements are legally protected. It is more secure for the environment – and far easier to keep track of.

2. It’s not ‘efficiency vs the environment’

Part of this debate centres around the idea that reducing return flows means less water for the environment. But in Victoria and New South Wales, before water is allocated to anyone (irrigators or the environment), a base level is set aside. This is the minimum required to keep the rivers physically flowing and to meet critical human needs.

Efficiency projects mainly affect this base-level flow of the river. This means the water reduction is shared across everyone who holds a water licence – the majority of which are irrigators.

This policy means it does not make sense to compare the effect of efficiency projects directly with the recovery of environmental water.

3. Volume is a crude measure of environmental benefit

The focus of the debate around return flows has been based on the annual volume of returned environmental water in comparison to the stated Basin Plan target.

However, the real objective of the water recovery is to achieve environmental objectives in the Basin. This is not just about annual volumes, but the quantity, timing, and quality of fresh water.

How should we move forward?

Our review has particularly highlighted the need for better ongoing data collection and regular evaluations.




Read more:
Aboriginal voices are missing from the Murray-Darling Basin crisis


Both taxpayer investments and the water market are changing irrigation to become more efficient and reducing the river’s base flow. With this in mind, we need to regularly reexamine how we share water between everyone (and everything) that needs it, particularly in extended dry periods.

The Murray-Darling Basin is a constantly changing system, both in terms of climate and irrigation. Return flows are one of a number of potential threats to the Basin Plan. As the system is continually changing, these threats will need to be reassessed with each Basin Plan review.


A Four Corners program on the $13 billion Murray-Darling Basin Plan will air on ABC at 8.30pm on July 8.

This article was co-written by Glen Walker, a former CSIRO employee and now private consultant, who worked with the University of Melbourne on the independent review.The Conversation

Q J Wang, Professor, University of Melbourne and Avril Horne, Research fellow, Department of Infrastructure Engineering, University of Melbourne

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

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What other countries can teach us about ditching disposable nappies



Look familiar? Don’t fret, there are better ways.
Shutterstock.com

Kelly Dombroski

This year, the small Pacific Island nation of Vanuatu announced a plan to ban disposable nappies, as well as other throwaway items such as plastic bags. While some commentators praised the move, others worried about what the alternatives might be, and how this might affect household workloads, particularly for women.

While Vanuatu is the first nation to take such a bold step, it is not the first nation to recognise the environmental problems disposable nappies pose. Although most landfill waste in Australia and New Zealand consists of building waste, disposable nappies make up a significant percentage of household waste entering landfill – Australia uses an estimated 3.75 million of them every day.




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Does becoming a mother make women ‘greener’?


Many urban parents find that a week’s worth of nappies barely fits into their kerbside bin, especially for families with two children in nappies. I’ve certainly met these parents stalking the streets on the evening before bin day, searching for half-empty bins to dump their surplus dirty nappies.

But this is not the only problem: nappies are a significant source of contamination in the waste stream. Infant faeces are a source of live vaccine, bacteria such as E. coli, and many other hazardous contaminants. The correct procedure is to scrape faeces into the toilet before disposing of the nappy. But let’s be honest – the whole attractiveness of disposable nappies is not having to do this, especially while out and about.

Lessons from a bygone age

So what is the alternative? Obviously, before disposable nappies, parents had to use cloth nappies. In Australia, the standard was the fluffy terry cloth folded into a triangle; in New Zealand, the flat flannelette folded differently for boys and girls.

Traditional cloth nappies were much less absorbent, and therefore had to be changed about 15 times per day, before being washed, dried, and folded for next time. It’s no coincidence that this practice dates to an era when households typically featured a stay-at-home mother.

In recent years, modern cloth nappies have emerged, with more absorbent designs that require less frequent changing. They use modern materials such as microfibre, microfleece, polyurethane laminate, and fabrics derived from bamboo. These nappies may be snug in design, pleasing to the eye, and less prone to leaks. They also require less water for laundry, because they can be put straight into a washing machine rather than being soaked as traditional nappies were.

Yet, as Ni-Vanuatu commentators have already pointed out, these designs are not necessarily suitable for tropical climates or warmer weather due to the use of non-breathable fabrics. These fabrics might also encourage nappy rash and other related problems for babies’ delicate skin.

Lessening the load

The search for alternatives does not need to be limited to Oceania, however. My research with families with young infants in northwestern China examined a practice known as ba niao, or “holding out to urinate”. This method of infant hygiene involves very limited use of nappies, meaning laundry can feasibly be done by hand.

Briefly, it involves learning the signals and timing of a baby’s patterns of poop and pee, then holding them out over a basin, toilet or potty for them to release, nappy-free. Caregivers look for signs such as squirming, pushing, fussing, stillness, and other forms of more direct communication that precede an “elimination”. As babies get older and begin to walk, they can be taught to urinate in Chinese-style squat toilets or other appropriate places, with the help of pants with a hole cut out of the crotch.

Items used for ba niao in northwestern China.
Kelly Dombroski, Author provided

In colder parts of China, this is done by using several layers of pants, each with a hole, so babies do not have to be undressed. Caregivers tuck nappy-cloths made from old sheets or other soft rags up into the waistband of the pants, to be quickly and easily removed when a baby seems ready to “go”. If the caregiver misses the signal, the small, light cloth can be easily handwashed and dried on a balcony or radiator. If the caregiver is not near a toilet, the baby may even be held out over the ground or tiles, and urine cleaned up with a mop.

For faeces, babies are encouraged into a regular routine through a large morning feed of milk, and patient “holding out” until the morning elimination is done. If the baby’s bowel movements are less predictable, perhaps due to illness, some families use disposable nappy pads, tucked in the same way as the traditional nappies, but more as a backup for missing a signal rather than relying on it.

‘Holding out’ over a basin as part of traditional hygiene practices.
Kelly Dombroski, Author provided

Households without indoor toilets also use this method, including families who live in their shop and rely on public showers and toilets for hygiene.

This method is used by rich and poor families alike. Research by disposable nappy producers Proctor & Gamble estimated that Chinese consumers of disposable nappies use only one per day – or more accurately, per night. Even those who can afford disposable nappies tend to eschew them in favour of ba niao during daylight hours. Besides a lot less laundry, the reported benefits include less nappy rash, earlier toilet independence, and less crying and fussing.




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Toilet training from birth? It is possible


Is this a realistic practice for countries seeking to quit disposable nappies? It may seem far from westernised norms, but my research has also analysed the content of Australian and New Zealand-based web forums and Facebook groups, with collectively around 2,000 members. These caregivers, mostly mums, are trying to work out the best way to introduce a similar practice to everyday life here, too.

They are inspired by the fact that this is possible in other parts of the world, and may indeed be a key to reducing the laundry load. And if they’re not quite ready to quit disposable nappies altogether, they might at least give up the weekly raid on the neighbours’ rubbish bins.The Conversation

Kelly Dombroski, Senior Lecturer in Human Geography

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

Eelgrass keeps the oceans alive and preserves shipwrecks, so just cope when it tickles your feet



Sea grass meadows at Bonna Point.
Valentina Hurtado-McCormick, Author provided

Valentina Hurtado-McCormick, University of Technology Sydney

Sign up to the Beating Around the Bush newsletter here, and suggest a plant we should cover at batb@theconversation.edu.au.


Have you ever walked into the ocean from a stunning Australian beach and realised the sand was covered with hundreds of ticklish leaves? This submerged canopy is a seagrass meadow, and while you might see them as a nuisance to swim past, they’re a hidden treasure.

Seagrasses are the only group of flowering plants that have adapted to the marine environment. This group comprises nearly 60 species, which typically occupy tropical and temperate regions of the world distributed across 1,646,788 km2.

There is a disproportionately large number of temperate seagrass species in southern Australia, with Zostera species dominating extensive and very diverse meadows.

Eelgrass (Zostera muelleri) is one of the dominant meadow-forming species in Australia. It has the widest distribution of its family (Zosteraceae) in temperate Australian waters, and is vital to our oceans’ health.



The Conversation

Don’t call me weedy!

These aquatic plants have evolved myriad adaptations to survive in the seas, and contrary to what many people think, seagrasses are very different from seaweeds.

Seaweeds are comparatively simple organisms: they are macroalgae with no vascular tissue, which is what conducts water and nutrients throughout a plant. In comparison, eelgrass has leaves, root and rhizomes, with flowers, fruits and seeds for reproduction.


J. Maughn/Flickr, CC BY-SA

They do, however, share one thing. Seagrasses and seaweeds are “holobionts” – meaning that they each play host to a range of microorganisms such as bacteria, fungi and microalgae that help to support their health and survival.

Research has shown that these crucial host-microbe relationships can be easily disrupted.

Climate change is not just affecting the seagrass host; the entire holobiont and even the environment it occupies are suffering from rising temperatures.

Purple plants in warm waters

My research involves studying the response of seagrass and their associated microbes to environmental degradation. I realised how much warming oceans were affecting eelgrass when I suddenly came across purple shoots in a meadow I was sampling once a month.

I was shocked. I had never seen anything like it.

While previous research has described the phenomenon of seagrass leaf reddening, I’d never heard of seagrass going purple in this specific black-purple-white pattern.

We already knew that the eelgrass accumulates red pigments as a sunscreen against the increased UV radiation that results from ozone depletion and related consequences of climate change. My PhD (soon to be published) has found that this colour change has a strong effect on the microbial communities that live on seagrass leaves.

Seagrasses establish and maintain fundamental relationships with the microbes that live among them.
Valentina Hurtado McCormick, Author provided

Why should we care?

Besides producing weird sensations on human feet, eelgrass and its counterparts are a crucial part of our coastal ecosystems. Probably the best example is their nursery role in supporting juvenile fish and crustaceans.

They also provide food for a wide range of grazers, from dugongs to the green sea turtle (as featured in the movie Finding Nemo), which feed on bounteous seagrass meadows.

Finally, we can also thank them for sequestering huge amounts of organic carbon that would otherwise contribute enormously to the greenhouse effect. Referred to as “blue carbon sinks”, researchers have calculated seagrass meadows could store 19.9 gigatonnes of organic carbon worldwide.

I could keep writing about the virtues of Zostera species (and seagrasses in general) for much, much longer, but I will leave you with a single thought: we breathe and eat from a healthy ocean, and the ocean is not healthy without seagrass.

Not just grass under your feet

Seagrass is so protective, I think of them as one of the most altruistic plants on the planet. They keep waterborne pathogens in check and neutralise harmful bacteria, keeping coral reefs healthy, and acting as an important part of the ocean’s well-being.

On the other hand, these aquatic plants also help preserve human heritage. They create a thick sediment layer on the seafloor, beneath which shipwrecks and other treasures are buried and protected from decomposition.




Read more:
Seagrass, protector of shipwrecks and buried treasure


For some 400 million years, eelgrass and other seagrass species have protected the ocean, our planet, and the creatures who live here.

In return, we have managed to create uncountable ways to directly or indirectly threaten seagrass-based ecosystems. As a result, meadows have declined globally at the accelerated rate of 7% per year.

For many of us, seagrass meadows are simply an obstacle to get past on the way to the waves. But for those of us who spend our days with a snorkel and collection tubes, these little watery plants mean far more. When I look at a single seagrass leaf, I see an entire microcosm of interacting entities.


Sign up to Beating Around the Bush, a series that profiles native plants: part gardening column, part dispatches from country, entirely Australian.The Conversation

Valentina Hurtado-McCormick, PhD Candidate, University of Technology Sydney

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

No-take marine areas help fishers (and fish) far more than we thought



A juvenile Plectropomus leopardus from the Whitsundays.
David Williamson/James Cook University

Dustin Marshall, Monash University and Liz Morris, Monash University

One hectare of ocean in which fishing is not allowed (a marine protected area) produces at least five times the amount of fish as an equivalent unprotected hectare, according to new research published today.

This outsized effect means marine protected areas, or MPAs, are more valuable than we previously thought for conservation and increasing fishing catches in nearby areas.

Previous research has found the number of offspring from a fish increases exponentially as they grow larger, a disparity that had not been taken into account in earlier modelling of fish populations. By revising this basic assumption, the true value of MPAs is clearer.




Read more:
Protecting not-so-wild places helps biodiversity


Marine Protected Areas

Marine protected areas are ocean areas where human activity is restricted and at their best are “no take” zones, where removing animals and plants is banned. Fish populations within these areas can grow with limited human interference and potentially “spill-over” to replenish fished populations outside.

Obviously MPAs are designed to protect ecological communities, but scientists have long hoped they can play another role: contributing to the replenishment and maintenance of species that are targeted by fisheries.

Wild fisheries globally are under intense pressure and the size fish catches have levelled off or declined despite an ever-increasing fishing effort.

Yet fishers remain sceptical that any spillover will offset the loss of fishing grounds, and the role of MPAs in fisheries remains contentious. A key issue is the number of offspring that fish inside MPAs produce. If their fecundity is similar to that of fish outside the MPA, then obviously there will be no benefit and only costs to fishers.




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More fish, more fishing: why strategic marine park placement is a win-win


Big fish have far more babies

Traditional models assume that fish reproductive output is proportional to mass, that is, doubling the mass of a fish doubles its reproductive output. Thus, the size of fish within a population is assumed to be less important than the total biomass when calculating population growth.

But a paper recently published in Science demonstrated this assumption is incorrect for 95% of fish species: larger fish actually have disproportionately higher reproductive outputs. That means doubling a fish’s mass more than doubles its reproductive output.

When we feed this newly revised assumption into models of fish reproduction, predictions about the value of MPAs change dramatically.


Author provided

Fish are, on average, 25% longer inside protected areas than outside. This doesn’t sound like much, but it translates into a big difference in reproductive output – an MPA fish produces almost 3 times more offspring on average. This, coupled with higher fish populations because of the no-take rule means MPAs produce between 5 and 200 times (depending on the species) more offspring per unit area than unprotected areas.

Put another way, one hectare of MPA is worth at least 5 hectares of unprotected area in terms of the number of offspring produced.

We have to remember though, just because MPAs produce disproportionately more offspring it doesn’t necessarily mean they enhance fisheries yields.

For protected areas to increase catch sizes, offspring need to move to fished areas. To calculate fisheries yields, we need to model – among other things – larval dispersal between protected and unprotected areas. This information is only available for a few species.

We explored the consequences of disproportionate reproduction for fisheries yields with and without MPAs for one iconic fish, the coral trout on the Great Barrier Reef. This is one of the few species for which we had data for most of the key parameters, including decent estimates of larval dispersal and how connected different populations are.

No-take protected areas increased the amount of common coral trout caught in nearby areas by 12%.
Paul Asman and Jill Lenoble/Flickr, CC BY

We found MPAs do in fact enhance yields to fisheries when disproportionate reproduction is included in relatively realistic models of fish populations. For the coral trout, we saw a roughly 12% increase in tonnes of caught fish.

There are two lessons here. First, a fivefold increase in the production of eggs inside MPAs results in only modest increases in yield. This is because limited dispersal and higher death rates in the protected areas dampen the benefits.




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However the exciting second lesson is these results suggest MPAs are not in conflict with the interests of fishers, as is often argued.

While MPAs restrict access to an entire population of fish, fishers still benefit from from their disproportionate affect on fish numbers. MPAs are a rare win-win strategy.

It’s unclear whether our results will hold for all species. What’s more, these effects rely on strict no-take rules being well-enforced, otherwise the essential differences in the sizes of fish will never be established.

We think that the value of MPAs as a fisheries management tool has been systematically underestimated. Including disproportionate reproduction in our assessments of MPAs should correct this view and partly resolve the debate about their value. Well-designed networks of MPAs could increase much-needed yields from wild-caught fish.The Conversation

Dustin Marshall, Professor, Marine Evolutionary Ecology, Monash University and Liz Morris, Administration Manager, Monash University

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

Regardless of what the Federal Court says, you shouldn’t put ‘flushable’ wipes down the loo


In the aftermath of a sewer overflow, “flushable” wipes are entangled in the vegetation.
Sydney Water Corporation

Ian Wright, Western Sydney University

On Friday the Australian Federal Court found in favour of Kimberly-Clark’s “flushable wipes” in a legal action brought by the Australian Competition and Consumer Commission (ACCC).

There was insufficient evidence to convince Justice Gleeson that Kimberly-Clark’s wipes were primarily responsible for significant blockages and were therefore unsuitable for flushing down the toilet.

This was a very different outcome to a 2018 court case, also in the Federal Court, in which White King Flushable Wipes were fined A$700,000 for misleading claims.




Read more:
Don’t believe the label: ‘flushable wipes’ clog our sewers


The water industry has responded with disappointment to the latest ruling. Sydney Water claims 75% of sewer blockages involve wet wipes. Part of the problem is that, once flushed, wipes are anonymous and the blame for blockages cannot be laid at a specific company’s door.

This case highlights the need to determine what “flushable” really means. Does it mean you can physically flush it down a toilet? Or that it will biodegrade without major issue in the sewerage system, in the manner of toilet paper?

Flushable problems

ACCC Chairman Rod Sims explained that the commission pursued the case against Kimberly-Clark because of increasing reports from Australian water authorities of “non-suitable products being flushed down the toilet and contributing to blockages and other operational issues”.

Consumer groups such as Choice have also expressed concern about the impact of these products for years. Choice has produced a video that demonstrates how poorly some wipe products disperse in water, compared with toilet paper.

The water industry is frustrated with frequent sewer blockages, many of which are caused by materials people should not have flushed down the toilet. The industry slogan is that only the “three Ps” – pee, poo, and (toilet) paper – should be flushed down the toilet.

What is all the fuss about?

Blocked sewers are deeply unpleasant for everyone involved: professionals who have to unblock them, local residents, and the animals and plants that live nearby.

This is also linked to another chronic problem in sewers: fats. These mainly come from cooking fats and oils that coagulate in sewers. They have combined to create horrific “fatbergs”, often photographed with disgusted fascination.

‘Fatbergs’ are made when fats and oils coagulate in sewers, trapping other material – like so-called ‘flushable’ wipes.
Courtesy of Sydney Water

Much less common are the images showing the discharge of liquid sewage due to the blockages. In my previous career as a scientist in the water industry, I visited hundreds of such scenes.

They are smelly and unsightly, but of more concern is the public health hazard they pose. Raw sewage is dangerous due to its abundance of disease-causing organisms. Overflows can happen anywhere, often in very public places.

Sewers are underground, and often beside waterways. This means they might be blocked and leak raw sewage for weeks before it is noticed.

Tree roots and drought

Drought and trees are also contributing to the problem wipes pose. Currently much of southeastern Australia is in drought. Many trees in our cities are desperate for water, and their roots invade sewers.

Wipes and similar materials are readily entwined in tree roots. Wipes have a well-known tendency to become entangled and accumulate gradually to build a blockage.

Whose standard do you believe?

The industry body Water Services Australia is currently working on an Australian industry standard for testing “flushability”. This is expected later in the year.




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Microplastic pollution and wet wipe ‘reefs’ are changing the River Thames ecosystem


On the other hand, many wipes companies claim their products do break down when flushed – although Kleenex, for example, advises not flushing more than two wipes at a time. These wipes comply with an existing industry standard for “flushability”, although this standard was developed by two trade associations that represent wipe manufacturers.

The development and application of a comprehensive Australian standard is urgently needed to address this problem.The Conversation

Ian Wright, Senior Lecturer in Environmental Science, Western Sydney University

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

White cedar is a rare bird: a winter deciduous Australian tree



Scamperdale/Flickr, CC BY-SA

Gregory Moore, University of Melbourne

Sign up to the Beating Around the Bush newsletter here, and suggest a plant we should cover at batb@theconversation.edu.au.


White cedar (Melia azedarach) grows naturally across Queensland and northern New South Wales, but is widely planted as an ornamental tree all over Australia. It also grows across much of Asia, and belongs to the mahogany family.

This wide dispersal sees the species given a very wide and diverse range of common names, including: umbrella cedar, pride of India, Indian lilac, Persian lilac, and Chinaberry. It Australia it is known as white cedar due to its soft general-purpose timber.

The name Melia was the Greek name given to the ash tree, which has similar foliage, and azedarach means “poisonous tree” – parts of it are toxic.




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White cedar is something of a rarity among Australian native trees, as it loses its leaves in winter or early autumn. Winter deciduous trees are highly valued in landscape design as they provide all the benefits of summer shade, but allow winter light.



The Conversation

While Australia has an abundance of evergreen tree species and a variety of summer deciduous trees that lose their leaves in summer when water is scarce, we have few winter deciduous native trees. White cedar fits the bill beautifully, and despite a few shortcomings has some very attractive traits.

White cedar is usually a small spreading tree with a rounded canopy up to about 6m in height, but under the right conditions trees can be more than 20m tall, with a canopy spread of 10m or more. They have quite dense foliage composed of dark compound leaves up to 500mm long, which transition from dark green to a pale yellow in autumn.

As a winter deciduous tree they are a very popular native tree that has been widely planted as street trees and in domestic gardens, where specimens of 10-12m are common. The trees are often considered to be short-lived (around 20 years), but in gardens and where irrigation is available some may live for 40 years or longer.

Good specimens of white cedar have many small flowers (20mm) that are white with purple/blue stripes and a wonderful, almost citrus-like scent. The fruits are about 15mm in diameter and bright orange in colour. They are usually retained over winter and so the trees provide a seasonal smorgasbord – shade in summer, autumn foliage colour, orange fruits in winter, and attractive scented flowers in spring.

Many specimens are prolific in their production of fruits and seeds, which readily germinate, underscoring the weed potential of the species under the right circumstances. They can be an invasive species in some parts of Asia and Africa.

Unfortunately as the fruits mature and dry they become as hard as ball bearings. If you mow over them they can fire from under a mower like bullets, and if they land on a hard paved surface they can be a tripping hazard for people who unexpectedly find themselves skating. The fruits and foliage can also be quite toxic if eaten. So this would appear to put a bit a dampener on the use of the tree. However, in recent years non-fruiting varieties of white cedar have become available and these have proven popular as street and garden trees.

A toxic treat

Many parts of the tree are toxic – interestingly, though, not the fleshy part of the fruit. It has evolved to be attractive to the birds that disperse seed. However the seeds are very poisonous, and as few as 6 or 8 seeds can be fatal for children. Fortunately, the seeds are very hard and do not taste very pleasant, so the risk of humans eating them is quite low.

Despite this, white cedar has been widely used as a medicinal plant by indigenous cultures, especially for intestinal parasites. The seeds have been widely used to make beads by indigenous peoples in Asia and Australia, and in some places the tree is called the bead tree.

An easy grower

One of the good things about white cedar is they are easily grown, and cope quite well with the low rainfall in many parts of Australia. They also tolerate a variety of soil types, which is why they have been so widely and successfully spread.

The trees are quite resistant to termite damage and their poison does protect them from grazing mammals and some insects. They can be prone to root problems and it is not uncommon for their trunks to break off at ground level, especially if they have been poorly propagated or planted, which can be a big problem when they are planted as a street tree.




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Built like buildings, boab trees are life-savers with a chequered past


Although they are related to mahogany, their wood can be quite brittle and easily broken, which means care should be taken when pruning or working on them. When the wood dries it shatters easily and can send shards in all directions when you try to snap it. In Australia the wood can range from light cream to dark brown in colour, and while it is quite a useful wood for carving and furniture, it is not widely used.

As a winter deciduous native tree of smallish stature, with many attractive characteristics, the white cedar really is an Australian rarity, despite how widely it occurs or is planted.


Sign up to Beating Around the Bush, a series that profiles native plants: part gardening column, part dispatches from country, entirely Australian.The Conversation

Gregory Moore, Doctor of Botany, University of Melbourne

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