.

  • Written by Gregory Moore, Doctor of Botany, University of Melbourne
River red gums' iconic silhouette is found across Australia. The Conversation/Wikimedia Commons, CC BY-SA

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


River red gums, Eucalyptus camaldulensis, are among the most iconic of Australia’s eucalypts. They are the most widely distributed of all the eucalypts. They grow along rivers, creeks, waterways and flood plains where many Australians like to picnic, so most of us get to know and love them.


Read more: This centuries-old river red gum is a local legend – here's why it's worth fighting for


Formerly known as Eucalyptus rostrata, the species was one of the first eucalypts encountered in parts of Australia by European settlers. Curiously, the name camaldulensis comes from the Italian monastery of Camaldoli near Naples, where a specimen grown from seed in a private garden was given the name Eucalyptus camaldulensis in 1832. No one knows how the seed got to be there!


The Conversation

River red gums can be very large spreading trees with huge trunks more than 5 metres around. In parts of Australia, such as along the Murray River, they can be very erect trees reaching more than 45m tall.

Most specimens have smooth bark with a mottling of multiple colours ranging from creams to orange and red, but there may be a skirt of fibrous grey bark for the first few metres of the base. They are called river red gums because they grow along rivers and their wood when freshly exposed is a bright red; almost blood-coloured.

River red gums have been used by Indigenous people for canoes, bowls, shields, and other utensils. The wood is red is because it contains very high levels of chemicals such as polyphenols, which are a natural antiobiotic when combined with air.

River red gums growing along the Murray River. Elizabeth Donoghue/Flickr, CC BY-NC-SA

These chemicals not only protect the living tree from disease and some pest attacks, but make the timber very durable. These chemicals meant river red gums were used for medicinal purposes by Indigenous people. The wood has been widely used for railway sleepers, fence posts, and piers and wharfs where durability and water resistance are desirable. They have been widely planted overseas and in some countries pose a serious weed problem.

The trees can have very long lives, and may reach 1,000 years of age. They grow very rapidly when conditions are favourable and so become large trees quite quickly. But as they get older it is very difficult to age them without damaging the tree and putting it at risk of disease and decay. So their ages are estimated, as no one wants to be responsible for killing a grand old tree just to confirm its age!

Older specimens almost always develop large hollows, which can take centuries to form. The hollows provide refuges for birds, mammals and reptiles. The nesting sites are often raucously defended by brightly coloured parrots. The trees and the nectar from their small white flowers are also very important for honey production – a large tree in full flower over the warmer months can attract so many bees that the whole tree can be heard humming from many metres away; it’s a wonder the tree doesn’t take off.

Trees in full flower can hum with bees. Rexness/Flickr, CC BY-NC-SA

At certain times of the year, often during summer, river reds can be very heavily grazed by insects to the point where their leaves are skeletonised. The trees look as though they are about to die, but they are very resilient and a few months later most are back to a full and healthy canopy. Another insect, the psyllid, also feeds on and skeletonises the leaves. It has a sweet, waxy covering called a lerp that protects the vulnerable insect nymphs beneath. Some Indigenous groups scrape off the lerps, roll them into a ball, and eat them like a lolly.

Surviving floods and driving rain

Any tree that can live for a millennium must be adaptable, so like some other eucalypt species, river red gums can shed up to two-thirds of their foliage when soils dry out during a drought, which reduces water demand and prevents the trees from wilting. This shedding often causes people to complain about the trees when they grow in towns and cities, but when the rains come a few months later they rapidly produce new leaves and are soon once again in full canopy.


Read more: The glowing ghost mushroom looks like it comes from a fungal netherworld


River red gums can tolerate immersion in flood waters for up to nine months. They do this by having extensive roots, some of which contain a spongy, air-filled tissue called aerenchyma that allows for the accumulation and transport of much-needed oxygen in waterlogged soils. This adaptation to stressed soils also means river red gums can do quite well in disturbed urban soils when the urban sprawl impinges on their natural domain.

River red gums readily seed after flooding events and great numbers of young trees may germinate. However, relatively few survive to maturity due to competition from other red gums, other trees, and weeds. They may also struggle to survive in some places due to a lack of water.

Because river reds occur in some of the driest and harshest parts of the Australian mainland, you might think they are very efficient users of water. However, nothing could be further from the truth. The trees can have very deep, spreading and searching root systems, which tap into subterranean water, even if the water is many metres from the trunk. They are luxury water users with very little capacity for water use control. If water becomes really limiting, they simply wilt.

Territorial trees

E. camaldulensis produces a water-soluble chemical that is washed from its leaves by rain. These chemicals inhibit the growth of other plants, including river red gum seedlings, under the canopy. This phenomenon is called allelopathy, and along with a dense canopy inhibits plant growth under the trees. These chemicals are washed from the soil by flood water, which makes way for the germination of seedlings after floods. This is a wonderful mechanism that ensures seedlings do not germinate when conditions are dry and where they would compete with the parent tree for limited water, but germination is facilitated when there is plenty of water and soils are wet.

River red gums clear out the ground around them with toxic chemicals that discourage the growth of competitors. allelopathy/Flickr, CC BY-NC-SA

Some people think river red gums are dangerous because they shed large limbs without warning on calm, still, summer days. There is no doubt this does happen, but there is no clear evidence they shed limbs more often than other species.

The problem is complex, because they tend to grow everywhere people want to go. They provide shade along waterways on a hot, dry continent. In going to places where the trees grow, people tend to compact the soil with their vehicles and footpaths, which can be causes of limb shedding. The compaction of the soil affects soil moisture and aeration, which can lead to limb shedding.


Read more: Warrigal greens are tasty, salty, and covered in tiny balloon-like hairs


In other contexts such as farms where limbs are shed, many old river red gums are growing in highly disturbed or changed ecosystems. Furthermore, many of these remnant specimens are often stressed and getting older and so more prone to shedding.

River red gums trace the watercourses of mainland Australia, and are easily seen from aeroplanes as you cross the continent. They connect the continental fringes with its arid heart. Their lives can span many human generations and it is nice to think that the majestic old trees that pull at our heartstrings have done the same to previous generations and, if we and they are lucky, will continue to do so for generations of Australians yet to come.


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

Gregory Moore does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.

Authors: Gregory Moore, Doctor of Botany, University of Melbourne

Read more http://theconversation.com/the-river-red-gum-is-an-icon-of-the-driest-continent-118839

Your Airbnb guest could be a tenant. Until the law is cleared up, hosts are in limbo

A Victorian court decision that an Airbnb agreement had the status of a lease has profound implications for guests and hosts. Daniel Krason/ShutterstockWith summer holidays around the corner, many Vic...

Bill John Swannie, Lecturer in College of Law and Justice, Victoria University - avatar Bill John Swannie, Lecturer in College of Law and Justice, Victoria University

5 reasons I always get children picture books for Christmas

Children who love being read to are more likely to find learning to read easier. from shutterstock.comChristmas is just around the corner. If you’re wondering what to get your child, your friend...

Kym Simoncini, Associate professor Early Childhood and Primary Education, University of Canberra - avatar Kym Simoncini, Associate professor Early Childhood and Primary Education, University of Canberra

Tough nuts: why peanuts trigger such powerful allergic reactions

The humble peanut. Tasty for most, treacherous for some. Dr Dwan Price, Author providedFood allergens are the scourge of the modern school lunchbox. Many foods contain proteins that can set off an ove...

Dwan Price, Molecular Biologist and Postdoc @ Deakin AIRwatch pollen monitoring system., Deakin University - avatar Dwan Price, Molecular Biologist and Postdoc @ Deakin AIRwatch pollen monitoring system., Deakin University

Must end soon! But not too soon! The catch in time-limited sales tactics

Time-limited offers leverage risk-aversion. That is, the more you dislike risk, the more likely it is you will take the bait and buy now. www.shutterstock.comAs Christmas shopping ramps up, you may be...

Daniel Zizzo, Professor and Academic Dean of the School of Economics, The University of Queensland - avatar Daniel Zizzo, Professor and Academic Dean of the School of Economics, The University of Queensland

Refugees without secure visas have poorer mental health – but the news isn't all bad

Refugees without permanent visas can experience a prolonged sense of insecurity and displacement. From shutterstock.comThere are more than 29.4 million forcibly displaced asylum seekers and refugees a...

Yulisha Byrow, Postdoctoral Research Fellow, UNSW - avatar Yulisha Byrow, Postdoctoral Research Fellow, UNSW

God made the rainbow: why the Bible welcomes every colour in the gender spectrum

The Bible affirms, in various ways, the inclusion of those who diverge from male-female gender norms. ShutterstockThis article is part of a series exploring gender and Christianity “God made ...

Robyn J. Whitaker, Senior Lecturer in New Testament, Pilgrim Theological College, University of Divinity - avatar Robyn J. Whitaker, Senior Lecturer in New Testament, Pilgrim Theological College, University of Divinity

Jojo Rabbit: Hitler humour and a child's eye view of war make for dark satire

Jojo's allegiances in the film are split between an imagined friends and a real hideaway. Fox SearchlightJojo Rabbit is not Disney Studios’ first foray into Hitler parody. In 1943, it produced ...

Benjamin Nickl, Lecturer in International Comparative Literature and Translation Studies, University of Sydney - avatar Benjamin Nickl, Lecturer in International Comparative Literature and Translation Studies, University of Sydney

Boosting Your Child’s Learning through Play

Being a parent is probably the highest responsibility one has in a lifetime. Once it happens, it becomes ongoing and keeps posing new challenges to us. Of course, it may seem easy from some perspe...

Diana Smith - avatar Diana Smith

Different ideas of Christmas Gifts to give to your beloved ones

"CHRISTMAS GIFTS – one of the best festival gifts to give to your closed ones. Find Christmas presents for everybody on your checklist. Christmas is now here, and if that you haven't got a hop on ...

News Company - avatar News Company

The Ultimate Guide to Sneakers and Sneaker Brands

When it comes to finding the perfect pair of sneakers, it can be hard to know where to start. Finding the right pair for any kind of occasion can be difficult, so brushing up on your knowledge of sn...

News Company - avatar News Company

Conservative landslide at UK's Brexit election; Trump's ratings rise on strong US economy

Led by Boris Johnson, the Conservatives won 56% of the vote and will have an 80-seat majority. AAP/EPA/ VIckie FloresAt the December 12 UK election, the Conservatives won 365 of the 650 House of Commo...

Adrian Beaumont, Honorary Associate, School of Mathematics and Statistics, University of Melbourne - avatar Adrian Beaumont, Honorary Associate, School of Mathematics and Statistics, University of Melbourne

Johnson's thumping win an electoral lesson in not just having policies, but knowing how to sell them

With Johnson's crushing win, Brexit will now happen. But this may also be the start of the break-up of the UK. AAP/EPA/Vickie FloresSo for all the talk of narrowing polls, tactical voting, and possib...

Simon Tormey, Professor of Politics, University of Bristol - avatar Simon Tormey, Professor of Politics, University of Bristol

View from The Hill: Morrison won't have a bar of public service intrusions on government's power

Scott Morrison has rejected or sidelined a number of recommendations from the long-awaited Thodey review. AAP/Paul BravenScott Morrison has rejected or sidelined a number of recommendations from the l...

Michelle Grattan, Professorial Fellow, University of Canberra - avatar Michelle Grattan, Professorial Fellow, University of Canberra

VIDEO: Michelle Grattan reflects on the year in politics

For their last video for the year, University of Canberra Vice-Chancellor Deep Saini and Michelle Grattan look backwards to the big issues which have shaped political discourse. They discuss the surpr...

Michelle Grattan, Professorial Fellow, University of Canberra - avatar Michelle Grattan, Professorial Fellow, University of Canberra

Choosing a Heavy Weighted Bathmats

Decorating your bathroom doesn’t finish with the paint choice or tile colours. You can change the whole room with the change of your towel set. There are no rules that say that you need to have a ...

News Company - avatar News Company

God as man, man as God: no wonder many Christian men today are having a masculinity crisis

How men saw God shaped how they saw themselves, and in turn, how they saw women. WikimediaThis article is part of our Gender and Christianity series. To understand contemporary Christian ideas about...

William Loader, Emeritus Professor of New Testament at Murdoch University, Murdoch University - avatar William Loader, Emeritus Professor of New Testament at Murdoch University, Murdoch University

Australia needs a national crisis plan, and not just for bushfires

Bushfires aren't the only catastrophic emergency Australia is likely to see. AAP Image/Mick TsikasCalls are growing for a national bushfire plan, including from former prime minister Malcolm Turnbull...

Andrew Gissing, General Manager, Risk Frontiers, Adjunct Fellow, Macquarie University - avatar Andrew Gissing, General Manager, Risk Frontiers, Adjunct Fellow, Macquarie University

Your Christmas shopping could harm or help the planet. Which will it be?

Many Australian consumers are concerned at the environmental impact of their shopping habits, especially at Christmas. AAPAustralian shoppers are set to spend $52.7 billion this Christmas. In the word...

Louise Grimmer, Senior Lecturer in Marketing, Tasmanian School of Business and Economics, University of Tasmania - avatar Louise Grimmer, Senior Lecturer in Marketing, Tasmanian School of Business and Economics, University of Tasmania

Right-swipes and red flags – how young people negotiate sex and safety on dating apps

For many young people, app dating is just part of regular dating life. freestocks.org/UnsplashPopular commentary on dating apps often associates their use with “risky” sex, harassment and ...

Kath Albury, Professor of Media and Communication, Faculty of Health, Arts and Design, Swinburne University of Technology - avatar Kath Albury, Professor of Media and Communication, Faculty of Health, Arts and Design, Swinburne University of Technology

Sick and Tired of Your Dead End Job? Try Teaching!

Tired of the same old grind at the office? Want an opportunity to impact lives both in your community and around the world? Do you love to travel and have new experiences? Teaching English is the perfect job for you! All you need is a willingness to ...

News Company - avatar News Company

The Impact of an Aging Population in Australia

There’s an issue on the horizon that Australia needs to prepare for. The portion of elderly citizens that make up the country’s overall population is increasing, and we might not have the infrastructure in place to support this. Australians h...

News Company - avatar News Company

LifeStyle

Boosting Your Child’s Learning through Play

Being a parent is probably the highest responsibility one has in a lifetime. Once it happens, it...

Different ideas of Christmas Gifts to give to your beloved ones

"CHRISTMAS GIFTS – one of the best festival gifts to give to your closed ones. Find Christmas pr...

How to Have a Peaceful Retirement

Retirement is the time to treat yourself after a lifetime of working, to complete your bucket list...

Latest Wednesday Lotto Results

Wednesday Lotto draw 3917 Lucky numbers for this draw were 43 followed by 25. The rest of the...