The river red gum is an icon of the driest continent


River red gums’ iconic silhouette is found across Australia.
The Conversation/Wikimedia Commons, CC BY-SA

Gregory Moore, University of Melbourne

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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.




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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!



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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.




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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.




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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.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.

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This centuries-old river red gum is a local legend – here’s why it’s worth fighting for


Euan Ritchie, Deakin University

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In Dr Seuss’s The Lorax, his titular character famously said:

I am the Lorax. I speak for the trees. I speak for the trees, for the trees have no tongues.

In the midst of a global extinction crisis, the Lorax’s call to preserve what is precious couldn’t be more apt. The greatest threat to the survival of species globally continues to be habitat destruction and modification.




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A potential and local victim of this ongoing environmental catastrophe is a single tree, and a tree I have a deep personal connection with. The tree I refer to is Bulleen’s iconic 300-year-old river red gum (Eucalyptus camaldulensis).

To me this tree has been a constant in my life. While everything else has changed around me, it has stood there, solid, just as solid as its red gum fibres are known to be.

As a child I fondly remember looking up at this tree in awe, as we’d often stop at the nearby service station on a hot summer’s day to buy a cold drink or ice-cream on the way to Saturday sport, the nearby Birrarung (Yarra River), or my grandmother’s house.



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Bulleen’s majestic river red gum

It’s estimated to be approximately 20 metres in height with a canopy spread of 17 metres. And its trunk measures a whopping two metres across.

The tree is thought to be the oldest remnant of a once substantial red gum forest, and was saved by a local resident when the rest of the area was cleared for the construction of a service station.

It now faces destruction, as it is within the preferred path of construction for Victoria’s North East link.




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While the measurements of this tree are impressive, the splendour and value for me is that it has survived for so long and, in more recent times, against tremendous odds.

Surviving against all odds

The Bulleen red gum stands beside one of Melbourne’s busiest roads and the immediate area is covered with concrete and bitumen. The tree’s roots and health have therefore been challenged for a long time, and yet this massive red gum stands, as if in defiance of the modern world and the development that has encircled it.

Since this tree has survived for so long, it undoubtedly holds a special connection with so many: the Wurundjeri-willam people of the Kulin Nation, members of Australia’s famed Heidelberg school of artists who lived and worked in the near vicinty, everyday commuters that have driven or walked by or stopped to admire it, or the war verteran Nevin Phillips who once apparently defended it with his rifle against it being chainsawed.

Very old trees such as Bulleen’s river red gum deserve our respect and protection, for these trees have substantial environmental, economic and cultural value.
National Trust

Further proof of the value of this tree to so many is that it was awarded The National Trust of Australia’s (Victoria) 2019 Victorian Tree of the Year.

Why we must speak for and save old trees

I grew up near this tree and, like the Lorax, I would like to speak for it.
Trees as old as the Bulleen river red gum are now increasingly rare in our world, and beyond their strong personal and cultural values, including in some places as Aboriginal birthing sites, they are tremendously important for other reasons as well.




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These trees provide shade and help keep our cities cooler, improve our mental health and wellbeing, and store considerable amounts of carbon aiding our fight against climate change.

Perhaps most importantly, under their bark and in their cracks and hollows, they provide homes for many of Australia’s precious but increasingly imperilled native wildlife, including bats, birds, possums and gliders, snakes and lizards, insects and spiders.

These homes are prime wildlife real estate, especially in our big cities, where such large old trees are vanishingly rare but where considerable wildlife, common and threatened, still persists. And yet more could survive with a helping hand from us.

A powerful owl chick in a tree hollow, in outer Melbourne.
John White (Deakin University)

As cities like Melbourne continue to grow around the world, there will be more and more cases where arguments of progress are used to justify the further destruction of what nature remains. But progress shouldn’t come at any cost, and in the case of preserving iconic and valuable trees such as Bulleen’s river red gum, it would seem there’s more than enough reasons to ensure this tree’s life and its many values continue.

Perhaps again the wise sage, the Lorax, says it best.

Unless someone like you cares a whole awful lot, Nothing is going to get better. It’s not.


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

Euan Ritchie, Associate Professor in Wildlife Ecology and Conservation, Centre for Integrative Ecology, School of Life & Environmental Sciences, Deakin University

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