Mountain Ash / Eucalyptus Regnans

Dalia Nassar

The giant of the Tarkine and Styx river valley in Tasmania, the Eucalyptus regnans or mountain ash is a symbol of the struggle between conservationists and loggers in that state. But it is also a symbol of Australia’s fraught relationship with fire. The tree stands at the centre of both the 1939 Black Friday and the 2009 Black Saturday fires in Victoria, and its highly flammable character and particular geography are regarded as causes of the devastation that those fires wrought.

And yet, while it poses danger, it is also itself in danger. Once spread across eastern and southern Victoria, the mountain ash has been replaced by farmland, and can only be found in the great divide between Mt Disappointment in the west and the Thomson River in the east. In Tasmania, the mountain ash is the favourite of the timber industry, where it is more widely known as Tasmanian oak. Anyone passing through Tasmania will not fail to recognise the massive trunks stacked on trucks, leaving old growth forests on an almost hourly basis. While the Valley of the Giants is now protected from logging, fires have taken the life of the tallest living member of the species in Tasmania. Standing at 87 meters, the Arve Giant, as it was known, succumbed in 2019.

The mountain ash is by all accounts a magnificent tree. Approaching a mountain ash forest, one is struck by the transition, perhaps from the open space of a recently clear-felled forest, to a lush and vibrant grove teeming with manferns, myrtle beeches, and these enormous trees—majestically towering above everything else. While their grey-green trunks taper as they rise, at the bottom their girth is wide and covered in moss. You sense their age, but also their generosity. In their hollows lie the critically endangered Leadbeater possums. On their branches, which are so high you can barely distinguish them, sit yellow-tailed black cockatoos. You feel like you’ve arrived in an enchanted forest, a magical, wise and ancient place. And you recall how these forests have often been described by visitors as ‘green cathedrals’. Perhaps you feel the need to pray in them—or to them. 

‘The supreme expression of the genus eucalyptus’, as botanist David Asthon put it, the mountain ash is a tree of wonders—and its height may be only the most visible of these wonders.[i]

Not only is the mountain ash the tallest flowering plant in the world, it is also the tallest hardwood in the world and it may have once been the tallest tree in the world. A living Tasmanian tree measured at 99.6 metres and there is a convincing historical record of a Victorian mountain ash that reached 114.3 metres. How can a hardwood achieve such heights? (The tallest recorded California redwoods, which are a softwood, grew to 111 meters.) How can the mountain ash grow so quickly? In just 20 years, it can climb to 40 meters, and in 300 years, it can reach 100 meters. 

But perhaps even more astounding is the way that the mountain ash lives—and dies. Unlike other eucalypts, the mountain ash does not flourish in dry, arid regions, but in cool wet environments, where rainforest species abound. While the mountain ash dominates the overstory, the understory is layered with myrtle beech, southern sassafras and ferns. This cohabitation of eucalypt and rainforest species has perplexed ecologists, so much so that mountain ash forests have been given the name ‘mixed forests’, or wet eucalypt forests.

The mountain ash’s height, some have conjectured, is connected to the wet climate in which it grows. Abundant water and rich soil allow for extreme height without extreme age. And although in its first stage of growth, the mountain ash competes with its rainforest cohabitants, in the middle and later stages—after establishing itself as the forest’s highest tree—it facilitates rainforest generation.

Eucalyptus regnans by Blahovičník Královský is licenced under CC BY-SA 4.0.

Like other rainforest dwellers, the mountain ash is very sensitive to fire, and dies from intense fires. And unlike other eucalypts, it has not developed lignotubers under the ground from which it can renew itself. This means that the mountain ash is unusually dependent on seeds for its survival.

And it is here where the story becomes complicated. Although it dies from extreme fires, the mountain ash is also dependent on fire, because it is only through intense fires that its seeds are released from their hard capsules. Without intense fires, which should occur every 400-500 years, the mountain ash cannot survive.

The mountain ash is two to three times more flammable than other eucalyptus and the Woi wurrung and Daung wurrung people who lived near Melbourne’s mountain ash forests knew not to enter these forests in the height of summer. This high flammability might have to do with the tree’s surroundings. If the tree is to catch fire, it must do so with great intensity. And this means that total devastation is the mark of the encounter between tree and fire. What is left are the seeds. During the fire, the seeds are protected by aerial capsules. They are released after they fall to the scorched earth, which the fire has prepared for them with nutrients that encourage germination. This dependence on fire, which might be better described as a collaboration with fire, has been called ‘mass suicide’: a readiness on the part of the tree to sacrifice itself and every one of its kind for the future of the forest.[ii]

In need of both rain and fire, the mountain ash’s existence is structured by exactness and time. It is only a certain kind of fire at the right time that will kill the old trees while also allowing for the seeds to germinate. If the fire is too frequent, as has been the case since European colonisation, the trees do not attain the necessary maturity to produce seeds—and cannot reproduce. If it is too infrequent—the trees also die.

The combination of logging and increasing fire frequency has put the mountain ash population at severe risk. In 2017, conservationists appealed to the Victorian government to classify the mountain ash as an endangered species, but the appeal was rejected. More recently, ecologists have argued that the mountain ash ecosystem is collapsing.[iii] 

The consequences of this collapse are enormous: for the birds, possums and other animals that depend on these magnificent giants, and for us. Mountain ash forests are the most carbon-dense forests on earth. And they play a crucial role in hydrological cycles, with much of the water for the city of Melbourne coming from water catchments dominated by mountain ash forests.

We must protect these magnificent beings. Not only because of the so-called ecosystem services they provide us or the complex ecologies that they support, but also because of their simple sublimity. This means that we must transform—transform the way we think about life, death and fire. If anything, what the mountain ash shows is how these three are deeply interrelated, and our task is not to fight fire, but to learn to work with fire: just as the mountain ash does.

A tree that flourishes only in rainforests, but is also fire dependent, that dies in order to live on: the mountain ash unsettles our categories and the ways we think about and imagine danger. Fire, the mountain ash tells us, is only a danger if we fail to work with it. And so long as we continue to misunderstand it, we will be unable to protect these magnificent fire-dependent trees, and all the animals and plants that rely on them. 


Dalia Nassar is a philosopher at the University of Sydney. Her work is at the intersection of the history of philosophy, the history of science, environmental philosophy and aesthetics. She is currently completing a book manuscript on the role of art, and artistic tools and devices, in the emergence of ecological thinking in the eighteenth and nineteenth centuries.


[i] Ashton, David. 1981. “Tall-open forest.” In Australian Vegetation, ed. R. H. Groves, 121-151. Cambridge: Cambridge University Press.

[ii] Griffiths, Tom and Christine Hansen. 2012. Living with Fire: People, Nature and History in Steels Creek. Collingwood, Victoria: CSIRO Publishing.

[iii] Lindenmayer, David B. and Chloe Sato. 2018. “Hidden collapse is driven by fire and logging in a socioecological forest ecosystem,” PNAS 115 (20) 5181-5186.

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