The tree is also found to be a single ‘genet’, as genetically distinct individuals are termed; it is perpetuating itself by cloning. Furthermore, that genet is of  ‘potentially great age’. An estimate of the spread of the lignotuber – and the diameter of the stems arranged above – ‘corresponds to the remarkable age of 6,380 years’, a figure later revised upwards to 6,600. It seems to produce no viable seed – a three-year search produces nothing.[iv]

Posters and stickers are printed instructing visitors to take care of this precious thing. ‘Declared Rare Flora’ markers are installed at one of its stands, while its specific location is elided to assist its protection. The infringing car park is removed, and rehabilitation of the site begins. Experiments successfully use the tree’s tissue to clone new individuals.

A sixteen-step interim recovery plan is drafted and the shire in which the eucalypt resides is ‘formally notified of the presence and threatened nature’ of this organism.[v] Rachel Sussman, an American artist undertaking a project to photograph ‘the oldest living things’, flies to Perth to meet one of the conservation biologists working on the tree. ‘I was handed a branch snapped off a propagated sapling in a research garden,’ she writes later, and ‘instructed … to match the leaf shape with that of the clonal eucalyptus I was in search of.’ She drives south for several hours and bushwhacks through ‘thorny underbrush’ to find ‘the leaf shape and structure … just where I was told to look for it’.[vi] And then, as the new millennium’s first decade ends, fire sweeps through the landscape where this tenacious tree grows. Two passing eucalypt specialists – Dean Nicolle and Malcolm French – discover that there is indeed a nearby population of trees that could have provided that other long-ago hybrid parent. ‘In 2010,’ they write, ‘following an earlier wildfire which burnt the E. phylacis genet and allowed easier access through, and visibility within, surrounding vegetation, a population of E. virginea consisting of about ten clumps of plants was discovered approximately 250 metres south.’[vii]

The Cazneaux Tree, Eucalyptus camaldulensis (red river gum), near Wilpena Pound, South Australia; made famous by Harold Cazneaux, who won first prize at an international photographic exhibition in 1937 with his photograph of the tree entitled The Spirit of Endurance (photograph by Dean Nicolle)

So the Meelup mallee is not now a unique species but a first-generation hybrid – most likely E. decipiens pollen crossed with an E. virginea ovule. ‘E. phylacis is currently listed as Threatened Flora in Western Australia,’ write Nicolle and French. ‘We recommend that it be delisted due to its probable hybrid status ...’[viii] This 6,600-year-old tree remains unique, but is now seen through a new prism of information.

This mallee stands; the tree remains.

Here is one of the most captivating and seductive things about the nature of scientific enquiry: it is cumulative, incremental; information grows as new technologies come online; new questions can be posed, new discoveries come to light. What we know continues to expand as each new researcher devotes attention, imagination, to something and frames a new hypothesis, and as each external variable leans in and exerts its own pressure.

But however we name or define this organism, by whatever new scientific methods we seek to interrogate or understand it, in whatever changing context we need to understand what it does or may do next, and whatever quantities of information and knowledge we amass: through all this, the eucalypt itself persists – in this case, through thousands of years.

The tree stands on the ridge, overlooking the ocean. The watcher on the hill.

On the other side of the continent, the western edge of the Cumberland Plain touches the darkly inked lip of the Blue Mountains’ scarp. With the noise and heft of Sydney more than sixty kilometres south-east, here is a special sort of forest, a luscious mix including Eucalyptus tereticornis (the forest red gum), E. crebra (a narrow-leafed ironbark), and E. moluccana (the grey box). According to recent botanical thinking,[ix] it looks today much as it looked 227 years ago – just prior to the arrival of European settlers: ‘a tree canopy with an open grassy understorey with some localized shrubby areas’. While much of the plain has been cleared, farmed, settled, and otherwise disappeared,[x] this pocket is relatively intact. But it’s not this – nor its flora – that make it unusual.

Stand here a moment. See where that magpie is perched; see the mynah bird balanced on that wire? See how the grey-day sunlight turns those eucalypts’ trunks to silver? Something else glints silver here: lines of thick rectangular piping etch a series of precise pathways to six pockets of this forested space, each delineated by a kind of cage that resembles the skeleton of a tank, its struts the same sandy beige as the nearby E. tereticornis trunks. Higher again, one for each of the tanks, the spire of a fine green crane looms above the trees, while the ground below is busy with an assortment of scientific detritus: sensors, baskets, buckets, monitors, and bright tape.

The breeze in the trees’ leaves makes a sound like the ocean. Beneath that there is another whirring hum, the sound of blowers that feed three of these six arrays with elevated levels of carbon dioxide – the equivalent of 550 parts per million (ppm). That’s almost 150 ppm above the levels of CO₂ in the atmosphere today, and the equivalent of the levels the earth is expected to reach in twenty to thirty years’ time, if we continue along the casual-sounding ‘business as usual’ path delineated by the combined voices of the Intergovernmental Panel on Climate Change (IPCC).

And now, take a big breath. Standing here you are breathing the air of the future – as are, of course, these eucalypts. This air tastes no different, smells no different – exudes no different sensation at all. But it is the air we will all be inhaling in my lifetime, in a different sort of world – the air with twice the concentration of CO₂ than before industrialisation; the air that is well beyond the planet’s designated ‘safe’ operating limit of 350 ppm; the air with the upper limit of that one greenhouse gas that, once achieved, sees the onset of what scientists predict will be the more serious effects of global warming. Earlier this century, we thought we would reach this level around 2050; now, we are on track to arrive earlier, perhaps as soon as the mid-2030s.

This unique steampunk assemblage of old trees (some date back more than a century) and cutting-edge technologies is ‘EucFACE’. Part of the impressive facilities housed by Western Sydney University’s Hawkesbury Institute for the Environment (HIE), it is now the world’s only Free Air CO₂ Enrichment (or FACE) experiment currently running in native forest, despite the usefulness of these experiments in terms of addressing ongoing uncertainties around ecosystems’ responses to rising CO₂ levels and helping to ‘fundamentally improve predictive understanding of the Earth system’.[xi]

The FACE facilities are like time machines that allow scientists to collect and collate actual data from an iteration of the future and from an established and whole forest ecosystem rather than from young trees planted specifically for study. The latter approach, in the words of HIE researcher David Ellsworth, is ‘akin to applying paediatrics to the elderly’.[xii]

In any part of the globe, in any biogeographical region, flora – particularly forests – are fundamental to discussions about climate change. As one HIE study into the adaptive capacities of two eucalypt species puts it, ‘because forests dominate the terrestrial carbon cycle and climate projections are sensitive to carbon cycle feedbacks, the response of forest trees to warming is particularly important’.[xiii] Plants take up and store CO₂ via photosynthesis and return it via respiration; if trees are cut down or burnt, large amounts of CO₂ are released into the air, like a great big exhalation. On the one hand, the planet’s forests – if they are cleared, degraded or overused – currently account for about one-sixth of all global carbon emissions. On the other, carbon sequestration – via intact and functional forests – could also see absorption of about one-tenth of global emissions.[xiv]

‘By the turn of the millennium, scientists know of more than 240 different species of eucalypts in the south-west region of Western Australia, thirty-five of which are considered rare and endangered, and thirteen of which are known to grow in only one spot’

About sixteen per cent of Australia is covered by forest, comprising 123 million hectares of native forest and about two million hectares of plantations.[xv] To talk about forests in Australia is to talk about that vast and dominant trio of genera – Eucalyptus, Corymbia, Angophora: the eucalypts. Three-quarters of our native forests’ trees are eucalypts, as are roughly half of our plantations. Wherever they grow – in gardens, in parks, in plantations, in that grab-bag space ‘the bush’ – they are quintessentially Australian; diverse, iconic, familiar, and ubiquitous. On the Cumberland Plain, they comprise three of the four prominent tree species – and the other non-gum now only ranks as ‘rare’.[xvi]

EucFACE currently hosts around ninety different experiments for researchers from Australia and collaborators from seven other countries, and its six twenty-five-metre-diameter rings – each of which had to be constructed with no disturbance to this remnant forest – are the engineering epitome of treading lightly. Three rings carry today’s air into their cages to generate comparable baseline data (‘they’re very expensive controls,’ says HIE researcher Mark Tjoelker), while the other three run that futuristic air. The extra CO₂ is an industrial by-product, captured north of Sydney and driven here to be stored, vaporised, and released. Because of its provenance, it carries a different isotope to the local air, making it trackable; and because it is stuff that would ordinarily be released at its original site, its release in this old-growth forest adds no extra carbon to the world’s equations: it simply relocates it.

When that carbon dioxide was first turned on back in 2012, there was an almost immediate increase in the soil’s CO₂ respiration level. ‘We gave extra carbon to the trees and what did they do? They spat it back out.’ Tjoelker laughs. ‘Why is that happening? Are the fine roots getting it and growing more fine roots and that’s why there is more respiration? Are the roots exuding carbon compounds into the soil that are being used, or are they sloughing off and that’s being used by the microbial community, the fungi and the bacteria that use plant-based carbon as a substrate for their processes? There’s a whole host of interesting questions.’

The EucFACE will run, he says, for ‘three, four, five more years – the idea was for ten years; that’s our ultimate goal, but whether we’ll get there, we don’t know.’ Longer time frames are integral to some of the more intriguing questions that might be asked: ‘There are lots of different mechanisms and cycles that can be examined in isolation on shorter time scales,’ says Tjoelker, ‘but then there are these feedback processes that take a longer time to manifest themselves – and feedbacks are what make ecosystems. The reasons we see patterns in vegetation and structure in ecosystems is due to trade-offs and feedback mechanisms that help shape whole communities. And it takes a while to trace the carry-on effects.’

In a way, plants breathe a counterbalance for us: we take in oxygen and expel CO₂; they take in CO₂ and expel oxygen via photosynthesis. Through photosynthesis and respiration, they enable the transfer of moisture, CO₂ and oxygen to and from the atmosphere. To stand in a large forest on a quiet day – among, say, the giant E. regnans of the Styx Valley, west of Hobart – is to almost hear the in and the out, and to feel yourself breathing in time. Some forests in the northern hemisphere have been breathing more deeply recently, ‘inhaling’ more CO₂ in the summer, and ‘exhaling’ it in the winter. They cycled an extra 1.3 billion tonnes of carbon in 2011 compared to 1961.[xvii] They’re taking a deep breath too.

EucFACE construction (courtesy of the Terrestrial Ecosystem Resarch Network, photograph by Rebekah Christensen)

This imagery of ebb and flow also fits the mechanics of evolution – the perennial adaptation – of the eucalypts themselves: ranges contracting; ranges expanding: a very slow pulse of coming and going. But the other analogy that is often invoked is that of the forest as a sponge, soaking up some of our extraneous carbon dioxide. It is the idea of the trees as the planet’s lungs.

‘Understanding forests’ capacity to take up CO₂ is really important,’ says Tjoelker. ‘Right now they do take up quite a bit of our anthropogenic emissions. One concern is that there could be limits to that – a saturating response – and if that happens, that means an immediate acceleration of increased CO₂ in the atmosphere without us having done anything. We’re pretty good at predicting our emissions from fossil fuels, combustion, land use change and the like – and right now forests are putting the brakes on that. If that green sponge were to be saturated, we don’t have a lot of other places to go. That’s probably a really important prediction for policy-makers to know about.’

For as long as there have been people in the landscape with eucalypts, there have been stories about these trees. The first eucalypts with which British convicts and colonists became familiar had a specific D’harawal creation story, delineating the stringybark (Bay’yali), the spotted gum (Boo’angi), and the ironbark (Mugga’go) among others.[xviii] There were names before Linnean binomials.

Then colonial history created its own stories from those eucalypt forests, suspiciously evergreen yet not quite the right green at all. They became the perfect setting for swathes of lost-child narratives, in texts, on canvases, on celluloid, and beyond. May Gibbs’s Cuddlepie – a gumnut baby himself – was blown out of home and almost lost in the forest on the first page of his own book.

The most direct and arresting translation of the eucalypts into stories came with Murray Bail’s novel Eucalyptus (1998), the tale of a girl, Ellen, and her father, Holland, who revises his plans to grow all available eucalypts into a decision that his daughter will marry whoever can identify them all. The thing is, as any number of Australian foresters will tell you, is that eucalypts are notoriously difficult to distinguish.

Bail sings his trees. The mighty E. regnans is ‘a monarch … which shakes the earth as it falls and provides enough timber to build a three-bedroom house’. The ghost gum is for some ‘the most beautiful tree in the world’. And ‘the impulse is to pick up and admire a piece of jarrah – stroke it like a cat’.[xix] Holland’s acreage teems with the busy bulk of this massive genus while his daughter works to avoid her fate.

The idea of vast collections of eucalypts is not unusual. We have collected specimens, carefully pressed and dried and attached to the regulation rectangles of herbarium sheets, since Joseph Banks reached Botany Bay in 1770. We have encouraged species’ examples to thrive – in real-world arboreta and other botanic gardens, and in more modern and virtual spaces such as Australia’s Virtual Herbarium and the Atlas of Living Australia. And we have assembled xylaria or wood collections.

Australia has two national xylaria, one at the Australian National University, which includes a series of large blocks shelved to create a ‘wood library’ for consultation, and an earlier and larger catch-all assembled by CSIRO since 1928. Its first contribution, E. obliqua, came from a Mr Stubbs of Hobart that December, and it expanded from an initial focus on eucalypts to encompass more than 13,000 species from Australia, Papua New Guinea, Malaysia, and the south-west Pacific.

‘The eucalypts just wouldn’t behave properly,’ says Gordon Dadswell, a historian currently undertaking a PhD on the history of Australian xylaria. ‘The timber might have short fibres that clogged saws; some rotted and others you couldn’t get a nail into; or you could look at two specimens and say they were identical when they weren’t.’ Forestry needed a ready reference.

The latest tally of eucalypts – including all three genera: Eucalyptus, Corymbia, and Angophora – totals in excess of eight hundred and defines, to a large extent, what Australia looks like. Divide Australia into squares measuring one degree latitude by one degree longitude and you would have 808 squares (each roughly 100 km²) – with eucalypts present in all but thirty-five. These trees are multifarious. They range from the mallees, which may be less than a metre tall, to the towering giants of E. regnans (the mountain ash) that grow in Tasmania and Victoria. The tallest currently standing – the ‘Centurion’, in Tasmania’s Arve Valley – measures 99.6 metres, placing it just behind the North American redwoods in terms of stature. But there are historical reports of a mountain ash felled south-east of Melbourne in 1880 that measured 114.5 metres, which would have made it the world’s tallest tree at the time.[xx]

‘To stand in a large forest on a quiet day ... is to almost hear the in and the out, and to feel yourself breathing in time’

They come with rough bark, smooth bark or shedding bark in an extraordinary palette of colours from deep mauves and rich oranges to palest blondes and silvers; leaves bright or dull, variously shaped; seeds that provide a design primer ranging from saucer- and boat-shaped to cuboid, pyramidal, D-shaped, linear and more.

‘They’re amazing species,’ says Mark Tjoelker, ‘and they inhabit a range of habitats from the desert to snowy mountains – that’s an amazing range of biological adaptation.’

Which makes a small parcel of land – 32.5 hectares – just inland from the mouth of the Murray on the South Australian coast an even more remarkable spot. Because at Currency Creek Arboretum, Dean Nicolle (unraveller of the pedigree of the Meelup mallee) has been growing as many species of Australia’s iconic trees as possible since 1993 (when average CO₂ levels were just over 357 ppm, already above that safe operating limit).

Of course, Currency Creek presents just one set of climatic conditions – it can’t be deserts and Alps, coastal and highland all at once. Yet here are rows of unlikely bedfellows, like a yellow-blossomed gum from a granite island off Western Australia’s coast with a snow gum from Mt Kosciuszko. Here is a veritable menagerie of trees: a Corymbia from Kakadu; a mountain blue gum from Sydney’s Hawkesbury River; a coastal mallee from Kangaroo Island; a varnished gum from Tasmania’s Hartz Mountains (the smallest of the eucalypts, Murray Bail has one of Ellen’s suitors literally trip as it tangles around his feet); and the two parents of E. phylacis from WA – E. decipiens and E. virginea, the latter from seed collected at Meelup itself.[xxi] All present and correct and thriving. His most recent census lists more than 8,000 individual plants.

I visited Dean Nicolle back in 2002; I was about to publish a book called Gum: The Story of Eucalypts and Their Champions, and he looked like the best modern example of a eucalyptographer, as people used to call the enthusiasts whose stories I had told. His trees were mostly less than a decade old then, planted in groups of four per species, first one, and then another to create a mosaic of different shapes, different greens, with the bright punctuation of scarlet buds here, soft white ones there. I had finished Gum with a line about eucalypts being ‘adaptable, diverse, tenacious, interactive, opportunistic’ – much like the people whose stories they defined. Seeing them in these rows, all getting along together, side by side, in a habitat quite unlike their original landscapes in many cases, only underscored my sense of their resilience and adaptability.

Block of trees at Currency Creek Arboretum, photographed at the time of their planting in September 2010 (photograph by Dean Nicolle)

Through the subsequent decade, as it became clear there were any number of species on the list of things we should worry about in terms of changing climatic conditions (not least our own), I held Nicolle’s rows at the back of my mind, and worried less about the eucalypts.

And then, I read a Climate Institute briefing on the most recent report by the Intergovernmental Panel on Climate Change – released in September 2013, when CO₂ levels were at 393.31 ppm. It projected what might happen to various organisms if the world should achieve an increase in temperature of more than 3˚C (the report itself forecast increases of between 1.4˚C and 6.4˚C by the end of this century[xxii]): wheat and grapes and sheep – and eucalypts. The word shot from the page like a flare. What had happened to ‘hardy’, ‘opportunistic’, and ‘tenacious’? What would happen to our sponge – our lungs? And how did Dean Nicolle’s trees speak to this?

It is important, here, to acknowledge the idea of husbandry, of tending, of nurturing. If you plant a eucalypt – any tree – anywhere and nurture it, there is a good chance it will thrive. When Nicolle started Currency Creek, he knew he needed a site with a particular kind of soil – ‘well-drained so it could grow species from the WA sandplains, free from limestone, and with a neutral or slightly acidic pH’.[xxiii] As he planted, he also undertook weed control, pruning and other management of his saplings in their first few years. His species list gives a running commentary on their status – mature, immature, and occasionally, deceased.

But here is another truth about all those eucalypts. In the natural landscape, without anyone to tend or nurture them, running the gamut of temperature and rainfall and all the other climatic variables – not to mention any unexpected pests or blights these combinations of conditions might bring on – many of them have a surprisingly small range. And we have known that for almost twenty years.

Various semi-mature and mature plantings at Currency Creek Arboretum, photographed from the windmill and overlooking Hindmarsh Island in 2005 (photograph by Dean Nicolle)

In the mid-1990s, Lesley Hughes – now Pro-Vice Chancellor (Research) at Macquarie University and better known, perhaps, for her ongoing work with the publicly funded Climate Council – made the first analysis of climatic range size for what she calls a ‘big Australian group’: the eucalypts.

Hughes had just finished a PhD and was casting around for something different. She ended up among the gums thanks to her supervisor, who suggested, ‘you know, climate change might be an issue’. She had access to the largest digitised dataset of species information, which, in the 1990s, was the Australian National Herbarium’s GUMNUT database of eucalypt collections. In addition, she had access to the world’s first climate-interpolation model for species distribution – BIOCLIM, developed by CSIRO in the 1980s. Her supervisor suggested that they drive to Canberra, pick up GUMNUT’s floppy disc from the herbarium, drive it across town to the modeller at CSIRO ‘who would run [the records] through the models’, and then drive home to Sydney that same day.

It didn’t quite happen like that. Hughes spent six months working with the GUMNUT data to clean up the database, checking for duplicates, correcting transcription errors, and checking the identification for some species whose taxonomy was uncertain or contested – sometimes by consulting botanists who could look at a record and say, ‘Yes, I know that tree, that’s out the back of the pub’, because they had collected it. ‘I mapped every species on an overhead with a map of Australia on it,’ she says of the technology available. ‘That was all we had.’

‘We posed the very simple question: how broad was the climatic range of each species? In other words, what ranges of temperature and rainfall did each species currently experience,’ she says. ‘And the most obvious thing about the results was that the climatic ranges of many species were really narrow.’ Hughes showed, for the first time, the restricted living space of many of these trees, despite what a casual observer could mistake for ubiquity.

Her two papers in Global Ecology and Biogeography Letters delivered a stark message. This was in 1996, the year of the second IPCC report, when its summary for policy-makers declared, ‘the balance of evidence suggests that there is a discernible human influence on the global climate’.[xxiv] This was 1996, when levels of carbon dioxide in the atmosphere averaged 362.64 ppm.

As Hughes’s first paper explained, ‘unless current projections greatly overestimate future climate change in Australia, within the next few decades many eucalypt species will have their entire present day populations exposed to temperatures and rainfalls under which no individuals currently exist’.[xxv] Her second paper underscored this by explaining that sixty-eight per cent of eucalypt species had ranges that covered less than one per cent of the continent, and only three per cent of eucalypt species grew in ranges spanning more than ten per cent of Australia’s available land.

At its most fundamental, every conversation about climate change comes down to a question of adaptation – what a species will need to do in terms of surviving and thriving in a changing environment, and how, if at all, it will be best able to achieve those things. It is relatively easy to think about if the organism is an animal that might need to move further to find food or a more comfortable ambient temperature. But plants, and trees in particular, are a different case. In order for trees, or indeed any other type of plant, to ‘move’ to other places, their seeds need to be dispersed, and they then need suitable conditions – water, light and soil characteristics – to enable them to establish and grow.

In terms of our flora, says Hughes, ‘in many terrestrial environments, trees are the most important structures that provide the habitat for other species.’ If the present-day distribution of a particular eucalypt represents the full extent of where it is able to live, then many of our Australian icons could be in real trouble as the climate changes rapidly, she says.

‘Icons’ is such an interesting word. We often imagine the world changing in terms of iconic animals, like pandas, elephants, or rhinos. Imagine a landscape without its iconic trees.

That kind of idea could take your breath away.

If the eucalypts were to magically disappear overnight from the length and breadth of Australia, they would still have populations in other parts of the world. These trees were probably global travellers even before the first British boats arrived in Australian waters. While Joseph Banks collected specimens during Cook’s first voyage, the name ‘eucalyptus’ was coined for a specimen collected seven years later, from Bruny Island, during Cook’s third and final expedition. Every subsequent visiting naturalist and collector scooped up branches of this, stems of that, shipping them to botanical experts on the other side of the world.

‘If the present-day distribution of a particular eucalypt represents the full extent of where it is able to live, then many of our Australian icons could be in real trouble as the climate changes rapidly’

But it wasn’t only pressed and dried eucalypt specimens that were sent off-shore. Seeds made their way too, and enthusiastic growers in the northern hemisphere – aristocrats, merchants, botanists, and nurserymen – tried their hand with this distinct new genus. By the 1830s one prominent London firm, Loddiges and Sons, was advertising more than thirty species of eucalypt for sale. The Horticultural Society’s botanic garden in London had a swamp mahogany (E. robusta) growing; the gardens at Kew had a eucalypt flowering by 1825; and growers on the French Riviera shipped ‘petal-laden branches’ of at least four species to the Paris flower market.[xxvi]

Exports of eucalypt seeds soared with the enthusiasm of Ferdinand von Mueller, director of Melbourne’s Royal Botanic Gardens from 1857 to 1873. A passionate advocate for these species, Mueller evangelised and proselytised in the name of eucalypts for decades. They were the prince of trees. They were the best of lumber. They were transformers of climate – stemming everything from fevers to malaria. They ‘reminded him of the “tree of life” described in the Apocalypse whose “leaves … shall be for the healing of the nations”’.[xxvii] In 1861 alone, he dispatched 51,290 packets of seeds from Melbourne,[xxviii] and a letter later that decade boasted of shipments to Natal, the Indian highlands, Jerusalem, the Atacama desert and the Plata plains, Algeria, the prairies of Kansas, and Egypt.[xxix]

Thanks to champions such as Mueller, eucalypts have been one of our most successful exports. Hundreds of kilometres of eucalyptic windbreaks have protected citrus orchards in California (and fuelled dramatic Californian forest fires). In north-western Uruguay, where eucalypt forests make up almost a third of all plantations, they achieved forestation rates of 300 per cent. Addis Ababa, the capital of Ethiopia, was said to have been so-named – ‘new flower’, in Amharic – in honour of the blue gums planted around the city in the 1890s as a speedy source of firewood. More recently, China has undertaken trial plantings of some 200 species in deciding on the best crops for four million hectares of plantation. The world’s most widely planted hardwood, they cover more than twenty million hectares of plantation in more than 100 countries across six continents[xxx](the International Union of Forestry Research Organisation equates this to fifteen per cent of the world’s total plantations[xxxi]). This includes three and a half million hectares of plantation[xxxii], predominantly E. grandis, in Brazil alone.

Grandis trunks look polished, their splendid silver rising out of a rough cuff of grey-brown bark close to the ground. They are satin smooth, flawless, and their tall, thin trunks run on like the stripes in a magic-eye puzzle.

Think smaller than the trunk, smaller than the wood, than the vessels and the fibres of the tree, and you reach its DNA, the nucleic acids that store all the biological information that defines what an organism is, and what it does. All life comes down to these famous double-helix strands of nucleotides and their four different compounds: cytosine (C); guanine (G); adenine (A); thymine (T). The genetic code reduces an organism’s distinct complexity to particular combinations and repetitions of those letters – C, G, A, T – and the E. grandis code was only the second tree genome ever sequenced. Anyone with Internet connection can gaze at the intricate density of its pattern, split into dozens like eggs or bread rolls: caacattgac cagaaatcgt tgatgtggtg gcggcatagt caatgtcgat tgtcctaagt[xxxiii] – and on it goes.

The advent of increasingly affordable DNA sequencing has expanded exponentially the questions that can be asked of all the planet’s organisms. It changed the way things could be identified. It revealed different biological mechanisms – why jasmine rice had a fragrance that other rice lacked; whether mosquitoes’ eyes were black or white,[xxxiv] why some river red gums were more drought-tolerant than others. Work out which gene makes which things possible, and you might start to ‘select’ as you breed – just as agricultural crops have always selected for the best growth, the best crop, the best produce.

‘This resource,’ wrote the authors of the E. grandis genome, ‘expands our understanding of the unique bio-logy of large woody perennials and provides a powerful tool to accelerate comparative biology, breeding and biotechnology.’[xxxv]  Media coverage made much of specially selected eucalypt genes which, when combined with bacteria or yeasts, could turn them into ‘bio-factories to manufacture advanced biofuels’. The irresistible idea of a jumbo jet powered by ‘renewable eucalyptus-based fuel’ took hold.[xxxvi]

Even better than E. grandis, suggests Robert Henry, director of the Queensland Alliance for Agriculture and Food Innovation (QAAFI), is Corymbia variegata. A tropical species, it is already better suited to both monsoons and extended droughts. ‘Corymbia grow faster under these conditions,’ he says, ‘and they have a composition that’s easier to convert to the molecules we might use to replace oil in non-fuels – materials, plastics, all those other things we use oil for. We’ve also got to find an alternative carbon source and eucalypt wood – particularly Corymbia wood – is amongst the easiest to convert.’

At the moment, his lab is trying to unravel how more efficient trees might be bred for those future oils and biofuels. ‘It’s about coming up with trees with a higher carbohydrate composition and carbohydrates that are more easily converted to sugars. These then become a substrate for fermentation to any particular molecule you might want,’ he explains. And converting a tree to biofuel? ‘Ethanol from eucalypts is easy; with eucalypts, we’re currently getting more than 200 g/kg of ethanol and I think we can get 300–500 g/kg with just a little bit of science. Then there’s jet fuel, where the yields are very low, but the conversion is easy to do.’

But if genomics feeds these molecular-level potentials, at the other end of the scale come broader questions of spatial and landscape ecologies – and how we can understand what different eucalypts do under different circumstances. In his work with agricultural crops, Henry has collected and sequenced specimens of particular species across a range of altitudes – say, from sea level, up and over the Alps, and back down again. ‘I’ve been keen to look at populations growing across an environmental gradient to see what’s different about the ones in the hot, dry environment compared to the cool, wet environment. How have they adapted? That tells us what’s happening under natural selection – and maybe those clues will tell us what we should do to adapt to the same sort of climate change.’

What he finds is that plants ‘normally can cope with temperature but they can’t cope with the new organisms they’re going to encounter … breeding plants that will cope with a hotter future is probably breeding plants that will cope with a wider scope of pests and diseases.’ In several instances, species have displayed lower genetic diversity in populations living at optimal conditions and much more variation out at their range. ‘There’s a lot more experimentation going on in those populations,’ says Henry, ‘trying to find the combination of genes that works to survive at those extremes.’

There is something appealing about the idea of an organism running its own series of experiments, out on the limits of the space in which it can exist. Walking up to see Lesley Hughes at Macquarie, I had paused at a courtyard of lemon-scented spotted gums (Corymbia citriodora), standing about like so many tall and elegant legs in shimmeringly worsted stockings of silver, blush, titanium, flaxen, and rose-gold. This tree’s home range runs north from Coffs Harbour (30˚S, 153˚E) and on past my place in Brisbane to the bottom of the Cape York Peninsula.[xxxvii] Macquarie University, by contrast, sits to the north-west of Sydney’s CBD, at roughly 33˚S, 151˚E; not where these trees naturally grow. As I inhaled the trees’ aroma, I pictured some mechanical metaphor for the choices they had made – what had been altered, turned on, turned off – to allow them to thrive. Here they were, a successful transplant, more than 500 kilometres further south than the southern limit of their range. Going along.

Like Dean Nicolle, Hughes had spoken of husbandry and of its more scientific version: experiments that would take species beyond their natural ranges, watch them grow, and measure what happened. ‘There are certain types of questions you can only answer this way,’ she’d explained, ‘but they’re not often done. Because they’re bloody hard; they’re very labour intensive; they take a long time; and they’re very expensive.’

These experiments transpose a species in space as effectively as EucFACE transposes them in time. They would be one sure way of understanding how trees would behave in new environments, under new conditions.

But here’s the best bit: the eucalypts have been undertaking their own version of these experiments for years. And now the results are coming in.

One of the researchers employed by CSIRO back in the 1970s to improve methods of predicting where and how well particular trees will grow was Trevor Booth, an English ecologist with a background in modelling grazing systems – ‘how grass grew, how cows ate it, how that affected milk’. Booth had studied at a university conveniently located near an aircraft factory – and the university had installed a very large computer to assist aeronautical studies. ‘I got interested in using computers in ecology,’ he says.

That simple sentence has led him through decades of work unravelling how well different eucalypts will grow both in Australia and overseas and – as one of his research papers puts it – which ‘biodiverse plantings’ are ‘suitable for changing climatic conditions’.[xxxviii]

‘But here’s the best bit: the eucalypts have been undertaking their own version of these experiments for years. And now the results are coming in’

As well as BIOCLIM and his own programs, Booth uses the Atlas of Living Australia (which holds more than 725,000 occurrence records for eucalypt species[xxxix]) to generate this knowledge, making it accessible to ‘anyone from school kids to species’ experts’. This allows users to see not only what is already growing in their own landscape but other places where those same species are growing – and whether these match projections for climatic change in their own local landscape.

What the eucalypts have in addition to this, and ahead of any other genus, is the combined knowledge of those millions of seeds sent around the world by enthusiastic botanists and foresters. Hundreds of eucalypt species have already been trialled and grown outside Australia, often in conditions that are completely different to their home ranges. Which means we already have all this interesting information, these insights, about how they’ve performed under different conditions.[xl] And it is this information that Booth is ‘voraciously gathering … from trials and commercial plantings, both in Australia and around the world’.

‘Here’s an example of how eucalypts overseas are telling us interesting things,’ he goes on. ‘There’s E. nitens, the shining gum, grown as a plantation species in South Africa, and it doesn’t flower there – at most plantations – because it’s growing under slightly warmer conditions. If it doesn’t flower, it won’t produce seed, and if it doesn’t produce seed, it can’t reproduce. Now that may be one of the things to look out for as conditions change. If things are getting stressed, if they’re not flowering, you can see that from the capsules on the ground.’

It is something Dean Nicolle has noticed at Currency Creek. He can grow the majority of eucalypt species, but the site’s climatic conditions mean very few will reproduce. And unless they can do that, they cannot survive beyond one generation – even if that generation itself survives thousands of years. This is, as Nicolle sees it, ‘a critical point regarding the eucalypts’ survival and climate change’.

In the broadest terms, says Booth, eucalypts are possibly in ‘a fortunate position – they set the stage on which things happen,’ he says, meaning that they impact more on other, smaller organisms than those smaller organisms usually impact on them. ‘And what could be considered limitations in some ways, ecologically, make eucalypts particularly interesting for climate change studies. There’s the fact that they’re long-lived – okay, if you’re looking at fruit flies, then you can show they’re adapting, because you can breed them much more quickly. But eucalypts could live for a couple of hundred years, and they’re not going to change dramatically or move.’

If the migration of trees brings to mind Birnam Wood on the march to Dunsinane, the reality is a little less dramatic. Trees tend to be one of the least nimble of organisms in terms of their capacity to adapt to a shift in something like climate by managing to shift their own range.

Eucalypts get three chances to ‘move’ through their landscape: via their fruit capsules, if they are transported in some way; via the seeds encased in those capsules, when they fall and split; or via their pollen which is often moved by beetles (such as cetonids and jewel beetles), birds, and bees. Some have mechanisms that prevent seedlings from growing too close to established plants: river red gums drop ‘an inhibitor in their reject leaves and bark that prevents their seeds germinating under them where they would have little chance of surviving’.[xli]

If a tree’s pollen contains its ‘nuclear’ or paternal genome, a tree’s seed contains its ‘mitochondrial’ or maternal genome. ‘Pollen moves a lot further than the seed, so the nuclear genomes move around more than the maternal genomes,’ says Robert Henry. ‘We’ve done work on the paternity of stands that looks at the relationship of a tree to all the trees going away from it. There are trees 400 or 500 metres away at low frequency that are related, but relatives tend to be the trees that are pretty close.’

What his group has discovered is that eucalypts like to share: they’re ‘highly promiscuous,’ is how he describes it. ‘We see all these different species but there seems to be incredible gene flow between them.’ Which means, he suspects, that the species ‘can all evolve together. If there’s a nuclear gene that’s really advantageous, it will spread across the whole system.’ He smiles. ‘Being able to share the best things – that’s nice. That’s the advantage of some sort of swarm. But as a biological concept it certainly challenges the species concept; you’ve got to think, what is a species?’

Henry is personally interested in the answer to that question for one gum: Corymbia henryi – ‘which a series of students of mine have shown is not a distinct species at all’ but rather a small version of C. variegata. ‘Taxonomists will say they’ve got twenty traits that separate variegata from henryi,’ he says, ‘bigger leaves, bigger seeds, wider capsules – it’s all about size! But one gene can do all that if it’s developmental. The end of henryi is just a matter of time …’

And so another name may disappear from the planet’s register, while the trees themselves remain, busily propagating new combinations of themselves.

‘And so another name may disappear from the planet’s register, while the trees themselves remain, busily propagating new combinations of themselves’

At the end of July, then, came National Tree Planting Day – a community event celebrating its twentieth anniversary this year and intended to put more than twenty-two million trees and plants into the ground in that time. This year, for the first time, you could register to plant at home.

We love big numbers of plantings. In 1989, the venerable eco-historian Eric Rolls described Bob Hawke standing ‘at Wentworth on the Murray, from where he could almost command three states, and [shouting] a program for the growing of a billion trees’. The country’s newspapers responded with the impossible maths of the enterprise. (It came out at around 10,000 trees per hour, by the most crude back of the envelope calculation.) But Rolls responded by making a vast road trip through landscapes that had already seen concerted planting for more than a century. He canvassed everything from ‘still standing model forests of river red gums’ that had been planted in the 1870s to a Victorian farmer who had converted his farm from a ratio of fifty of those same E. camaldulensis in a 1,560-hectare space to somewhere holding in excess of 35,000 trees on just twelve per cent of its landscape.[xlii]

To do our bit this year, we registered with the official National Tree Day system and headed across Brisbane to a not-for-profit nursery dedicated to the propagation of native plants across south-east Queensland and the ‘return [of] our native flora and fauna to its appropriate place in the landscape’.[xliii] We told the nursery attendant we were after eucalypts, and we chose three tubestock E. curtisii – the Brisbane mallee (which only reach seven metres); a comparatively small eucalypt that’s native to Queensland and listed as near threatened (E. propinqua: twenty to thirty metres); and a sapling of that deliciously scented lemon spotted gum I had smelt on my way to meet Lesley Hughes (C. citriodora: thirty-five metres).

‘Not brave enough to try anything taller?’ the attendant joked.

On the last Sunday of July, people at more than 3,000 locations in Australia planted trees. My boy and I were among them, in our front yard, with five acacias, our five eucalypts, and a self-struck avocado. We dug holes and prepared them with water, with food. We shook our tiny trees free from the embrace of their dirt and looked at their roots, those delicate, intricate fibres that anchor and nourish. We bedded them in and watered them – one of us being relatively careful, the other more cavalier as he attempted to make the hose produce perfect rainbows. And we stood for a while with our trees – the ones that have grown in the years we’ve been here, and the new ones just put in.

We talked about why it’s good to plant trees – why it’s especially good to plant trees these days. It is an interesting thing, aiming for the right balance, the right words, when you are talking climate change with a six year old. We talked about the way trees breathe, and my boy leaned in to our tiny new mallees to blow his breath gently across their leaves.

‘Just giving them a bit more air,’ he explained.

(photograph by Jo Daniell)

How many trees would we need to breathe for the world? When I had asked Mark Tjoelker that kind of impossible question, he had told me that while tree planting is good for a number of reasons – ‘it engages people; and trees, particularly in environments that include humans and communities, are just great’ – we couldn’t make the maths work. ‘The numbers tell us that we cannot plant enough trees to take care of our problem,’ he said. ‘But that doesn’t mean we shouldn’t plant trees.’

A couple of days before National Tree Day, I had come across new research into correlations between contact with nature and human well-being.[xliv] The study, published in Nature journal’s Scientific Reports series, found that ‘having 10 more trees in a city block, on average, improves health perception in ways comparable to an increase in annual personal income of $10,000 and moving to a neighbourhood with $10,000 median income or being seven years younger’.[xlv]

We have had so many prisms through which to look at our eucalypts – at any organism on the face of the earth – from the first indigenous reckonings of the trees’ properties and on through the centuries. Even as distinct and unique a thing as a 6,600-year-old clonal mallee can prove to be malleable when considered through different lenses. There is a marvellous confluence between the technologies we have now – models, sensors, sequencers, all the ways we have of asking questions – and the scale of a matter like climate change.

We can answer specific questions about how photosynthesis changes when temperatures rise or how leaf respiration is altered by drought. We can investigate eucalypts’ ‘carbon safety mechanisms’ and their ‘carbon assimilation rate’. We can understand what will happen to eucalypts under a changing climate in terms of nitrogen, potassium, and sodium – or the impacts of phosphorous and ‘endogenous rhythms’ on the way forest red gums breathe overnight. We can learn that judiciously applied rhinoceros beetles can reverse the effects of elevated CO₂ on blue gum seedlings’ roots – and the way environmental stress affects sap flow in E. urophylla, the species that is native to Indonesia and Timor.

What we know about eucalypts and climate change now runs to scores of published papers and continues to grow. Some models of some of their ranges – projected for ten, forty, and seventy years hence – suggest that ‘many species in the eastern and southern seaboards will be pushed toward the continental limit’ while ‘large tracts of currently treed landscapes, especially in the continental interior, will change dramatically in terms of species composition and ecosystem structure’.[xlvi] Some are more optimistic about their plasticity.[xlvii]

There is no doubt that the politics of climate change can feel beset and exhausting, or that the coalface work of climate science can cause some of the most pragmatic of investigators to despair.[xlviii] But in November the world goes to Paris for the United Nations Climate Change Conference (COP21) with the widely accepted goal that temperature rises must be capped at 2˚C above pre-industrial levels to avoid the most dangerous impacts. It is a big ask, to achieve a legally binding agreement from the world’s countries, but we have an ever-growing mountain of information available to help us to adapt, and to lay out the likely consequences of inaction. Around the world, different researchers, different laboratories are assembling information about the complexity of our vast systems, the eucalypts among them. Piece by piece by piece.

‘In some ways,’ says Trevor Booth, ‘we’re embarking on the experiment no one would allow us to do in terms of the globe. If I put in a proposal saying, you know, I’d like to increase the temperature by two or three degrees in this particular location, and arc up CO₂ levels, just imagine how difficult it would be to get approval …’ He takes a breath. ‘It’s a beautiful but concerning problem, and we’re very fortunate that the eucalypts fit into this so interestingly because they have been moved around so much.’

Mark Tjoelker sees them as a model system ‘from an evolutionary standpoint since they exhibit adaptive radiation from one particular phylogenetic branch’. He sees them as fascinating models of adaptation within species, too. ‘Along the east coast of Australia there are widely distributed eucalypts, and narrowly distributed eucalypts – that’s been a question in ecology for a long time: why is that? Have they always been rare? Are they a relict population from a bygone era when maybe they were more widespread? One of our studies found marked differences in species in populations from cooler climates – they showed an intrinsic capacity to respond more positively to warming than populations of the same species from Queensland where they were perhaps growing at the edge of their thermal tolerance.’  Tjoelker pauses. ‘These are really important questions: is there a climate envelope that you can circumscribe around the whole species – is that what’s making it be there? Or are there other factors that are important?’

If we truly wanted to experiment with how all those pieces fit together – single species, feedback mechanisms, and us and all we do – how they might change and what they might become, we would need three planets to make the experiment rigorous. And here we are with one.

All this work; all this data: it grows and grows, sometimes slowly, incrementally, like the almost imperceptible stretch of an old jarrah, and sometimes with explosive and astonishing speed, like the burst of lush new canopy cover when a long, dry spell breaks. And these pieces are always in play. On top of which, we have our two peerless spyholes into the future: our time-travelling forest on the Cumberland Plain; and our unrivalled dataset of how our trees have already performed in all sorts of other environments under all sorts of other conditions.

There are stories of sailors heading towards Australia’s landmass, towards the east coast with its ubiquitous forest red gums, the west coast with its tiny Meelup mallee spot, and being able to smell the eucalypts before the country itself appeared; you could literally navigate by the gums. Maybe, in a different and very twenty-first-century, scientific way, we still can.

We stand on the hill, my boy and I, and we watch our new trees, sniffing at the delicate lemon-scent of that C. citriodora and basking in the sun. In our world, that warm winter’s morning, the latest carbon dioxide level is tracking at just over 401 ppm, and rising, still rising.

Rising still.

Ashley Hay’s most recent novel, The Railwayman’s Wife (Allen & Unwin, 2013), won the Colin Roderick Award and the NSW Premier’s Prize People’s Choice Award. Her earlier, more botanically inclined books include Herbarium (with visual artist Robyn Stacey, Cambridge University Press, 2004), and Gum: The Story of Eucalypts and Their Champions (Duffy & Snellgrove, 2002).

Acknowledgments: Thanks to various people for various conversations while I was thinking about this work – in particular, Bob Beale, Nigel Beebe, Trevor Booth, Gordon Dadswell, John Dargavel, Robert Henry, Lesley Hughes, Krissy Kneen, Vinod Kumar, Gail MacCallum, Dean Nicolle, Kris Olsson, Mark Tjoelker, and Charlotte Wood. And thanks to Australian Book Review, Ruth A. Morgan, and the Bjarne K. Dahl Trust for enabling me to write some more about these trees. Access the Atlas of Living Australia at www.ala.org.au

This is the second ABR Dahl Trust Fellowship we have offered. We gratefully acknowledge the generous support of the Bjarne K. Dahl Trust.

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[i]These descriptions of the Meelup mallee are based on information in Department of the Environment
[ii]Hill and Johnson (1992), p. 593
[iii]Rosetto et al (1999), p. 321
[iv]Rosetto et al (1999), pp. 328-329
[v]Patten (2004), p. 4
[vi]Sussman (2015), p. 52
[vii]Nicolle and French (2012), p. 448
[viii]Ibid
[ix]Benson and Howell (2002), p. 648
[x]For information on the Cumberland Plain see NSW Office of Environment and Heritage (2014)
[xi]Medlyn et al (2015), p. 528
[xii]Tait (2015)
[xiii]Drake (2015), p. 459
[xiv]Food and Agriculture Organization of the United Nations (2012)
[xv]Australian Government/Department of Agriculture (2015)
[xvi]Benson and Howell (2002), p. 636
[xvii]Biello (2013)
[xviii]Hay (2002a), p. 7
[xix]Bail (1998), pp. 80, 59
[xx]Taylor (2013)
[xxi]Nicolle (2011)
[xxii]The Climate Institute (2013)
[xxiii]Hay (2002b)
[xxiv]The IPPC’s 'Second Assessment Report', pp. 17, 22
[xxv]Hughes et al (1996a), p. 23
[xxvi]Doughty (2000), pp. 31-32
[xxvii]Moore (1997), p. 382
[xxviii]Doughty (2000), p. 54
[xxix]Mueller (1868) in Whitehead (2007), p. 25
[xxx]Myburg et al (2014), p. 356
[xxxi]See www.euciufro2015.com/en/
[xxxii]Ledford (2014), p. 257
[xxxiii]The full sequence for E. grandis
[xxxiv]Aryan et al (2013), p. e60082
[xxxv]Myburg et al (2014), p. 356
[xxxvi]Doyle (2014)
[xxxvii]Species’ information is available via Euclid
[xxxviii]See Booth (2012a), (2012b)
[xxxix]The Atlas of Living Australia
[xl]See also Booth and Williams (2012), pp. 267-268
[xli]Rolls (1993), p. 77
[xlii]Rolls (1993), pp. 54, 68
[xliii]Details of this lovely nursery
[xliv]See Hutchinson (2015), and the original study, Kardan et al (2015)
[xlv]Kardan et al (2015)
[xlvi]Butt et al (2013), p. 5011
[xlvii]Booth (2015)
[xlviii]Some recent interesting coverage includes Richardson (2015) and the collection of handwritten letters assembled by Joe Duggan (2015)