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Dr. Miranda Melcher
This is a real good story about Bronx and his dad, Ryan, real United Airlines customers.
Professor Stephen Hopper
We were returning home and one of the flight attendants asked Bronx if he wanted to see the flight deck and meet Kath and Andrew. I got to sit in the driver's seat.
United Airlines Customer or Flight Attendant
I grew up in an aviation family and seeing Bronx kind of reminded me of myself when I was that age.
Dr. Miranda Melcher
That's Andrew, a real United pilot.
United Airlines Customer or Flight Attendant
These small interactions can shape a kid's future.
Professor Stephen Hopper
It felt like I was the captain. Allowing my son to see the flight deck will stick with us forever.
United Airlines Customer or Flight Attendant
That's how good leads the way.
Dr. Miranda Melcher
Hablas spritz du dzoich Com Dul nosq.
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New Books Network Host
Welcome to the New Books Network.
Dr. Miranda Melcher
Hello and welcome to another episode on the New Books Network. I'm one of your hosts, Dr. Miranda Melcher, and I'm very pleased today to be speaking with Professor Stephen Hopper about his book titled Eucalyptus, published by reaction in 2025. Examining well, as you might expect, the eucalyptus, which are absolutely iconic obviously in Australia, but in other places too. And this book helps us understand why the eucalyptus is so important culturally in terms of art, but also in terms of actual just biology and nature and the environment and of course in terms of Aboriginal indigenous knowledge too. So there's a whole lot to discuss with the eucalyptus here. Steve, thank you so much for Joining me on the podcast.
Professor Stephen Hopper
It's a pleasure to be here.
Dr. Miranda Melcher
Mariana, could you please start us off by introducing yourself a little bit and tell us why you decided to write this book?
Professor Stephen Hopper
Sure. I'm a conservation biologist, have been for 50 years and also served as a botanic gardens director. So 12 years in Kings park and Botanic Garden in Perth, Western Australia, and six years at the Royal Botanic Gardens, Kew in London. Most of my research over the 50 years has been in mainly in Southwest Australia, an area called the Southwest Australian Floristic Region. And I decided to work on eucalypt conservation early in the 1980s, when I was appointed to a role in conservation. At that stage, I knew a lot about kangaroo pores, the state floral emblem and nothing much else. So I decided to work on eucalypts because they are the dominant overstory tree in Western Australia and indeed across most of Australia. So I partnered up with a gentleman, Dr. Ian Brooker, who's no longer with us, unfortunately, but at the time he was in csiro, Australia's premier science industrial science institution, and he and I collaborated for 20 years, over which we ended up describing about 100 new species and subspecies in the genus. So there's about 900 species currently recognized. About a ninth of the genus came from that collaboration. I've also worked with Aboriginal elders, especially over the past two decades, on caring for country, seeing if we can learn better ways to care for country than Western technological science has advocated. Because biodiversity in Australia, as in, indeed in most places on Earth, continues to decline, and Aboriginal people have lived in Australia for the best part of 60, 70,000 years. So the prospect seemed reasonable that they would have insights that could help us in caring for many things, including eucalypts. And lastly, I developed new theory for conserving plants on old landscapes, which set the southwest of Australia as a classic example. And I wondered, how did this apply to eucalypts? So that combination of features led me to write the book.
Dr. Miranda Melcher
That's a lot of knowledge that all went into this. So thank you for that background to give us a good foundation for the discussion, given the range then of information included and obviously the background you bring to this. How did you decide kind of how to make this all comprehensible for a more general audience? What do you, for example, hope readers will take away from this book?
Professor Stephen Hopper
It is the first attempt to give priority to Aboriginal knowledge systems on eucalypse, and that required a narrative style presentation because it's an oral tradition. In Aboriginal cultures, there's something like 250 languages and growing that we know about across Australia. So it's quite a diverse and dispersed literature, but I thought it was well worth doing. As a gesture of reconciliation, apart from anything else, I also wanted to highlight recent advances in Western science approaches to the study of eucalypts, because there's been some exciting work across a range of topics that I think will appeal to a general reader. And I've tried to write in a way that is accessible to, you know, undergraduates, postgraduates, academics and anyone generally interested in natural history. And despite hundreds of papers and books already written about eucalypts, they still have their secrets and discovery is ongoing. Essentially, every species, every subspecies, every hybrid has its own story. And I haven't tried to cover them all, but there's enough there, I think, to appeal to an international audience.
Dr. Miranda Melcher
Yeah. And even just the fact that there are still discoveries ongoing is quite exciting to read about. So thank you for giving us a sense of these trees in the book, but I wonder if we can pick up perhaps first on the importance for the eucalyptus to Aboriginal histories, traditions. Can you help us understand why this tree is so important in that context?
Professor Stephen Hopper
Well, eucalypts are ubiquitous across Australia. They were dubbed the universal Australians in the 1970s in a paper written by two eminent Australian botanists. And so when Aboriginal people first encountered Australia, they first encountered eucalypts in all their richness and diversity. They dispersed across the continent, it is believed, just over a couple of thousand years. So that gave a very long period of time to develop reverence and rational uses of eucalypts for life, ways that would support Aboriginal cultures. Respect for country and totems in Aboriginal culture really demands a focus on eucalypts. And, you know, I've found firsthand in working with Aboriginal people in southwest Australia, but also in the broader literature that's quite diverse about Aboriginal approaches to caring for eucalypts and using eucalypts. They're remarkably diverse in approaches and uses, everything from medicine to the construction of wooden implements like spears and boomerangs and the like. And one of the great exciting discoveries, I believe, for me, was that many Aboriginal cultures would modify the eucalypt horticulturally, manipulate them to produce marker trees in the landscape to signify important cultural places, important people to store water in dry habitats and to celebrate totems. So culturally modified eucalypts are something that I feature in the book.
Dr. Miranda Melcher
Thank you for helping us understand the importance there. In the kind of bigger picture, you also include in the book some particular stories or practices that have developed from these histories. Might you be able to share some examples of that here?
Professor Stephen Hopper
Yeah, I could give you, give you a couple of examples. So the first chapter in the book reviews Aboriginal cultures across Australia and their interactions and Dreamtime stories and the like that concern eucalypts. There's some wonderful stuff increasingly now being published by Aboriginal authors themselves. The second chapter relays seven stories from the south coastal southwestern Australia where I have lived and worked with elders. And there's a place I live in a town called Albany on the south coast. And just 80 kilometers to the west of Albany is a town called Denmark. And it's like Albany and a few other places, has a big estuary and has granite hills that are small and subdued, but have been around for a very long period of time for tens of millions of years and consequently have some quite remarkable plants and animals and feature prominently in Dreamtime stories. One such hill is called Warrumbup, or in English it's called Weedon Hill. And near the top of that is a place that the owners call the Magic Circle. It's got karry trees on it. Karri are the second tallest eucalypt of all, so will grow to 80 meters easily, sometimes 90 meters tall. And at this Magic Circle there are several trees that are but big boulders of granite. So when I'm, I'm talking 5 meters diameter sort of size boulders. And when their trunks, lower trunks have rubbed against these rocks, they create a callus like tissue that gradually grows outwards and around the boulder. And my primary elder teacher, a lady called Lynette Knapp in her family, this is the place known for where the trees gave birth to the rocks. And as a Western scientist, you know, that takes a little bit of thinking to get into the mode of Aboriginal dreaming. But it does indeed look like that with this callus like tissue beginning to surround the rocks that adjacent to the trees themselves. So that place is very, very important. Warrumbat war in the local Noongar dialect. The Aboriginal dialect means female kangaroo, but also means place for women. And this is very much a women's place. It's where men weren't allowed to go unless they went with a very elderly senior lady. And the Noongaras firmly believe that this is where all the rocks that are now spread across southwestern Australia. All the granite rocks originated at this point. And there's another species on the slopes of the hill called Mary in a closely related genus to Eucalyptus in Perymbia. And it too has examples of trees where callus like tissue has developed as it's grown in amongst and around and up on top of granite rocks. So that story was kept by the Knapp family as a family secret, essentially, until I started working with Lynette more than a decade ago. And we agreed that she was very keen to have her family stories recorded, but recognized in a way that was clearly of her family. Pardon me. And it's now in the book, and it's the opening story. Of these seven. There are other uses of eucalypts across the south coast. Another one, which is an example of manipulation of parry trees, again occurs along the shores of Princess Royal harbor, which is what Albany sits on. And there's a place where we often taught field courses. And this place had a lawn behind the buildings with about 20 carry trees that were in an oval shape. And furthermore, every one of them was twin trunked. And normally carry is a single trunked tree. And I hadn't paid too much attention to it early on. But I ended up taking a closer look three or four years ago and had a very careful look at the twin trunks and thought maybe it was re sprouting of the eucalypt after white fellas had chopped down the original trunk. But I couldn't find any chainsaw marks, any steel axe marks at all, but wounding tissue that's caused by stone axes. And I asked Lynette to have a look at it, and she said, of course, yeah, this is a very big place, a very big place for camping and for ceremony, particularly for women. And the trees are twin trump because it relates to a dreaming story about the original spirit woman who was punished with her husband for picking up spirit babies, which were little rocks all across the Southwest. And to atone for her picking up these rocks and transporting them where they shouldn't go, she was trampolined up into the night sky and her long silver hair became the Milky Way. She was banished from ever walking on earth again. But she could come back to earth and stand on her head. And if you look carefully at these trees, that's exactly what they look like. The twin trunks are her legs and a short body. Her butts the legs and then sits on top of the soil and her hair forms the root structure. So, second example, I guess, really, as a white person trained in science, you've got to abandon lots of preconceptions. But a very powerful story about the importance of caring for children and the punishment that's meted upon women who don't behave appropriately with baileys, that sort of thing. That's just two examples of Several stories that I provide from across Australia and on the south coast in the Boufk.
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Dr. Miranda Melcher
Yeah, those are some really great examples. So thank you for sharing them here as well. That definitely gives us a sense of the importance of, of these trees. I realize though that we may have skipped over kind of a really obvious question, which is the name for these trees that we've been using. How do we get the name Eucalyptus?
Professor Stephen Hopper
Well, that's classic Western science and goes back to the enlightenment. So listeners may well be aware of Linnaeus and his push to change the then current practice of using what are called polynomials for every species. That is a long sentence in Latin or Greek to describe them, reducing that down to a binomial. Just two words, the first being that of what we call these days the genus and the second the species. So Eucalyptus is a generic genus name and it was named from Tasmanian collections which got back to England as seed and were germinated at the Royal Botanic Gardens, Kew. They were collected on the Cook Expeditions and in particular on his third expedition. And by the late 1780s plants at Kew were listed in the in the catalogs that they had as glass house shrubs, so they reached the height of 2 or 3 meters and could only be grown in glass houses at that stage. And there's a French botanist and magistrate, Charles Laherete, and he was very interested in helping Linnaeus name every species on the planet. So he had some young men who helped him collect garden plants from the parks and residences of Paris, and any that were unnamed, he was putting names on. He also became involved in a French joint French and Spanish expedition to South America, with the lead botanist being French. And when their collections came back, La Huerta was very keen on naming as many species as possible, but the Spanish government objected and said, no, we have first fall on being able to do that. So Laheritier had the collections at that stage and he engineered an opportunity to go to London with the collections and take the specimens over there so that he could, in exile, if you like, name anything new. Joseph Banks was back in London and preeminent in local science and a friend of King George iii. So Royal Botanic Gardens, Kew was underway under his directorship, and La Hereta eventually got Bank's approval to work on the specimens in Banks big house in Soho. And Laheritier ultimately started looking in the gardens as well and in the glass houses and came across this tree, which very obviously was new. So he named Eucalyptus. The name he chose means well covered, and it alludes to a cap that sits over the bud and it's a fusion of petals and sepals. In eucalyptus, it's called the bud cap or the calyptera or the operculum. And that's a very diagnostic feature that most people can see. So that's how eucalyptus ended up being named by a Frenchman from English collections.
Dr. Miranda Melcher
Yeah, that is a very convoluted way of getting a name. So thank you for helping us understand that naming history. And of course, that's very separate from the development and evolution of the tree itself. So can you maybe tell us a bit about that story?
Professor Stephen Hopper
Yeah. The eucalypts occur predominantly in Australia. Of the 900 species, only 12 extend beyond the shores of Australia Northwinds. And for a long time, people had noticed that the nearest genera to Eucalyptus up until the mid-1990s were rainforest margin trees from tropical Australia and New Guinea. Four very small genera of plants and also fossil eucalypts had been discovered and described from Argentina and New Zealand. So it was very clear from the fossils that they were also either in rainforest or adjacent to rainforest in South America. The South American fossil site was One volcanic in origin. So people hypothesize that eucalypts must have arisen on the margins of rainforest and due to the frequency of fire associated with, with volcanic soils. And that was the widespread hypothesis that people believed for many years. I've been a little troubled by that. It doesn't really explain why Australia therefore should have the lion's share of the known eucalypt species today. And fossils, of course, occur in wet, damp, clay based soils usually associated with lakes and the like. And I just wondered, could it be that in fact, you know, the original eucalypts were in drier habitats that didn't fossilize very well? And the body of theory that I developed to try and explain the evolution of incredibly rich floras like that of southwest Australia on very old landscapes reasonably close to the coast in phosphorus deficient soil, seemed to have some promise in offering an alternative explanation for the origin of eucalypts. And that was that they were out of these old climatically buffered infertile landscapes where sclerophyll vegetation is very strongly selected. Sclerophyll is hard leaves, it literally means, and there's essentially drought tolerant leaves, which are classic for most eucalypts. And there seem to be a number of biological patterns that supported more this idea that they might have come from Australian old climatically puffered infertile landscapes than being rainforest neighbors that were frequently burnt. And so all I can say is there are now these two creation hypotheses for eucalypts, and I published mine specifically in relation to eucalypts just in 2021. So very early days, a lot more research needed and we can devise ways of testing which is more likely. But the evidence is yet to come in to convince most people.
Dr. Miranda Melcher
That is very interesting indeed. And goes back to what you were saying earlier about kind of how much this research and discovery is still ongoing, which is of course fascinating to hear about. And also brings me back to a thread you mentioned earlier about kind of just the number of different kinds of eucalyptus that there are, which is also something I found really surprising reading the book. So can we talk a little bit more about kind of how many different kinds and how distinct they are from each other? Like for example, if you put three different kinds next to each other, would they look really different to an uninformed eye?
Professor Stephen Hopper
It varies a lot, miranda. There's about 900 species now known, of which 850 species and subspecies have been formally described by taxonomists. About 50 still need to be described in that way, and depending upon which species concept people apply, it may be that there's another hundred or more still to come. So the description of eucalyptus is an ongoing scientific challenge in relation to how easy are they to tell apart. Many of them are in groups of very close relatives, and you require many techniques to really be sure that you're looking at different species or subspecies these days. Fortunately, DNA sequencing has revolutionized the classification of Euclipse. And the latest DNA approaches called next generation sequencing enable you to literally generate thousands of characters to test whether things are genetically similar or genetically different, different enough to be recognized as species. We're only just getting into some of the big species complexes in eucalyptus with next generation sequencing, and the finding has been that by and large, most of the species previously recognized hold up. And indeed, many things that were in the past recognized as subspecies or in some cases even hybrids, have turned out to be species in their own right as well. So we have this marvelous arsenal of modern techniques applying DNA sequencing which will enable us to say, I would say within another couple of decades, much more accurately than we can say at the moment, what the total number of eucalypts is within what most people would regard as Eucalyptus. We now know there are four major groups, and these four major groups have each been given a generic name. So there's Eucalyptus itself, and that's about 750 of the 900 species. There's a genus, small genus, up and down the east coast called Angophora. There's a larger group of eucalypts, predominantly called Bloodwoods, which are in the genus now, Corymbia, which was named in 1995. Angora was named much earlier in the 1830s. And very recently, just in 2024, a group of Corymbias were pulled out based on the latest DNA sequencing, and they form another genus, which is the name has been around as a subgenus in Eucalyptus called Blake Hella. So Eucalyptus in the strict sense has three sister genera, smaller than Eucalyptus itself. And there are also, you know, they're easy enough to tell apart once you know what to look for. And on top of that, there are several sub genera now recognized in Eucalyptus itself. So there's a couple of big ones. Symphyomotis is the biggest one that's got three or 400 maybe even more species. And there is, on the other extreme, very distinctive eucalypts that are a subgenus in their own right. So one example is from southeast Queensland, a species called Eucalyptus curtisi, and it's placed in its own subgenus called Acerosae and it's got many distinctive characters. One of it is the seeds form long linear columns, whereas most eucalyptus are cuboid, more or less in shape, except for some Corymbias, which have wings surrounding the cuboid bit and blow around a bit in the wind. But Eucalyptus curtisi, unlike all other eucalyptus, the petals and the sepals have infused entirely. So the bud gap, which normally looks whole in the overwhelming majority of eucalypts in courtesy eye, has these sutures in it. So that's an indication that it's a species that's been around a very long period of time, probably 40, 50 million years in fact, and hasn't quite formed the defining character of eucalyptus. It's still placed in eucalyptus, however. So there you have it. There are very distinctive eucalypts like courtesy eye, which you can tell at a glance once you know what to look for. There are the four genera of eucalypts, which equally, you know, you can pick them once you know what to look for. And then there are these radiations of, you know, sometimes up to 30, 40, 50 species, which are very closely related. And the evidence is that they've speciated explosively in the last couple of million years. So very hard to tell apart. It's actually a lifetime commitment to get to know all the eucalypt species well enough to identify them.
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Dr. Miranda Melcher
Yeah, that's a lot of learning to do, which is really interesting. So thank you for telling us a bit about that. And of course, with that range, it therefore begins to kind of make more sense that the eucalyptus is in so many parts of Australia and has been successfully brought to places beyond it as well. So can you tell us a bit more about kind of the environments in which they live and if there's any particular aspects that have made them be able to go beyond Australia?
Professor Stephen Hopper
Yeah, they certainly are widespread within Australia. They're only really absent from the driest parts of the deserts. The modern collections we have have been digitized, you know, right across the world now, literally hundreds of thousands of specimens. And we now know where species are concentrated and have a good feel for the habitats in which they grow. So the eucalypts are actually richest in the country that I come from, in southwestern Australia, which enjoys a Mediterranean climate. So it has semi arid woodlands. It has forms of eucalypts that are called mallee, after a species in Victoria, which have multiple stems coming from an underground woody structure called a lignotuber. And there are two other places that are almost as rich in species as the south coast of Western Australia, subtropical Sydney, the Sydney region I'm talking about. So Blue Mountains included is incredibly rich. It's also where the leading experts in taxonomy of eucalypts have resided for two or three generations. So very well studied over there. And then on the northern New South Wales, southeast Queensland border country near the coast, and standing in that inland for a couple of hundred kilometers is the third place incredibly rich in species. They also extend into snow country in southeast Australia in the Great Dividing Range, but also in Tasmania. They occupy a prominent position in tropical savannah in the top end in the Northern Territory, North Queensland and Kimberley region of Western Australia. And there are some a small number of rainforest edge specialists in the eucalyptus that are essentially rainforest trees, in fact, and a relatively small number, but quite widespread that occupy our vast desert region. So the most widespread eucalyptus of all is river red gum that occurs from the west coast right across to the Great Dividing Range and jumps over the range in a few places. So they really have occupied Australia in a big way. The 12 or so species that occur in Papua New guinea and Indonesia tend to be in savannah country. And what attributes do they have that enables them to occupy such a diverse range of habitats and, and spread so far and wide? They're easy to germinate from seed, so you really just have to add water to soil and keep that soil hygienic, so, you know, keep pathogenic fungi, for example, at bay. They're incredibly fast growing. So some species tried in India in the 1800s grew four times faster than the local teak trees for the same age. They provide firewood, of course, they're hardwood species and they've been planted worldwide for that reason. Timber, you know, the timber of old growth eucalyptus is almost second to none as a hardwood. They're also medicinal and really important cultural plants, as we've talked about, and they can be used in environmental manipulation and repair. So perhaps one of the most famous ones was draining swamps in Italy that were riddled with malaria, was achieved by planting bluegums, in particular Tasmanian blue gums. So they have a number of tricks up their sleeve. They're often disturbance opportunists. And by disturbance I mean fire obviously is a big one in Australia. But also flooding can cause disturbance that encourages these plants to proliferate. Grazing also can cause it. So any sort of form of disturbance that destroys the above ground vegetation they can bounce back from if they're given half a chance.
Dr. Miranda Melcher
Well, that definitely makes sense for why then they've been able to be successful in so many different places and be used in so many different ways, as you've just described. It's interesting to me then that despite this prevalence and how important they are, many are also under threat today. Why is that?
Professor Stephen Hopper
Yeah, that's a really interesting area, one that's been central to my career and studies of eucalypts, that they're incredibly long lived, or they can be, particularly the mallee forms of eucalypts, the ones with the underground woody structure called a lignotuba. People have measured how fast these lignotubers grow outwards, and it's only 1 or at most 2 centimeters per year. And some of these mallees, particularly in Western Australia, but also in parts of the east, are up to more than 30 meters in diameter. So if you do the math, you work out fairly quickly that you know that must be of an age approaching if not exceeding 10,000 years old. And those have been looked at by people who categorize threatened species. Many of the trees as well are quite localized and slow growing. Not all of them are fast growing. And so when people have categorized eucalypts, unlike most Australian plants, they focused on numerical rarity as the attribute to call a species endangered or threatened or not. So a lot of these very old mallees, for example, aren't numerically abundant at all. Some of them are only known from less than 10 individuals. That's a global population. And they were listed very early on in the listing of threatened species for Australia as endangered. What most people, most species these days are judged upon to be listed as threatened or endangered or vulnerable is their turnover in generations. Because eucalypts are so long lived, that's much harder to measure. But a group of which I was one in the last five years took a look at eucalypts from this point of view and what became very obvious was that many species that aren't numerically rare but occur in southern Australia, in the wheat growing country, in particular in southwest Australia, but also in Victoria, South Australia and in New South Wales, many of them have had more than a third of their geographical range destroyed by agricultural clearing and therefore qualify as being regarded as threatened, and some of them are endangered or critically endangered, if you look at that way of classifying species as endangered. So we published a paper on that and most state governments and the Commonwealth government have remained silent on this new interpretation, which says not only do you have to look at numerical rarity, but you could have species that are relatively common as woodland trees and the like growing in wheat growing country, but have had vast areas of their range cleared and no longer extant and in those places. So this is another area of ongoing controversy in Euclid studies. I'm inclined to think that it's looking not only at numerical rarity, but also rates of decline in generational terms is a sensible thing to do with eucalyptus. And if you do that, then close to a quarter of the known eucalypts are in fact threatened to some degree. So that's a bit of a turnaround from it was a smaller number when only numerically rare eucalypts were listed. And the primary cause is, as I say, agricultural clearing, but also urban infrastructure. And clearing destroys habitat. Anything that involves replacing native vegetation with exotic vegetation or buildings or infrastructure is going to be a threat to these eucalypts, and we therefore have considerable cause for concern. One observation, however, that really became apparent as I wrote up the book was that in fact not a single known eucalypt has gone extinct. And that's quite unusual for plants in general. Often 10%. Even more of species that have been described have gone extinct since Linnaean times. And so we have this anomaly, you know, with the eucalypts are incredibly resilient, as I've mentioned, they're capable from bouncing back from destructive events, but if a quarter of them are threatened, then in the longer term we really do have to help some of them survive. Of course, climate change is the biggest threat that we're all increasingly becoming aware of. I wasn't overly concerned about it because with eucalypts we have many highly localized species along the south coast of Western Australia, which by rights should all be threatened and under dire threat by climate change. Because the models people use for climate change to estimate threat just assume that the only way that you can survive is to move into wetter places below rainfall isohots. And that clearly isn't happening. But what the models fail to take account of is, say you're confined to a single hill or mountaintop, then one way you can cope with climate change is simply by moving around the hill at the same altitude into wetter soil off. And that seems to be what is going on? Many, most eucalypts in fact continue to thrive and don't seem to be in trouble. But in southwest Australia just two summers ago, we had the worst drought on record and the driest spring on record. And for the first time, on very shallow soils, common trees like Mary trees started to die or at least lose their canopies. And that was the first signal we've seen here where maybe there are thresholds applying and therefore climate change should be taken as a serious threat and perhaps we'll have to manage for that into the future.
Dr. Miranda Melcher
Yeah, well, speaking in fact of the future, this is clearly a topic that you have committed a massive amount of time and energy to. So what might you be working on now that this book is out to more general audiences across the world? Are you continuing to research, research and protect eucalyptus trees or moving on to something else?
Professor Stephen Hopper
I'm doing a little bit on eucalypts. One species I've worked on for most of my career, Eucalyptusia. We have unpublished detail on that that really needs to be published. I did my PhD on kangaroo paws and their relatives, wonderful little herbs that are colorful and bird pollinated. And I have some papers, I just actually published a checklist of the family to which they belong and describe several new species in kangaroo poison related genera. I've got further work to publish on them. But the main thrust of what I'm doing now is to continue to work with Aboriginal elders on caring for country. They really are highlighting approaches that Western science needs to take serious consideration of in Australia if we are to care for what remains of the tremendously localized and endemic flora and fauna that we have. So I'm working on that. And as part of that, there are a couple of books in various stages of preparation now giving female and male perspectives on caring for country. And I have a couple of other books, one on the old landscape theory that I published first in 2009. And another habitat I've worked on, which looms large in the Euclid book as well is that of granite outcrops which provide islands in a terrestrial sea of other vegetation and geology in southwest Australia. So that's keeping me pretty focused on writing up work that is like a eucalyptus. In fact, the euclid book took 10 years in final gestation. And I have these similar other long standing projects that I really hope I can work up into publication with students and Aboriginal elders.
Dr. Miranda Melcher
Yeah, this is clearly a lot of work and a lot for you to keep working on too. So for any listeners who want to learn more the book is available Eucalyptus, published by reaction in 2025. Steve, thank you so much for telling us about your research on the book.
Professor Stephen Hopper
My great pleasure, Miranda. Thanks for the opportunity.
Podcast: New Books Network
Episode: Stephen D. Hopper, "Eucalyptus" (Reaktion, 2025)
Date: November 23, 2025
Host: Dr. Miranda Melcher
Guest: Professor Stephen Hopper
In this episode, Dr. Miranda Melcher interviews Professor Stephen Hopper about his new book, Eucalyptus (Reaktion, 2025). The discussion explores the ecological, cultural, and historical significance of eucalyptus trees, with a focus on their centrality in Australian and Aboriginal life, their scientific diversity and adaptability, current conservation challenges, and ongoing research. Hopper’s unique perspective bridges Western botanical science and centuries-old Aboriginal knowledge, aiming to foster broader understanding and more effective conservation strategies.
Hopper introduces himself as a conservation biologist with 50 years of experience, former director of both Kings Park (Perth) and Royal Botanic Gardens, Kew (London).
He began focusing on eucalypt conservation in the early 1980s and collaborated with Dr. Ian Brooker to describe ~100 new species/subspecies (about a ninth of the currently recognized genus).
The book is distinguished by its prioritization of Aboriginal knowledge systems and integration with Western scientific advances.
Hopper has collaborated with Aboriginal elders for over 20 years, emphasizing traditional ecological knowledge in managing biodiversity.
"It is the first attempt to give priority to Aboriginal knowledge systems on eucalypts, and that required a narrative style presentation because it's an oral tradition."
— Professor Stephen Hopper [05:24]
Eucalypts are referred to as "the universal Australians," omnipresent across the continent and central to Aboriginal culture.
Aboriginal peoples developed a multitude of uses for eucalypts—medicine, tools, marker trees, water storage, and more.
Culturally modified trees and Dreamtime stories are crucial, such as trees shaped to commemorate places, totems, or store water, and narratives linking trees to landscape formation and cultural norms.
"Many Aboriginal cultures would modify the eucalypt horticulturally, manipulate them to produce marker trees in the landscape to signify important cultural places, important people, to store water in dry habitats and to celebrate totems."
— Professor Stephen Hopper [08:29]
Hopper recounts specific Dreamtime stories and landscape features from southwest Australia, like the Magic Circle on Warrumbup Hill, where karri trees and granite boulders intertwine, believed by the Knapp family to be where trees gave birth to rocks.
An example also discussed are twin-trunked karri trees, culturally modified to symbolize elements of spiritual narratives (such as the spirit woman and the Milky Way).
"This is the place known for where the trees gave birth to the rocks...it does indeed look like that with this callus-like tissue beginning to surround the rocks adjacent to the trees themselves."
— Professor Stephen Hopper [11:00-12:00]
"She was trampolined up into the night sky and her long silver hair became the Milky Way...the twin trunks are her legs and a short body..."
— Professor Stephen Hopper [14:00-15:00]
The name “Eucalyptus” was coined by French botanist Charles Louis L'Héritier from English collections at Kew Gardens during the Enlightenment period.
The term means “well covered,” referencing the distinctive cap over the flower bud.
"He named Eucalyptus...the name he chose means well-covered, and it alludes to a cap that sits over the bud and it's a fusion of petals and sepals..."
— Professor Stephen Hopper [21:10]
Traditional theory held eucalypts originated on rainforest margins—recent theory (Hopper 2021) suggests their roots are in ancient, dry, infertile Australian landscapes where sclerophyll (hard, drought-tolerant leaves) evolved.
Fossils support both hypotheses, but more testing is needed to resolve the debate.
"There are now these two creation hypotheses for eucalypts...the evidence is yet to come in to convince most people."
— Professor Stephen Hopper [25:40]
About 900 species are known, with 850 formally described and more likely to be found.
DNA sequencing is revolutionizing Eucalyptus classification, confirming or reclassifying species, subspecies, and hybrids.
Eucalyptus as currently classified comprises four major genera:
Identification can range from easy (distinct species) to highly challenging (closely related radiations).
"Many of them are in groups of very close relatives, and you require many techniques to really be sure that you're looking at different species or subspecies these days."
— Professor Stephen Hopper [27:44-28:00]
Eucalypts thrive in nearly every Australian habitat except the driest deserts and have been introduced globally due to their quick germination, rapid growth, utility for timber/firewood, and disturbance resilience.
Certain species have become essential in environmental management, like draining swamps in Italy.
"They are incredibly fast growing...They provide firewood, of course, they're hardwood species and they've been planted worldwide for that reason...They can be used in environmental manipulation and repair."
— Professor Stephen Hopper [35:55-36:45]
Threats include agricultural clearing, urban infrastructure, and potentially climate change.
Classification of threat has shifted from mere rarity to range reduction and generational turnover.
Remarkably, no Eucalyptus species are known to have gone extinct since European scientific records began, though about a quarter are now considered threatened, especially under expanded criteria.
"We have this anomaly, you know, with the eucalypts are incredibly resilient, as I've mentioned, they're capable from bouncing back from destructive events, but if a quarter of them are threatened, then in the longer term we really do have to help some of them survive."
— Professor Stephen Hopper [42:44]
"Climate change is the biggest threat that we're all increasingly becoming aware of...for the first time...common trees like Mary trees started to die or at least lose their canopies."
— Professor Stephen Hopper [43:56-44:38]
Hopper continues to publish on specific eucalypt taxa and on kangaroo paws (his doctoral focus).
He works closely with Aboriginal elders to integrate indigenous and scientific approaches to land stewardship and plant conservation.
Upcoming projects include books presenting male and female Aboriginal perspectives on “caring for country,” a volume expanding his “old landscape theory,” and research on granite outcrop habitats.
"The main thrust of what I'm doing now is to continue to work with Aboriginal elders on caring for country. They really are highlighting approaches that Western science needs to take serious consideration of in Australia..."
— Professor Stephen Hopper [46:49]
On integrating Aboriginal knowledge:
"It is the first attempt to give priority to Aboriginal knowledge systems on eucalypts, and that required a narrative style presentation because it's an oral tradition."
— Professor Stephen Hopper [05:24]
On cultural landscape and Dreamtime stories:
"This is the place known for where the trees gave birth to the rocks...it does indeed look like that with this callus-like tissue beginning to surround the rocks adjacent to the trees themselves."
— Professor Stephen Hopper [11:00-12:00]
On evolution and research uncertainty:
"There are now these two creation hypotheses for eucalypts...the evidence is yet to come in to convince most people."
— Professor Stephen Hopper [25:40]
On resilience and threat:
"Not a single known eucalypt has gone extinct. And that's quite unusual for plants in general. Often 10%, even more of species that have been described have gone extinct since Linnaean times."
— Professor Stephen Hopper [42:12]
The episode offers a vivid blend of science, history, and culture, revealing why eucalyptus trees are not just botanical icons but also enduring symbols in ecology, art, and indigenous heritage. Professor Hopper’s Eucalyptus provides an accessible, authoritative guide to their story—one that continues to unfold amid environmental change and cross-cultural collaboration.