Growing Greener Podcast – Trees with Dr. Ned Friedman

Ground-Breaking New Takes on Trees from the Oldest Arboretum in the United States

Ned Friedman, Director of Harvard’s Arnold Arboretum discusses that institution’s programs to preserve the DNA of tree species and populations threatened with extinction by climate change, helping trees flourish in an increasingly challenging environment, and how you can share in his passion for these extraordinary organisms by bonding with one tree.

Read Ned’s thoughts about why he especially to look at loves trees in winter in our PRFCT Perspective story.

August 26, 2026

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Transcript

Growing Greener host Tom Christopher

Welcome to Growing Greener, your guide to environmentally informed gardening. Produced in partnership with the Perfect Earth Project, this program brings you, each week, some expert who puts you in touch with a different aspect of gardening in partnership with nature. Our goal is to make your personal landscape healthier, more beautiful, more sustainable, and more fun.

This is your host, Tom Christopher, and today I will be talking to Ned Friedman, Professor of Organismic and Evolutionary Biology at Harvard University, and the Director of the University’s famed Arnold Arboretum. Ned, as anyone who talks to him soon learns, is passionate about trees, and not just in a scientific sense. He is fascinated by every aspect of them, from their beauty to their ecological function, and their sheer diversity. This fascination is something he loves to share, as you will learn from the inspirational conversation that follows.

Ned is also deeply concerned about the future of trees in this era of environmental challenges, and under his leadership, the Arnold Arboretum has become a center for innovative programs to identify tree species and populations that are at risk and take measures to try and ensure their survival.

Before we go to my conversation with Ned, however, I want to thank Growing Greener’s sponsor, the Garden Conservancy, a national nonprofit dedicated to preserving, sharing, and celebrating America’s gardens and diverse gardening traditions. Through preservation, education, and public access, the Conservancy helps to protect those living works of art for future generations. Learn more and discover gardens near you at GardenConservancy.org.

Welcome to Growing Greener, Ned!

Ned Friedman

Thank you, Tom. It’s great to be here, and I’m really excited to have a conversation with you today.

Tom Christopher

Let’s talk first about Arnold Arboretum, just for listeners who may not know it. So, as I understand it, it was founded in 1872. It’s the oldest public arboretum in the United States, and it represents a partnership, because I believe the land actually belongs to the city of Boston, but it’s leased to Harvard University, which has always directed the arboretum’s activities. The design for the landscape, I want to add, was the work of one of my heroes, Frederick Law Olmsted, who, of course, was a designer of a lot of great park systems, including Boston’s Emerald Necklace. Anyway, that’s a remarkable beginning.

Ned Friedman

Well, this is where Olmsted has to have a partner in crime, so to speak, and he does. The first director of the Arnold Arboretum was a man by the name of Charles Sprague Sargent. He was one of the Boston Brahmin family, Sargent, and tremendous ambitions, a really remarkable, driven person. So he wanted to create a scientific institution that studied temperate woody plants, and he could have done that by just planting out a lot of stuff around the world and just do research on it, but he really began to partner very quickly with Frederick Law Olmsted, and the partnership turned into something where the goal was to create a scientific collection that could be studied, new species could be described, and all of those things, but not just rows of trees, but a great public landscape, a magnificent landscape.

Tom Christopher

Yes, having visited the Arboretum on a number of occasions, I’ll join in testifying that it is a very rare blend of scientific function with landscape beauty. Olmsted and Sargent transformed the site, addressing everything from its topography to its vistas. For any gardener, I think, a walk around the Arboretum, even during winter, will lift the spirits as well as educate. Something I wasn’t aware of until recently, and I was doing some reading about the Arboretum in preparation for this conversation, was that the first major program there was to carry out a census of American trees, and they described some 400 species initially with maps of each of their ranges and information about each, and this eventually led to the publication by Sargent of a 14-volume Silva of North America, which was expanded to include 585 tree species. But this endeavor served as the foundation for any comprehensive study of trees on this continent, and that’s really still the case today, I would think.

Ned Friedman

Yeah, it is. Sargent was extraordinary. His grasp and his ambition, he really wanted to tackle these big, at that time, standing topics, which we were in the process as a species of really getting a catalog of the basic biodiversity of the world. And in the United States in the late 19th century, territories that had been opened up to science and to botanists, some of them had not been very thoroughly surveyed, so you had plant explorations, which still goes on today in North America. There are new species that are being found still. But a lot of it was very early days for knowing the catalog of, in this case, trees of North America. And that 14 volumes, they’re magnificent to look at. The illustration artwork was done by a wonderful illustrator at the Arboretum. Really, it’s gorgeous stuff to look through.

Tom Christopher

And I think this again was Sargent, that he somehow grasped, perhaps you can correct me on this, he somehow grasped that there was a connection between the flora of temperate East Asia and North America. This flora of temperate Eastern Asia became a focal point for the Arboretum’s plant expeditions.

Ned Friedman

Right. Now, Sargent actually wasn’t the one who figured this out. He was aware of it because he was mentored by Asa Gray, who was the botany professor and Darwinist, who fought for Darwin here in America. And actually, I teach about this in one of my first-year seminars about Charles Darwin. What’s really interesting is that Asa Gray, Harvard botany professor, began in the 1840s to notice. You talked about coming up with a survey of the trees of North America. Well, Asia was also being explore,d and things were opening up and there were these Western descriptions. It’s not that people who lived where the trees were didn’t know what they were. But for Western science, people were beginning to learn about the different species in general that lived in Eastern Asia. And that would be the Korean Peninsula, Japan, and Eastern and Central China. And what happens is really interesting.

Asa Gray begins to notice and Charles Darwin and Asa Gray begin to correspond about this strange thing that the species in Eastern North America, particularly the woody plant species, some of them they thought might even be the same identical species as what you find in Eastern Asia, or if not, a close relative. And there was only two ways to explain this. There was natural laws of the world or miracles. Like this was created here and this is created here. And this is in the 1840s before Darwin had published On the Origin of Species, which is 1859. Although he was well on his way to figuring everything out in private.

And they went back and forth, and Darwin kept pressing Asa Gray because Asa Gray was a great expert on these things. And what he said is it’s really interesting. The trees are halfway around the world from each other. And you’d think things would be in North America. Maybe there’d be things that are closely related in Eastern North America to Western North America. But that just wasn’t the case. And the same for Europe. So by the mid 1850s, it became evident to both of them that this was a tale of migration. And this is less about continental drift, but climate change. We’re living in what we might call an icehouse Earth. This is a relatively cold period of Earth’s history. Most of the time it’s been a lot warmer. And a lot of our temperate species that you would find in Eastern Asia and Eastern North America and Europe, they were way north of here because it was way warmer. And you had these land bridges, for example, between Asia and North America. The barren land bridges, now it’s got water in it, but sea levels went up and down.

And so what happened is things would move up. They sort of circled the globe as a species. And then they might be pushed down in colder eras to different continents where they’d go their own way. And this has been going on for, you know, 40, 50 million years. So we knew early on, really early on, that there was what we would call a biogeographic story here. What’s so exciting is for whatever reasons, and people have thought and studied this and come up with some partial answers, Eastern Asia, temperate Asia, has twice as many woody plant species as temperate North America. And we have, I think, about twice as many temperate woody plant species as Europe. So you can imagine if your goal is to collect and have representation of the world’s temperate woody plants, you certainly collect a lot in North America, and we do, particularly at the hot spots like the southeastern U.S., where a lot of species are found. And you go to where everything else is, which is Japan, the Korean Peninsula, and China. And we have expeditions. Like last year, we had an expedition to collect in South Korea. We had expeditionary work in China, and we had expeditionary work in Japan.

So we are still working very hard to go around the world to bring that biodiversity back to be studied in terms of research, climate change research, global change research, you name it. And also for public horticulture, so people can learn what trees, if you went to Japan, you might see. It’s a great story.

Tom Christopher

Yeah, no, it is, and it’s not so coincidental then that a lot of the standard trees of horticulture in northeastern and eastern North America came to this country through the Arboretum. Things like the Katsura tree, or the Davidia, the dove tree, or the paperbark maple, these all came to North America through the explorations of Arnold Arboretum.

Ned Friedman

Yeah, so the early days of exploration, starting in the 1890s, when Sargent did go to Japan, and then really cranking up in 1905, and really up through the 20s, what was happening is the Arnold Arboretum was sending a number of different plant explorers, remarkable, remarkable tough people who had to really get on the road in places that sometimes were dangerous, just for the terrain, also for the political situations, and so forth. And they were bringing back material that was unknown to taxonomy in the West. And so the Arboretum wasn’t there for economic reasons. They were really there because we just love trees. The idea that you could have a dove tree, this magnificent Chinese tree, that looks like when it’s in flower, a thousand white doves flapping their wings in a light breeze, is a pretty wonderful thing. And so these then became things that were introduced into the horticultural trade, and many of them remain there as wonderful additions to people’s yards and gardens, and also cityscapes. So you’re absolutely right. That was an age of what you can think of plant exploration associated with the discovery and cataloging and the ecology, understanding where these plants lived and where they thrived, of things that were simply unknown to Western scientists, botanists.

Tom Christopher

So as you’ve said, that interest is still maintained at the Arboretum. But there’s also, I think, if I’m understanding correctly, a new focus, too, on a better understanding of how our trees are responding to the current environmental crises of climate change and the associated threats to biodiversity. Could you tell me a bit about that?

Ned Friedman

Absolutely. So in a funny way, science and knowledge march on, and you have to ask with any collection that’s a biological collection, what are the most pressing questions of the day? It’s not that we don’t occasionally describe a new species that’s new to science. That still goes on. But what we really are facing are the challenges of global change and the threats to species that can go extinct on our watch. And we have lots of different ways of assessing whether certain species or even populations that are very special are under threat. They can be under threat to climate change. Invasive pests and diseases can threaten, as you’ve seen, the ashes of North America, the ash trees. We have emerald ash borer now that has wiped out everything. Now we have beach leaf disease adding to beach bark disease, adding to the pressures on our native beaches here. And these lists go on and on. And then we just have habitat fragmentation. The fact is we keep putting parking lots and buildings up. And so what we now do is we prioritize our collections. When we go off to get species, when I got to the Arboretum, we weren’t doing a lot of systematic annual collecting. And now we do at least three major expeditions a year. Some to Europe. This past year we went to Bosnia-Herzegovina for a single species of conifer, the Serbian spruce. It’s got a habitat that is essentially going to be taken away from it by climate change and warming. And we need to get the genetics into what we call ex situ conservation, meaning it’s in gardens where if it goes extinct, at least the species still lives on. And if there’s a way to somehow repatriate the genetics, we can do that. But we’ll go for one thing if it’s important.

And on top of that, with all the research that we do, and we have visiting scholars from around the world, what we find is that if we have a really good collection, people who, for example, want to know what are the effects of increasing drought on temperate woody plants. And different species will react differently. And we want to understand why they react differently. Or, for example, decreasing snowpack in the winter, which can really be hard on the root systems. In New England, we’ve had a few years where we’ve had virtually no snowpack. And then you get a very cold night. And that’s actually very stressful for trees. So, there are all kinds of things that we bring all these species from around the world. It’s sort of like one-stop shopping. If we have the right stuff, a scientist from China, a scientist from Japan, a university of Washington, whatever, can come to the Arboretum, spend weeks or months, but studying with their graduate students or undergraduates or themselves, all kinds of biology that can help us understand what is going to be more threatened with increasing drought, what might be more resilient, what we can do with the threats of new pests and diseases.

I was just out on the grounds with my horticultural crew and leadership, looking at our beach collection. I mean, it’s really terrifying to see this beautiful collection and understand that we’ve got this problem with beech leaf disease that’s just going to require right now interventions. But it’s not sustainable on the long haul. And there are research groups working on this. But we have to figure out how to grow plants with ever greater challenges, is what I say. And so that’s what we’re busy doing. So, the collecting is really motivated by the kinds of science we do. And that could be genomics. It could be just basic biology questions like the evolution of groups of trees. And I have a graduate student getting a Ph.D. who’s working on the evolution of floral sex in maples. Most maples have unisexual flowers, but they’re all different ways of doing this. And it really hasn’t been understood from just a basic evolutionary perspective very well. But we have one of the world’s great maple collections. So, she can actually be based at the Arnold Arboretum and studying the maples of the world to attack these evolutionary questions she’s interested in.

So that’s what we do. We go out there now with slightly different motivations. But at the end of the day, because we’re part of Harvard University, we’re an academic institution that’s committed to using the biodiversity that we take care of to drive science.

Tom Christopher

Ned, I need to pause for just a moment here to remind listeners that this radio station is WESU 88.1 FM. And this program is Growing Greener, a weekly conversation about gardening in partnership with nature. This is your host, Tom Christopher.

And today I am speaking with Dr. Ned Friedman, director of Harvard University’s Arnold Arboretum, about that institution’s impact on our understanding of trees and how it has evolved over the decades.

So, Ned, your involvement with plants isn’t just an abstract scientific interest, obviously. From what I hear in your voice when you talk about them, you’re really passionate about plants and have a real emotional involvement with their beauty.

Ned Friedman

I do. I’m a botanist. And proudly I say, you know, there’s nothing better than being a botanist. And I fell in love with botany my first year of college. Just I didn’t know I was going to love plants. Typical high school biology classes when I was young, you know, 99% of it was not about plants. You had maybe a day on photosynthesis and then you moved on. And then I started to learn about plants in college. And I just found a deep personal attachment and curiosity about all manner of what it means for plants to go about their lives. And that just became obvious. So the next thing I did is I went off to graduate school and got a Ph.D. in botany from the University of California at Berkeley. And it was there that I really figured out what I liked. And I love life cycles. I love understanding how plants go around from generation to generation. And I worked on the ginkgo tree, which has a very unusual life cycle, one that was one of the last kinds of life cycles to be discovered among plants. And I just fell in love with ginkgo. I fell in love with trees. I fell in love with their structure, their physiology. And I went on to become a professor at the University of Georgia, which I loved. And then I was in the botany department there. And then mid-career, I was at the University of Colorado, which brought me to the Rocky Mountains. And I’d done a post-doc in Arizona, so I love the desert. So, I’ve had this wonderful geographic journey as a botanist. And my final home has been back here on the East Coast at the Arnold Arboretum.

But I love thinking about trees. And I do a lot of photography in the Arnold Arboretum. If you go to our website at the Arnold Arboretum, I’ve posted, I think, 16,000 roughly images of the trees of the Arnold Arboretum. Any of them can be used by anyone for educational purposes. They all have a tag number, so everything’s correctly identified. And I just like looking at them.

And that then led to something that I tried out that turned out at the very beginning of the pandemic in 2020. I wanted to teach a first-year seminar for first-year students at Harvard to connect them with the natural world. And not from a scientific perspective, but from a more, I would say, emotional and from the heart. And I called the class Tree. And I didn’t know whether anyone would sign up. But we were going to read poetry. We were going to read some literature. We were going to read some science. For example, we spend a week thinking about when did arborescence become a thing? I mean, there was a time.

And I’m an evolutionary historian, so I think a lot about actually 400 million years ago and 300 million years ago. But there was a time when if you were walking around on this planet, let’s say 300, 400 million years ago, the tallest plant would have come up to your waist. And then almost in the blink of an eye, there was this race to the sky, as Lucretius would have described it on the nature of things.

And the world’s first forests were born. And so, we read about these. We actually go into the collections at Harvard, the palaeobotanical collections, where students can hold a 350-million-year-old tree. Not a picture of it, but the real fossil. So, we do things like that.

They all have to pick a tree to observe weekly. They can photograph. They can journal. But the goal is ultimately to interrogate what the essence of a tree is. There are no answers. You ask on day one, what’s a tree? I can give you formalistic definitions that there are such things. But they don’t really capture my personal love of trees. And they might not capture your personal love of trees or anyone else’s. So, it’s really a journey for each of these students to interrogate and think about what it means to connect to trees. But more broadly, what it means to be deeply rooted and connected to the natural world, which is important to me because these students will have to steward the world that we’ve given them as an inheritance, which is not in very good shape. So, we come back to, again, the Arnold Arboretum. We’re trying to raise the public’s awareness of the importance of preserving biodiversity. I’m teaching in that world. And hopefully we’re slowly but surely changing things for the better so that people are more, I’d say, engaged and activist in thinking through everything from what we eat to how we go about our daily business to how we, I would say, engage with the challenges that humans have created for living in harmony with the biological world.

Tom Christopher

This really speaks to me, frankly, because I’m a great believer that people have to develop a healthier and deeper connection to nature if we aren’t going to continue down this awful road we’re on of devastating the planet. And I think personally, gardening for me is a great way to involve people with nature because you can’t garden very long without learning that there are systems in nature and that if you ignore them, the results are bad. You know, you’ll see it in your own backyard, which is very persuasive. I think that the study of plants more generally, which has always been the Arnold Arboretum’s mission, can be a really formative experience, even for people like me who are not scientists. And that sounds like what your freshman seminar is about.

Ned Friedman

That’s right. And this is where gardening and gardens and arboreta are so important. You can learn a lot of science, and that’s fine. But I always tell people, just go up to a tree, look at its bark, see its leaves blowing in the breeze. If it’s in flower, just look. And all the scientific terminology in the world won’t help you find that attachment. You have to, as you say, with your own hands, garden, watch plants thrive or not thrive because you haven’t understood how they really are connected to an ecology and to a bigger system. All of those things, it’s really important for people to understand, are the best way to engage with the natural world. And so it’s true, I am a botanist in the professional sense of it. But I think I probably do far more work engaging with people, not through my having a PhD, but in fact, because I just love looking and thinking about plants. And that’s, I think, the key to everything is don’t worry whether you know the binomial. It doesn’t. At the Arnold Arboretum, every tree has a tag. If you don’t know the name of it, all you got to do is go to the base of the tree and there’s a copper-colored tag that’ll tell you its common name, its binomial in Latin. But that kind of knowledge, it’s a thing, it’s knowing things. But much more important, as you describe yourself, Tom, is that kind of engagement that comes from your hands in the soil or touching the bark or just standing back and being in awe of something that’s been growing for hundreds of years in a single spot. And that does not require a textbook.

Tom Christopher

So, Ned, typically I close this program with a tip for gardeners from the guest. And in that vein, I have a question for you. It is also a question that I’m really interested in the answer to personally. There’s an old saying about not being able to see the forest for the trees. But I think the reverse is also true. And we stand in front of one of these amazing living organisms composed of a complex of wood and leaves and roots. And it’s something that’s so fundamental for the health of our world. And yet, typically, we just say, oh, a tree, and move on. So, how would you suggest, and maybe this takes me back to your class for the freshmen and freshwomen at Harvard. But how would you suggest we learn to really look at a tree to begin to appreciate how unique and fascinating each one is?

Ned Friedman

Yeah, that’s a great question. And I do think you’re right that most people go through their lives, they see just green stuff in the background. They don’t actually see anything. I mean, if you think about it, we’re just surrounded by plants. You walk across a campus, you walk down a street, there’s plants. And you almost tune them out. Our minds are thinking about X, Y, and Z, and we’re not. So, I think of it as a practice. And this is why my students each get to pick a single tree. Now, all of our trees at the Arboretum have provenance. We know where that seed was collected. We know who it was collected by. We know that it was raised in a greenhouse operation to a sapling, and then it went into the ground. And maybe that happened 100 years ago. So, I tell people, start by giving standing to a single tree.

Make it something that has its own life story, just like you have your own life story. You were brought into this world, and you start as a single cell, a zygote, so does a tree. And individuate that tree. So, instead of seeing, if you’re in the woods, yes, there’s the forest. But stop, if you’re on a hike, and just admire a single beautiful tree that catches your eye. Just begin that practice or come to the Arnold Arboretum and pick a tree. But you can do it in your own backyard, your front yard. If you don’t have a yard, and you’re in a city, find a tree that somehow you just connect with. Now, there are no rules to this. And make it a practice to look, to stop. If you’re walking, and this tree’s on your way to the subway or whatever, just stop for five minutes. Or three minutes, if it’s an everyday thing. Or once a week. And just look. And the tree will surprise you that it is never the same any two days. Especially if it’s a temperate tree, and you have the fall colors, and then you have the leaves drop. But then you start saying, well, I’m going to look at bark. I had no idea that bark could change, in some cases, through the seasons. It could be so beautiful. Then you stand back, and maybe it’s the architecture. Or you’re looking at the leaves and the venation patterns. Or all of a sudden, you’re noticing that there are lichens on the tree.

And I would say, if you just make it mindful. You just say, I’m going to stop. I’m going to slow it down. In this world with pixels, everything’s a facsimile of reality. I’m just going to look one set of eyeballs and one tree, and I’m going to think about it. And, again, not scientifically. I’m just going to give it some standing in my life and give it room for it to affect me. That’s all I would do.

Tom Christopher

Well, thank you very much. This has been really inspiring and an awful lot of fun.

Oh, well, thank you.

Ned Friedman

I could not be more pleased than to have had this chance to have a conversation with you, Tom. I’m a great admirer of your work, and I’m really, really happy to have been able to have this conversation with you.

Tom Christopher

That brings us to the end of this week’s Growing Greener. Please join us again at the same time next week on this radio station, WESU 88.1 FM for another episode, or listen to Growing Greener as a podcast at www.thomaschristophergardens.com. If you have comments or suggestions, please share them with me, Tom Christopher, via the same website, www.thomaschristophergardens.com. Growing Greener is produced as a community service in partnership with the Perfect Earth Project, a nonprofit dedicated to educating, engaging, and inspiring individuals, land care professionals and decision makers to adopt toxic-free, nature-based, and climate-responsible landscaping practices.

 Transcribed by TurboScribe.

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