
For much of history, tree canopies were pretty much completely ignored by science. It was as if researchers said collectively, "It's just going to be empty up there, and we've got our hands full studying the trees down here! So why bother?" But then around the mid-1980s, a few ecologists around the world got curious and started making their way up into the treetops using any means necessary (ropes, cranes, hot air dirigibles) to document all they could find. It didn't take long for them to realize not only was the forest canopy not empty, it was absolutely filled to the brim with life. You've heard of treehouses? How about tree gardens?! This week, we bring you a story we first released in 2022. We journey up into the sky and discover forests above the forest. We learn about the secret powers of these sky gardens from ecologist Korena Mafune, and we follow Nalini Nadkarni as she makes a ground-breaking discovery that changes how we understand what trees are capable of. P.S. Th...
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Latif Nasser
Yeah, wait, you're listening.
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Lulu Miller
All right. Okay.
Robert Krulwich
All right.
Lulu Miller
You're listening to Radio Lab.
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Radio Lab from wnyc.
Lulu Miller
Rewind.
Latif Nasser
Hey, I'm Latif Nasser. This is Radiolab. One of our all time most popular episodes was From Tree to Shining Tree, which was about these vast networks hidden in the forest floor.
Robert Krulwich
She began thinking about the forest that exists underneath the forest.
Latif Nasser
That's Robert Krulwich, who was one of our hosts at the time. If you haven't heard the episode, you really should. We profiled this scientist, Suzanne Simard, who discovered, to even her own great surprise, these deeply complex interwoven mats of tree roots and mushroom threads connecting trees together, helping them communicate, even share resources. Like there's a literal underground economy in every forest you've ever been to.
Robert Krulwich
Turns out one tree was connected to 47 other trees all around it. It was like a huge network.
Nalini Nadkarni
The trees that were the biggest and
Lulu Miller
the oldest were the most highly connected. It's just this incredible communications network that, you know, people had no idea about in the past because we didn't know how to look.
Latif Nasser
So that was back in 2016. Couple years after that, the producer of that episode, Annie McKeown, brought to us another story that shocked us all over again because we realized that whole forest floor thing, that was just half of the story. So in celebration of spring and all the things growing around us right now, we wanted to replay that episode about the other half of the story of what's going on in forests. And to do so, of course, that perfect pairing of producer Andy McKeown and emeritus Radiolab host Robert Krulwich.
Robert Krulwich
Okay, we're ready. We're at long last ready to begin.
Lulu Miller
Okay. Okay, so for this episode, I wanted to call you because I recently learned about this new layer to the story. Okay, so in Tree to Shining Tree, we look down under the ground, right? Where do you think we should look now?
Robert Krulwich
Well, I guess I'd be inclined if there was more news, I'd do more down, I think.
Lulu Miller
Well, how about. Okay, how about instead of looking down, we peer into a type of down that is in the up.
Robert Krulwich
Oh, okay.
Lulu Miller
And to take us there.
Nalini Nadkarni
Alrighty.
Lulu Miller
Forest royalty, I've read that you are known as the queen of the canopy. Is that true?
Karina Mifune
Is that correct?
Lulu Miller
Where did that come from?
Nalini Nadkarni
I have no idea where that came from. I've also been called the mother of the forest canopy. And now that I'm 67 years old, I think it's going to be sort of the dowager queen or the grandmother. Forest canopies.
Lulu Miller
What about the Empress? This is ecologist Nalini Nadkarni, who, like a lot of kids, spent a large part of her childhood up in trees.
Nalini Nadkarni
You know, you grab a branch, you put your leg over it and suddenly you're up in the treetops. And for me, it was like kind of my place. I had this sort of chaotic large family. You know, I'd come home from school with chores and homework, but the treetops of these eight maple trees that lined my parents driveway were kind of my refuge.
Lulu Miller
She'd spend whole afternoons up there just sitting and wondering.
Nalini Nadkarni
I look at the leaves and I go, like, why does this branch have much yellower leaves than that branch which has orange or leaves?
Lulu Miller
Yes, that's such a good question.
Nalini Nadkarni
And it's, well, what is going on? Why? What is this branch independence? Or, you know, I'd watch squirrels jumping from one tree to another and just think, God, you know, where do they go? And what if I attached a spool of thread to the back of one of them and I could trace where they go? So. But it was a place for my imagination to sort of run wild.
Lulu Miller
Nalini grew up and followed that imagination to study ecology in grad school.
Nalini Nadkarni
This was back in like the early 1980s and I was just starting out and I came to my graduate committee and it said, I know what I want to do with the rest of my career. I want to study the forest canopy. And they said, well, that's kind of like Tarzan and Jane stuff, you know, with so many questions to ask and answer on the forest floor, why do you have to go into the canopy?
Lulu Miller
At that time, canopies were just basically not studied. They were hard to get up into and there didn't seem to be a lot of point. The scientific thinking was there's just not a lot going on up there.
Nalini Nadkarni
But there was something about the canopy that I kind of just had this intuition that it's not enough to just stand on the ground and look up.
Lulu Miller
And so with some modified mountain climbing equipment, she began to climb these giant old growth trees in the Olympic rainforests
Nalini Nadkarni
of western Washington, which is what's called a temperate rainforest.
Robert Krulwich
Are these the places where in the morning the fog from the Pacific Ocean comes rolling in?
Lulu Miller
Yeah.
Robert Krulwich
And the tree just gets in every morning bath of just. Yeah.
Lulu Miller
And the chi just goes.
Robert Krulwich
Yeah.
Lulu Miller
So Nalini climbs up into the canopy of this giant big leaf maple tree
Nalini Nadkarni
and I throw my leg over a branch and I'm sitting up there and I'm anchored with my rope and I'm looking around, I just see this enormous three dimensional panoply of moving leaves and moving twigs.
Lulu Miller
The branch she's sitting on, as well as all the branches surrounding her are covered in this super thick layer of
Nalini Nadkarni
this amazing growth of mosses and lichens. And kind of like the tree is
Lulu Miller
wearing this very unruly green shag carpet.
Nalini Nadkarni
You get this sense of being in a place that looks very simple from the forest floor, but is actually this kaleidoscope of life.
Lulu Miller
Her job up there was to take samples of the moss that was growing on these branches.
Nalini Nadkarni
I had to cut off chunks of it.
Lulu Miller
So using some clippers, she begins to cut down into that moss on the branch she's sitting on.
Nalini Nadkarni
And as I peeled back those mats
Lulu Miller
of mosses beneath, instead of just bare branch,
Nalini Nadkarni
I saw that there was all this soil up there.
Lulu Miller
This branch has a foot of soil piled up on it.
Robert Krulwich
Oh, wow.
Lulu Miller
Soil that formed over many, many years of mosses and leaves dying and decomposing right there on the branch.
Nalini Nadkarni
It's so weird because you're sitting up there in the canopy like 100ft above the ground, and then you're digging your fingers into the soil that could be the soil that's, you know, in your backyard garden, for goodness sake.
Lulu Miller
You can imagine getting your gardening gloves out and planting rows of tulips 100ft in the air.
Nalini Nadkarni
There were like invertebrates in it, there were earthworms in it.
Lulu Miller
Tree worms.
Nalini Nadkarni
Yes.
Lulu Miller
That is so weird.
Nalini Nadkarni
I know, I know.
Lulu Miller
Even the stars of the old episode, the fungi, were there.
Robert Krulwich
Really. So the mushrooms have climbed up the tree as well to sort of do their thing.
Lulu Miller
Yes, they're sharing resources. They're helping the tiny plants up there
Nalini Nadkarni
communicate with one another the same as on the forest floor.
Lulu Miller
It's almost like she stumbled into a perfect miniature of the forest floor she had just climbed up away from. And straddling a branch, way up high in the air, she's like, huh, well that's cool. This was in the 80s and since then there have been so many more. Well, that's cools. Because more and more scientists have been accessing this new world using cranes and ropes or building platforms or. My favorite way up into a tree is this French guy, Francis Allee, who pioneered the use of the dirigible to access the canopy. Oh wow, there's incredible pictures.
Robert Krulwich
So it's a balloon trip.
Lulu Miller
It's a balloon that floats. Yeah, that floats over the tops of this green ocean, just kissing the tops of the trees. And the scientists can just gently lean and trim this and that. Anyway, so one way or another, all over the world, scientists began getting themselves up into trees and documenting what they saw there. And some of the coolest discoveries were found on the west coast in the old growth redwood forests. And oh my gosh, these giants were found to be holding these pockets of soil up to three feet deep. And growing in this soil were flowers, berry bushes, mosses, lichens. They found salamanders living hundreds of feet in the air, who spend their entire lives never touching the ground.
Robert Krulwich
I'm waiting for you, say a small deer or something like that or something very weird.
Lulu Miller
I mean, I don't have a smell deer for you, but I do have something that I find totally bizarre, which is that up in redwoods scientists have found these tiny aquatic creatures.
Robert Krulwich
An aquatic creature?
Lulu Miller
It's aquatic, yeah, it's like the shrimp.
Robert Krulwich
Like they found a fish pretty much.
Lulu Miller
It's like this shrimp like thing, a species of something called a copepod, Copepods, which is actually this whole subclass of creatures. They're the most abundant animal in the ocean and a huge part of the diet of the baleen whales. This thing is like swimming around in these mossy mats and no one knows how it got there. Anyway. These tree canopies that up until the mid-80s everyone thought were just pretty much empty. Not only Are they not empty? They actually hold about 50% of all terrestrial life on the planet.
Robert Krulwich
A lot of that is 50%.
Lulu Miller
55. 0. Yeah.
Robert Krulwich
Wow. That's a weird number that you're saying 50% of it is up in the air somewhere.
Lulu Miller
Yeah, up in the air, up in trees.
Robert Krulwich
Whoa.
Lulu Miller
Which, you know, sounds kind of unbelievable, but when you think of places like the Amazon, all those bugs, birds, plants, animals, it adds up. And most of this life has made a home in these canopy soils. What soil?
Karina Mifune
On the tree branches.
Lulu Miller
And when ecologist Karina Mifune learned about
Karina Mifune
these canopy soils, I felt I fell in love with. I was like, okay, there's like a forest in a forest, on a forest. I need to research this.
Lulu Miller
And she told me that thinking about these canopy soils, like these tiny, perfect replicas of the forest floor below, wasn't quite right, because these canopy soils, they have something that the forest wants.
Robert Krulwich
Huh. Well, what would that be?
Lulu Miller
Well, back when she was a grad student in the Washington Olympic Peninsula, Karina collected soil samples from the forest forest floor throughout the year.
Karina Mifune
And she noticed that in the spring growing season, there aren't as many nutrients available.
Lulu Miller
Specifically, there was a lack of phosphorus and nitrogen, two important things that every plant in the springtime wants to help them, you know, put forth new leaves to help them grow.
Robert Krulwich
And those are rare. Plants love that, right? Yeah.
Lulu Miller
And in contrast to the last episode where we talked about trees cooperating with
Robert Krulwich
each other, all these trees, all these trees that were of totally different species were sharing their food underground. Like, if you put.
Lulu Miller
Karina told me that in that same sharing forest, when resources are scarce, there's
Karina Mifune
a ton of competition on the forest for trees have roots grafted together. There's mycorrhizal networks, you know, that are spanning across. There's this big battle to, you know, uptake nutrients.
Lulu Miller
But Karina had also taken samples of the canopy soils, and she saw that during these times of sleep, scarcity below
Karina Mifune
these canopy soils had so much more nitrogen and phosphorus available for plant uptake compared to their forest floor counterparts.
Lulu Miller
Meaning that this soil for a plant was creme de la creme.
Karina Mifune
It's just amazing.
Lulu Miller
Downstairs there's shortage, upstairs there's abundance. When it's crumbs down below, up in the sky, held aloft above the plebeian masses is like a Thanksgiving dinner. And when Karina learned this, she thought,
Karina Mifune
I don't know, what do these canopy soils mean? Because they're not just hanging out there. They're not just there for no reason. Right.
Lulu Miller
She's right. They're not these sky gardens. They get even better.
Robert Krulwich
Better at what?
Nalini Nadkarni
Hmm.
Robert Krulwich
Better at what?
Lulu Miller
Well, let's just say they're not alone up there.
Robert Krulwich
What's what's about to happen?
Lulu Miller
Well, I'm going to tell you all righty right after this short break.
Latif Nasser
Radiolab is supported by Strawberry Me. As a Radiolab listener, chances are you're a curious person who asks how things work and why people do what they do, trying to make sense of the world around you. But what about turning that same curiosity inward, especially when it comes to your work? Because so many people know what it feels like to show up every day, get through the to do list and still wonder things like is this what I really want? Could this be different? Maybe you felt stuck or restless or just quietly ready for something more, but aren't sure what that looks like or how to get there. That's where Strawberry Me comes in. Strawberry connects you with a thoughtful career coach who helps you step back and reflect on what motivates you, what's missing, and what kind of work can actually fit the life you want. Think of it as bringing the same curiosity you have about the world to your own career. Explore your path Forward at Strawberry Me Radiolab and get 50% off your first coaching session. That's Strawberry Me Radiolab at the Home
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Lulu Miller
Lulu Latif Radiolab Back to Annie and Robert, where we were just about to learn the true superpower of those gardens in the sky. Right? So to understand this wizardry, we need to go back to Nalini. Fine with me and this amazing discovery that you made.
Nalini Nadkarni
Okay. So I remember sitting on this tree.
Lulu Miller
She's back up in a tree in the Washington rainforest, digging around in this canopy soil.
Nalini Nadkarni
And I began seeing these root systems that were running up and down the branches of these trees.
Lulu Miller
They didn't look like they belonged to moss or ferns or any other plant you could see up there.
Nalini Nadkarni
And there were fine roots all the way up to. Some of them were the diameter of my wrist. I mean, these were gigantic roots. And I thought, well, that's weird. What are these roots doing here? So I began just tracing the roots that I was finding.
Lulu Miller
Like, you took hold of one root in your hand and sort of, like, went backwards. Like a string.
Nalini Nadkarni
Exactly.
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Like.
Nalini Nadkarni
It's like following a string. Exactly.
Lulu Miller
She gently excavates this root, scooting along the branch as she uncovers it.
Nalini Nadkarni
I was tied in so I could sort of swing around and move from one branch to another. I had my water bottle with me. So then whenever it began difficult to sort of unstick the root, I could just throw a little water on it, keep going, keep following it. It was like. I don't know, it was like being a detective.
Lulu Miller
But what did you think it was gonna lead to?
Nalini Nadkarni
I had no idea. I thought, well, maybe there's some sort of vascular plant that I'm not aware of that's here, but I don't think it is.
Lulu Miller
So then she follows the root all the way back to its beginning, and.
Nalini Nadkarni
Oh, my gosh. Its origin was a dead end in the tree itself.
Robert Krulwich
What?
Lulu Miller
The big tree, the one Nalini is sitting in, is growing roots from its
Nalini Nadkarni
branch and snaking underneath these mats of soil, of canopy soil.
Robert Krulwich
Let me think about this. Somehow it realizes that it could find soil high up somewhere, like. And so it just takes its roots, and its roots travel up and go whoop to the left and say, let's root not only where we normally root down there, but let's root up here.
Lulu Miller
Yes.
Robert Krulwich
Whoa. So things that you thought were below can move above, way above, high above you?
Nalini Nadkarni
Yes. It was a real revelation.
Lulu Miller
And Karina thinks that it's during a drought or during spring growing season, when resources on the forest floor are scarce,
Karina Mifune
that these big trees, that's when they can tap into their canopy soils. It's like they're like, hey, there's a
Nalini Nadkarni
bunch of really great stuff here to suck on. So why don't you put out a root out here? And that's exactly what these trees do.
Karina Mifune
I kind of always compare it to, like, A secret cabinet that has all the good snacks in it. It's like if you were teaching a preschool. It's like while all of the school children are fighting over the snacks and fighting over these resources, you just go into your, you know, canopy soil closet and you got your good snacks up there.
Robert Krulwich
Because we're looking for those special minerals like the phosphorus and stuff. And that's where we can find it.
Lulu Miller
Right. And it's finding it in its hat.
Robert Krulwich
And you're finding it in its hat. That's a nice way of putting it. Yes.
Lulu Miller
Yeah,
Robert Krulwich
that's a lovely way of putting it. Yes. The expression I'm gonna eat my hat has now got a whole new meaning.
Lulu Miller
Yes, Robert, I love that. One thing that both Karina and Nalini told me is that this is a new field.
Karina Mifune
There is just so many things to be found high above the forest floor.
Lulu Miller
Like for instance, Karina told me sometimes there are actual trees growing up there.
Karina Mifune
And I've seen like a five foot spruce growing out of a nook of canopy soil.
Latif Nasser
Wow.
Karina Mifune
And you'll see a lot of like baby maples growing up in the old maple. So it's like, you know, like a little nursery.
Robert Krulwich
Wait a second. You mean there's a tree growing on the tree?
Lulu Miller
That's right.
Robert Krulwich
On the branch?
Lulu Miller
In the soil on the branch.
Latif Nasser
Oh.
Lulu Miller
And who knows, maybe as more people study the canopy, we'll find little trees on those trees and maybe there will be little trees on those trees. On those trees.
Robert Krulwich
Yeah. It's fractal, like littler plants off the ground then live on them is the moss, which is little plants on top of little plants. So there's like, there's little layers and layers and layers of life. And the more you go up, the more the layers you will find. It's sort of cool.
Lulu Miller
Thank you, Annie McEwan for reporting and producing that gorgeous episode and leaving us with that image of not turtles all the way down, but trees all the way up.
Latif Nasser
This episode was reported and Produced by Annie McEwan. Special thanks to Kiyomi Taguchi, Michelle Ma and Nina Ernest. A huge thank you to Michael Werner and Joe Hanson and the team at PBS Overview. They tipped us off about Karina's research. They were the ones who got us excited about canopy soil in the first place. You can actually see all that gorgeous shag carpeting in the forest in their beautiful video Vivid color. The video features Karina and other people who have dedicated their lives to saving what's left of the old growth forest. You can check that out on our website or on theirs. So thank you to them. And special thanks, of course, to the the many ringed tree trunk that is Robert Krulwich coming back on the show to talk trees with us. Thank you for doing that, Robert. We love you. That guy's all bark, no bites, you know what I mean? That's why I like him. That's all for us. Catch you next week.
Gabby Santis
Hi, I'm Gabby. I'm from the Bay Area, California, and here are the staff credits. Radiolab is hosted by Lulu Miller and Latif Nasser. Soran Wheeler is our Executive editor. Sara Sandbach is our Executive director. Our Managing editor is Pat Walters. Dylan Keefe is our director of Sound design. Our staff includes Jeremy Bloom, W. Harry Fortuna, David Gable, Maria Paz, Gutierrez Sindhu, Naina Sambandan, Matt Kielty, Mona Margaukar, Annie McEwen, Alex Neeson, Sara Khari, Natalia Ramirez, Rebecca Rand, Anissa Vitce, Arian Wack, Molly Webster and Jessica Young, with help from Gabby Santis. Our fact checkers are Diane Kelly, Emily Krieger, Natalie Middleton, Angeli Mercado and Sophie Semay.
Lulu Miller
Hi, I'm Aubrey calling from Salt Lake City, Utah. Leadership support for Radiolab's science programming is provided by the Simons foundation and the John Templeton Foundation.
Karina Mifune
Foundational support for Radiolab was provided by
Lulu Miller
the Alfred P. Sloan Foundation.
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Air Date: April 24, 2026
Hosts: Lulu Miller and Latif Nasser
Guests: Robert Krulwich, Nalini Nadkarni, Karina Mifune
Producer: Annie McEwen
This episode explores the mysterious and vibrant world high above the forest floor—the forest canopy—and its hidden “soil in the sky.” Building on their previous hit “From Tree to Shining Tree,” which revealed the complex life and underground networks linking trees, Radiolab turns its gaze upward to discover entire ecosystems and nutrient economies thriving in the tree canopies. The episode features ecologists Nalini Nadkarni (the “queen of the canopy”) and Karina Mifune, whose research uncovers the vital, underappreciated role of canopy soils and their influence on forest health, biodiversity, and resilience.
Radiolab’s signature blend of playful curiosity and deep reporting brings a magical yet grounded sense of wonder to the episode. The forest canopy is revealed not just as “the up,” but as a thriving frontier—full of secrets still being uncovered, and essential not just for forest life, but for understanding the fractal exuberance of nature itself. The final image is an evergreen one: forests stacked on forests, “not turtles all the way down, but trees all the way up.”
For lush visuals of canopy life and more on this episode’s science, visit the Radiolab website or the PBS Overview team video.