[RADIOLAB INTRO]

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.

[ARCHIVE CLIP, Robert Krulwich: She began thinking about the forest that exists underneath the forest.]

LATIF: 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.

[ARCHIVE CLIP, Robert Krulwich: Turns out one tree was connected to 47 other trees all around it. It was like a huge network.]

[ARCHIVE CLIP, Suzanne Simard: The trees that were the biggest and 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: So that was back in 2016. Couple years after that, the producer of that episode, Annie McEwen, 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 Annie McEwen and emeritus Radiolab host Robert Krulwich.

ROBERT: Okay. We're ready. [laughs] At long last ready to begin.

ANNIE MCEWEN: Okay. Okay, so for this episode, I wanted to call you because I recently learned about this new layer to the story.

ROBERT: Okay.

ANNIE: So in "Tree To Shining Tree," we looked down under the ground.

ROBERT: Right.

ANNIE: Where do you think we should look now?

ROBERT: Well, I guess if there was more news I'd do more down.

ANNIE: Okay. [laughs]

ROBERT: I think.

ANNIE: Well, how about—okay, how about instead of looking down, we peer into a type of down that is in the up?

ROBERT: Oh, okay.

ANNIE: And to take us there ...

NALINI NADKARNI: Alrighty.

ANNIE: ... forest royalty.

ANNIE: I've read that you are known as the "Queen of the Canopy." Is that true?

NALINI NADKARNI: Yes. That's correct.

ANNIE: Is that ...

NALINI NADKARNI: That's true.

ANNIE: 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."

ANNIE: Oh my goodness!

NALINI NADKARNI: And now that I'm 67 years old, I think it's gonna be sort of the "Dowager Queen" or the "Grandmother of the Forest Canopy." [laughs]

ANNIE: I think you should be the empress! What about "The Empress?"

ANNIE: 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 from school with chores and homework, but the treetops of these eight maple trees that lined my parents' driveway were kind of my refuge.

ANNIE: She'd spend whole afternoons up there just sitting and wondering.

NALINI NADKARNI: And look at the leaves, and I'd go, like, "Why does this branch have much yellower leaves than that branch which has orangey leaves?"

ANNIE: Yes, that's a good question!

NALINI NADKARNI: And it's like, well what is going on? 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.

ANNIE: 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 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?"

ANNIE: 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.

ANNIE: And so with some modified mountain climbing equipment, she began to climb these giant old-growth trees in the Olympic Rainforest of western Washington.

NALINI NADKARNI: Which is what's called a temperate rainforest.

ROBERT: Are these the places where in the morning the fog from the Pacific Ocean comes rolling in?

ANNIE: Yeah.

ROBERT: And the tree just gets an every morning bath of just pure moisture?

ANNIE: Yeah the tree just goes [slurps].

ROBERT: Yeah.

ANNIE: 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.

ANNIE: 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 ferns.

ANNIE: Kind of like the tree is 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.

ANNIE: 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.

ANNIE: 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 of mosses ...

ANNIE: Beneath, instead of just bare branch ...

NALINI NADKARNI: I saw that there was all this soil up there.

ANNIE: This branch has a foot of soil piled up on it.

ROBERT: Oh, wow!

ANNIE: 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, a hundred feet above the ground, and then you're digging your fingers into this soil that could be the soil that's, you know, in your backyard garden, for goodness sake!

ANNIE: You could imagine getting your gardening gloves out and planting rows of tulips a hundred feet in the air.

NALINI NADKARNI: There were, like, invertebrates in it, there were earthworms in it.

ANNIE: Tree worms?

NALINI NADKARNI: Yes!

ANNIE: That is so weird!

NALINI NADKARNI: I know! I know!

ANNIE: Even the stars of the old episode, the fungi, were there.

ROBERT: Really? So the mushrooms have climbed up the tree as well to sort of do their thing?

ANNIE: Yes. They're sharing resources, they're helping the tiny plants up there communicate with one another.

NALINI NADKARNI: The same as on the forest floor.

ANNIE: It's almost like she's 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!"

NALINI NADKARNI: "Well, that's cool!"

ANNIE: 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 Hallé, who pioneered the use of the dirigible to access the canopy.

ROBERT: Oh, wow!

ANNIE: There's incredible pictures of ...

ROBERT: So it's a balloon trip that he takes? Leaning out of a balloon?

ANNIE: It's a balloon that floats—yeah, that floats over the tops of this green ocean, just kissing the tops of the trees.

ROBERT: Oh, wow.

ANNIE: 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: [laughs] I'm waiting for you to say, "A small deer," or something like that. Or something very weird.

ANNIE: [laughs] I mean, I don't have a small 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: An aquatic creature?

ANNIE: It's aquatic, yeah. It's like this shrimp-like ...

ROBERT: They found a fish? [laughs]

ANNIE: Pretty much. It's like a shrimp-like thing. A species of something called the copepod.

ROBERT: Oh!

ANNIE: 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 baleen whales.

ROBERT: [laughs]

ANNIE: 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 percent of all terrestrial life on the planet. A lot of that is ...

ROBERT: Did you say 50 percent? 50 percent?

ANNIE: Fifty. 5-0. Yeah.

ROBERT: Wow, that's a weird—you're saying 50 percent is up in the air somewhere?

ANNIE: Yeah, up in the air, up in trees.

ROBERT: Whoa!

ANNIE: 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.

KORENA MAFUNE: What? Soil in the tree branches? I was like ...

ANNIE: And when ecologist Korena Mafune learned about these canopy soils ...

KORENA MAFUNE: I fell in love. I was like, "Okay, there's, like, a forest in a forest on a forest. I need to research this."

ANNIE: 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 htapave something that the forest wants.

ROBERT: Huh. Well, what would that be?

ANNIE: Well, Back when she was a grad student in the Washington Olympic Peninsula, Korena collected soil samples from the forest floor throughout the year. And she noticed that ...

KORENA MAFUNE: In the spring growing season, there aren't as many nutrients available.

ANNIE: 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: And those are rare. Plants love that.

ANNIE: Right.

ROBERT: Yeah.

ANNIE: And in contrast to the last episode where we talked about trees cooperating with each other ...

[ARCHIVE CLIP, Robert: All these trees, all these trees that were of totally different species were sharing their food underground. Like, if you put ...]

ANNIE: Korena told me that in that same sharing forest when resources are scarce ...

KORENA MAFUNE: There's a ton of competition on the forest floor. Trees have roots grafted together, there's mycorrhizal networks they're spanning across. There's this big battle to, you know, uptake nutrients. But ...

ANNIE: Korena had also taken samples of the canopy soils, and she saw that during these times of scarcity below ...

KORENA MAFUNE: These canopy soils had so much more nitrogen and phosphorus available for plant uptake compared to their forest floor counterparts.

ANNIE: Meaning that this soil for a plant was creme de la creme.

KORENA MAFUNE: It's just amazing.

ANNIE: 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.

ROBERT: [laughs]

ANNIE: And when Korena learned this, she thought, "I don't know."

KORENA MAFUNE: What do these canopy soils mean? Because they're not just hanging out there. They're not just there for no reason, right?

ANNIE: She's right. They're not. These sky gardens, they get even better.

ROBERT: Better at what?

ANNIE: Hmm?

ROBERT: Better at what?

ANNIE: Well, let's just say they're not alone up there.

ROBERT: Well, what's—what's about to happen?

ANNIE: Well, I'm gonna tell you.

ROBERT: Alrighty.

ANNIE: Right after this short break.

LULU: Lulu.

LATIF: Latif.

LULU: Radiolab. Back to Annie and Robert, where we were just about to learn the true superpower of those gardens in the sky.

ANNIE: Right. So to understand this wizardry, we have to go back to Nalini.

NALINI NADKARNI: Fine with me.

ANNIE: And this amazing discovery that she made.

NALINI NADKARNI: Okay. So I remember sitting on this tree.

ANNIE: 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.

ANNIE: They didn't look like they belonged to moss or ferns or any other plant she 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.

ANNIE: Wow! What?

NALINI NADKARNI: And I thought, "Well, that's weird. What are these roots doing here?"

ANNIE: Huh.

NALINI NADKARNI: So I began just tracing the roots that I was finding.

ANNIE: Like, you took hold of one root in your hand and sort of like went backwards?

NALINI NADKARNI: Yes, exactly.

ANNIE: Like a string?

NALINI NADKARNI: Exactly like following a string. Exactly.

ANNIE: 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 became 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.

ANNIE: Well, 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 so."

ANNIE: Wow!

NALINI NADKARNI: So then ...

ANNIE: She follows the root all the way back to its beginning.

NALINI NADKARNI: And oh my gosh! Its origin was a dead-end in the tree itself.

ROBERT: What?

ANNIE: The big tree, the one Nalini is sitting in, is growing roots from its branch ...

NALINI NADKARNI: And snaking underneath these mats of soil, of canopy soil.

ROBERT: Let me think about this. Somehow it realizes that it can 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."

ANNIE: Yes.

ROBERT: Whoa! So things that you thought were below can move above, way above. High above you.

NALINI NADKARNI: Yes. It was a real revelation.

ANNIE: And Korena thinks that if during a drought or during spring growing season when resources on the forest floor are scarce, that these big trees ...

KORENA MAFUNE: That's when they can tap into their canopy soils.

NALINI NADKARNI: Like, they're like, "Hey! There's a 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.

KORENA MAFUNE: 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, well, all of the schoolchildren 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: Because we're looking for those special minerals like the phosphorus and stuff, and that's where we can find it.

ANNIE: Right. And it's finding it in its hat.

ROBERT: Yeah, finding it in its hat. [laughs] That's a nice way of putting it, yes.

ANNIE: Yeah.

ROBERT: That's a lovely way of putting it. The expression, "I'm gonna eat my hat" has now got a whole new meaning.

ANNIE: Oh yes! Robert! I love that. [laughs]

ROBERT: Yeah.

ANNIE: One thing that both Korena and Nalini told me is that this is a new field.

KORENA MAFUNE: There is just so many things to be found high above the forest floor.

ANNIE: Like for instance, Korena told me sometimes there are actual trees growing up there.

KORENA MAFUNE: That I've seen, like, a five-foot spruce growing out of canopy soil.

ANNIE: Wow.

KORENA MAFUNE: And you'll see a lot of, like, baby maples growing up in the old maples, so it's like, you know, like a little nursery.

ROBERT: Wait a second. You mean, there's a tree growing on the tree?

ANNIE: That's right.

ROBERT: On the branch.

ANNIE: In the soil on the branch.

ROBERT: Oh!

ANNIE: 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: Yeah. It's fractal. Like, littler plants off them.

ANNIE: Mm-hmm.

ROBERT: And then 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. That's sorta cool.

LULU: Thank you Annie McEwen 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: This episode was reported and produced by Annie McEwen. Special thanks to Naomi Taguchi, Michelle Mah and Nina Ernest. A huge thank you to Michael Werner and Joe Hanson and the team at PBS Overview. They tipped us off about Korena'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 Korena and other people who have dedicated their lives to saving what's left of the old-growth forests. You can check that out on our website or on theirs. Thank you to them.

LATIF: And special thanks, of course, to 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 bite. You know what I mean? That's why I like him. That's all for us. Catch you next week.

[LISTENER: 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. Soren Wheeler is our executive editor. Sarah 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 Gebel, Maria Paz Gutiérrez, Sindhu Gnanasambandan, Matt Kielty, Mona Madgavkar, Annie McEwen, Alex Neason, Sarah Qari, Natalia Ramirez, Rebecca Rand, Anisa Vietze, Arianne Wack, Molly Webster and Jessica Yung, with help from Gabby Santas. Our fact-checkers are Diane Kelly, Emily Krieger, Natalie Middleton, Angely Mercado and Sophie Sanahee.]

[LISTENER: 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. Foundational support for Radiolab was provided by the Alfred P. Sloan Foundation.]

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