Forests on Forests

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. This episode is a layer cake of arboreal surprises (including the reappearance of a certain retired host. LATERAL CUTS:From Tree to Shining Tree (https://zpr.io/4cHtDdYTuNxT): The episode that started this journey, where we look down instead of up. EPISODE CREDITS: Reported by - Annie McEwenProduced by - Annie McEwen EPISODE CITATIONS: Videos - Inside the Fight to Save an Ancient Forest (and the Secrets it Holds) (https://zpr.io/XKipP2z4NFiM), by Michael Werner, Joe Hanson, and the PBS Overview team. We first learned about the magical world of the canopy from this beautiful video. It features Korena Mafune’s research up in the treetops, as well as the people who have dedicated their lives to saving what’s left of the old growth forests. We highly recommend checking it out! Signup for our newsletter!! It includes short essays, recommendations, and details about other ways to interact with the show. Sign up (https://radiolab.org/newsletter)! Radiolab is supported by listeners like you. Support Radiolab by becoming a member of The Lab (https://members.radiolab.org/) today. Follow our show on Instagram, Twitter and Facebook @radiolab, and share your thoughts with us by emailing [email protected]. 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.

• 0:01Speaker 00

  Wait, you're listening.

• 0:09Speaker 01

  You're listening to Radiolab.

• 0:11Speaker 00

  Radiolab.

• 0:12Speaker 01

  From?

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  WNYC.

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  Rewind.

• 0:21Speaker 02

  Hey, I'm Latif Nasr. 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.

• 0:36Speaker 03

  She began thinking about the forest that exists underneath the forest.

• 0:40Speaker 02

  That's Robert Kralwich, 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.

• 1:10Speaker 03

  Turns out, one tree was connected to 47 other trees all around it. It was like a huge network.

• 1:17Speaker 04

  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.

• 1:30Speaker 02

  So that was back in 2016. Couple of 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 Kralwich.

• 2:10Speaker 03

  Okay, we're ready. We're at long last ready to begin.

• 2:13Speaker 05

  Okay. Um, okay. So for this episode, I wanted to call you because I recently learned about this new layer to the story.

• 2:23Speaker 03

  Okay.

• 2:24Speaker 05

  So in tree to shining tree, we look down, under the ground.

• 2:27Speaker 03

  Right.

• 2:28Speaker 05

  Where do you think we should look now?

• 2:30Speaker 03

  Well, I guess I'd be inclined, if there was more news, I'd do more down.

• 2:35Speaker 03

  I think.

• 2:36Speaker 05

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

• 2:45Speaker 03

  Oh, okay.

• 2:47Speaker 05

  And to take us there?

• 2:48Speaker 06

  All righty.

• 2:48Speaker 05

  Forest royalty. I've read that you are known as the queen of the canopy. Is that true?

• 2:54Speaker 06

  Yes.

• 2:55Speaker 05

  Where did that come from?

• 2:56Speaker 06

  I have no idea where that came from. I've also been called the mother of the forest canopy.

• 3:00Speaker 05

  Oh, my goodness.

• 3:01Speaker 06

  And now that I'm 67 years old, I think it's going to be sort of the dowager queen or, or the grandmother of forest canopies.

• 3:08Speaker 05

  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.

• 3:16Speaker 06

  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.

• 3:35Speaker 05

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

• 3:39Speaker 06

  And look at the leaves and I go like, why is this branch have much yellower leaves than that branch, which has orangey leaves?

• 3:46Speaker 05

  Such a good question.

• 3:47Speaker 06

  And it's like, 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.

• 4:04Speaker 05

  Nalini grew up and followed that imagination to study ecology in grad school.

• 4:08Speaker 06

  This was back in like, the early 1980s. And I was just starting out. And I came to my graduate committee and I 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 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?

• 4:27Speaker 05

  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.

• 4:37Speaker 06

  But there was something about the canopy that I kind of just had this intuition

• 4:43Speaker 06

  that it's not enough to just stand on the ground and look up.

• 4:48Speaker 05

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

• 4:57Speaker 06

  Which is what's called a temperate rainforest.

• 4:59Speaker 03

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

• 5:04Speaker 05

  Yeah.

• 5:05Speaker 03

  And the tree just gets an every morning bath of just pure moisture.

• 5:08Speaker 06

  Yeah, and the tree just goes phew.

• 5:10Speaker 05

  So Nalini climbs up into the canopy of this giant big leaf maple tree.

• 5:14Speaker 06

  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.

• 5:27Speaker 05

  The branch she's sitting on, as well as all the branches surrounding her, are covered in this super thick layer of-

• 5:33Speaker 06

  This amazing growth of mosses and lichens and ferns.

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  Kind of like the tree is wearing this very unruly green shag carpet.

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  You get the sense of being in a place that looks very simple from the forest floor, but is actually this kaleidoscope of life.

• 5:52Speaker 05

  Her job up there was to take samples of the moss that was growing on these branches.

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  I had to cut off chunks of it.

• 5:58Speaker 05

  So using some clippers, she begins to cut down into that moss on the branch she's sitting on.

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  And as I peeled back those mats of mosses-

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  Beneath, instead of just bare branch-

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  I saw that there was all this soil up there.

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

• 6:15Speaker 03

  Oh, wow.

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  Soil that formed over many, many years of mosses and leaves dying and decomposing right there on the branch.

• 6:24Speaker 06

  It's so weird because you're sitting up there in the canopy, like 100 feet 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.

• 6:35Speaker 05

  You can imagine getting your gardening gloves out and planting rows of tulips 100 feet in the air.

• 6:40Speaker 06

  There were like invertebrates in it, there were earthworms in it.

• 6:42Speaker 05

  Tree worms?

• 6:43Speaker 06

  Yes.

• 6:44Speaker 05

  That is so weird.

• 6:45Speaker 06

  I know, I know.

• 6:46Speaker 05

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

• 6:49Speaker 03

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

• 6:53Speaker 05

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

• 6:56Speaker 06

  The same as on the forest floor.

• 6:59Speaker 05

  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.

• 7:08Speaker 06

  Well, that's cool.

• 7:10Speaker 05

  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 Allais, who pioneered the use of the dirigible to access the canopy.

• 7:29Speaker 03

  Oh, wow.

• 7:30Speaker 05

  There's incredible pictures of these.

• 7:31Speaker 03

  So it's a balloon trip, like tanks leaning out of a balloon?

• 7:35Speaker 05

  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.

• 8:18Speaker 03

  I'm waiting if you say a small deer, or something like that, or something very weird.

• 8:23Speaker 05

  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.

• 8:35Speaker 03

  An aquatic creature?

• 8:36Speaker 05

  It's aquatic, yeah, it's like this shrimp-like.

• 8:39Speaker 03

  They found a fish?

• 8:40Speaker 05

  Pretty much, it's like this shrimp-like thing. Species of something called the copapod.

• 8:44Speaker 03

  Oh.

• 8:44Speaker 05

  Copapods, 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. This thing is like swimming around in these mossy mats and no one knows how it got there.

• 9:07Speaker 05

  Anyway, these tree canopies that up until the mid eighties, 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.

• 9:21Speaker 03

  Did you say 50%?

• 9:22Speaker 05

  Fifty, five zero. Yeah.

• 9:24Speaker 03

  Wow, that's a weird note. You're saying 50% of it is up in the air somewhere?

• 9:28Speaker 05

  Yeah, up in the air, up in trees.

• 9:30Speaker 03

  Whoa.

• 9:31Speaker 05

  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.

• 9:42Speaker 04

  What, soil on the tree branches?

• 9:44Speaker 05

  And when ecologist Karina Mafune learned about these canopy soils.

• 9:48Speaker 04

  I fell, I fell in love. I was like, okay, there's like a forest in a forest on a forest. I need to research this.

• 9:56Speaker 05

  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.

• 10:12Speaker 03

  Huh. Well, what would that be?

• 10:15Speaker 05

  Well, back when she was a grad student in the Washington Olympic Peninsula, Karina collected soil samples from the forest floor throughout the year. And she noticed that in the spring growing season, there aren't as many nutrients available. 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.

• 10:38Speaker 03

  And those are rare. Plants love that.

• 10:40Speaker 05

  Right.

• 10:40Speaker 03

  Yeah.

• 10:41Speaker 05

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

• 10:45Speaker 03

  All these trees, all these trees that were of totally different species were sharing their food underground. Like if you put.

• 10:53Speaker 05

  Karina told me that in that same sharing forest, when resources are scarce.

• 10:57Speaker 04

  There's a ton of competition on the forest floor. Trees have roots grafted together. There's mycorrhizal networks, you know, that are spanning across.

• 11:05Speaker 01

  There's this big battle to uptake nutrients.

• 11:10Speaker 01

  But-

• 11:10Speaker 05

  Karina had also taken samples of the canopy soils. And she saw that during these times of scarcity below.

• 11:18Speaker 01

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

• 11:26Speaker 05

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

• 11:31Speaker 01

  Is just amazing.

• 11:32Speaker 05

  Downstairs,

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  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.

• 11:50Speaker 05

  And when Karina learned this, she thought, I don't know.

• 11:54Speaker 01

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

• 12:01Speaker 05

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

• 12:06Speaker 03

  Better at what?

• 12:08Speaker 05

  Hmm?

• 12:08Speaker 03

  Better at what?

• 12:09Speaker 05

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

• 12:13Speaker 03

  What's about to happen?

• 12:14Speaker 05

  Well, I'm going to tell you.

• 12:15Speaker 03

  All righty.

• 12:16Speaker 05

  Right after this short break.

• 12:36Speaker 00

  This week on the New Yorker Radio Hour, will House Democrats try once again for impeachment? Let's not make a fetish out of impeachment. Let's not make a taboo out of impeachment. We understand it's not a panacea, but it is an essential tool in the constitutional toolbox that's always there. Congressman Jamie Raskin joins us next-

• 12:55Speaker 01

  Time on the New Yorker Radio Hour from WNYC. Listen wherever you get your podcasts.

• 13:09Speaker 01

  Lulu. Lot there. Radio Lab, back to Annie and Robert, where we were just about to learn the true superpower of those gardens in the sky.

• 13:18Speaker 05

  Right. So to understand this wizardry, we need to go back to Nalini.

• 13:22Speaker 06

  Fine with me.

• 13:22Speaker 05

  And this amazing discovery that she made.

• 13:24Speaker 06

  OK, so I remember sitting on this tree.

• 13:26Speaker 05

  She's back up in a tree in the Washington rainforest, digging around in this canopy soil.

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  And I began seeing these root systems that were running up and down the branches of these trees.

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  They didn't look like they belonged to moss or ferns or any other plant you could see up there.

• 13:41Speaker 06

  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.

• 13:56Speaker 01

  Like you took hold of one root in your hand and sort of like went backwards like a string?

• 14:00Speaker 06

  Exactly, like following a string, exactly.

• 14:04Speaker 05

  She gently excavates this root, scooting along the branch as she uncovers it.

• 14:08Speaker 06

  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.

• 14:23Speaker 01

  Well, what did you think it was gonna lead to?

• 14:25Speaker 06

  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's here. So then.

• 14:31Speaker 05

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

• 14:34Speaker 06

  And, oh, my gosh! Its origin was a dead end in the tree itself.

• 14:41Speaker 03

  What?

• 14:42Speaker 05

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

• 14:47Speaker 06

  And snaking underneath these mats of soil, of canopy soil.

• 14:52Speaker 03

  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.

• 15:07Speaker 06

  Yes.

• 15:08Speaker 03

  Whoa. So things that you thought were below can move above, way above, high above you.

• 15:15Speaker 06

  Yes. It was a real revelation.

• 15:20Speaker 05

  And Karina thinks that it's during a drought or during spring growing season, when resources in the forest floor are scarce, that these big trees...

• 15:28Speaker 01

  That's when they can tap into their canopy soils. It's 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.

• 15:43Speaker 01

  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 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.

• 15:59Speaker 03

  Because we're looking for those special minerals like the phosphorus and stuff, and that's where we can find it.

• 16:05Speaker 05

  Right, and it's finding it in its hat.

• 16:08Speaker 03

  Yeah, finding it in its hat. That's a nice way of putting it, yes.

• 16:13Speaker 05

  Yeah.

• 16:15Speaker 03

  That's a lovely way of putting it, yes.

• 16:19Speaker 03

  The expression, "I'm gonna eat my hat", has now got a whole new meaning.

• 16:23Speaker 05

  Oh, yes, Robert, I love that.

• 16:31Speaker 05

  One thing that both Karina and Malini told me is that this is a new field.

• 16:35Speaker 01

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

• 16:39Speaker 05

  Like, for instance, Karina told me sometimes there are actual trees growing up there.

• 16:44Speaker 01

  And I've seen like a five-foot spruce growing out of a nook of canopy soil.

• 16:48Speaker 05

  Wow.

• 16:48Speaker 01

  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.

• 16:54Speaker 03

  Wait a second, you mean there's a tree growing on the tree?

• 16:57Speaker 05

  That's right.

• 16:57Speaker 03

  On the branch?

• 16:58Speaker 05

  In the soil, on the branch.

• 17:00Speaker 03

  Oh.

• 17:02Speaker 05

  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.

• 17:11Speaker 03

  Yeah, it's fractal, like littler plants off the ground and then little 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 of the layers you will find. That's sort of cool.

• 17:35Speaker 05

  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.

• 17:47Speaker 02

  All the way up.

• 17:59Speaker 02

  This episode was reported and produced by Annie McEwen. Special thanks to Kyomi 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 forests. You can check that out on our website or on theirs. So, thank you to them. And special thanks, of course, to the many

• 18:44Speaker 02

  ringed tree trunk that is Robert Kralwich, 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.

• 19:04Speaker 01

  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. Sauron Wheeler is our executive editor. Sarah Sandback is our executive director. Our managing editor is Pat Walters. Dylan Keefe is our director of sound design. Our staff includes Jeremy Blum, W. Harry Fortuna, David Gabel, Maria Paz Gutierrez, Sindhu Naina Sambandan, Matt Keelty, Mona Margaucher, Annie McEwen, Alex Neeson, Sarah Kari, Natalia Ramirez, Rebecca Rand, Anissa Vitza, Arianne Whack, Molly Webster, and Jessica Young, with help from Gabby Santos. Our fact checkers are Diane Kelly, Emily Krieger,

• 19:51Speaker 01

  Natalie Middleton, Angela Mercado, and Sophie Semai.

• 19:57Speaker 01

  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.