Forests on Forests

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0:59Rewind. 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. She began thinking about the forest that exists underneath the forest. That's Robert Krolwich, 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.

1:46Like there's a literal underground economy in every forest you've ever been to. Turns out one tree was connected to 47 other trees all around it. It was like a huge network. 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. So that was back in 2016. A couple of 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.

2:30So 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 McKeown and emeritus Radiolab host Robert Kralwich. Okay, we're at long last ready to begin. 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? Well, I guess I'd be inclined, if there was more news, I'd do more down, I think.

3:17Well, how about, okay, how about instead of looking down, we peer into a type of down that is in the up? Oh, okay. And to take us there, forest royalty. I've read that you are known as the queen of the canopy. Is that true? Yes, that's true. Where did that come from? 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 of forest canopy. 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.

3:58You 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. She'd spend whole afternoons up there just sitting and wondering. And look at the leaves and I go like, why does this branch have much yellower leaves than that branch, which has orange leaves? Yes, that's a good question. And it's like, well, what is going on?

4:30What 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. Nalini grew up and followed that imagination to study ecology in grad school. 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 of like Tarzan and Jane stuff.

5:03You know, with so many questions to ask and answer on the forest floor, Or why do you have to go into the canopy? 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. 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. And so, with some modified mountain climbing equipment, she began to climb these giant old-growth trees. in the Olympic rainforests of western Washington, which is what's called a temperate rainforest.

5:40Are these the places where in the morning the fog from the Pacific Ocean comes rolling in? Yeah. And the tree just gets an every morning bath of just pure moisture. Yeah, and the tree just goes... Yeah. So Nalini climbs up into the canopy of this giant big leaf maple tree. 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. The branch she's sitting on, as well as all the branches surrounding her, are covered in this super thick layer of this amazing growth of mosses and lichens and ferns.

6:18Kind of like the tree is wearing this very unruly green shade carpet. You get the sense of being in a place that looks very simple from the forest floor, but is actually this kaleidoscope of life. Her job up there was to take samples of the moss that was growing on these branches. I had to cut off chunks of it. So using some clippers, she begins to cut down into that moss on the branch she's sitting on. And as I peeled back those mats of mosses beneath, instead of just bare branch, I saw that there was all this soil up there. This branch has a foot of soil piled up on it. Oh, wow. Soil that formed over many, many years of mosses and leaves dying and decomposing right there on the branch.

7:05It'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. You can imagine getting your gardening gloves out and planting rows of tulips 100 feet in the air. There were like invertebrates in it. There were earthworms in it. Tree worms. Yes. That is so weird. I know. I know. Even the stars of the old episode, the fungi, were there. Really? So the mushrooms have climbed up the tree as well to sort of do their thing? Yes, they're sharing resources, they're helping the tiny plants up there communicate with one another.

7:38The same as on the forest floor. 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 Allais, who pioneered the use of the dirigible to access the canopy. Oh, wow. There's incredible pictures of these.

8:13So it's a balloon trip? It's a balloon 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.

8:59I'm waiting if you say a small deer or something like that or something very weird. 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. An aquatic creature? It's aquatic. Yeah, it's like the shrimp like. They found a fish? Pretty much 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 baleen whales. This thing is like swimming around in these mossy mats and no one knows how it got there.

9:48anyway 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 um a lot of that is 50 percent 50 five zero yeah wow that's a weird note that You're saying 50 % of it is up in the air somewhere? Yeah, up in the air, up in trees. Whoa. 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 on the tree branches?

10:25And when ecologist Karina Mifune learned about these canopy soils. I fell in love. I was like, okay, there's like a forest in a forest on a forest. I need to research this. 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. Huh. Well, what would that be? 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.

11:10Specifically, 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. And those are rare. Plants love that. Right. And in contrast to the last episode where we talked about trees cooperating with each other. All these trees, all these trees that were of totally different species were sharing their food underground. Karina told me that in that same sharing forest, when resources are scarce... There's a ton of competition on the forest for trees have roots grafted together. There's mycorrhizal networks, you know, that are spanning across.

11:46There's this big battle to, you know, uptake nutrients. But Karina had also taken samples of the canopy soils. And she saw that during these times of scarcity below... These canopy soils had so much more nitrogen and phosphorus available for plant uptake compared to their forest floor counterparts. Meaning that this soil for a plant was creme de la creme. It's just amazing. Downstairs, there's shortage. Upstairs, there's abundance. when its 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, I don't know, what do these canopy soils mean?

12:36Because they're not just hanging out there. They're not just there for no reason, right? She's right, they're not. These sky gardens, they get even better. Better at what? Hmm? Better at what? Well, let's just say they're not alone up there. What's about to happen? Well, I'm going to tell you. All righty. Right after this short break.

13:28We'll be right back. It's called Planet Visionaries, hosted by Alex Honnold, who you might recognize as the climber from Free Solo and Skyscraper Live. Now Alex is turning his focus to the biggest challenge of all, protecting our planet. Every episode brings you stories that aim to prove climate optimism isn't naive. It's a strategy. You'll hear from experts and storytellers who are reshaping the future in practical and inspiring ways. Upcoming guests include Gregoire Cortine and Jocelyn Bloch, the neuroscientist and neurosurgeon duo advancing spinal cord injury treatment with groundbreaking neural implants.

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15:24Lulu, 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 she made. Okay. So I remember sitting on this tree. She's back up in a tree in the Washington rainforest, digging around in this canopy soil. And I began seeing these root systems that were running up and down the branches of these trees. They didn't look like they belonged to moss or ferns or any other plant you could see up there. And there were fine roots all the way up to, some of them were the diameter of my wrist.

16:00I mean, these were gigantic roots. What? And I thought, well, that's weird. What are these roots doing here? Huh. So I began just tracing the roots that I was finding. Like you took hold of one root in your hand and sort of like went backwards like a string? Exactly, like following a string. Exactly. She gently excavates this root. scooting along the branch as she uncovers it. 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.

16:35It was like, I don't know, it was like being a detective. Well, what did you think it was going to lead to? 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. So then she follows the root all the way back to its beginning. and oh my gosh, its origin was a dead end in the tree itself. What? The big tree, the one Nalini is sitting in, is growing roots from its branch and snaking underneath these mats of soil, of canopy soil. Let me think about this. Somehow it realizes that it could find soil high up somewhere like me and so it just takes its roots and its roots travel up and go whoop to the left to say, let's root not only where we normally root down there, but let's root up here.

17:21Yes. Whoa. So things that you thought were below can move above, way above, high above you. Yes. It was a real revelation. And Karina thinks that it's during a drought or during spring growing season when resources on the forest floor are scarce that these big trees... 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.

17:57I 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. Because we're looking for those special minerals like the phosphorus and stuff, and that's where we can find it. Right. And it's finding it in its hat. You're finding it in its hat. That's a nice way of putting it. Yes. Yeah. That's a lovely way of putting it. The expression, I'm going to eat my hat, has now got a whole new meaning.

18:37Oh, yes, Robert. I love that.

18:45One thing that both Karina and Nalini told me is that this is a new field. There is just so many things to be found high above the forest floor. Like, for instance, Karina told me sometimes there are actual trees growing up there. And I've seen like a five-foot spruce growing out of a nook of canopy soil. Wow. 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. Wait a second. I mean, there's a tree growing on the tree? That's right. On the branch. In the soil on the branch. Oh. And who knows? Maybe as more people study the canopy, we'll find little trees on those trees.

19:23And maybe there will be little trees on those trees on those trees. 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 little layers and layers and layers of life. And the more you go up, the more the layers you will find. That's sort of cool.

19:49Thank you, Annie McKeown, 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.

20:12This episode was reported and produced by Annie McEwen. 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 uh the video features karina and other people who have dedicated their lives to saving what's left of the old growth forest uh you can check that out on our website uh or on theirs so thank you to them and special thanks of course to the many ringed tree trunk that is robert crawl which uh coming back on the show to talk trees with us thank you for doing that Robert, we love you.

21:08That 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.

21:18Hi, 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. Sarah Sandback 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 Nainasambandan, Matt Keelty, Mona Modgauker, Annie McEwen, Alex Neeson, Sarah Kari, Natalia Ramirez, Rebecca Rand, Anissa Vitsa, Arian Wack, Molly Webster, and Jessica Young, with help from Gabby Santis. Our fact checkers are Diane Kelly, Emily Krieger, Natalie Middleton, Anjali Mercado, and Sophie Semayi 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.

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