The Real Science Behind the Wood Wide Web

Claire Brooks

Walk into a dense stand of Douglas fir. Or paper birch. Pick your conifer.

Oliver Hart

Happily.

Claire Brooks

It's quiet, right? Still. Nothing obviously happening. Peaceful.

Oliver Hart

That's the appeal. That's the whole reason people go.

Claire Brooks

And for the last twenty-five years, we have all been told that beneath your boots, that stillness is a lie. That under the soil there's a vast, bustling, humming — I want to be fair here —

Oliver Hart

Say it.

Claire Brooks

Socialist utopia.

Oliver Hart

Ah. The underground postal service. The wood wide web, as the headline writers cannot stop themselves from calling it.

Claire Brooks

Trees aren't just standing there competing for light. They're talking. Nursing their seedlings. Couriering carbon to sick neighbors. Blowing chemical warning whistles when the bark beetles show up.

Oliver Hart

It's a stunningly attractive story.

Claire Brooks

It's the most beloved story in popular biology. And today I'm going to walk you through what happened when three ecologists sat down and audited it line by line.

Oliver Hart

And I want to say, before we start —

Claire Brooks

Here we go.

Oliver Hart

I like this story. I have told this story on stage. I would like it to survive the next forty minutes.

Claire Brooks

Noted.

Oliver Hart

That's not a yes.

Claire Brooks

It isn't.....Welcome back to The Odd Branch — the show about the strange twigs on the tree of life. I'm Jules, and this week I'm driving, because I called this one.

Oliver Hart

He called it on air. Last week. With some relish.

Claire Brooks

I've been waiting months. And here's why this episode is different from every other one we've done.

Oliver Hart

Normally we take something that sounds impossible and show you it's real.

Claire Brooks

Last week: a dog's tumor that outlived the dog by thousands of years and is currently alive on five continents. True. Verified. Sequenced.

Oliver Hart

Genuinely true.

Claire Brooks

This week we're running it backwards. Today's story is one that sounds beautiful, that millions of people believe, that's in the documentaries and the bestsellers and the poster in your dentist's office —

Oliver Hart

And the evidence for it is much thinner than anyone wants it to be.

Claire Brooks

So the question we're actually chasing isn't "do trees talk." It's a sharper one. Where does the genuine subterranean fungal ecology end —

Oliver Hart

— and where does the human fairy tale take over?

Claire Brooks

That's the episode.

Oliver Hart

I'd like the record to show I'm entering this in good faith and bad spirits. Start with the origin, because there is a real paper at the bottom of this. This isn't invented from nothing.

Claire Brooks

No, and that matters. 1997. Suzanne Simard publishes in Nature. She uses carbon isotopes to trace carbon moving between paper birch and Douglas fir seedlings in British Columbia.

Oliver Hart

Isotope tracing — you're essentially tagging carbon atoms so you can tell whose they were.

Claire Brooks

Carbon-14, which is the radioactive one, and carbon-13, which is stable but heavier, so you can pick it out on a mass spectrometer. Two different tags, same basic idea.

Oliver Hart

And that paper is where "wood wide web" enters the language.

Claire Brooks

Coined there or popularized there, depending who you ask. And then the media picked it up.

Oliver Hart

Picked it up is generous.

Claire Brooks

The media sprinted with it. You go from a very specific, carefully bounded study about seedling carbon transfer —

Oliver Hart

Bounded. Note that word.

Claire Brooks

— to Peter Wohlleben's The Hidden Life of Trees, which sold millions of copies worldwide. And then James Cameron takes it to Avatar and gives us the Tree of Souls.

Oliver Hart

At which point mature trees are no longer big plants.

Claire Brooks

They're mother trees. Caring, conscious matriarchs, watching over their babies down in the shade.

Oliver Hart

And I want to sit on that for a second, because the interesting question to me isn't whether it's true. We'll get there. It's why that. Why did that specific story catch fire, that hard, in the late nineties and two thousands?

Claire Brooks

You have a theory. You always have a theory.

Oliver Hart

Because it's a moral mirror. We want cooperation to be the fundamental law of the universe. Not cold, brutal competition — that's the version we got handed in school and nobody enjoyed it.

Claire Brooks

We want the forest to be friendly.

Oliver Hart

We want the forest to be friendly. And here comes a peer-reviewed paper that appears to say: it is. Nature agrees with you. Your politics are load-bearing all the way down to the root tips.

Claire Brooks

Which is exactly the condition under which you should get suspicious.

Oliver Hart

Which is exactly the condition under which I did not get suspicious. Continue.

Claire Brooks

So let's strip the fairy tale off and go look at the actual physiology. Because there is something down there, and it's remarkable, and I don't want anyone switching off thinking I'm about to tell them fungi aren't real.

Oliver Hart

Thank you.

Claire Brooks

Roots meet fungi. Fungal species — Amanita, Boletus, that family of players — form a symbiotic relationship with tree roots called mycorrhiza. Literally "fungus root."

Oliver Hart

And the fungal threads, the hyphae, push out into the soil.

Claire Brooks

And they're fine. Much finer than a root. They get into microscopic pores in the soil that a tree root could never physically reach.

Oliver Hart

So the tree is effectively renting a much better sensory organ than it could ever grow itself.

Claire Brooks

That's a fair way to put it. The fungus harvests dissolved nitrogen and phosphorus and delivers those minerals to the tree. And in exchange, the tree hands over carbon sugars from photosynthesis.

Oliver Hart

How much?

Claire Brooks

Up to twenty percent of the tree's total carbon budget goes straight to the fungus.

Oliver Hart

A fifth. That's not a tip. That's a mortgage.

Claire Brooks

And notice what it is. It's a trade. I give you sugar, you give me fertilizer.

Oliver Hart

It's not altruism.

Claire Brooks

It is not altruism, it's a rigorous market. Now — here's where people get excited, and where the story starts to run ahead of the data. Sometimes a single fungal individual attaches its hyphae to the roots of two or more separate trees.

Oliver Hart

And that's the network everyone's talking about.

Claire Brooks

That's a Common Mycorrhizal Network. CMN. And I want you to think about what it would take to actually prove one exists out in a real forest.

Oliver Hart

Okay. You'd have to show that the same fungal individual — the same genetic identity, not just the same species —

Claire Brooks

Keep going.

Oliver Hart

— is continuously connected. Physically. Tree A through to tree B. Unbroken.

Claire Brooks

Right. So: how many studies, in the entire history of ecology, have done the high-resolution genetic mapping needed to trace those continuous physical bridges across a forest plot?

Oliver Hart

I dislike your tone, which means the number is small.

Claire Brooks

Two.

Oliver Hart

Two.

Claire Brooks

Two studies globally. In a handful of tree species. Mostly Douglas fir and ponderosa pine.

Oliver Hart

Two. Against how many documentaries?

Claire Brooks

Against a genre. And even where the physical connections do exist, there's a second hurdle, and this is the one that really got me. The fluid mechanics.

Oliver Hart

Meaning when you watch carbon move from one tree toward another —

Claire Brooks

How do you know it went through a fungal pipe?

Oliver Hart

Oh. Oh, that's annoying. Because it could just leak. Carbon exits one root into the soil water, drifts through the mud, gets taken up by soil bacteria, gets released, gets absorbed by a neighboring root.

Claire Brooks

Same start point, same end point, completely different mechanism. It's soil solution and soil microbes. Not a dedicated subterranean fiber optic cable.

Oliver Hart

So the superhighway might be a puddle.

Claire Brooks

The superhighway might be a puddle.

Oliver Hart

The internet cable turned out to be leaky runoff.

Claire Brooks

And nothing in the isotope data, on its own, tells you which one you're looking at. Which brings us to 2023, when the cozy version hit a wall.

Oliver Hart

Names.

Claire Brooks

Three mycorrhizal ecologists. Justine Karst at the University of Alberta. Melanie Jones at UBC Okanagan. Jason Hoeksema at the University of Mississippi. They decided to audit the literature.

Oliver Hart

Not to run a new experiment. To go back and check the paperwork.

Claire Brooks

Published in Nature Ecology and Evolution. They reviewed twenty-six field studies that claimed to test resource transfer through fungal networks. And what they found is a mess — but it's a specific, diagnosable kind of mess.

Oliver Hart

Which is?

Claire Brooks

Scientific telephone. Positive citation bias.

Oliver Hart

Explain it like I've never seen a bibliography.

Claire Brooks

They took peer-reviewed papers published in 2022 that cited those original field studies, and they checked whether the citations were accurate. Fewer than half were.

Oliver Hart

Fewer than half.

Claire Brooks

Under fifty percent of the statements being made about the original studies actually reflected what those studies found.

Oliver Hart

Give me a concrete one, because that's an abstract kind of horrifying.

Claire Brooks

Best example. There's a well-known 2009 study that used genetic tools to map the spatial distribution of mycorrhizal fungi. Where the fungi are.

Oliver Hart

A map.

Claire Brooks

A map. And modern papers routinely cite it as evidence that trees transfer nutrients to each other through fungal networks. The original study never investigated transfer at all.

Oliver Hart

They're citing a map as proof of traffic.

Claire Brooks

They're citing a map as proof of traffic. And you can watch it happen over decades — the original authors' caveats and alternative explanations get quietly shaved off with each retelling, until all that's left is the headline.

Oliver Hart

Okay. Now do the big one. The mother tree claim. Mature trees nursing seedlings through the network so they survive under heavy canopy shade.

Claire Brooks

Karst's team reviewed twenty-eight seedling experiments.

Oliver Hart

And?

Claire Brooks

Completely mixed. Results depend on soil type, tree species, timing. There's no clean signal. But here's the number I'd tattoo on the episode. In field conditions — where seedling roots are allowed to interact with mature roots naturally, the way they actually do —

Oliver Hart

Not in a pot.

Claire Brooks

Not in a pot. In eighty-two percent of cases, any potential positive network effect was overwhelmed by direct root competition for water and light.

Oliver Hart

Eighty-two percent.

Claire Brooks

Four out of five real-world trials.

Oliver Hart

So in four out of five, the mature tree isn't feeding the seedling. It's outcompeting it.

Claire Brooks

It's taking the water first.

Oliver Hart

That's the opposite of the story. That's not a weaker version of the story, that's the reverse.

Claire Brooks

And here's the detail that made me actually respect this paper rather than just enjoy it. Melanie Jones — one of the three authors — coauthored one of the original nineties papers.

Oliver Hart

She audited her own work.

Claire Brooks

She's on record saying that back then they fell into confirmation bias. They were excited. It was a new, gorgeous idea and they wanted it to hold.

Oliver Hart

That's a hard thing to say out loud with your name on both documents.

Claire Brooks

And Karst's line about it, roughly, is that a distortion is a distortion regardless of whether you happen to like the direction it points. It still has to get called out.

Oliver Hart

Which is the uncomfortable bit, isn't it. Everyone's fine policing bad science when it's inconvenient to them.

Claire Brooks

This one was convenient to almost everybody.

Oliver Hart

Right. It's technically your segment this week "The Internet Lied to You" —

Claire Brooks

The whole episode is my segment this week.

Oliver Hart

— which is why I'm taking it. Because there's a second lie in this story, and it's the one we are at risk of starting in the next ten minutes.

Claire Brooks

Go on.

Oliver Hart

Somebody is going to clip forty seconds of this episode and post it as "scientists admit the wood wide web is fake." So let me be precise about what is not being claimed.

Claire Brooks

Please.

Oliver Hart

Mycorrhizal fungi are real. This is not a debunk of mycorrhizae. The symbiosis is ancient, it's ubiquitous, it is genuinely one of the most important relationships on land, and most plants on Earth depend on it. That's not in dispute by anyone.

Claire Brooks

Correct.

Oliver Hart

Common mycorrhizal networks are also real. A single fungus does sometimes connect two trees. That's been shown.

Claire Brooks

Twice, well. But shown.

Oliver Hart

What's unsupported is the leap from "connection exists" to "the forest is a cooperative society deliberately routing aid to its members." That specific leap. Three separate claims got welded together and only the first one is solid.

Claire Brooks

The connection, the transfer, and the intent.

Oliver Hart

The connection is real. The transfer is contested and often better explained by soil. The intent is a story we brought with us.

Claire Brooks

And "trees scream when cut" and "trees are conscious" —

Oliver Hart

Not in evidence, no. Plants do release volatile compounds under stress, and neighbors do respond to them, which is a real and well-studied thing happening in the air, not the soil, and it doesn't require anybody to be conscious.

Claire Brooks

So the honest summary is: less certainty than you were sold, but nothing here says the forest is boring.

Oliver Hart

Nothing here says the forest is boring. Hold that thought, because it's my act. So if trees aren't selflessly sharing supper — what are the fungi doing? What's their incentive? Because nobody in this story is a volunteer.

Claire Brooks

The fungus is acting entirely in its own interest. Fungi are selfish organisms.

Oliver Hart

How selfish?

Claire Brooks

When conditions get tough, fungi don't distribute resources to prop up the trees. They hoard carbon in their own tissue and restrict nutrient transfer.

Oliver Hart

They hold out for better terms.

Claire Brooks

They hold out for better terms.

Oliver Hart

They're holding the tree hostage.

Claire Brooks

Functionally, yes. And it gets more ruthless. Do you want the mycoheterotrophs?

Oliver Hart

I always want the mycoheterotrophs.

Claire Brooks

Ghost pipe. Monotropa uniflora. You've seen these.

Oliver Hart

Those spooky white waxy things coming up out of the leaf litter, look like little clay pipes, look like something that shouldn't be photographed.

Claire Brooks

Completely white. Zero chlorophyll. Which means no photosynthesis, at all, ever.

Oliver Hart

So it can't make a single sugar of its own.

Claire Brooks

So how does it live? It taps into the mycorrhizal network connecting the surrounding trees, and it drains carbon sugars straight out of the fungal hyphae. And it returns nothing. Not one atom of carbon.

Oliver Hart

It's stealing the neighbors' wifi.

Claire Brooks

It's an underground pirate. It hacks the system for purely parasitic gain.

Oliver Hart

And notice — that only works because the network is real.

Claire Brooks

...Say that again.

Oliver Hart

The ghost pipe is the best evidence in this whole episode that something is genuinely connected down there. Because it's a plant that survives with no leaves and no sugar of its own by plugging into it. It's not proof of a cooperative society. It's proof of a system worth robbing.

Claire Brooks

That's — yeah. That's a better argument than I wanted you to have.

Oliver Hart

I have to admit something on air, though. A part of me is genuinely disappointed. I liked the fairy tale. I liked picturing the forest as a big friendly family holding hands under the soil.

Claire Brooks

I understand the impulse. I do. But to me the messy, competitive, exploitative version is infinitely more interesting than the warm and fuzzy one.

Oliver Hart

So why do we keep doing it? Why are we this desperate to project our own social ideals — socialism, altruism, family, whatever's in fashion — onto fungal threads?

Claire Brooks

Because it makes us feel connected. And I want to be clear that I don't think that impulse is stupid. It's the same impulse that gets people to care about forests at all.

Oliver Hart

But there's a cost.

Claire Brooks

There's a real scientific cost. When hype and confirmation bias set the narrative, it distorts research priorities. It shapes forestry policy and conservation funding around romantic assumptions instead of evidence.

Oliver Hart

And that's not abstract, is it. Give me the concrete failure.

Claire Brooks

If you manage a timber forest on the assumption that mother trees will nurse your seedlings through an underground network, you might leave those seedlings under mature canopy —

Oliver Hart

— where eighty-two percent of the time, the mature roots are going to take the water.

Claire Brooks

And you've just killed your regeneration because you believed something lovely.

Oliver Hart

So here's where we land, and it's the same place as every episode, at the boundary. Last week the boundary was between one organism and another, and it turned out to be porous — a dog became a disease became arguably its own thing.

Claire Brooks

And this week?

Oliver Hart

This week the boundary is between the ecology and the story we tell about it. And that one's porous too. It's just that we're the ones doing the leaking.

Claire Brooks

What we gain by dropping the myth is the actual thing. The raw, chaotic complexity of real ecology. Forests don't need to be conscious societies to be magnificent.

Oliver Hart

They're dynamic battlegrounds and marketplaces. Millions of individual, self-interested interactions, running for millions of years, with nobody in charge.

Claire Brooks

So maybe instead of looking at nature to validate how human society ought to behave —

Oliver Hart

— we let nature be weird, complicated, and completely indifferent to us.

Claire Brooks

Less hype, more hyphae.

Oliver Hart

I hate that you saved that. That's Episode 4 of The Odd Branch.

Claire Brooks

If you came in loving the wood wide web and you're leaving slightly bereaved, that's the correct reaction and I'd argue it's a good day.

Oliver Hart

Subscribe wherever you get your podcasts, and tell a friend. Ideally before they tell you about mother trees at a party.

Claire Brooks

Next time — the platypus.

Oliver Hart

Electroreception. Venomous spurs. Glows under UV light. Sweats milk. Lays eggs.

Claire Brooks

Which is a list that sounds like someone lost a bet.

Oliver Hart

When the first specimen reached London, naturalists assumed it was a hoax. A duck bill stitched onto a mole. People went looking for the seam.

Claire Brooks

And here's why it's the right follow-up to this week. Today we took a beautiful story away from you because the evidence wasn't there.

Oliver Hart

Reluctantly. Under protest.

Claire Brooks

Next week is the opposite problem. An animal that reads like a fabrication, where every absurd claim checks out — and which keeps getting weirder the more of its genome we sequence.

Oliver Hart

No projection required. Nobody needed to make the platypus more interesting than it is. Nobody could.

Claire Brooks

Sources are in the show notes, including the 2023 audit and the original 1997 paper, so you can read both and make your own call.....I'm Nadia.

Oliver Hart

I'm Dr. Ketchup. Stay curious.

Claire Brooks

Stay odd.