How trees talk to each other | Suzanne Simard

Summary

This script tells the story of a forester's journey to understand the hidden world beneath forests, revealing a complex network of communication between trees through mycelium. The speaker's experiments with isotopes demonstrate trees' interdependence and challenge conventional forestry practices. The narrative emphasizes the need for sustainable methods that respect forests' inherent resilience and complexity, advocating for diverse, locally informed forest management.

Takeaways

• 🌳 Forests are more than just trees; they are complex systems with an underground network that connects them, allowing communication and cooperation.
• 🌍 The speaker's personal journey began in British Columbia, learning about forests from their grandfather, a horse logger, and developed a deep curiosity about the forest ecosystem.
• 🔬 Scientific research has shown that trees can share resources like carbon through their root systems, challenging the view of trees as solely competitors.
• 🐻 Conducting forest research involves overcoming challenges such as wildlife encounters, as humorously illustrated by the grizzly bear anecdote.
• 📈 The speaker's experiments with isotopes demonstrated a two-way communication of carbon between paper birch and Douglas fir, indicating a cooperative relationship.
• 🍄 Mycorrhizal networks, formed by symbiotic fungi and tree roots, play a crucial role in the forest's communication system, facilitating the exchange of nutrients and signals.
• 🌴 'Mother trees' act as hubs in mycorrhizal networks, supporting the growth and survival of younger trees, including their own kin, through the transfer of resources and information.
• 🌲 Forests' resilience is linked to their complexity, including multiple hub trees and overlapping networks, which allow for adaptation and feedback mechanisms.
• 🚫 Current forestry practices like clear-cutting and monoculture plantations harm forest complexity and resilience, making them more vulnerable to disturbances.
• 🌿 To promote forest health and resilience in the face of climate change, a shift towards sustainable forestry methods is needed, including diverse species regeneration and retention of old-growth forests.
• 🌳 The speaker encourages a change in perspective, viewing forests not as mere collections of competing trees but as complex, interconnected systems capable of self-healing and cooperation.

Q & A

What is the 'other world' the speaker refers to in the context of forests?

The 'other world' refers to the underground network of biological pathways that connect trees, allowing them to communicate and behave as a single organism.

What is the speaker's profession and background?

The speaker is a forester who grew up in the forests of British Columbia and followed in the footsteps of their grandfather, a horse logger.

What was the speaker's 'aha' moment that sparked their interest in the underground world of forests?

The speaker's 'aha' moment occurred when their dog fell into an outhouse pit, and while rescuing the dog, they became fascinated by the roots and soil layers beneath the forest floor.

What was the controversial hypothesis the speaker had about forests that made it difficult to get research funding?

The speaker hypothesized that trees in real forests might share information below ground through a network, similar to the laboratory findings that one pine seedling root could transmit carbon to another.

What experiment did the speaker conduct 25 years ago to test their hypothesis about trees communicating underground?

The speaker grew 80 replicates of three species: paper birch, Douglas fir, and western red cedar, and used radioactive carbon-14 and stable isotope carbon-13 to trace the transfer of carbon between trees.

What did the speaker discover about the relationship between paper birch and Douglas fir in their experiment?

The speaker discovered that paper birch and Douglas fir were in a lively two-way conversation, with birch sending more carbon to fir, especially when the fir was shaded, and the relationship was found to be interdependent.

What is the role of mycorrhiza in the communication between trees?

Mycorrhiza, a mutualistic symbiosis involving fungi and tree roots, forms a dense mycelium network that connects different trees, allowing for the exchange of carbon, nutrients, water, and defense signals.

What are 'mother trees' and how do they contribute to the forest ecosystem?

Mother trees are hub trees that nurture their young, the understory seedlings, by sending them excess carbon and nutrients through the mycorrhizal network, increasing seedling survival and resilience.

How do trees recognize their own kin and what benefits do they provide to them?

Trees recognize their own kin through mycorrhizal networks and provide benefits such as larger mycorrhizal networks, more carbon, and reduced root competition, favoring their kin's growth and survival.

What are the speaker's four simple solutions to help forests deal with climate change?

The four solutions are: 1) Get out in the forest and reestablish local involvement; 2) Save old-growth forests as repositories of genes and networks; 3) Practice selective logging that saves mother trees, networks, and genetic diversity; and 4) Regenerate forests with a diversity of species, genotypes, and structures.

What is the significance of the speaker's story about their dog Jigs falling into the outhouse?

The story of Jigs falling into the outhouse was a pivotal moment that led the speaker to discover and appreciate the underground world of forests, which ultimately changed their view of forests and inspired their research.

Outlines

00:00

🌳 Discovering the Forest's Hidden World

The speaker begins by inviting the audience to envision a forest and then challenges the common perception of forests being merely collections of trees. They introduce the concept of an underground network that connects trees, suggesting a form of intelligence within the forest. The speaker shares personal anecdotes from growing up in British Columbia, learning about forests from their grandfather, and a pivotal moment when their dog fell into an outhouse pit, sparking curiosity about the forest floor's biological components. This leads to the speaker's pursuit of forestry studies and a conflict of interest with commercial forestry practices, prompting further research into the below-ground interactions between trees.

05:02

🔬 Unveiling the Subterranean Communication in Forests

The speaker recounts their research journey, starting with a laboratory discovery of carbon transmission between pine seedling roots, which inspired them to investigate the same phenomenon in real forests. Despite facing skepticism and funding challenges, they conducted an experiment with 80 replicates of three tree species, using radioactive and stable isotope carbon dioxide gases to trace the flow of carbon below ground. The experiment involved a makeshift setup with plastic bags, duct tape, and borrowed scientific instruments, including a Geiger counter. The results showed a two-way communication between paper birch and Douglas fir, with the birch providing more carbon to the fir, especially in shaded conditions. This finding indicated a cooperative relationship between tree species, contrary to the prevailing view of competition.

10:03

🌐 The Mycorrhizal Network: Forests' Internet

The speaker delves into the science behind the communication between trees, revealing that it occurs not only in carbon but also in nitrogen, phosphorus, water, defense signals, and more, facilitated by mycorrhizal networks. These networks, formed by fungal threads called mycelium, connect individual trees and act like an underground internet. The speaker describes the structure of these networks, with 'hub trees' or 'mother trees' playing a central role in nurturing younger trees within the network. They also discuss experiments that show mother trees favor their kin by providing larger networks and more resources. Furthermore, injured or dying mother trees pass on defense signals and carbon to seedlings, enhancing their resilience to future stressors.

15:05

🌳🔄 Forests as Complex Systems: Resilience and Vulnerability

The speaker emphasizes the complexity of forests as systems with overlapping networks and hubs that allow for communication and adaptation, contributing to the forest's resilience. However, they also highlight the vulnerability of forests to disturbances such as logging and climate change, which can disrupt the network and lead to system collapse. The speaker reflects on the impact of their research on forestry practices, noting the ongoing issues of clear-cutting and monoculture plantations in Canada. They propose four solutions: local involvement in forest management, preservation of old-growth forests, retention of mother trees and networks during logging, and regeneration of forests with diverse species and genotypes. The speaker concludes by reinforcing the idea that forests are not just collections of competing trees but a community of supercooperators.

Keywords

💡Forest Ecosystem

A forest ecosystem refers to a complex community of living organisms, including trees, plants, animals, and microorganisms, interacting with each other and their physical environment. In the video, the forest is portrayed as more than just a collection of trees, highlighting the interconnectedness of its components and the communication pathways that exist beneath the surface.

💡Mycelium

Mycelium is the vegetative part of a fungus, consisting of a network of fine white filaments (hyphae). The script describes the mycelium as the 'white' layer beneath the forest floor, which plays a crucial role in connecting trees and facilitating communication and nutrient exchange within the forest ecosystem.

💡Carbon Isotopes

Carbon isotopes, such as carbon-14 and carbon-13 mentioned in the script, are variants of the carbon element with different numbers of neutrons. The speaker used these isotopes in an experiment to trace the flow of carbon between tree species, demonstrating a form of communication and support within the forest community.

💡Mycorrhiza

Mycorrhiza is a symbiotic association between a fungus and the roots of a plant. The script explains that mycorrhizae, literally meaning 'fungus root,' are involved in the nutrient exchange within the forest, with the fungal threads forming a vast network that connects different trees.

💡Hub Trees

Hub trees, as described in the video, are central and influential trees within the mycorrhizal network that act as 'mother trees,' nurturing and providing resources to younger trees in the understory. They are vital for maintaining the resilience and health of the forest ecosystem.

💡Sustainable Forestry

Sustainable forestry is the practice of managing forests in a way that meets the needs of the present without compromising the ability of future generations to meet their own needs. The speaker advocates for a shift from destructive practices like clear-cutting to more holistic and sustainable methods, inspired by the understanding of the forest as a complex, interconnected system.

💡Resilience

Resilience in the context of the video refers to the forest's ability to recover from disturbances and adapt to changing conditions. The interconnected networks of trees, facilitated by mycorrhizae and hub trees, contribute to the overall resilience of the forest ecosystem.

💡Clear-Cutting

Clear-cutting is a forestry practice where all trees in a given area are cut down, leaving the land bare. The script criticizes this method as it disrupts the complex networks within the forest, leading to a loss of biodiversity and ecosystem services.

💡Biodiversity

Biodiversity is the variety of life in all its forms and interactions, including the genetic diversity within species, the diversity of species, and the variety of ecosystems. The video emphasizes the importance of maintaining biodiversity in forests to ensure their health, resilience, and ability to adapt to environmental changes.

💡Climate Change

Climate change refers to long-term shifts in temperatures and weather patterns, primarily caused by human activities. The script discusses how climate change is exacerbating forest disturbances and stresses the need for forests to be managed in a way that enhances their ability to cope with these changes.

💡Conservation

Conservation in the video is the act of preserving, protecting, and managing the natural environment and its resources. The speaker calls for a conservationist approach to forestry, emphasizing the need to protect old-growth forests, retain genetic diversity, and promote natural regeneration.

Highlights

The forest is more than just trees; it's a complex underground network that connects trees, allowing them to communicate and behave as a single organism.

The speaker's childhood experiences and grandfather's teachings shaped their curiosity and understanding of forests.

An 'aha' moment involving a dog's mishap led to the discovery of the importance of roots and soil in forest foundations.

The speaker's work in forestry was initially aligned with commercial interests, but they became conflicted due to the extent of clear-cutting.

Laboratory experiments inspired the hypothesis that trees might share information below ground in real forests.

The speaker faced skepticism and difficulty securing funding for their unconventional research ideas.

A unique experiment involving radioactive isotopes was conducted to trace carbon exchange between tree species.

The discovery of a two-way communication between paper birch and Douglas fir, indicating a cooperative relationship rather than competition.

The use of unconventional materials like plastic bags and duct tape in the experimental setup due to budget constraints.

The role of mycorrhizal networks in facilitating communication and nutrient exchange among trees.

The concept of 'mother trees' that act as hubs, nurturing their young and sharing resources within the network.

Trees can recognize their kin and prioritize resource sharing with related seedlings.

Injured or dying mother trees pass on messages and resources to the next generation, increasing their resilience.

The speaker's hope that their research would lead to a shift in forestry practices towards more sustainable methods.

Despite the research, current forestry practices in Canada have led to high rates of forest disturbance and environmental impacts.

The speaker proposes four solutions to reinforce forests and help them deal with climate change, emphasizing the importance of diversity and local involvement.

The final message that forests are supercooperators, challenging the traditional view of trees as merely competitors.

Transcripts

Imagine you're walking through a forest.

I'm guessing you're thinking of a collection of trees,

what we foresters call a stand,

with their rugged stems and their beautiful crowns.

Yes, trees are the foundation of forests,

but a forest is much more than what you see,

and today I want to change the way you think about forests.

You see, underground there is this other world,

a world of infinite biological pathways

that connect trees and allow them to communicate

and allow the forest to behave as though it's a single organism.

It might remind you of a sort of intelligence.

How do I know this?

Here's my story.

I grew up in the forests of British Columbia.

I used to lay on the forest floor and stare up at the tree crowns.

They were giants.

My grandfather was a giant, too.

He was a horse logger,

and he used to selectively cut cedar poles from the inland rainforest.

Grandpa taught me about the quiet and cohesive ways of the woods,

and how my family was knit into it.

So I followed in grandpa's footsteps.

He and I had this curiosity about forests,

and my first big "aha" moment

was at the outhouse by our lake.

Our poor dog Jigs had slipped and fallen into the pit.

So grandpa ran up with his shovel to rescue the poor dog.

He was down there, swimming in the muck.

But as grandpa dug through that forest floor,

I became fascinated with the roots,

and under that, what I learned later was the white mycelium

and under that the red and yellow mineral horizons.

Eventually, grandpa and I rescued the poor dog,

but it was at that moment that I realized

that that palette of roots and soil

was really the foundation of the forest.

And I wanted to know more.

So I studied forestry.

But soon I found myself working alongside the powerful people

in charge of the commercial harvest.

The extent of the clear-cutting

was alarming,

and I soon found myself conflicted by my part in it.

Not only that, the spraying and hacking of the aspens and birches

to make way for the more commercially valuable planted pines and firs

was astounding.

It seemed that nothing could stop this relentless industrial machine.

So I went back to school,

and I studied my other world.

You see, scientists had just discovered in the laboratory in vitro

that one pine seedling root

could transmit carbon to another pine seedling root.

But this was in the laboratory,

and I wondered, could this happen in real forests?

I thought yes.

Trees in real forests might also share information below ground.

But this was really controversial,

and some people thought I was crazy,

and I had a really hard time getting research funding.

But I persevered,

and I eventually conducted some experiments deep in the forest,

25 years ago.

I grew 80 replicates of three species:

paper birch, Douglas fir, and western red cedar.

I figured the birch and the fir would be connected in a belowground web,

but not the cedar.

It was in its own other world.

And I gathered my apparatus,

and I had no money, so I had to do it on the cheap.

So I went to Canadian Tire --

(Laughter)

and I bought some plastic bags and duct tape and shade cloth,

a timer, a paper suit, a respirator.

And then I borrowed some high-tech stuff from my university:

a Geiger counter, a scintillation counter, a mass spectrometer, microscopes.

And then I got some really dangerous stuff:

syringes full of radioactive carbon-14 carbon dioxide gas

and some high pressure bottles

of the stable isotope carbon-13 carbon dioxide gas.

But I was legally permitted.

(Laughter)

Oh, and I forgot some stuff,

important stuff: the bug spray,

the bear spray, the filters for my respirator.

Oh well.

The first day of the experiment, we got out to our plot

and a grizzly bear and her cub chased us off.

And I had no bear spray.

But you know, this is how forest research in Canada goes.

(Laughter)

So I came back the next day,

and mama grizzly and her cub were gone.

So this time, we really got started,

and I pulled on my white paper suit,

I put on my respirator,

and then

I put the plastic bags over my trees.

I got my giant syringes,

and I injected the bags

with my tracer isotope carbon dioxide gases,

first the birch.

I injected carbon-14, the radioactive gas,

into the bag of birch.

And then for fir,

I injected the stable isotope carbon-13 carbon dioxide gas.

I used two isotopes,

because I was wondering

whether there was two-way communication going on between these species.

I got to the final bag,

the 80th replicate,

and all of a sudden mama grizzly showed up again.

And she started to chase me,

and I had my syringes above my head,

and I was swatting the mosquitos, and I jumped into the truck,

and I thought,

"This is why people do lab studies."

(Laughter)

I waited an hour.

I figured it would take this long

for the trees to suck up the CO2 through photosynthesis,

turn it into sugars, send it down into their roots,

and maybe, I hypothesized,

shuttle that carbon belowground to their neighbors.

After the hour was up,

I rolled down my window,

and I checked for mama grizzly.

Oh good, she's over there eating her huckleberries.

So I got out of the truck and I got to work.

I went to my first bag with the birch. I pulled the bag off.

I ran my Geiger counter over its leaves.

Kkhh!

Perfect.

The birch had taken up the radioactive gas.

Then the moment of truth.

I went over to the fir tree.

I pulled off its bag.

I ran the Geiger counter up its needles,

and I heard the most beautiful sound.

Kkhh!

It was the sound of birch talking to fir,

and birch was saying, "Hey, can I help you?"

And fir was saying, "Yeah, can you send me some of your carbon?

Because somebody threw a shade cloth over me."

I went up to cedar, and I ran the Geiger counter over its leaves,

and as I suspected,

silence.

Cedar was in its own world.

It was not connected into the web interlinking birch and fir.

I was so excited,

I ran from plot to plot and I checked all 80 replicates.

The evidence was clear.

The C-13 and C-14 was showing me

that paper birch and Douglas fir were in a lively two-way conversation.

It turns out at that time of the year,

in the summer,

that birch was sending more carbon to fir than fir was sending back to birch,

especially when the fir was shaded.

And then in later experiments, we found the opposite,

that fir was sending more carbon to birch than birch was sending to fir,

and this was because the fir was still growing while the birch was leafless.

So it turns out the two species were interdependent,

like yin and yang.

And at that moment, everything came into focus for me.

I knew I had found something big,

something that would change the way we look at how trees interact in forests,

from not just competitors

but to cooperators.

And I had found solid evidence

of this massive belowground communications network,

the other world.

Now, I truly hoped and believed

that my discovery would change how we practice forestry,

from clear-cutting and herbiciding

to more holistic and sustainable methods,

methods that were less expensive and more practical.

What was I thinking?

I'll come back to that.

So how do we do science in complex systems like forests?

Well, as forest scientists, we have to do our research in the forests,

and that's really tough, as I've shown you.

And we have to be really good at running from bears.

But mostly, we have to persevere

in spite of all the stuff stacked against us.

And we have to follow our intuition and our experiences

and ask really good questions.

And then we've got to gather our data and then go verify.

For me, I've conducted and published hundreds of experiments in the forest.

Some of my oldest experimental plantations are now over 30 years old.

You can check them out.

That's how forest science works.

So now I want to talk about the science.

How were paper birch and Douglas fir communicating?

Well, it turns out they were conversing not only in the language of carbon

but also nitrogen and phosphorus

and water and defense signals and allelochemicals and hormones --

information.

And you know, I have to tell you, before me, scientists had thought

that this belowground mutualistic symbiosis called a mycorrhiza

was involved.

Mycorrhiza literally means "fungus root."

You see their reproductive organs when you walk through the forest.

They're the mushrooms.

The mushrooms, though, are just the tip of the iceberg,

because coming out of those stems are fungal threads that form a mycelium,

and that mycelium infects and colonizes the roots

of all the trees and plants.

And where the fungal cells interact with the root cells,

there's a trade of carbon for nutrients,

and that fungus gets those nutrients by growing through the soil

and coating every soil particle.

The web is so dense that there can be hundreds of kilometers of mycelium

under a single footstep.

And not only that, that mycelium connects different individuals in the forest,

individuals not only of the same species but between species, like birch and fir,

and it works kind of like the Internet.

You see, like all networks,

mycorrhizal networks have nodes and links.

We made this map by examining the short sequences of DNA

of every tree and every fungal individual in a patch of Douglas fir forest.

In this picture, the circles represent the Douglas fir, or the nodes,

and the lines represent the interlinking fungal highways, or the links.

The biggest, darkest nodes are the busiest nodes.

We call those hub trees,

or more fondly, mother trees,

because it turns out that those hub trees nurture their young,

the ones growing in the understory.

And if you can see those yellow dots,

those are the young seedlings that have established within the network

of the old mother trees.

In a single forest, a mother tree can be connected to hundreds of other trees.

And using our isotope tracers,

we have found that mother trees

will send their excess carbon through the mycorrhizal network

to the understory seedlings,

and we've associated this with increased seedling survival

by four times.

Now, we know we all favor our own children,

and I wondered, could Douglas fir recognize its own kin,

like mama grizzly and her cub?

So we set about an experiment,

and we grew mother trees with kin and stranger's seedlings.

And it turns out they do recognize their kin.

Mother trees colonize their kin with bigger mycorrhizal networks.

They send them more carbon below ground.

They even reduce their own root competition

to make elbow room for their kids.

When mother trees are injured or dying,

they also send messages of wisdom on to the next generation of seedlings.

So we've used isotope tracing

to trace carbon moving from an injured mother tree

down her trunk into the mycorrhizal network

and into her neighboring seedlings,

not only carbon but also defense signals.

And these two compounds

have increased the resistance of those seedlings to future stresses.

So trees talk.

(Applause)

Thank you.

Through back and forth conversations,

they increase the resilience of the whole community.

It probably reminds you of our own social communities,

and our families,

well, at least some families.

(Laughter)

So let's come back to the initial point.

Forests aren't simply collections of trees,

they're complex systems with hubs and networks

that overlap and connect trees and allow them to communicate,

and they provide avenues for feedbacks and adaptation,

and this makes the forest resilient.

That's because there are many hub trees and many overlapping networks.

But they're also vulnerable,

vulnerable not only to natural disturbances

like bark beetles that preferentially attack big old trees

but high-grade logging and clear-cut logging.

You see, you can take out one or two hub trees,

but there comes a tipping point,

because hub trees are not unlike rivets in an airplane.

You can take out one or two and the plane still flies,

but you take out one too many,

or maybe that one holding on the wings,

and the whole system collapses.

So now how are you thinking about forests? Differently?

(Audience) Yes.

Cool.

I'm glad.

So, remember I said earlier that I hoped that my research,

my discoveries would change the way we practice forestry.

Well, I want to take a check on that 30 years later here in western Canada.

This is about 100 kilometers to the west of us,

just on the border of Banff National Park.

That's a lot of clear-cuts.

It's not so pristine.

In 2014, the World Resources Institute reported that Canada in the past decade

has had the highest forest disturbance rate of any country worldwide,

and I bet you thought it was Brazil.

In Canada, it's 3.6 percent per year.

Now, by my estimation, that's about four times the rate that is sustainable.

Now, massive disturbance at this scale is known to affect hydrological cycles,

degrade wildlife habitat,

and emit greenhouse gases back into the atmosphere,

which creates more disturbance and more tree diebacks.

Not only that, we're continuing to plant one or two species

and weed out the aspens and birches.

These simplified forests lack complexity,

and they're really vulnerable to infections and bugs.

And as climate changes,

this is creating a perfect storm

for extreme events, like the massive mountain pine beetle outbreak

that just swept across North America,

or that megafire in the last couple months in Alberta.

So I want to come back to my final question:

instead of weakening our forests,

how can we reinforce them and help them deal with climate change?

Well, you know, the great thing about forests as complex systems

is they have enormous capacity to self-heal.

In our recent experiments,

we found with patch-cutting and retention of hub trees

and regeneration to a diversity of species and genes and genotypes

that these mycorrhizal networks, they recover really rapidly.

So with this in mind, I want to leave you with four simple solutions.

And we can't kid ourselves that these are too complicated to act on.

First, we all need to get out in the forest.

We need to reestablish local involvement in our own forests.

You see, most of our forests now

are managed using a one-size-fits-all approach,

but good forest stewardship requires knowledge of local conditions.

Second, we need to save our old-growth forests.

These are the repositories of genes and mother trees and mycorrhizal networks.

So this means less cutting.

I don't mean no cutting, but less cutting.

And third, when we do cut,

we need to save the legacies,

the mother trees and networks,

and the wood, the genes,

so they can pass their wisdom onto the next generation of trees

so they can withstand the future stresses coming down the road.

We need to be conservationists.

And finally, fourthly and finally,

we need to regenerate our forests with a diversity of species

and genotypes and structures

by planting and allowing natural regeneration.

We have to give Mother Nature the tools she needs

to use her intelligence to self-heal.

And we need to remember that forests aren't just a bunch of trees

competing with each other,

they're supercooperators.

So back to Jigs.

Jigs's fall into the outhouse showed me this other world,

and it changed my view of forests.

I hope today to have changed how you think about forests.

Thank you.

(Applause)