The Roots of Plant Intelligence

Stefano Mancuso
at TEDGlobal 2010

July 2010

from TED Website



Plants behave in some oddly intelligent ways:

fighting predators, maximizing food opportunities...

But can we think of them as actually

having a form of intelligence of their own?

Italian botanist Stefano Mancuso

presents intriguing evidence...










Sometimes I go browsing [through] a very old magazine.


I found this observation test about the story of the ark. And the artist that drew this observation test did some errors, had some mistakes - there are more or less 12 mistakes. Some of them are very easy. There is a funnel, an aerial part, a lamp and clockwork key on the ark.


Some of them are about the animals, the number. But there is a much more fundamental mistake in the overall story of the ark that's not reported here. And this problem is: where are the plants? So now we have God that is going to submerge Earth permanently or at least for a very long period, and no one is taking care of plants.


Noah needed to take two of every kind of bird, of every kind of animal, of every kind of creature that moves, but no mention about plants. Why?


In another part of the same story, all the living creatures are just the living creatures that came out from the ark, so birds, livestock and wild animals. Plants are not living creatures - this is the point. That is a point that is not coming out from the Bible, but it's something that really accompanied humanity.

Let's have a look at this nice code that is coming from a Renaissance book. Here we have the description of the order of nature. It's a nice description because it's starting from left - you have the stones - immediately after the stones, the plants that are just able to live. We have the animals that are able to live and to sense, and on the top of the pyramid, there is the man. This is not the common man.


The "Homo studiosus" - the studying man. This is quite comforting for people like me - I'm a professor - this to be over there on the top of creation. But it's something completely wrong. You know very well about professors. But it's also wrong about plants, because plants are not just able to live; they are able to sense.


They are much more sophisticated in sensing than animals. Just to give you an example, every single root apex is able to detect and to monitor concurrently and continuously at least 15 different chemical and physical parameters. And they also are able to show and to exhibit such a wonderful and complex behavior that can be described just with the term of intelligence.


Well, but this is something - this underestimation of plants is something that is always with us.

Let's have a look at this short movie now. We have David Attenborough. Now David Attenborough is really a plant lover; he did some of the most beautiful movies about plant behavior. Now, when he speaks about plants, everything is correct. When he speaks about animals, [he] tends to remove the fact that plants exist.


The blue whale, the biggest creature that exists on the planet - that is wrong, completely wrong. The blue whale, it's a dwarf if compared with the real biggest creature that exists on the planet - that is, this wonderful, magnificent Sequoiadendron giganteum. (Applause)


And this is a living organism that has a mass of at least 2,000 tons.


Now, the story that plants are some low-level organisms has been formalized many times ago by Aristotle, that in "De Anima" - that is a very influential book for the Western civilization - wrote that the plants are on the edge between living and not living. They have just a kind of very low-level soul.


It's called the vegetative soul, because they lack movement, and so they don't need to sense. Let's see.

Okay, some of the movements of the plants are very well-known. This is a very fast movement. This is a Dionaea, a Venus fly trap hunting snails - sorry for the snail. This has been something that has been refused for centuries, despite the evidence. No one can say that the plants were able to eat an animal, because it was against the order of nature.


But plants are also able to show a lot of movement. Some of them are very well known, like the flowering. It's just a question to use some techniques like the time lapse. Some of them are much more sophisticated. Look at this young bean that is moving to catch the light every time. And it's really so graceful; it's like a dancing angel.


They are also able to play - they are really playing. These are young sunflowers, and what they are doing cannot be described with any other terms than playing. They are training themselves, as many young animals do, to the adult life where they will be called to track the sun all the day.


They are able to respond to gravity, of course, so the shoots are growing against the vector of gravity and the roots toward the vector of gravity. But they are also able to sleep. This is one, Mimosa pudica. So during the night, they curl the leaves and reduce the movement, and during the day, you have the opening of the leaves - there is much more movement.


This is interesting because this sleeping machinery, it's perfectly conserved. It's the same in plants, in insects and in animals. And so if you need to study this sleeping problem, it's easy to study on plants, for example, than in animals and it's much more easy even ethically. It's a kind of vegetarian experimentation.

Plants are even able to communicate - they are extraordinary communicators. They communicate with other plants. They are able to distinguish kin and non-kin. They communicate with plants of other species and they communicate with animals by producing chemical volatiles, for example, during the pollination.


Now with the pollination, it's a very serious issue for plants, because they move the pollen from one flower to the other, yet they cannot move from one flower to the other. So they need a vector - and this vector, it's normally an animal. Many insects have been used by plants as vectors for the transport of the pollination, but not just insects; even birds, reptiles, and mammals like bats rats are normally used for the transportation of the pollen. This is a serious business.


We have the plants that are giving to the animals a kind of sweet substance - very energizing - having in change this transportation of the pollen. But some plants are manipulating animals, like in the case of orchids that promise sex and nectar and give in change nothing for the transportation of the pollen.

Now, there is a big problem behind all this behavior that we have seen. How is it possible to do this without a brain? We need to wait until 1880, when this big man, Charles Darwin, publishes a wonderful, astonishing book that starts a revolution.


The title is "The Power of Movement in Plants."


No one was allowed to speak about movement in plants before Charles Darwin. In his book, assisted by his son, Francis - who was the first professor of plant physiology in the world, in Cambridge - they took into consideration every single movement for 500 pages. And in the last paragraph of the book, it's a kind of stylistic mark, because normally Charles Darwin stored, in the last paragraph of a book, the most important message.


He wrote that,

"It's hardly an exaggeration to say that the tip of the radical acts like the brain of one of the lower animals."

This is not a metaphor. He wrote some very interesting letters to one of his friends who was J.D. Hooker, or at that time, president of the Royal Society, so the maximum scientific authority in Britain speaking about the brain in the plants.

Now, this is a root apex growing against a slope. So you can recognize this kind of movement, the same movement that worms, snakes and every animal that are moving on the ground without legs is able to display. And it's not an easy movement because, to have this kind of movement, you need to move different regions of the root and to synchronize these different regions without having a brain.


So we studied the root apex and we found that there is a specific region that is here, depicted in blue - that is called the "transition zone." And this region, it's a very small region - it's less than one millimeter. And in this small region you have the highest consumption of oxygen in the plants and more important, you have these kinds of signals here.


The signals that you are seeing here are action potential, are the same signals that the neurons of my brain, of our brain, use to exchange information. Now we know that a root apex has just a few hundred cells that show this kind of feature, but we know how big the root apparatus of a small plant, like a plant of rye. We have almost 14 million roots.


We have 11 and a half million root apex and a total length of 600 or more kilometers and a very high surface area.

Now let's imagine that each single root apex is working in network with all the others. Here were have on the left, the Internet and on the right, the root apparatus. They work in the same way. They are a network of small computing machines, working in networks.


And why are they so similar? Because they evolved for the same reason: to survive predation. They work in the same way. So you can remove 90 percent of the root apparatus and the plants [continue] to work. You can remove 90 percent of the Internet and it is [continuing] to work. So, a suggestion for the people working with networks: plants are able to give you good suggestions about how to evolve networks.

And another possibility is a technological possibility. Let's imagine that we can build robots and robots that are inspired by plants. Until now, the man was inspired just by man or the animals in producing a robot. We have the animaloid - and the normal robots inspired by animals, insectoid, so on. We have the androids that are inspired by man. But why have we not any plantoid?


Well, if you want to fly, it's good that you look at birds - to be inspired by birds. But if you want to explore soils, or if you want to colonize new territory, to best thing that you can do is to be inspired by plants that are masters in doing this. We have another possibility we are working [on] in our lab, [which] is to build hybrids.


It's much more easy to build hybrids. Hybrid means it's something that's half living and half machine. It's much more easy to work with plants than with animals. They have computing power, they have electrical signals. The connection with the machine is much more easy, much more even ethically possible.


And these are three possibilities that we are working on to build hybrids, driven by algae or by the leaves at the end, by the most, most powerful parts of the plants, by the roots.

Well, thank you for your attention. And before I finish, I would like to reassure that no snails were harmed in making this presentation.


Thank you.


How Trees Talk to Each Other
Suzanne Simard
at TEDSummit

June 2016

from TED Website

Similar Spanish version

"A forest is much more than what you see,"

says ecologist Suzanne Simard.

Her 30 years of research in Canadian forests

have led to an astounding discovery

- trees talk, often and over vast distances.

Learn more about the harmonious

yet complicated social lives of trees

and prepare to see

the natural world with new eyes...






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 --


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.


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.


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 mosquitoes, and I jumped into the truck, and I thought,

"This is why people do lab studies."


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 allele chemicals 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.


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.


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.