How Trees Talk to Each Other: Suzanne Simard (Full Transcript)

Suzanne Simard

Suzanne Simard – ecologist 

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.

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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.

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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.

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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.

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