Listening to the Mother Trees

Anne Strainchamps: A lot of people are seeing trees in a whole new light today. In fact, there's this amazing new science of trees that's shifting the entire paradigm. Maybe you've heard of Suzanne Simard. She's the forest ecologist who discovered that trees use underground networks to communicate and also to cooperate with each other, which is a whole new vision of how nature works. I met her in a forest.

Anne Strainchamps: Okay. What's your background? How did you get into forestry?

Suzanne Simard: My family came from Québec and moved across and settled in the inland rain forests of British Columbia and my grandfather and my uncles all horse-logged. Every summer, we would spend in the cedar-hemlock forests that were so rich and diverse and huge playgrounds for kids. That just became part of me. I think I was always wired for forests and wired for Earth, so it's just a natural calling.

Anne: Let's walk in a little bit if we could. When I've read popular articles or blog posts about your work, the headlines often say, "Trees talk." Do you think trees can communicate?

Suzanne: Yes, absolutely. My work actually looks at one way that they communicate and I think there's multiple ways, but I'll just talk about what I know. I look at how trees are connected below ground by these mutualistic fungi called mycorrhizal fungi.

Anne: Mycorrhizal fungi.

Suzanne: You can think of them as extensions of the root system. The plant or the tree depends on that fungus to go out and explore the soil. The fungus goes and explores and grows into all these little, teeny-tiny niches or accesses nutrients that are unavailable to the tree.

Anne: Is this like a secondary or subsidiary root system almost?

Suzanne: It is. In fact, if you think about how much is down there compared to the root system itself under a single footstep in this forest, there would be hundreds of miles of a fungal network.

Anne: Wait. Under a single footstep?

Suzanne: Yes, under a single footstep.

Anne: What does this have to do then with whether trees can communicate with each other?

Suzanne: The way that communication happens is that through these mycorrhizal networks that link tree after tree after tree, they send resources back and forth. When I say "resources," I mean things like carbon, nitrogen, phosphorus, water, defense signals even. They all send resources or nutrients out to trees that might be struggling under stress. We've seen like the more shaded a tree is, the more a nearby tree that's in the sunlight will send to that shaded tree.

Anne: The trees are helping each other?

Suzanne: Yes, really turns upside down how we've traditionally thought and managed forests. We still manage to this very day on this competition model that there are individuals competing for resources. What I have found is that they're all connected together and that they're sharing these resources. It doesn't mean competition is not going on as well, but there's a multiplicity of interactions.

Anne: If any of us were to go walking in the woods, would you have to dig very far down to see--

Suzanne: To see the network?

Anne: Yes.

Suzanne: No. Actually, we can do that now. Let's see if can get some roots. You get some root and you start looking at the root tips. When you see the little bulbous parts at the end, see that little movement?

Anne: Where before it branches?

Suzanne: Yes. It's more fleshy. That's fungal material that's wrapped around the root tip. Out of that, even though you can't see those mycelium, there's emanating hyphae that come out of that little root tip.

Anne: They're so beautiful when you look at them. Branching, they're like a combination of hair and coral.

Suzanne: Yes. I know they have beautiful branching patterns that we've hardly studied at all. The fungi, when you go into my forest, when you pull up a root system, the fungi are abundant and they're all different colors. Each species has a different color. They have different shapes. Some of them have trilobate branching. Some of them have bifurcating branching or they branch into two. Also, in my forest at home, you can pull up this forest floor and see just big maps of fungal material underneath. It's like pulling off pages of a book. Literally, I can open up the forest floor and I can see these pages and pages of mycorrhizal fungal networks just right before me. It's incredible.

Anne: You've discovered a whole new world.

Suzanne: I have. [laughs]

Anne: Some of your work has involved what you call mother trees. Can you explain? What's a mother tree?

Suzanne: Yes. One of my graduate students, Kevin Beiler, and some other colleagues and I, we did this big study where we took a forest, Douglas-fir forest, and we looked at all of the connections in the forest. We were looking at two fungi, Rhizopogon vesiculosus and Rhizopogon vinicolor. I know that's a mouthful. Keep in mind, there's like 100 other species of fungi in that forest. We looked at two.

We found that every tree was connected to every other tree. The bigger and older the tree, the more connected it was. Those trees, we call them mother trees or hub trees. We call them mother trees because what we also found was that the young seedlings were regenerating within the network of the mother tree. You can think of this like a huge brain growing out through the forest from this single tree.

Anne: It sounds like neural networks, right?

Suzanne: Yes. Basically, they're like neural networks. We've actually found that the patterning of the network is just the same as a neural network.

Anne: Now, I read that you said somewhere something about when a tree like a mother tree gets ready to die, it will deliberately pass its resources onto its children, I guess.

Suzanne: One thing we found is that we have this thing called kin recognition known in animal species. Now, we're discovering that there's actually kin recognition between plants. We've done some experiments to show that these mother trees will actually send more carbon to genetically-related individuals than strangers. That means that the mother tree is nurturing her young to pass on her genes to future generations.

You asked about dying trees. We know and we're doing experiments with this in the beetle-killed forests of the North. The management paradigm is to cut the dying trees. We're trying to look at, and this is based on previous work done in grasslands, where when a tree starts to die and it knows it's going to die, it will start shoveling carbon or sending its own carbon and nutrients to linked trees in its understory. It's actually passing on what it has left to the next generation. Our studies are so simple.

All we've measured is carbon and phosphorous and we don't know if there's any other messages. Even if we can't figure out what those messages are, we know enough now that those trees are hugely important, those mother trees, or in Aboriginal cultures, they're called grandmother trees. We know that they're important for their genes, for what they pass on to their young. What we're doing is we cut them out because we are trying to capitalize on the wood before they die so that we can sell it on the market. To me, it's like a lost legacy. We're really cheating the ecosystem of its natural healing power.

Anne: That's a pretty powerful lesson in terms of resilience also, isn't it? I would think it would apply to human beings too. For the last decade or so, health researchers have proved, we all know anecdotally, people who have strong social networks, friends, family, live longer or healthier. It sounds like the same thing is true for trees.

Suzanne: It is true. The more connected those trees are, the more diverse and locally adapted the community is. The community that knows its own environment, the better off it's going to be. I'll just tell you my own personal experience. I had breast cancer a couple of years ago. I'm doing great, but the thing that really got me through was my connections. It's the friends I made.

It was this incredible, magical network where you could just feel the love going from person to person and we're all doing great. For me, it was like I was living the very thing I was seeing in the forest and I just feel so much comfort. I know I'm going to be okay and just like that tree is going to be okay as long as it stays within its community.

Anne: Thank you. Thank you so much.

Suzanne: You're welcome.

Anne: Suzanne Simard is a professor of forest ecology at the University of British Columbia in Vancouver.