The secret lives of trees
I talk to trees once in a while. I'm not even sure why. In fact, I’m standing in a forest not too far from my home on the northern edge of Washington state.
I come here to get away. To connect with nature and to be under the trees.
There’s something magical about trees that has always captured our imaginations. Our fascination with trees isn’t surprising considering that there are more than three trillion of them on this planet. That’s about 422 trees per person.
Usually when I’m in the forest I look to the sky. See if there are any birds or animals in the branches. I think it comes naturally to us all — to look up at those branches. Or to just listen to the leaves in the breeze.
Perhaps that's why people have, for so long, be unaware of what is going on with trees, between trees. Science is just now catching up with these lifeforms, and we're learning that trees have a lot more to say.
But to hear that, we have to go subterranean.
Science and legacy
I showed Dr. Teresa Ryan one of my favorite trees — every time I walk past it, I give it pat or a big hug. I call it my grandfather tree and think about all the time it has witnessed. Teresa is a researcher at the Department of Forest and Conservation Sciences at the University of British Columbia.
Teresa shares my love of trees, not only because she’s studied them but she’s also a member of the Tsimshian. They are an indigenous people of the Pacific Northwest Coast and have a close connection to the forest.
The Tsimshian call the cedar the “tree of life.”
"Hands down it is the most important tree because it provides us with our housing, our transportation in canoes, our totem poles, and all of our clothing was out of cedar," Teresa said. "Our masks that we use in ceremonies was out of cedar. Our boxes to hold our belongings were out of cedar to store food."
Dr. Teresa Ryan's expertise is the relationship between fish and forests. And it’s relationships like this that Teresa sees everywhere in the forest.
Like the cedar trees we were standing in front of, which are conifers, they have a relationship with maples, like my grandfather tree, which are deciduous.
"They love to grow up in any shaded areas where the deciduous trees have grown first and then the conifers will come up underneath it because ... the deciduous trees will protect the young conifer trees until they're strong enough to release and go up to them for their own sunlight," she said. "And then they they take over the space. But it's another symbiotic relationship that's evolved in these forests."
That's all above ground. And it's not the entire story of what is happening here.
"We've got layers and layers and layers of history in these soils," Teresa said. "And it's absolutely amazing."
The deciduous trees are the key players in these layers of history. As winter approaches, the deciduous trees, like my grandfather, drop their leaves to conserve energy as the weather gets colder. These leaves blanket the forest floor and start decomposing.
"As they decompose, they're releasing nutrients and the trees need nutrients, right, to survive, but they can't access those nutrients by themselves," Teresa said. "They rely on a shuttle, if you will. There is a relationship going on underground with tree root systems associated with fungus."
The leaves that have fallen to the ground contain glucose — a sugar made by photosynthesis. And if there’s one thing that fungus loves, it’s glucose. In exchange for this sugar, the fungus gives the tree roots essential nutrients like water, carbon, and nitrogen. Think of it as a giant underground barter system. The fungus is made up of tiny white filaments that all together make up something called the “mycorrhizal network.”
"As far out as the roots go," Teresa said, "so do the mycorrhizal networks. Well, fungus ... and they are just extending throughout this whole forest as well. That's also been mapped using DNA technology. So it's using science as well."
"So from an aboriginal or indigenous view, science is catching up with what we already know about these connections in the forest," she said.
A tree’s root system is twice the size of its crown. So this mycorrhizal network connecting these roots is massive. To put this into perspective, one teaspoon of soil contains several miles of fungal filaments in this network.
"One of the things that our students have found is that these networks, when they exchange nutrients where they pass along or transmit the nutrients, they will favor their own seedlings," Teresa said. "They'll still distribute to other seedlings, but they favor their own seedlings."
Now this might sound like fantasy — big trees watching over and caring for the little ones. But it’s all happening though this incredible mycorrhizal network. Researchers have even studied what happens when a mother tree is being cut down. It will shuttle carbon immediately through the root systems, particularly to their seedlings. It sends everything it has to the seedlings, to give them a chance at growing.
A mother tree sacrificing herself for her seedlings.
Trees also use this network to communicate and warn other trees when danger is approaching. It’s something that the journal Nature has dubbed the “wood wide web.”
Peter Wohlleben's love for trees came from an unexpected place.
He worked as a forester in Germany for 20 years. When he first took the job he thought he was going to take care of trees, like a forest shepherd. But he found that a lot of his work required cutting down trees. He became a self described “tree butcher.”
One day he was asked to cut down a dying birch tree and as that tree fell to the ground, something changed in him.
"And when the tree came down and with a certain sound, which is really not nice and was bleeding afterwards, a lot of water, I thought, 'Oh, no, that's a big living organism,'" he recalled. "And I was almost crying. And then it was the moment that, 'No, I can't go on treating forests like this.'"
So he started writing about them — writing about trees. And he wrote about them in a way that takes complex ideas and theories and strips them down to their essence. He makes trees understandable for the rest of us in his book “The Hidden Life of Trees.”
For example, the idea that trees actually communicate with one another. How does that happen? How does one tree know that another tree needs help?
"There are interesting theories about that," he said. "We know that the root tips, they are brain-like structures. In those root tips, there are brain like processes going on — in electrical and chemical ways. Like in our brains."
With all the roots acting like a brain, they work together to communicate.
"We don't know, so far, how they coordinate," he said. "But perhaps, it's just a guess — this is the brain of a tree."
And yes, Peter does say it's a lot like in the movie "Avatar." James Cameron must have read the same research.
Peter says this communication between trees is not just one way. It’s a two way conversation, with electrical and chemical signals sent back and forth. For example, trees are warning each other about insect attacks or heavy droughts, so they can prepare each other in advance.
Peter brings up a study from the University of Leipzig in Germany that showed how trees warn each other and help each other defend against predators like deer.
"When a deer is the feeding on little beech trees, then the little tree is able to judge by the saliva of the deer, 'Ah, that's a deer!'" Peter said. "And then it pumps poisonous substances in the leaves. And it's warning its companions -- surrounding little beech siblings."
The deer saliva triggers warnings. These warnings are sent with electrical signals from tree-to-tree across the mycorrhizal network that Teresa Ryan talked about — the wood wide web.
But this way of communicating does have a downside: it’s slow. Think about the days of dial-up modems. In the case of the deer eating the leaves, the leaf that’s gnawed on emits a signal. That signal then moves through the branch, down the trunk, then underground through the root system to the next tree. Then the signal travels to the new tree, up the trunk, out to the branches and onto the leaves. It takes a long time. But some trees have developed a faster way to communicate — through scent.
Yes, scent. Peter says scientists discovered this while observing giraffes feeding on acacia trees. If you’re a giraffe, you love acacia leaves.
"Scientists found out that giraffes are just feeding for some minutes on this acacia tree," he said. "And then the tree sprays poisonous substances into the leaves, really deadly substances."
These substances released into the leaves not only make them taste bad but they also make the leaves harder for giraffes to digest. The scientists watched the giraffes and they noticed that when the leaves emitted the poisonous substance, the giraffes would move on to the next acacia tree.
"And then they found out that the tree — the tree which which the giraffe fed on — warned the other trees by gassing out chemicals, which are something like a chemical warning," Peter said.
And once a neighboring tree catches the scent of the chemical warning it sends out the poisonous substances to its own leaves. The scientists learned about the chemical gassing because they observed that the giraffes started to somehow catch on and they started to feed upwind of the tainted trees. That’s because chemicals released by the original tree could only travel downwind.
"That was the first time that scientists discovered the communications between trees," Peter said.
So trees can communicate through scent, taste, and electrical signals. Now scientists think trees can even communicate through sound — 220 hertz to be exact.
"That's the frequency of flowing water in the underground," Peter said. "And that's the signal which trees or roots love. Because water is the most necessary element beside air. So trees are able to hear ... this sound of beloved water."
"And they are even able to hear if other roots make sounds in this frequency," he said. "And we don't know what they are telling each other, but we know that they are able to make active click sounds in this frequency. "
Did you get that?! A tree hears the frequency of water and then it can potentially communicate that source of water and availability of water to another tree of the same species or perhaps even different ones.
"And perhaps when you've you play this this sound for an hour, it's just the first name of the tree," Peter said with a laugh.
"A tree — it's like standing on his head with its head in the soil," Peter said. "... The tree is standing with the feet up in the sky."
Makes total sense.
"So I think the most important thing is going on under the soil," he said. "But our problem is we are a species which is living on top of the soil and which for us, it is really hard to imagine how living in the soil could be."
"We think it's maybe boring to live a whole life on a certain place without moving, but the tree is moving with its roots," he added. "They are growing in this direction, perhaps next year in this direction, and they are expanding use which are birds with the birch tree and perhaps next time with a neighboring Douglas Fir or the grass. We don't know if trees are also communicating with grass because there's no research about this."
Trees could be talking about you
Back at my local forest sitting on a tree stump among the cedars with Dr. Teresa Ryan, the researcher, she tells me that the way trees communicate with each other resonates with her Native American heritage and background as a scientist. She sees trees as living beings.
"These trees in here, in this forest, are communicating with each other," she said. "They could be talking about us right now. We don’t know what they are saying! They are beings and we have to respect that. There’s a heart-to-heart conversation that goes on with me in the forest. And I just want to do what I can to protect, to nurture them and make sure they are a part of the future. So that they have a future."
What’s interesting to me is the deep influence trees have had on Teresa and on Peter. Peter, a former logger turned tree advocate. Teresa, a scientist who leans on her Native American roots. She has a foot in both worlds of fact and spirituality. It seems like the trees have spoken to them both.
I get it. When I’m in a forest like this, I never feel alone. And perhaps its because I’m surrounded by a huge community of individuals that are quietly cooperating, looking out for each other, in ways we’re only just beginning to understand.
THE WILD is a production of KUOW in Seattle in partnership with Chris Morgan Wildlife and The UPROAR Foundation. It is produced by Matt Martin and edited by Jim Gates. It is hosted, produced and written by Chris Morgan. Fact checking by Apryle Craig. Our theme music is by Michael Parker.
Dyer Oxley contributed to this article.
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