Brendan George Ko / Penguin Random House
Trees are “social beings” who communicate with each other in ways of collaboration that also teach people lessons, says environmentalist Susanie Simard.
Simard grew up in the Canadian forests as a descendant of logging before becoming a forest ecologist. She is now a professor of forest ecology at the University of British Columbia.
The trees are connected to neighboring trees by an underground network of mushrooms which is similar to neural networks in the brain, she explains. In one study, Simard observed how a Douglas fir, which was injured by insects, appeared to send chemicals warning signals to ponderosis pine growing nearby. The pine tree then produces protective enzymes to protect against the insect.
“It was a breakthrough,” says Simard. The trees shared “information that is actually important for the health of the entire forest.”
In addition to warning each other of danger, Simard says trees are known to share nutrients at critical times to stay healthy. She says that the trees in the forest are often connected by an older tree, which she calls the “mother tree” or “center.”
“When connecting to all trees of different ages, [the mother trees] can actually facilitate the growth of these seedlings, “she says.” The seedlings will connect to the network of old trees and will take advantage of the huge capacity to absorb resources. And old trees would also give some carbon, nutrients and water to small seedlings at crucial moments in their lives, which actually help them survive. “
The study of the trees gained new resonance for Simard when she was diagnosed with breast cancer. During her treatment, she learned that one of the chemotherapy drugs she relied on was actually derived from a substance that some trees produce for their own protection. She explains her research on cooperation and symbiosis in the forest and shares her personal story in the new memoirs. Finding the mother tree: Discovering the wisdom of the forest.
Highlights from the interview
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Working for a logging company in British Columbia in his 1920s
It was the late ’70s when I started; they were clear and is just starting to plant trees. So, of course, it was very different from what I saw my grandfather and father and uncle do. They just took out the strange tree here and there. But this was the wholesale export of all trees, large and small. And this was my first job in the forest industry, which was quite shocking for me. But it was also extremely exciting because it was so dangerous. I was also one of the first girls in the industry.
As a young forester and realizing that fungi are key to forest health
In the forest floor … there are all kinds of bugs, but there are also many fungi. And the mushrooms are so colorful. There are yellows and purples and whites and … they grow right through the forest floor to the point where it looks like gauze, almost. And so I discovered this yellow sponge. And yet, when I pulled out seedlings that weren’t doing so well – they were yellow and dying – I realized that their roots were somehow black and straight. … So I wondered what was missing? Did they miss this fungus? Was this fungus … a pathogen or an auxiliary fungus?
And I finally realized that this is a special kind of auxiliary fungus called mycorrhizal fungus – which simply means that the fungus is of the type that grows through the soil and captures nutrients and water and returns it to the seedlings. … So in the end I managed to gather that these small seedlings, which did not do so well, lacked their mycorrhizal fungi.
On the critical relationship between trees and mushrooms
Keep in mind that all trees and all plants – except for a very small handful of plant families – have a binding relationship with these fungi. This means that they need them to survive and grow and produce cones and have fitness – in other words, to carry their genes to future generations. And fungi are dependent on the plant or the trees … because they themselves have no leaves [for photosynthesis]. And so they enter into this symbiosis, as they live together at the root and exchange these basic resources: the plant’s carbohydrates for fungal nutrients, in this two-way exchange, which is very tight, almost like a market exchange. If you give me five dollars, I will return five dollars. This is very, very strictly regulated between these two partners in the symbiosis. But yes, all the trees and all the plants in all our forests in the world depend on this connection.
About how trees can help each other by sharing nutrients[At the time] birches were considered weeds. There was a huge spraying and herbicide program on these trees to get rid of them, because foresters looked at birches as competing with Douglas fir, especially for light. However, I have observed in these plantations that when birches are sown, when they are sprayed or cut, that there is a disease in the forests that will simply begin to spread like wildfire. It was called Armillaria root disease. I really thought we were doing something wrong here. So I wanted to know if birches somehow protect the trees against this disease, and that when we cut them, it actually makes the situation worse.
I had learned about these mycorrhizal fungi and how they can actually protect trees from disease. And I had also heard of David Reed’s work in the UK, where he showed that in the laboratory, trees can be connected to each other by mycorrhizal fungi and leak carbon between them. So I tested this between birch and fir in my diseased plantations.
I planted birch, fir and cedar together in small triplets. … And I watched these carbon molecules move back and forth between the birch and the fir, and they didn’t actually end up in the cedars. Because cedars, they form a different type of mycorrhizal fungus, which is not associated with either birch or fir. Yes [the cedar] in fact, it was not in the net with birch and fir, and it caught almost nothing of this isotope.
I knew that birch and fir shared carbon underground – much against the prevailing wisdom that they competed only for light, and also that the more birch overshadowed the Douglas fir, the more carbon was sent to the Douglas fir. So there was a net transfer from birch to fir, which somehow mitigated its shading effect.
In this way, the ecosystem maintained its balance – birch and fir could coexist because of this joint behavior, which compensated for part of the ongoing competition.
About the ways in which her own breast cancer diagnosis shaped her research
It definitely had a big impact on me and as a result my life changed, but so did my research. Then I started working on recognizing relatives, seeing if these old trees, especially when they die, can recognize and help their relatives. And I had alumni who actually asked those questions. Do you know if the tree dies, do they send more [nutrients and other signals] to their relatives? And we found that they do.
Then I also started some research – one of the main chemotherapeutic drugs I was given was paclitaxel [also called Taxol]. Paclitaxel is a protective agent – actually a protective chemical – that is produced from the Pacific yew tree or, in fact, from all yews around the world. This was essential for my recovery – the compound that trees produce to protect themselves from disease.
So I thought, you know what, I want to know more about this. I started research with a new graduate student, Eva, and she looked at the yew neighborhood – whether they are related to old cedars and mothers and how their neighbors can affect their ability to produce high-quality taxol to increase their protection.
We have just learned that all these trees are connected together by this muscular mycorrhizal network, which provides them with opportunities to communicate this information. So, yes, we begin this work. I hope this will help us to preserve these trees because of their healing properties – because they are ingenious in what they have done. They have evolved over what we call drugs, but they also defend themselves against disease. Cancer treatment is what made me do this research. And I’m so excited to find out what we’re learning.
Why is it important to let an old tree go through only the long process of dying[Trees] I’m getting old. They eventually decrease. And dying is a process and takes a very, very long time. It may take decades for a tree to die. Many things happen in the process of dying. And one of the things I studied was where does their energy go – where is the carbon stored in their tissues stored? So we labeled some trees with carbon dioxide – C13, which is a stable isotope – and watched them actually cause the death of those trees. We stress them by pulling their needles and attacking them with worms and so on. And then we watched what happened to their carbon.
And we found that about 40% of the carbon is transmitted through networks in their neighboring trees. The rest of the carbon would just be dissipated through natural decomposition processes … but some of it goes straight to the neighbors. And thus these old trees actually have a very direct effect on the regenerative capacity of the new forest ahead.
This is a completely different way of understanding how old trees contribute to future generations – that they have freedom of action in future generations. And our timber rescue practices to get rid of dying trees or just dead or burned in forest fires – if we go in and cut them down right away, we’re actually short-circuiting this natural process.
Our studies suggest that this will have an impact on the upcoming regeneration. They will not be so well prepared for their lives ahead. So I try to tell people: Let’s refrain from this felling until the trees get a chance to transmit this energy and information to the new seedlings that are coming.
Sam Bridger and Thea Chalonner produced and edited this broadcast interview. Bridget Benz, Molly Gray-Nesper and Deborah Franklin adapted it for the network.