Brendan George Ko / Penguin Random House
Trees are “social creatures” that communicate with each other in collaborative ways that also hold lessons for humans, says ecologist Suzanne Simard.
Simard grew up in Canadian forests as a descendant of lumberjacks before becoming a forest ecologist. She is now Professor of Forest Ecology at the University of British Columbia.
Trees are attached to neighboring trees by an underground network of fungi similar to the neural networks in the brain, she explains. In a study, Simard saw how a Douglas fir that had been injured by insects apparently sent chemical warning signals to a ponderosa guy growing nearby. The pine tree then produced defense enzymes to protect against the insect.
“This was a breakthrough,” Simard says. The trees shared “information that is actually important to the health of the entire forest.”
In addition to warning each other of danger, Simard says trees have been known to share nutrients at critical times to keep each other healthy. She says that the trees in a forest are often linked to each other via an older tree, she calls a “mother” or “knot tree”.
“In the case of all trees of different ages, [the mother trees] can actually facilitate the growth of these underground seedlings, “she says. The seedlings will connect to the network of the old trees and benefit from the enormous capacity for resource uptake. And the old trees would also transfer a bit of carbon and nutrients and water to the little seedlings at crucial times in their lives that actually help them survive. “
The study of trees gained a 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 actually originated from a substance that some trees manufacture for their own mutual defense. She explains her research on collaboration and symbiosis in the forest and shares her personal story in the new memoir Find the mother tree: Discover the wisdom of the forest.
Penguin Random House
On working for a forestry company in British Columbia in the 20s
That was in the late 1970s when I started; they were ready and just started planting trees. And then, of course, it was completely different from what I saw my grandfather do and my father and uncles. They just took the odd tree out here and there. But it was wholesale to take out all the trees, the big ones and the small ones. And it was my first job in the forestry industry, which for me was quite shocking. But it was also very exciting because it was so dangerous. And I was also one of the first girls in the industry.
Being a young forester and realizing that fungus was the key to forest health
In the forest floor … there are all sorts of bugs, but there are also lots of fungi. And the mushrooms are so colorful. There are yellow and purple and white, and … they grow right through the forest floor to the point where it almost looks like gauze. And then I found this yellow fungus. And yet, when I pulled up the seedlings that were not doing so well – they were yellow and dying – I realized that their roots were kind of black and straight. … And then I wondered what they were missing? Did they lack this sponge? Was this fungus … a pathogen, or was it a helper fungus?
And eventually I learned that these were a special kind of helper fungus called mycorrhizal fungus – which just means that the fungus is the type that grows through the soil and collects nutrients and water and brings it back to the seedling. … So eventually I was able to put together that these little seedlings that were not doing so well were missing their mycorrhizal fungi.
About the critical relationship between trees and fungi
Remember that all trees and all plants – except a very small handful of plant families – have mandatory conditions for these fungi. That means they need them to survive and grow and produce cones and have fitness – in other words, to carry their genes to the next generations. And the fungi are dependent on the plant or the trees … because they do not have leaves themselves [for photosynthesis]. And then they join this symbiosis because they live together at the root, and they exchange these essential resources: carbohydrates from the plant for nutrients from the fungus, in this two-way exchange that is very tight, almost like a market exchange. If you give me five dollars, I’ll give you five dollars back. It is very, very closely regulated between these two partners in the symbiosis. But yes, all the trees and all the plants in all our forests around the world are dependent on this relationship.
About how trees can help each other by sharing nutrients[At the time] birch was considered a weed. There was a huge program to spray and herbicide these trees to get rid of them because the foresters considered the birches as competing with Douglas fir and especially for light. However, I observed on these plantations that when they shut the birches out, when they sprayed them or cut them, that there was a disease in the forests that would just start spreading like wildfire. It was called Armillaria root disease. I really thought we were doing something wrong here. And then I wanted to know if the birches somehow protected the fours from this disease, and that when we cut them out, it actually got worse.
I had learned about these mycorrhizal fungi and how they could actually protect trees from disease. And I had also heard of David Reed’s work in the UK, where he had shown that in the laboratory, trees could be associated with mycorrhizal fungi and carry carbon between them. So I tested this between birch and spruce in my sick plantations.
I planted birch and spruce and cedar together in small triplets. … And I trace how these carbon molecules went back and forth between birch and spruce, and they did not actually end up in the cedar trees. Because the cedar trees, the forms another kind of mycorrhizal fungus that does not connect either birch or spruce. So [the cedar] was actually not in the network of birch and spruce, and it took up almost none of this isotope.
I knew that birch and spruce shared carbon underground – much contrary to the prevailing wisdom that they only compete for light, and also that the more birch shadows Douglas fir, the more carbon sent to Douglas fir. So there was a net transfer from birch to spruce that diminished its shadow effect.
In this way, the ecosystem maintained its balance – birch and spruce could coexist due to this cooperative behavior, which set off some of the competition that took place.
In the ways her own breast cancer diagnosis shaped her research
It certainly had a huge impact on me and my life has changed as a result, but it also changed my research. That was when I started working on family recognition when I saw if these old trees, especially when they were dying, could recognize and help their family. And I got candidates to ask these questions. You know, if a tree is dying, they send more [nutrients and other signals] to their family? And we found out they do.
Then I also started some studies – one of the most important chemotherapy drugs that was administered to me was paclitaxel [also called Taxol]. Paclitaxel is a defense product – in fact a defense chemical – that is actually produced by the Pacific Ocean in the Pacific Ocean or in fact all the barlin deer around the world. It was important for my recovery – this compound that trees produce to defend against disease.
And then I thought, you know what, I want to know more about this. I started a study with a new graduate student, Eva, and she looks at the yews – whether they are associated with old cedar and corn sticks, and how their neighbors can affect their ability to produce high quality Taxol to increase their defenses.
We just found out that these trees are all connected together by this muscular mycorrhizal network, which allows them to communicate this information. So yes, we’re getting started on that work. I hope it will help us preserve these trees for their medicinal properties – because they are brilliant in what they have done. They have developed these what we call medicines, but they are for themselves also to defend themselves against disease. The cancer treatment is what made me perform this study. And I’m so excited to find out what we’re learning.
Why it is important to let an old tree go through the long dying process alone[Trees] getting old. They eventually fall. And dying is a process, and it takes a long, long time. It can take decades for a wooden door. During death, many things continue. And one of the things I studied was where does their energy go – where does the carbon stored in their tissues go – where does it go? And then we labeled some trees with carbon dioxide – with C13, which is a stable isotope – and we looked at how we actually make those trees die. We emphasize them by pulling their needles off and attacking them with budworms and so on. And then we saw what happened to their carbon.
And we found that about 40% of the carbon was transferred through networks to their nearby trees. The rest of the carbon would have just spread through natural degradation processes … but some of it is directed directly into the neighbors. And in this way, these old trees actually have a very direct impact on the regeneration capacity of the new forest in the future.
This is a completely different way of understanding how old trees contribute to the next generations – that they have agency in the next generations. And our salvage logging practice to get rid of dying trees or trees that have just died or been burned in forest fires – if we go in and cut them right away, we are actually short-circuiting the natural process.
Our studies suggest that it would have knock-on effects for regeneration to come up. They will not be so well prepared for their lives to emerge. So I’ve been trying to tell people: let’s hold back with this salvage logging until trees have had the chance to pass on this energy and information to the new seedlings that are coming up.
Sam Briger and Thea Chaloner produced and edited this interview for broadcast. Bridget Bentz, Molly Seavy-Nesper and Deborah Franklin adapted it for the Internet.