How trees talk, and why we should listen
Written and photographed by Yascha Wecker
What fungal networks teach us about the secret life of trees and our place in the world
For as long as she can remember, Suzanne Simard has been deeply fascinated with soils. Growing up in southern British Columbia, Canada, she turned the local old-growth forests into her playground. “I was one of those kids that was always playing in the dirt with my brother. I loved the coolness, the texture, the taste, everything about the soil,” she says.
As her fascination with soils grew, she started itching to dig deeper to learn about what was going on below the ground. But when she began studying forestry at university, she stepped into a male-dominated field focused solely on the aboveground competition between trees. She knew that her approach was going to be different. “I wanted to go where things were hidden and where few people went to look,” she recalls. There, in the belowground world of the forest, she found her calling.
HOW TREES TALK
Suzanne Simard is pioneer in research on mycorrhizal networks
Photo by Brendan Ko
Simard, now a professor of Forest Ecology at the University of British Columbia and author of hundreds of peer-reviewed articles, has been a pioneering force in discovering underground partnerships between trees through mycorrhizal networks. She has studied these systems in different climates, including the Arctic, for nearly three decades.
When she first set out to study these partnerships in the wild, there was little support and momentum for this type of research. “At the time I was doing my work, there was a lot of scepticism about whether these mycorrhizal networks were there, whether they did anything, whether plants are actually benefiting from networks. That was a big question at the time,” she recalls.
In her earliest and most famous experiments, she planted replicates of young Douglas fir and paper birch trees and covered them with individual plastic bags. She then injected the bags surrounding the paper birch trees with radioactive carbon dioxide gas, and the bags covering the Douglas fir with a stable carbon isotope. She also covered the fir seedlings with a shade cloth to block the sun. She hypothesized that after turning the carbon dioxide into sugars through photosynthesis and sending it down into their roots, the birch trees would send that carbon to their neighbours, which were deprived of sunlight.
Trees dynamically exchange resources through underground fungal pathways
What she found was that not only had the birch trees taken up the radioactive carbon dioxide gas and transferred it to the Douglas fir, but the two species were interdependent, sending carbon back and forth according to their respective seasonal needs. In the summer, carbon flowed from the birch trees to the smaller Douglas fir trees which were shaded and in need of nutrients for their growth. In the fall, that flow reversed, and the evergreen Douglas fir sent carbon to the birch which was losing its leaves. The trees were talking.
As she observed this lively dialogue between the trees, Simard knew that she was on to something big. “It was absolutely thrilling because the patterns were so clear,” she reminisces. “I had actually found something important, something significant.” Indeed, she was the first researcher to ever document such a dynamic exchange of resources through underground fungal pathways between trees in the wild, a feat that the prestigious scientific journal Nature recognized in 1997 with a cover story titled ‘The Wood-Wide Web’.
THE MYCELIAL NETWORK
Simard’s ground-breaking research in the forests of British Columbia revealed the central role of mycelial networks in an ecosystem. The communication highways formed by these fungal networks, which link nearly every tree in a forest, are what allow trees to talk.
The oldest trees in the forest are the most highly connected
These networks occur in all major terrestrial ecosystems, including grasslands, tundra, forests, and savannas. They are founded on the mutual symbiotic association between a fungus and a plant. The fungus uses biochemical signalling to connect with the roots of the plant and help it extract water and nutrients from the soil in exchange for the sugars the plants make through photosynthesis. Once that symbiosis is established, the fungus will grow using the energy provided by the plant and spread its fungal threads throughout the soil, forming a dense web called mycelium. This web colonizes the roots of all of the nearby trees and plants. The density of this network is such that there can be hundreds of kilometres of mycelium under a single footstep.
Mycelium grows into a network, which, over time, will form nodes and hubs. When Simard’s team of researchers mapped the mycelial network in the forest, they realized that the oldest trees were the most highly connected and acted as central hubs. These trees, which Simard fondly refers to as Mother Trees, have well-established mycorrhizal connections and can nurture their young, which are growing in the understory. By sending them excess carbon, the Mother Trees can substantially increase the seedlings’ survival.
Mother Trees can even recognize their kin. In her experiments, Simard found that specific tree species would favour their kin with bigger mycorrhizal networks and more carbon. When injured or dying, the Mother Tree would even send what Simard calls “messages of wisdom” by bequeathing carbon to the next generation and releasing defence signals into the network to increase the seedlings’ resistance to future stresses.
The mycelial network of a forest
Diagram from Belier et al. 2010
Simard’s research showed that the mycelial network creates an intricate underground ecosystem that ties the entire forest together. Trees use these fungal pathways to exchange carbon, but also nitrogen, phosphorus, water, defence signals, and hormones. The genius of this design lies in its efficiency, but also its resilience, Simard explains: “The reason that they're resilient, meaning that they can easily recover, is that you can have many points of contact. There are many routes and there are many connections between them. So, if you lose one, you still have many more to rely on. So, they are efficient and they are resilient and they have evolved, I think, through time, to have these patterns.”
This intelligence is not unique to mycelium. Similar patterns can be observed throughout nature, including in neural networks, and even in our man-made structures such as transportation networks and telephone networks. “We have the same patterns in our brains and we've mimicked them in our own human-built environments,” Simard says.
EXPOSING THE INVISIBLE THREADS
The work of researchers like Suzanne Simard throws into question some long-standing ideas about evolutionary ecology, and about how we define our place in the world. The idea that different species would selflessly help one another blatantly contradicts the core principles of Darwinism, and the view that competition, rather than cooperation, is the primary driver of evolution.
The existence of mycelial networks can shift our understanding of nature from viewing plants as individuals competing for resources to seeing them as part of a complex and interconnected ecosystem. This idea fascinated Katy Fox, a Luxembourg-based social anthropologist, community organiser, teacher, and eco-social designer, when she first heard about it at an ecovillage in the south of England.
“It really illustrates this web of life in terms of how the soil is not just inert matter where we put stuff in,” she says. “In the soil – just as in a society – there are many interactions. It’s true on a symbolic, on a metaphorical, but also on a very real scientific level.”
After a career in academia studying anthropology and social change, she decided she needed to find practical applications for her work and adopt a political stance.
Drawing inspiration from the idea of mycelium, she founded the Centre for Ecological Learning Luxembourg (CELL) in 2010, and later launched her own business, Mycelium Design, to focus her work on permaculture design, regenerative living, and community resilience capacity-building. She works with private individuals and municipalities in Luxembourg, providing consultation services for their ongoing projects.
In her work, Fox strives to deconstruct what she calls our “obsession with individualism” by integrating a more holistic, systems-based approach to ecological design. She focuses on participatory, place-based, and community-based solutions which are practical and grounded. Some of her work is very hands-on, like drawing up design plans and writing reports for municipalities or revamping people’s backyards using permaculture principles. Other projects involve analysing the social structure of an organization and helping restructure it in a non-hierarchical way.
Katy Fox, social anthropologist and founder of Mycelium Design
Photo by Mathilde Magne
Every mission is different, but they are all fuelled by Fox’s desire to increase the connections between people and to create relationships in the broadest sense. To achieve this, she focuses on the underground phenomena happening in social places and the invisible threads which connect people, just like mycelium links all the trees in the forest. “It’s really this underground collaboration of a lot of things coming together,” she says.
Fox believes that there are many ways to reconnect and see these invisible social threads in our lives. Unlearning, seeing things with a child’s eyes, and going into nature to observe and slow down are all useful techniques. In her view, realizing this interconnectedness is paramount: “I found that it’s really the shift we need for society.”
MYCELIUM FOR A MORE SUSTAINABLE WORLD
Danièle Waldmann, Professor in Engineering and researcher at the University of Luxembourg
Beyond its potential to inspire models of human interactions, mycelium is also arousing the curiosity of researchers and entrepreneurs who are exploring practical uses in sustainable development. Danièle Waldmann, a professor in Engineering and researcher at the Laboratory of Solid Structures at the University of Luxembourg, took on this challenge when she investigated the potential of using mycelium as building insulation.
The synthetic compounds currently used in building insulations have a high carbon footprint and are generally not sustainable and environmentally friendly. In June 2021, Waldmann and her team designed a research project where they combined mycelium with the fibres of miscanthus grass to create a self-growing, bio-composite building insulation material. Samples of the composite were grown in moulds where the mycelium weaves itself between and around the miscanthus fibres and acts as a binder. The samples were tested for thermal insulation, fire resistance, and water absorption.
“I think it’s very promising,” says Waldmann, who led the research team. “The most interesting thing that I found is that it is insulation which grows into the shape you want to have. It’s bio-based and also fully renewable.”
At this stage, the work of Waldmann and her colleagues is only a proof of concept and she says further research is needed to investigate the usability of the material. Waldmann is convinced, however, that mycelium opens up a promising research field.
Sculpture carved from a tree in Pacific Spirit Park, Vancouver, British Columbia
SEEING THE FOREST FOR THE TREES
Today, after decades of clear-cuts, the enchanted world of the old-growth forests where Suzanne Simard used to play growing up no longer exists. Yet, the inspiration that she drew from those places has led her to make discoveries that have caused a major paradigm shift in our understanding of forests and ecosystems. Instead of seeing trees as individual and passive features of a landscape, we can appreciate that they are parts of a single living organism.
Simard’s lifelong quest to prove that the forest is more than just a collection of trees is also a personal longing to reconnect. By looking into nature, she was trying to find herself, and her research has taught her a lot about the value of community and belonging. She believes that as a society, we can learn from these insights, too.
“Nature really is based on collaboration and symbiosis,” she says. “All these creatures have evolved and co-exist because of that. And we’re no different. We're just one more species in this whole soup of species. Even though we're kind of seeing ourselves as sepa - rate, we're not. We’re the same and we have the same ways of interacting. So, there are great lessons I think for how we can change course a little bit.”
Simard believes that many answers can be found in the forest. “Walking in the forest makes us feel good because this is where we belong. We've evolved to be in these places,” she says. Her vision is that her research will change the way we look at the forest and the way we look at ourselves. And maybe, she hopes, it will make us fall in love with the forest all over again.
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LEARN MORE
Read
Finding the Mother Tree by Suzanne Simard
Watch
Fantastic Fungi on Netflix