PDF Summary:Finding the Mother Tree, by Suzanne Simard

Are trees competitive or cooperative? In Finding the Mother Tree, ecologist Suzanne Simard delves into this question. Scientists and foresters have typically thought of trees as competing for water, sunlight, and nutrients, and they’ve favored growing marketable species while eliminating presumed competitors. However, ecologist Suzanne Simard explains in Finding the Mother Tree that trees in a forest are interconnected—they communicate and share resources through a complex underground network of fungi.

In this guide, we’ll show how Simard’s research has led to a shift in thinking about ecological relationships. We’ll explain how fungi work to connect the plant life in the forests, how “Mother Trees” take care of their communities and their offspring, and why the prevailing competition paradigm is shortsighted. Throughout, we’ll look at other research that supports or challenges Simard’s findings and discuss how this “new” paradigm of cooperation is not new at all—it’s been the prevailing model for understanding nature among indigenous peoples throughout history.

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The Experiment and Results

In this experiment, Simard created companion plots and clear-cut plots, in the same way she had with the alder and pine. In one plot, the birch trees were completely removed, leaving the fir trees to grow in a monoculture; in another, the two were left to grow alongside one another, as they would naturally. Again, she found that killing the “competitor” birch didn’t improve the growth of the cultivated fir trees, and in some cases it caused more of them to die—in this case, the results were a result of carbon trading.

Carbon trading: Carbon is an essential element of tree life, as trees convert it to sugars they need for energy. So Simard wanted to see if trees also share carbon with one another. During this experiment she used chemistry techniques to measure relative amounts of carbon in the birch and fir trees across the growing season. She found that carbon was moving back and forth between the trees; the birch that were viewed as competitors of the fir were actually sharing carbon with them. And in fact, her measurements showed that the birch were giving more than the fir were giving back.

Simard expected to find this carbon sharing, but an unexpected finding was that the more shade the birch trees cast on the firs, the more carbon the birch donated. So, Simard says, the birch trees actually compensate the firs for the light they’re depriving them of.

Later tests showed the fir giving more carbon to the birch during spring and fall, while the birch gave more to the fir in summer, so she says this shows the two species have a long-term, seasonal relationship, an observation that again would have been missed with a short-term experimental design.

Climate Change Affects Seasonal Cycles

Forest ecologists have noted recently that climate change is affecting cyclical seasonal patterns that are critical to plant life. Environmental conditions like light, temperature, and precipitation act as a “clock” that lets plants know when to do things like sprout new growth or drop seeds. These may also coincide with seasonal activities of pollinators and foragers. When this clock gets disrupted, it can negatively affect the symbiotic relationships between plants, animals, and insects.

As Simard noticed that birch and fir share carbon, and alder and pine share water, in seasonal cyclical patterns, these climatic shifts could affect that cycle and have a devastating effect on the forests. This is an important reason to recognize these complex interdependencies.

Fungal bacteria: Additionally, during the course of this experiment, Simard observed that when birch trees were cut down to increase the growth of fir, the fir were more likely to get fungal disease and die. She found that birch facilitate the growth of helpful bacteria that kill fungal disease, so therefore birch trees were actually producing the remedy the firs needed for their root disease.

Two decades later, Simard returned to some of these experiment sites and found that in the longer term, firs that were planted together with birch were substantially healthier, with higher levels of nutrition and less disease. And the birch that had provided nutrients to the young firs were now being helped in return by the mature firs who had outgrown them.

(Shortform note: In his 2015 book The Hidden Life of Trees, Peter Wohlleben draws on Simard’s work to describe the complex relationships among trees in a forest, arguing that they should be viewed as a supportive community rather than as individuals. He describes how some trees can warn one another of pests, allowing the forewarned trees time to generate chemicals in their leaves that ward off the pests.)

The Tree-Fungus Symbiosis

Simard’s experiment results up to this point had made it clear that trees were sharing resources with one another, but she was left wondering exactly how it happens. Her next task was to investigate the mechanism used to move nutrients between trees, and she suspected it had something to do with the fungus that she had observed on the trees’ roots. This question would lead Simard on a decades-long quest to understand the underground fungal/root networks in forests.

This section discusses those networks' two functions, nutrient sharing and information sharing, and how Simard discovered that they work. Her key findings discussed here include:

• There’s a complex symbiotic relationship between all the trees in a forest and the mycorrhizal fungi that colonize the trees’ roots.
• The fungi transfer resources between the trees while absorbing some for themselves.
• These fungi act as mechanisms for transfer of both nutrients and information.

(Shortform note: In addition to the transfer of nutrients between trees, scientists say fungi are crucial in the fight against climate change, because they absorb carbon from the trees and transfer it to the soil. This reduces the amount of carbon in the atmosphere, decreasing the greenhouse gas effect. It’s estimated that around 5 billion tons of carbon flow through mycorrhizal fungi every year.)

Nutrient Sharing

Through the process of photosynthesis, trees use the energy from sunlight and carbon dioxide from the air, along with minerals and water they absorb, to create carbon and sugars they need to sustain their life. As part of this process, those sugars circulate between the tree’s foliage and its roots, similar to how our own circulatory system works.

A type of fungus called mycorrhizal fungi lives underground, so it doesn’t get sun and therefore doesn’t produce its own sugars, although it needs sugars to live. So, Simard explains that mycorrhizal fungi living in the soil in forests colonize the roots of trees (meaning they grow on and around the roots), in order to absorb sugars from them. Then, she says, the fungi send out their mycelium (“fungal threads” that are like the root structures of the fungus) through the ground, which then attach to another tree’s roots. Simard discovered that it’s through this process that trees also share nutrients with each other.

She found that in addition to absorbing some of the nutrients from the tree roots, the fungi pass them from one tree to another. So, the trees weren’t absorbing nitrogen and other minerals directly from the soil as might be expected. Instead, the fungi were collecting it from the soil and providing it to the trees through their roots, in exchange for the sugars the trees produce.

Simard found over 100 species of fungi in the forests she studied, and she explains that each has different specialized functions. Some transfer water, while some transfer phosphorus or nitrogen. Some grow deeper, while others are shallow. Some are active in spring, others in fall. Through examining these underground networks, Simard found that fungi essentially connect all the trees in the forest.

Are Fungi Intelligent?

Simard’s research focuses more on the role of the trees in this system of symbiosis, but other recent scientific research has shown that fungi exhibit signs of intelligence, and even consciousness, as well. Like trees, fungi can learn, remember, and make decisions. Scientists who have studied them say that the behavior of fungi becomes even more complex when they interact with living trees.

The symbiosis between mycorrhizal fungi and the trees they colonize requires continuous sophisticated two-way communication via chemical signals, which researchers say is akin to language. The patterns of chemical activity generated by the fungi can be understood as unique words, and some fungi have been found to have a vocabulary of about 50 “words.”

Information Sharing

In addition to sharing nutrients through these fungal networks, trees also share information with one another. Simard discovered that trees send “warning signals” to one another in the presence of danger. In one area she studied, Douglas firs were dying from beetle infestation, but the ponderosa pines living among them survived. So, in an experiment, Simard and her colleagues planted pine and fir seedlings together, to see what dynamic might be at work. She says that when researchers “stressed” the firs by defoliating them or introducing beetles to them, the firs naturally began producing defense enzymes. And then within 24 hours, so did the pines planted near them. This only happened, she says, when the two were linked with mycorrhizal fungi on their roots. So, Simard concludes that the firs were “warning” the pines of danger.

How do Plants Speak to One Another?

This National Geographic video illustrates the way trees communicate via the fungal networks. Those networks have been mapped by Simard and her colleagues, demonstrating the high degree of interconnectedness among forest trees, as well as the importance of the old-growth trees that are more highly interconnected with all the others around them.

Ecologist Monica Gagliano’s 2018 book Thus Spoke the Plant describes her research on the way plants “talk” to one another. She has pioneered the field of plant bioacoustics, which studies the unique “voices” plants use to communicate, as well as how they interpret and respond to sounds in their environment. It’s worth noting that Gagliano has received substantial criticism for her work, similar to the early reaction to Simard’s work. One particularly harsh reviewer of her book calls her work “nonsense,” and accuses her of “suffering from drug-induced psychosis” and “going off the deep end.”

Simard’s Academic Research

Simard’s research throughout the 1990s on these cooperative relationships in forests would ultimately take her from the Forest Service to academia, where she became a researcher and professor at the University of British Columbia in 2002. Along with her graduate students, she began a systematic study of the complex underground fungal networks to understand the dynamic at work and how much of the resource sharing might be intentional.

In this section, we’ll discuss Simard’s findings about Mother Trees, how this concept works to explain the relationships between trees, and the crucial importance of old-growth trees. Some of her key findings in this area are:

• Trees don’t just transfer nutrients back and forth in a linear relationship; they’re intertwined in a complex network, with older ones (Mother Trees) sustaining younger ones.
• Resource sharing is selective, with trees having the capability to “decide” when, with whom, and how much to share.
• Mother Trees give preference to their own offspring.

Mother Trees

Simard came to discover that trees are intertwined via fungus in a complex resource-sharing network, with the older ones being “hubs” and the smaller ones “nodes.” She compares this to an internet satellite system, which she refers to as the “wood-wide web,” with the hub trees dubbed “Mother Trees.” Mother Trees are the oldest and largest trees in the forest and are linked to the greatest number of other trees.

Simard found that although Mother Trees send nutrients to their whole interconnected community, they recognize and favor their own offspring. In experiments where older trees were planted with seedlings that were their own offspring and others that were unrelated, she determined that the Mother Trees transferred more nutrients to their offspring. It was this realization that the trees were taking care of their “children” that inspired Simard’s coining of the phrase “Mother Trees.”

Another notable discovery Simard made is that when a Mother Tree is stressed and facing uncertainty (from disease, dehydration, or lack of nutrients) it will increase the amount of nutrients it transfers to its kin. She says that when one of these old trees is dying, it will release all of its nutrients and energy at the end of its life to the next generation, just as humans pass on their resources to their children.

All of these findings, according to Simard, provide evidence that the transfer of nutrients isn't simply a byproduct of the fungi attaching to multiple trees. The trees transfer nutrients selectively in different amounts, at different rates and different times, with more going to their kin than to strangers. So, Mother Trees favor their offspring and kin, she says, but they also take care of the whole community, because they “know” that it’s also essential to their offspring's health. A healthy community and ecosystem is the best place to ensure one’s offspring will grow up healthy.

Public Response to the Mother Tree Concept

The concept of the Mother Tree has captured mainstream media attention and the public imagination. In response to this attention, in 2015 Simard created the website The Mother Tree Project, an online hub for research, news, and media coverage on the topic, including a periodic newsletter, and links to related resources.

The concept of Mother Trees has influenced popular culture as well. In his 2018 Pulitzer Prize winning novel The Overstory, Richard Powers used Simard’s life and her findings about Mother Trees as the basis for a plotline. Even more well-known is James Cameron’s movie Avatar, which used the Mother Tree concept as the basis for the “Hometree,” an ancient and enormous tree that sustained the life and connected the souls of the entire alien Na’vi tribe.

A New Approach to Forest Management

While Simard's ideas have caught the public imagination, they’ve been resisted by the forestry establishment, as they challenge the long-held dominant paradigm of forests as spaces of competition. Simard argues that this paradigm must change if we are to have healthy forests and sustainable practices. She says it’s crucial to recognize the cooperation and interdependence that happens in forests because the long-term health of those forests depends on those relationships.

The theory that clear-cutting destroys the natural relationships between trees has been a sticking point with people who believe the idea of trees having relationships is an idealistic “hippie” notion, as Simard says her perspective has often been characterized.

In this section, we’ll discuss some of the reasons Simard’s research might be difficult for some to accept, and her overall conclusions about the implications her research has for the future of forest management.

Materialism vs. Animism

Much of the resistance to re-thinking relationships among trees is likely due to the “materialist” worldview that characterizes the Western scientific perspective. A materialist approach sees the natural world as mechanistic and unconscious, and this is how we’ve been socialized to understand the natural world. In contrast, the “animist” perspective that tends to underlie indigenous cultural worldviews sees everything in nature as conscious and interrelated. Even though many human cultures have held animist beliefs throughout all of human history, the modern scientific establishment tends to outright reject it, often characterizing such beliefs as primitive and irrational.

Robin Wall Kimmerer, a botanist, author of the best-selling book Braiding Sweetgrass, and member of the Potawatomi Nation, describes an indigenous perspective on interacting with nature. She explains that the Potawatomi languages are based on a “grammar of animacy.” This means that those languages categorize everything into living and nonliving, and use word forms to indicate that. For example, one cannot speak of anything alive as “it.” Instead everything in nature is addressed the same way your family is addressed. Because, she says, they are our family. Kimmerer herself consistently uses “she” when referring to trees or the sweetgrass. She says that this animacy is built into the entire language; you would also not use the same verb to describe an airplane flying that you’d use to describe a bird flying. One is living and one is nonliving, so those would be considered different actions.

Moving Toward a Long-Term Vision

Simard suggests that one of the reasons it’s been so difficult for people to accept her findings is that they appear inconsistent with previous observations. She says this is because those observations have often been short term, and forestry research requires a longer-term commitment.

Forest experimentation takes a very long time, Simard points out, because trees grow slowly, and they live far longer than researchers. The Forest Service and the logging industry are both invested in fast-growing trees so they can replenish clear-cuts as quickly as possible. But Simard says that the emphasis on “fast” has caused them to overlook important factors that occur over the longer timeline of forest growth.

As discussed above, some of Simard’s research shows that cultivated trees in clear-cut plots fared better in their earlier stages of life. But later they declined in health, while the trees planted with companions outpaced them. In the past, policies were put into place based on those earlier observations, without awareness of the shifts that can happen later in the trees’ life cycle.

Simard explains that because forest growth is a long and slow process, researchers can use statistical models to predict future outcomes based on current data, so she had models made based on her research results. Those models show that forest growth declines with each successive clear-cut and re-planting. So one policy change she advocates for is a move toward a longer-term model for research.

(Shortform note: Many researchers in the natural sciences and anthropology are now advocating for incorporating indigenous knowledge systems into forest management practices. Indigenous peoples of the Amazon region, for example, have a deep ecological knowledge gained over centuries. A Brazilian research team is suggesting that incorporating generational knowledge into local ecosystem management practices has the potential to improve the practices and contribute to regeneration of endangered ecosystems.)

Competition vs. Cooperation

Another reason Simard’s research has been so strongly resisted over time, she says, is simply the tenacity of the long-held competition model and the way it reflects the cultural perspective it grew out of. Competition for resources has been the prevailing paradigm for understanding nature throughout the history of modern Western science. In fact, it’s the predominant model for understanding all relationships, including those in human societies and economies.

Simard’s research suggests that competition is not the defining nature of the relationship between the trees and other plant life; the major dynamic is cooperation. Next, we’ll look at how this cooperation model reflects a different view of nature, one that’s more consistent with our understanding of how our own bodies work, as well as with how some non-Western traditional societies function.

Anthropomorphizing the Trees

Some ecologists still critique Simard’s conclusions and emphasize the importance of recognizing competition in ecosystems. This seems to be a major ongoing battle of perspectives.

Simard has been accused of “anthropomorphizing” the trees, while simultaneously overemphasizing their cooperative nature. However, seeing trees as inherently competitive is more modern-human-like. Perhaps the scientists who can’t imagine trees having a symbiotic cooperative nature are more guilty of anthropomorphizing them.

In an interview, Simard says, “Our culture is not merely one of competition for scarce resources and the profits inherent in that scarcity. It is competition for competition’s sake…we compete aggressively just to do that, not for any gain.”

Forests as Organisms

In terms of how its components function interdependently, Simard concludes that a forest is essentially a single organism, like the human body. The mycorrhizal network between trees, she says, is similar to the neural networks in our brains, with the mycelium being the synapses along which nutrients, like neurotransmitters, travel. And like our brains, this is also a communication network that she says is “wired for wisdom, sentience, and healing.”

Of course there is some amount of competition and dysfunction in a forest ecosystem, Simard acknowledges, just like in our bodies. We get diseases, and if we’re nutrient deficient our various organs and cells may compete for those nutrients. But if the body is healthy, the major operational mode is cooperation between the parts. Simard says a forest operates the same way.

(Shortform note: Michael Pollan, author of The Omnivore’s Dilemma and The Botany of Desire, says that until recently, even mentioning the possibility that plants could have intelligence would get you labeled a “whacko.” However, he says that the latest research supports the idea. The relatively new field of plant neurobiology shows that plants process sensory data in much the same way humans do. While that processing doesn’t happen via a brain, plants have their own sensory systems, and Pollan says plants have all the same senses as humans. He concludes that intelligence is an inherent feature of life.)

Ecosystems as Societies

Of course, there are more than just trees and fungi in a forest; a forest is a complex ecosystem of diverse flora and fauna. Simard says we can think of the larger forest ecosystems as similar to human societies. They’re complex, self-organizing, and adaptive. And, importantly, she says they are intelligent.

Because ecosystems operate similar to human societies, this could explain why we find a prevailing paradigm of competition in the modern scientific worldview, and a paradigm of cooperation in the traditional indigenous worldview. Each paradigm is modeled after the society within which it develops.

Simard points out that objectifying nature, thinking of humans as separate from it (and even above it) is a modern Western construct, and reflective of a colonialist mindset. First Nations tribes of the region had a symbiotic relationship with the land and existed entirely within these forest ecological communities, rather than viewing them from the outside. She ties all of this into the pressing issue of climate change.

Climate change, she argues, is occurring in large part because of human activities, and these activities are the product of a mindset that has moved away from viewing nature as living, sentient, and sacred, toward a mindset that can’t even imagine trees as sentient beings that have relationships. This, Simard argues, needs to change. Only when we recognize the forests as alive and intelligent will we have the wisdom to recognize that we must honor them, because our lives depend on it.

Should Trees Have Rights?

The idea that humans have an inherent right to dominate nature can be connected to the Christian notion of God giving humans “dominion” over the Earth. Alternatively, some Christians consider humans “stewards” of God’s creation, however this still sets humans apart from nature, and puts us at the top of a paternalistic kind of hierarchy. This perspective is being increasingly challenged by research like Simard’s as well as by environmental movements, like the “deep ecology” movement.

While the idea that trees have intelligence is still controversial in the scientific community, it’s by no means a new idea. In The Earth People Philosophy, Lakota elder Wallace Black Elk said in 1991 to anthropologist William S. Lyons: “The trees talk. They have a language of their own. So all this green that you see, they communicate…each one of the winged-people has a song….every creature has a song. Even that spider…he walks, he rolls, he flies, and he sings a song….so I want to tell you that you have a lot to learn.”

In a 1972 book Should Trees Have Standing? environmental scholar Christopher Stone proposed the idea that trees, oceans, rivers, and other nonhuman living beings in nature should have legal personhood and all the protections that entails. Considering what we now know about plant life, perhaps it’s time to revisit that question.