by Valentina Lagomarsino
figures by Hannah Zucker

When scientists first studied the structure of nerve cells that comprise the human brain, they noted their strong resemblance to trees. In fact, dendrites, the term to describe projections from a nerve cell, comes from the Greek word Dendron, for “tree.” While the connection in the appearance of nerve cells was made to trees, the comparison may have been more apt than originally realized: scientists are starting to uncover that trees have their own sort of nervous system that is capable of facilitating tree communication, memory and learning.

Forests are complex systems

Forests cover 30% of Earth’s land surface and hold over a billion trees. Forests are known as “carbon sinks” because trees absorb carbon dioxide from the air, store the carbon in their trunks, and exhale oxygen. Scientist have leveraged this property to measure the ratio between two naturally occurring forms of carbon (12carbon and 14carbon) to assign an age to trees, a technique termed carbon dating. Using this technique, scientists found that trees living in forests, like the tree colony called Pando, tend to live longer than trees living in urban environments, often in isolation. Dendrologists, scientists who study wooded plants, thought that perhaps trees that lived together were helping each other by sending resources through their roots. To test this out in North American forests, dendrologists utilized a technique called isotope tracing. In this experiment, scientists injected carbon dioxide gas replaced with radiolabeled 14carbon into the trunk of Birch trees (Figure 1). When nearby Fir trees were covered by shaded cloth, to block their ability to acquire nutrients through photosynthesis, scientists found a higher level of radiolabeled 14carbon in their trunk, meaning they must have received sugars from the Birch. These experiments confirmed that trees are indeed communicating with each other and sharing nutrients through their roots, forming a complex system sometimes referred to as the “wood wide web.” 

Figure 1: Isotope tracing. Birch trees (left) were injected with radiolabeled 14carbon dioxide gas. Fir trees (right) were shaded by a cloth to block their ability to perform photosynthesis and generate sugars from the sun. After a few hours, scientists measured radiolabeled 14carbon in the roots of Fir trees and discovered a high amount of 14carbon.

With a little help from my friends

This complex network connecting trees is dependent on a symbiotic relationship with microbes in the soil like fungi and bacteria. Symbiosis is when two separate organisms form a mutually advantageous relationship with each other. Fungi can cover a large surface area by developing white fungal threads known as mycelium. Mycelium spreads out on top of tree roots by up-taking sugars from the tree and by providing vital minerals back to the tree, such as nitrogen and phosphorus (Figure 2). This symbiotic relationship between tree roots and fungi is known as the mycorrhizal network (from Greek, Myco, “fungi” and Rhiza, “root”).

Figure 2: Symbiosis. Trees have a symbiotic relationship with microorganisms in the soil, like fungi. Fungi form white thread like colonies on tree roots as seen in the panel on the right. Trees give carbon to the fungi in the form of sugar and in return fungi give the trees essential minerals such as nitrogen and phosphorus.

To identify the species that constitute the mycorrhizal network, scientists have utilized recent technological advances in DNA sequencing and big-data analysis. Microbiologists have identified different species of fungi and bacteria that form symbiotic relationships with different species of trees. Scientists believe all trees have a mycorrhizal network, but trees only communicate with each other if the fungal and bacterial species that constitute their mycorrhizal networks are the same. The most common combination of fungi constitute the arbuscular mycorrhizal (AM) network, which has been found to be important for nutrient uptake in 65% of all trees and plant species. The remaining 35% of tree and plant species may have combinations of other fungi varieties that comprise their networks.

By investigating the different interactions between species of trees, scientists found that trees leverage similarities and differences in their microbial “makeup” to recognize other trees of their own species, and they preferentially share nutrients with them through their mycorrhizal network. This behavior, known as “kin recognition,” was recently explored when multiple families of Douglas Fir trees were planted in a plot and carbon tracing experiments indicated that trees of the same family shared more carbon than between trees of different families. Scientists are still investigating why this is happening, but it is hypothesized that all plants evolved to have kin recognition for reproductive purposes. Similarly, there is cross-talk between different species of trees that share the same mycorrhizal network, such as between Birch and Fir trees (Figure 3). Interspecies tree communication has been shown to increase the fitness and resiliency of trees.

Mycorrhizal networks are extremely important for tree health during times of danger. Certain species of fungi can facilitate tree resilience to certain environmental stressors such as predators, toxins, and pathogenic microbes that invade an ecosystem. By using a technique called allelopathy, in which a chemical signal is sent through the mycorrhizal network, trees can warn their neighbors about an invasive predator or to inhibit growth of invasive plant species. Surrounding trees can then defend themselves by releasing volatile hormones or chemicals to deter predators or pathogenic bugs. It was even found that trees can send a stress signal to nearby trees after a major forest disturbance, such as deforestation.

Figure 3: Mycorrhizal Networks. Trees communicate with other trees through their mycorrhizal network. Trees who share a mycorrhizal network, like the Birch (left) and Fir (right), are able to send nutrients to each other or signal to each other in times of stress.

Climate change affects the microbiome of the forest

Trees rely on a healthy forest ecosystem to thrive and protect themselves from danger. Humans rely on a healthy forest ecosystem to be able to inhale clean oxygen. Last year, millions of people around the world experienced the devastating effects of climate change. Not only is climate change impacting human health and wellbeing, but it is also affecting the ecosystem of our oceans and forests. Human-initiated deforestation contributes to climate change by reducing the number of trees that are available to soak up carbon dioxide. Deforestation not only removes the trees that are being cut down, but also impacts trees that are still alive by disrupting the mycorrhizal network that is important for intra-tree communication.

Changes in climate, as seen through increased droughts and extreme temperatures, may further disrupt the biodiversity of the microbes in the forest. This decline in biodiversity is known as human assisted evolution, or “unnatural selection”. The altered microbiota of the forest may then change the nutrients that trees are able to receive and we may start seeing changes in tree morphology, particularly in the shape of leaves. This would change the photosynthetic capacity of the tree; for example, smaller leaves have less surface area for light absorption, which will negatively impact their ability to absorb the sun’s rays and produce sugars through photosynthesis. This could potentially inhibit tree growth and the amount of carbon that trees can share with fungi. Furthermore, without a biodiverse mycorrhizal network, trees are becoming more susceptible to destruction from invasive, harmful insect species. It is clear that the impact we are making on the environment is self-perpetuating and heading in a dire direction for the health of our forests, but there is still hope. Some scientists are trying to combat climate change by using gene-editing techniques to restore ecosystems that have become extinct and by engineering synthetic microbes that are important for a thriving ecosystem.

Trees are considered to be the oldest living organisms on the planet. Over centuries, they have been resilient to changes in their environment due to their symbiotic relationship to fungi and other microbes. There are so many more discoveries to be made to understand the ancient wisdom of our forests and the invisible microbes that keep our ecosystems in harmony.

Valentina Lagomarsino is a first-year PhD student in the Biological Biomedical Sciences program at Harvard University.

Hannah Zucker is a second-year PhD candidate in the Program in Neuroscience at Harvard University. 

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17 thoughts on “Exploring The Underground Network of Trees – The Nervous System of the Forest

  1. My fave book on this subject is The Global Forest — early/ first; profound/ deeply- felt; an example how humans can optimally communicate — Wohlbein/ Simard? secondary quality.

    The Global Forest: Forty Ways Trees Can Save Us
    by Diana Beresford-Kroeger | May 13, 2010

  2. I live in house for 3 years. Wonderful trees sprout from ground and grow fast. If I did not pull out when small they would cover whole yard. Why can such a tree be used to help the planet. They spread only underground. Cannot be planted. Is this common or uncommon? I wonder if no one has thought about about this or if anyone has interest I would love to talk. The leaves shed every year and the beautiful single three feet long fall to ground. Today I looked for an old stump from previous owner that had chopped tree down to stump. But I could not see stump anywhere so the tree may have grown back from what was an ugly stump (stump now gone). Is this possible? How many other types of trees can grow back this way?

  3. Exploring the underground network of trees and the interconnectedness of the forest ecosystem is a fascinating and important area of study. It reveals the complex communication and cooperation that occurs between trees and other organisms, highlighting the importance of preserving and protecting these natural environments. Understanding the nervous system of the forest can also provide insights into how we can better manage and sustainably utilize our natural resources.

  4. So I had a Shamanic Journey about sending healing energy through this Wood Wide Network to people & places miles & miles away. Quite a vision. I’m curious about thoughts on this if anyone is familiar with Energy Medicine work.
    🙏🙌🏼🌲🍄⚡️ 🍄 🌲🙌🏼🙏

  5. A related book is “Finding the Mother Tree” by Suzanne Simard who conducted most of the basic research on forest mycorrhizal networks in British Columbia. She deserves most of the credit for the science.

    But there is also another interpretation of the science that is not presented by either Simard or Wohlleben. In this view, rather than being the passive “pipes” through which trees pass water, nutrients, and messages, the mycorrhizal fungi are the primary actors. Recall that a lichen is an obligate symbiosis between a fungus and an alga. The alga photosynthesizes and provides carbohydrates to both the fungus and itself. The fungus takes up water tightly bond to mineral substrate, as well as other necessary nutrients, and provides them to both the alga and itself. In a similar way, one can view the forest mycorrhiza and the trees in a flexible symbiosis, with the trees playing the pat of the algae in a lichen. It is in the fungus’ selfish interest to maintain healthy photosynthetic partners. From the fungus’ point of view “source trees” are not “sending” carbohydrates, water, or other signals to “sink trees,” the fungus is altering its distribution of these things in ways that maximize its own fitness, optimally maintaining its photosynthetic partners. The trees are not the “wise” partners from this point of view, the fungi are. All of the observations and experimental results remain true, but this interpretation places stress on the role of the fungi and is a little less “romantic” regarding the “wisdom of the forest.”

  6. If you like this then, as a layman, I advise you read a book now out that is written by a Professor of Forest Ecology at the University of British Columbia. It’s her first book, and I think it is an important contribution to the burgeoning idea that Tree’s are communities and intelligences in their own right. It seems in many ways that as short lived buzzing flies are to us, we are to Tree’s. Kind’a sort’a. Buzz buzz? 🤣🤣

    Anyway the book is entitled “Finding the Mother Tree, Discovering the Wisdom of the Forest,” by Suzanne Simard.

    Get it. I think you will like it.

      1. I loved this article. Have been traipsing through old growth 65 years. Was a bit disappointed in the lack of mathematical rigor, though, when reading there are over a billion trees on the planet. Neither the authors or readers corrected that error.

    1. Actually, Suzanne Simard (author of Finding the Mother Tree) is one of the scientists that conducted several of the experiments described in the original article here.

  7. This is soooooo cool!!!! I’d like to know how the communication actually works tho. Like how do the trees communicate with the mycorrhiza? Also how do trees recognize similarities and differences between the fungi around their roots? How does the transfer of nutrients work? Does the fungus decompose organic matter around the roots? At the beginning of the article it also said that trees have their own nervous system in a way and that it was capable of learning and having memory. Is there any information about that?
    I really liked the connection between urbanization and climate change and the damage of the networks. This really reminds me of the movie Avatar with the Na’vi. It reminds me about how all of the nature there was connected and the trees had memories and connections through the whole jungle. I think it would be amazing to study an area like a jungle that has barely been touched by man and see the difference in the way that the fungus and trees interact. Also it would be interesting to see the size of the mycorrhiza networks. I think understanding the connection between plants is very important. I think that it could unlock a lot to helping to stop climate change and improve the interaction we have with our environment. This could create better agricultural methods that could improve yield and reduce impacts on the soil. I’d be interested in leaning how crop rotation would affect the network. If each year a farmer were to match different species of mycelium and plants would that be worse for the plants? I’ve never commented on a website before so idk how this works or if this is a bit much. I was just so excited about everything that I learned and all of the questions that I still had. Thank you so much for posting this. I’m looking forward to leaning more!

    1. Hey Ed,

      Thanks for your thoughtful comments!

      I highly recommend a book by Peter Wohlleben: “The Hidden Life of Trees: What They Feel, How They Communicate.”
      It highlights a lot of research he did in a relatively untouched forest in Canada.
      The transfer of nutrients and communication is by chemical molecules, much like neurotransmitters in our nervous system (which are now thought to have evolved from molecules microorganisms generate).

  8. This article is well written and informative. I’m just curious about the interest a neuroscientist and biologist have in this mycorrhizal network.

    1. See also:
      “‘Biocentrism’ How Life Created the Universe – Technology & Science – Science _ NBC News.Htm [‘Biocentrism’ How Life Created the Universe – Technology & Science – Science _ NBC News.Htm – 2016-06-16.Txt – Original Search] https://Nortonsafe.Search.Ask.Com/,” n.d.
      I have been interested in the universal connections in life, since time immemorial.
      Michael Clark – CDN

      1. This says it all for me. There is a common pattern and connection between everything. The examination of the similarities often brings about a greater capacity for understanding how Science as a whole, is a collaboration. I’m not a Scientist but I find that this kind of study has implications for understanding many things in life.

    2. This could scientifically explain the mass change in consciousness. The earth could be using the same means to send the warning to humans. We are in a since like a micro ion the planet. This would connect science to PSI studies as well as the psychological field and be the missing link between quantum physics to say cosmological physics. The change in our perception could be the event horizon. It definitely has not been done before. Which mean it has a higher statistical rate of success.

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