The Longest Game of Telephone Happens Right Beneath Our Feet: How Trees Utilize an Underground Network (Mycorrhizae) to Communicate
Typically when we enter a forest, we are captivated by the rustling, towering canopy and diverse wildlife. But what lies underneath? Many scientists theorize that trees “chat” with one another via mycorrhizae, a network of symbiotic mycelium that reside at the root of plants.
When we see mushrooms, we are observing the fruiting body of fungi; whereas mycelium is the underground, connective portion of fungi.
In exchange for carbon produced by photosynthesizing plants, mycorrhizae increase the bio-availability of nutrients to the plant. Elements such as zinc, iron, aluminum, and phosphorous are necessary for plant growth, but plants struggle to absorb these elements due to the physical limitations of their roots and insoluble nature of these compounds in soil. Mycorrhizae expand the territory of plants underground and help break down the insoluble soil compounds so that the plant, or tree, can absorb more nutrients at its roots.
What does this have to do with tree communication? Well, researchers theorize that trees communicate between one another using a kaleidoscopic network of mycorrhizae called the Common Mycellium Network. It is via this network that plants often direct “messages” to other plants.
For example, select species of trees (Pine, Camphor, and Eucalyptus among many others) maintain gaps between their canopy and neighboring tree tops, a phenomenon called “crown shyness”. As these trees grow they emit negative allelochemicals to create physical boundaries. Negative allelochemicals (aka “plant poisions”) are growth inhibiting metabolites that restrict neighboring plants from encroaching on the emitter plant’s space. When mycorrhizae are present, plants emit negative allelochemical to other plants in competition for territory more effectively. Researchers demonstrated an increase of “plant poisions” in targeted plants downstream of MCN supported allelochemical producing emitters compared to plants that were not connected by MCN.
Scientist disagree on the extent to which mycorrhizae are driving tree-to-tree interactions. There is even discussion on the potential for harm when describing tree-to-tree interactions as “talk”. Although plant-mycorrhizae relationships are well documented, they are not completely understood.
However there is a global industry ($6.4 billion in North America agricultural sector alone) seeking to understand the mechanisms of mycorrhizae on plant health. These findings further inform agricultural products, natural disaster mitigation (think:stronger trees decrease erosion after super-storms, early activation of conifers responses to drought stress, and halophytes (salt tolerating plants) halophyting!).
Many theories explaining the specific roles of mycorrhizae in forestry are based on short-term studies or data from lab simulations. Even when field biologist are able to observe a stand of trees over the course of years, it only accounts for a fraction of the lifespan of mature trees. Therefore creative, full bodied research design is essential to assesses which variables are dependent upon another in the natural world.
Scientists introduced tree-fungi interactions to the global stage in the 1980s, when tree canopy scientists uncovered the “8th continent”, a term dubbed due to the unprecedented biodiversity found living in the canopy. Dr. Meg Lowman, CEO of TREE Foundation, was among pioneering scientists discovering a correlation between tallest and biggest trees and mycorrhizae in the Australian Rain forest. Her exploration into the upper levels of the forest canopy (prior to Meg’s research field biology was done on foot at the ground level) prompted more holistic understanding of forestry and interpretation of data. A recent 2021 study conducted by scientists in Europe illustrates a similar correlation between tree height and mycorrhizae presence.
Today our tool belt for research includes mathematical modeling and AI. Although these tools are great for meta analysis, they are still dependent on in-field data collection and research methods.
So as the Wood Wide Web continues to spark debate, scientists agree that more research is necessary so that we can truly understand tree forests, its canopies, and its unsolved mysteries. Until then we will marvel at the beautiful world of trees we can see.
