The Fascinating Social Network of Trees: The Wood Wide Web
Discover why you will never see again any tree as an isolated individual.
Scientists now agree: we can no longer think of trees as isolated life forms. In fact, we must understand them as communities that are connected by a complex set of ecological relationships.
An incredible feat that’s invisible to the naked eye
Trees are closely linked to other organisms of the same species — and those of different species, too. We know of many examples of this kind of relationship. For instance, dead tree roots harbor larvae such as that of stag beetles, which can feed on fallen timber for up to eight years before reaching their adult form. Or consider the colonies of ants that nurture aphids on the leaves of deciduous trees in order to extract the sweet honeydew produced by these small insects — albeit at the expense of the tree itself.
And there’s much more. Amid the soil and tree roots, millions of bacteria and fungi species exchange nutrients, forming a vast network of interconnected organisms that runs all the way through the forest. Trees are vitally intertwined with fungi, which enable them to transmit and absorb nutrients through their roots. The fungi gather minerals as they move through the soil, extracting and drilling all kinds of particles from mineral-rich soil rocks — a task made easier by microtubules that extend deeper than any tree root. In return, the tree delivers 20–80% of its carbon to the fungi, an essential food source required by the fungus to build its composition, given that it can’t perform photosynthesis or consume CO2 itself.
The most extensive relationship on earth
All over the world, a large amount of research is being carried out into the communication that occurs between trees above and below the ground. From the early 90s, Kristina Arnebrant and others in Sweden were showing evidence that alder and pine trees exchange nitrogen-based nutrients through a shared network of mycorrhizae (the name given to the symbiotic association between tree roots and fungi).
In 1997, Suzanne Simard, Professor of Forest Ecology in the Department of Forest and Conservation Sciences at the University of British Columbia, published her thesis showing that Douglas fir and paper birch were using mycelial networks to transfer carbon between each other. Over the course of a summer, Simard studied how firs in shaded areas received carbon from birches that were positioned in the sun. The opposite happened in the autumn — the birches received carbon from the firs as they began to lose their leaves. The researcher discovered that this exchange takes place underground through a ‘mycorrhizal network’, a symbiotic relationship between a fungus and the roots of its host plant.
This highly evolved, mutually beneficial relationship observed between fungi and plants is one of the most widespread and ecologically important mutualisms on earth and the most extensive relationship known.
The wood wide web
In this two-way relationship, fungi provide nutrients and water to plants and, in turn, receive carbohydrates. The fungus, however, is just the fruiting body of a much larger mycelium — an underground network of root-like fibres that can grow to be many kilometres long. Fungi are reproduced by spores when they germinate, and this produces a mass of single-celled, thread-like structures called hyphae, collectively known as mycelium. Often referred to as ‘the web of life’, these mycelial networks transport and deliver nutrients to other plants that need them. Although it is generally invisible to the naked eye, mycelium is practically everywhere. It permeates almost all of the landmasses on our planet, where just one cubic centimetre of soil can contain more than 5 km of mycelial cells.
Mycelia transmit information through their vast networks using the same chemicals as the neurotransmitters in our brains. A fungus can form mycorrhizae with more than one plant at a time, thereby establishing a connection between two completely different plants and generating the underground networks that facilitate communication and cooperation among trees. The connections are made by strands of fungi that grow in and around the roots of plants, which are also responsible for the production of many of the forest fungi that are familiar to us.
So closely are trees bound together by these connections that, the more you know about this underground network, the more difficult it becomes to see any tree as an isolated individual.
This network of infinite and interwoven fungi threads and roots that connect trees is referred to as a mycorrhizal network or ‘wood web’.
The secret underground network between trees
The mycorrhizal symbiosis between soil and terrestrial plants is considered by scientists one of the most widespread and ecologically important mutualisms on earth. Some trees, which scientists have coined mother trees, use this network to provide sugar to smaller trees growing under their canopies. Meanwhile, trees can alert each other to dangers like insect infestations, and diseased trees use the network to offload valuable nutrients to other neighbouring trees. Other species, such as the walnut tree, can release toxins via the wood web, while some types of tree can even sabotage their rivals. Similarly, plants like orchids are able to hack into these networks to obtain nutrients.
A social network nearly 500 million years old
We know that mycorrhizal fungi and the plants that they connect are very old. But now, we have found that these connections are deeper than they originally thought. Scientists believe that the evolution of mutualisms formed by the the soil microorganisms that form a symbiosis with 80% of terrestrial plants and form arbuscules, vesicles and hyphae within the cortical cells of plants they colonize (arbuscular mycorrhizal root), played an extraordinary role in facilitating the colonization of land by plants about 500 million years ago. Near the village of Rhynie in Scotland, researchers have found traces of arbuscular mycorrhizae associated with plant fossils dating back 407 million years
As we advance our understanding on how this network functions, new questions arise surrounding where these species begin and end, the meaning of their communication and the exchange that occurs between living things and plants.
For researchers like Suzanne Simard, the forest appears to function as a single organism. After meticulous study, Simard and her team of international botanical experts were able to uncover the initial outlines of this very fine, intricate structure made up of multiple layers and dimensions, as well as discerning its possible connection to other networks.
A new way of looking at trees and forest
These findings leave us with more to think about the ubiquitous and vital fungi that wind through every environment on earth. As the decomposers — and, therefore, the food suppliers — these fungi play a fundamental role in most terrestrial ecosystems. Without mycelia, no plant community could exist.
When we think of forests, we can no longer simply imagine a group of trees. Now we can appreciate that the core of the forest is actually below ground. But not only do trees communicate about the needs of others through their shared roots, but also through smells, sounds and signals. What’s more, this doesn’t just occur in one direction — researchers have now discovered that two-way communication exists.
There is a long tradition of studying how species interact among ecologists, but until the last 10 years much of the work was focused on networks involved in a single form of interaction, or recently, mutually beneficial interactions, such as those between insect pollinators and flowering plants. For biologists, many questions about the social network that connects plants remain unanswered.
Nevertheless, one thing is certain: the interconnection between organisms in ecosystems is even deeper than scientists had ever imagined. It seems we still have much to learn about what exchange or even ‘friendship’ can mean between plants and other organisms.
Questioning the extent of our understanding
The models and metaphors that inspire us and help us to navigate the world can also restrict us. Through the studies of these scientists, we’re learning to see things differently. And as such, we’re now beginning to unravel and lay bare a secret of the earth that has always been invisible: the heart of the ecosystem that lies beneath layers of the forest. Seen in this new light, a forest is more than just a collection of trees. The forest is a territory, a multidimensional multiplicity powered by an intricate rhizomatic network. Inside it, all kinds of creatures are connected, and coexist, cooperate and give back to benefit the forest as a whole. This new way of looking at trees and forest is giving scientists a better understanding of the ecological, evolutionary, and coevolutionary processes that shape these networks and how they may respond to future changes.
Without a doubt, the implications of the wood wide web will prompt us to reconsider how we relate to beings that do not have nervous systems.
We must think about the possibility of kinship and collaboration that exists in an infinite network of connections, reevaluate the notion of common ground and fundamentally question the extent of our understanding of life interconnectedness.
Now that many of us have to remain enclosed at home, we might be also sensing more than ever the forest within our minds.
Next time you have the chance to step into a forest, I encourage you to celebrate the opportunity to be embraced by this powerful and extraordinary dynamic architecture . And remember this: there is a forest within that forest, whispering above and below your feet.
“The fascinating social network of trees” is an excerpt from the original text: All life is profoundly interconnected, from “The Human In Us: The creative process of being Human” by Macrina Busato.
