The Wood Wide Web: How Trees Talk to Each Other

An academic exploration of the underground mycorrhizal networks that connect forest trees — covering the science, the key researchers, the remarkable discoveries, and the ongoing scientific debate about how much trees truly communicate.

The Wood Wide Web

Underground Networks, Hidden Communication, and the Social Life of Forests

The Path Ahead

Rethinking the Forest

Resource Exchange & Defence

The Discovery: Suzanne Simard

The Scale of Connection

How Mycorrhizal Networks Function

Scientific Debate & Critique

Mother Trees: Hubs of the Forest

Implications & Takeaways

For Centuries, We Misunderstood Forests

Forests were long viewed as collections of individual trees locked in competition for sunlight, water, and nutrients — a Darwinian struggle where each organism fights alone. But research over the past three decades has revealed a fundamentally different reality: an underground network of communication and resource sharing that connects trees into a single, interdependent living system. This network, formed by mycorrhizal fungi, challenges the reductionist, excessively competitive vision of the forest and replaces it with something far more complex — and more hopeful.

Sources: 2, 7

Let us begin with the paradigm we are overturning. For centuries — really, since the birth of modern biology — forests were understood through the lens of competition. Every tree was an individual, struggling against its neighbours for light, water, and soil nutrients. This view made intuitive sense: you can see the race for the canopy with your own eyes. But starting in the 1990s, a series of discoveries began to complicate this picture. Researchers found that trees of different species were physically connected underground by fungal filaments. And these connections were not passive — they were conduits. Carbon, water, nutrients, even information was moving from tree to tree. The forest, it turned out, was not a warzone. It was a community. This conceptual shift is at the heart of everything we will discuss today.

03

The Discovery

Mycorrhizal Fungi: Nature's Underground Internet

The term 'mycorrhizal' comes from the Greek mykós (fungus) and riza (root). These fungi form a dense mat of microscopic filaments — hyphae — that colonise tree roots and extend far into the surrounding soil. The hyphae of a single fungal network can connect dozens of trees, sometimes across different species, creating a physical infrastructure for chemical exchange. An estimated 90% of all land plants participate in these networks. The symbiosis is ancient: fossil evidence dates the mycorrhizal relationship to approximately 450 million years ago — around the time the first plants colonised land.

Sources: 1, 5

So what exactly is this network? At the physical level, it is remarkably straightforward — and yet its implications are profound. Mycorrhizal fungi are thread-like organisms that grow in and around the roots of plants. The word itself tells the story: 'myco' for fungus, 'rhizal' for root. These fungi are not passive passengers; they are active trading partners. The fungal hyphae — microscopically thin filaments — penetrate tree roots and extend outward through the soil, sometimes for metres. When hyphae from the same fungal organism encounter roots from different trees, they create a physical bridge. Suddenly, two trees that appear separate above ground are linked below. And here is the staggering figure: roughly nine out of every ten plant species on Earth form these associations. This is not a niche curiosity. This is the norm. And it has been the norm for four hundred and fifty million years — since before the dinosaurs, since before the first vertebrate walked on land.

Mother Trees: The Elders That Sustain the Forest

Older, larger 'hub' trees function as central nodes — recognising kin, nurturing saplings, and directing resources to where they are most needed.

Sources: 4, 11, 12

At the heart of Simard's research is a concept that has captured the public imagination: the Mother Tree. In a healthy forest, not all nodes in the network are equal. The oldest, largest trees — what Simard calls Mother Trees or hub trees — serve as the central anchors of the mycorrhizal network. They are connected to hundreds of other trees around them. Simard's research shows something remarkable: these Mother Trees can recognise their own offspring — trees grown from their seeds — and preferentially channel carbon and nutrients toward them. They appear to reduce their own root competition to make space for their kin. When a Mother Tree is dying, it can dump its remaining resources back into the network, a kind of last transfer to the community it has sustained. This is not anthropomorphism — it is a measurable pattern of resource allocation, demonstrated through isotope tracing in the field. The implications for how we manage forests — particularly how we log them — are profound and deeply consequential.

A Two-Way Exchange: What Flows Through the Network

What Trees Contribute

The Fungal Fee

Carbon-rich sugars from photosynthesis — the primary energy currency of the forest. Trees also share water during drought stress and emit chemical defence signals when under attack by pests or pathogens.

Mycorrhizal fungi retain approximately 30% of the sugar that connected trees produce. In exchange, the fungi mobilise phosphorus, nitrogen, and other mineral nutrients from the soil — resources tree roots cannot access alone. It is a mutualistic bargain 450 million years in the making.

Sources: 4, 6

Let us now examine what actually moves through this network — the currency of the underground economy. On the left, we see what the trees contribute. Through photosynthesis, trees fix atmospheric carbon into sugars. Some of that sugar is not used by the tree that produced it — it enters the mycorrhizal network and travels to other trees. This is not trivial: carbon transfer between trees has been tracked using radioactive isotopes, confirming that the movement is real and measurable. Trees under drought stress can also receive water through the network. And when pests attack, chemical warning signals travel through the same channels. Now, why would fungi facilitate all this? They are not altruists. On the right, we see the answer: the fungi retain roughly thirty percent of the sugar flowing through the network as their payment. In return, they provide the trees with something equally valuable — access to soil nutrients, particularly phosphorus and nitrogen, which fungal hyphae can extract from soil pores far too small for roots to penetrate. This is mutualism — both parties benefit. Neither is being exploited. And this arrangement has been stable for four hundred and fifty million years.

An Early Warning System Beneath the Soil

When a tree is attacked by insects or a pathogen, it releases chemical distress signals into the mycorrhizal network — a molecular alarm. Neighbouring trees that receive these signals respond by upregulating the production of defensive compounds, such as tannins and volatile organic compounds, priming their immune systems before the threat reaches them. This inter-plant signalling transforms the forest from a collection of vulnerable individuals into a coordinated defensive front.

Sources: 2, 6

One of the most compelling functions of the Wood Wide Web is its role in forest defence. Imagine this scenario: a bark beetle lands on a pine tree and begins to burrow. The tree detects the attack and immediately releases chemical signals — volatile organic compounds and other distress markers — into its tissues. Some of those signals enter the mycorrhizal network and travel through the soil to neighbouring trees. Those neighbours, upon receiving the signal, begin producing defensive chemicals pre-emptively. They ramp up their immune systems. They are not yet attacked, but they are preparing — and this preparation can mean the difference between survival and mortality. The network, in other words, serves as an early warning system. It is not a conscious warning in any human sense — trees do not have brains — but it is a functional signal that produces a defensive response. And it illustrates a crucial point: in a connected forest, no tree faces a threat entirely alone.

90%

An Almost Universal Connection

of all land plant species form mycorrhizal associations — this is not an exception; it is the rule governing terrestrial plant life

Sources: 1, 5

I want to pause here and let the scale of this sink in. Ninety percent. Nine out of every ten plant species on land form mycorrhizal associations. This is not a rare symbiosis found in a few obscure ecosystems. This is the dominant mode of plant life on Earth. When you walk through a forest, a meadow, or even a suburban garden, you are walking above a living network. The mycorrhizal symbiosis is also extraordinarily ancient: the fossil record places its origin at around four hundred and fifty million years ago, coinciding with the moment plants first colonised terrestrial environments. In fact, many paleobotanists now believe that plants could not have colonised land at all without fungal partners — that the mycorrhizal relationship was not an optional add-on, but a prerequisite for terrestrial plant life. The Wood Wide Web, in other words, is not a recent discovery about forests. It is a discovery about the deep history of life on Earth.

How Much of the Story Is Scientifically Settled?

A 2024 paper in PNAS and critiques by Karst et al. argue that evidence for substantial and ecologically decisive net resource transfer between adult trees under natural conditions remains limited. Many claims about tree 'communication' and 'parental care' may reflect anthropomorphic overinterpretation. Yet even the most critical reviews acknowledge that functional common mycorrhizal networks exist and that carbon movement between connected plants has been demonstrated. The debate concerns magnitude, ecological significance, and the language we use — not whether trees are connected at all.

Sources: 7, 8, 9

I would be doing you a disservice if I did not address the scientific debate surrounding this topic. In recent years, a number of researchers have pushed back against what they see as an overinterpretation of the Wood Wide Web evidence. Justine Karst and colleagues published a critical review suggesting that many commonly cited claims — particularly about substantial net resource transfer between adult trees — rest on limited or context-dependent evidence. A 2024 paper in the Proceedings of the National Academy of Sciences made similar arguments. The critics make an important point: demonstrating that carbon can move between trees in a laboratory or a manipulated field plot is not the same as demonstrating that this movement is ecologically decisive in a natural forest. And some of the language we use — 'communication,' 'parental care,' 'warning' — carries anthropomorphic baggage that may mislead as much as it illuminates. However, and this is crucial, even the strongest critics do not dispute that functional common mycorrhizal networks exist, that carbon and other compounds can and do move through them, and that these networks are ecologically important. The debate is about how much, under what conditions, and with what consequences. Good science lives in this tension — between the exciting finding and the rigorous critique.

10

Rethinking the Forest

Let me close with a reflection on why this matters — beyond the science, beyond the debate. The Wood Wide Web is conceptually important because it challenges a deeply ingrained narrative: that nature is fundamentally competitive, that every organism is an island, that the strong survive and the weak perish. This narrative has shaped not just ecology but economics, politics, and culture. What the mycorrhizal network reveals is that cooperation, interdependence, and mutual aid are not recent human inventions — they are ancient, biological, woven into the very fabric of terrestrial life. Forests are not collections of individuals. They are communities. They are systems. And understanding them as such changes not only how we study them, but how we manage them, how we conserve them, and how we relate to the living world. The trees have been talking to each other for four hundred and fifty million years. We are only just beginning to listen.

References

[1] The Wood Wide Web: How trees secretly talk to and share with each ... — thekidshouldseethis.com [2] Understanding the Wood Wide Web - EcoMatcher — ecomatcher.com [4] Underground Networking: The Amazing Connections Beneath Your ... — nationalforests.org [5] Mycorrhizal network - Wikipedia — en.wikipedia.org [6] Inter-plant communication through mycorrhizal networks mediates ... — pmc.ncbi.nlm.nih.gov [7] Wood Wide Web: The underground network that connects trees — boscum.com

[8] The wood-wide web: A story too good for its own good? — gabepopkin.substack.com [9] Where the 'Wood-Wide Web' Narrative Went Wrong — undark.org [11] Suzanne Simard interview: How I uncovered the hidden language of trees | New Scientist — newscientist.com [12] 'Mother Tree' Ecologist Suzanne Simard Shares Secrets Of Tree Communication : Shots - Health News : NPR — npr.org Trees communicate with each other through astonishing networks | EcoTree — ecotree.green Suzanne Simard - Wikipedia — en.wikipedia.org

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