The Wood Wide Web: How Forests Think as One

In 1997, a young ecologist named Suzanne Simard published a paper on the cover of Nature that quietly rewrote everything we thought we knew about forests. The paper was titled “Net Transfer of Carbon Between Ectomycorrhizal Tree Species in the Field,” and its core finding was simple, radical, and beautiful: trees share food with each other through underground fungal networks.

Simard had grown up in the logging forests of British Columbia, watching her grandfather and father selectively harvest trees in ways that kept the forest alive. When she entered forestry school, she was trained in the prevailing paradigm: trees are individuals competing for resources. Forests are battlefields. The job of a forester is to remove the competition — clear-cut everything and replant with a single commercial species.

But what Simard saw in the forest did not match the theory. When foresters clear-cut birch trees to reduce “competition” for the commercially valuable Douglas fir, the fir seedlings did not thrive. They got sicker. They died in greater numbers. Something about removing the birch was killing the fir. The textbooks could not explain it. Simard decided to find out what was actually happening underground.

The Experiment That Changed Everything

For her landmark 1997 experiment, Simard planted paper birch, Douglas fir, and western red cedar seedlings together in a British Columbia forest. She then did something ingenious: she placed plastic bags over the birch and injected radioactive carbon-14 as CO2. She bagged the fir and injected a different isotope — carbon-13. The cedar served as a control because it does not share the same mycorrhizal fungi as the other two species.

Then she waited. She let the trees photosynthesize for a couple of hours, converting the tagged carbon dioxide into sugars. When she analyzed the tissues afterward, she found the isotopes had moved. Carbon-14 from the birch had traveled into the Douglas fir. Carbon-13 from the fir had traveled into the birch. The carbon was moving bidirectionally between two entirely different tree species through the fungal network connecting their roots.

But the transfer was not random. It was intelligent. Simard found that more carbon flowed from birch to fir when the fir was deeply shaded — when it needed the carbon most. The fungal network was not just a pipe. It was a redistribution system, moving resources from those who had surplus to those in deficit. The forest was not a collection of competing individuals. It was a cooperative economy.

Mycorrhizal Networks: The Architecture of Connection

The mechanism behind this transfer is the mycorrhizal network — a vast web of fungal threads (called hyphae) that connect the roots of plants to each other and to the soil. The word “mycorrhiza” comes from the Greek: myco (fungus) and rhiza (root). It describes a symbiotic relationship that is between 400 and 450 million years old, predating the evolution of roots themselves. Plants did not colonize land alone. They did it in partnership with fungi.

The numbers are staggering. Between 80 and 90 percent of all land plant species form mycorrhizal associations. Arbuscular mycorrhizal (AM) fungi alone partner with roughly 80 percent of plant species and account for about 70 percent of global plant biomass. A single ectomycorrhizal fungal network can span up to 90 square meters. In a single footstep on a forest floor, you are walking on hundreds of kilometers of fungal hyphae.

There are two main types of mycorrhizal networks. Arbuscular mycorrhizal fungi penetrate into root cells, forming tree-shaped structures (arbuscules) where nutrients are exchanged. They are the older and more widespread type, connecting most tropical and temperate plant species. Ectomycorrhizal fungi wrap around root tips in a sheath and extend their hyphae into the soil like fingers reaching for water. They associate with only about 2 percent of plant species — but those species happen to be the dominant trees in boreal, temperate, and many tropical forests: pines, oaks, birches, beeches, Douglas firs.

The term “Wood Wide Web” was actually coined by Nature editor Fiona Harvey in 1998, in a commentary on Simard’s paper. It stuck because the analogy is almost disturbingly accurate. Like the internet, the mycorrhizal network is a decentralized communication and resource-sharing system with hubs, nodes, and pathways. Like the internet, it connects entities that would otherwise be isolated. And like the internet, it can be used for both cooperation and exploitation.

Mother Trees: The Hubs of the Forest

Simard’s research deepened over the following decades. Using DNA microsatellite analysis, she mapped the network connections of individual trees in old-growth forests and discovered something remarkable: the network is not random. It has architecture.

The largest, oldest trees — what Simard calls “Mother Trees” — function as central hubs. A single mother tree can be connected to hundreds of other trees through the mycorrhizal network. These hub trees have massive root systems that can extend as wide as the tree is tall, fed by the enormous photosynthetic capacity of their crowns.

Mother trees do something extraordinary: they recognize their own kin. Using her isotope tracing methods, Simard demonstrated that a tree will preferentially send more carbon through the network to its own seedlings — its genetic offspring — than to unrelated seedlings. The tree can distinguish family from strangers underground, through chemical signals exchanged via the fungal network.

When a mother tree’s seeds germinate in spring, the seedlings tap into the existing fungal network within a month or two. They begin receiving carbon, nutrients, and water from the old tree — a kind of underground breastfeeding that continues until the seedlings develop enough leaf area to support themselves. Simard’s research showed that seedlings growing near mother trees with intact mycorrhizal connections had a survival rate two to four times higher than seedlings without this connection.

When a mother tree is dying — from disease, logging, or old age — Simard found that it increases its carbon transfer to surrounding seedlings. The dying tree dumps its remaining resources into the network. It is, functionally, writing a will. It is investing its final energy into the survival of the next generation.

Carbon, Nutrients, and Chemical Warnings

The mycorrhizal network transfers far more than carbon. Nitrogen, phosphorus, water, and defense signals all flow through the fungal threads. When a Douglas fir is attacked by western spruce budworm, it sends chemical alarm signals through the mycorrhizal network that trigger neighboring trees to increase their production of defensive enzymes — before the insects even reach them.

The economics of the exchange are complex. The fungi are not altruists — they take a cut. Mycorrhizal fungi receive 20 to 30 percent of the carbon that a tree produces through photosynthesis. In return, they provide the tree with phosphorus and nitrogen that their fine hyphae can extract from soil particles too small for roots to access. The fungal hyphae increase the effective absorbing surface area of a root system by 100 to 1,000 times.

But the network can also be exploited. Some plants — called mycoheterotrophs — have abandoned photosynthesis entirely and simply tap into the network to steal carbon from their photosynthesizing neighbors. The ghost orchid and Indian pipe are famous examples. They are the hackers of the Wood Wide Web, extracting resources without contributing anything in return.

The Forest as Superorganism

What emerges from Simard’s work, and from the broader research on mycorrhizal networks, is a picture of the forest not as a collection of individual trees but as a single interconnected superorganism. The trees are the visible architecture — the leaves, trunks, and branches that we see. But the real intelligence of the forest lives underground, in the mycorrhizal network that connects everything.

This is not a metaphor. The network exhibits properties that we associate with intelligent systems: resource allocation based on need, kin recognition, defense coordination, memory (the network persists and carries information across seasons and years), and even something resembling decision-making about where to invest resources.

Simard established the Mother Tree Project in 2015 at the University of British Columbia to study how retaining mother trees and mycorrhizal networks affects forest regeneration under climate change. Her research has profound implications for forestry practices. Clear-cutting does not just remove trees — it destroys the network. It rips apart the underground internet that took centuries to develop. The seedlings planted in a clear-cut have no network to tap into. They are orphans in a severed web.

In her 2021 memoir “Finding the Mother Tree,” Simard wrote about how her decades of research led her to see forests as cooperative communities rather than competitive battlefields. The book became a bestseller and was optioned for a film.

What This Means for How We See the World

The mycorrhizal network is one of the most powerful demonstrations of a principle that consciousness researchers keep rediscovering: intelligence does not require centralization. It does not require a brain. It does not even require a single organism. Intelligence can emerge from the connections between organisms — from the network itself.

A forest is a mind distributed across thousands of individual organisms and millions of kilometers of fungal threads. It processes information, allocates resources, responds to threats, supports its young, and adapts to changing conditions. It does all of this without a single neuron.

The Buddhist concept of Indra’s Net describes a vast web in which every jewel reflects every other jewel — a vision of total interconnection in which each node contains the whole. When Simard mapped the mycorrhizal network of an old-growth forest, she found something remarkably similar: a web in which every tree is connected to every other tree, where resources and information flow in all directions, where the health of each depends on the health of all.

We built the internet and thought we had invented something new. But beneath every forest floor, a far older, far more sophisticated network has been running for 450 million years.

If a forest is not a collection of individuals but a single interconnected intelligence, what does that say about the boundaries we draw around our own selves — and how real those boundaries actually are?