Why Trees Talk in Chemicals

A forest is not quiet. It sounds quiet — birdsong, wind, the occasional crack of a branch adjusting its weight — but underneath all of that, something else is happening. Something that has no sound at all.

Trees communicate. Not in any way that resembles language, not with intention the way we understand it, and not through any mechanism that was designed to be noticed. They do it through chemistry: volatile compounds released into the air, electrical signals sent through root systems, and nutrients transferred across underground networks of fungi that have been doing this work for roughly 450 million years.

The science behind this is real, documented, and more interesting than most of the ways it gets described.

The Air Between Them

When certain species of trees are attacked by herbivorous insects — caterpillars feeding on leaves, beetles boring into bark — the damaged tissue releases volatile organic compounds into the surrounding air. These aren't distress signals in any conscious sense. They're chemical byproducts of cellular damage that happen to carry information.

What makes this interesting is what neighboring trees do with that information. Research published across multiple studies over the past four decades has shown that undamaged trees in the vicinity of an attacked tree will sometimes begin producing defensive chemicals — tannins, phenolics, protease inhibitors — before the insects reach them. The timeline varies. The mechanism isn't fully understood. But the pattern is consistent enough across species and studies to be taken seriously.

The first major study to document this was published in 1983, when researchers observed that willow trees near damaged willows began increasing their production of phenolic compounds. The finding was controversial at the time. Some researchers couldn't replicate it under controlled conditions. Others could. The field spent the next twenty years arguing about whether the phenomenon was real, an artifact of experimental design, or something that only happened under specific conditions.

The current consensus, built on decades of follow-up research, is that airborne chemical signaling between trees does occur — but that its significance in natural forest conditions is variable and context-dependent. It's not a telephone call. It's closer to a change in the air that some nearby organisms are equipped to detect and respond to.

 

 

The Network Underfoot

The underground story is more complex and, in many ways, more remarkable.

Most terrestrial plants form symbiotic relationships with mycorrhizal fungi — thread-like organisms that colonize root systems and extend outward into the soil like a secondary root network. The plant provides the fungus with carbon (sugars produced through photosynthesis). The fungus provides the plant with water and mineral nutrients (particularly phosphorus and nitrogen) that its hyphae can access from a much larger volume of soil than roots alone could reach.

This much has been established science for over a century. What's newer — and what captured public imagination under the name "wood wide web," a term coined by the journal Nature in 1997 — is the discovery that these fungal networks can connect multiple trees simultaneously, creating pathways through which resources and chemical signals can move from one tree to another.

The foundational research here comes from forest ecologist Suzanne Simard, whose work in the late 1990s demonstrated that carbon could transfer between Douglas fir and paper birch trees through shared mycorrhizal networks. The transfer wasn't random — it moved preferentially toward shaded seedlings, suggesting that the network functioned in a way that directed resources toward individuals that needed them most.

Subsequent research has expanded on this in several directions. Studies have shown that trees connected through mycorrhizal networks can transfer not just carbon but also nitrogen, phosphorus, water, and defense-related chemicals. There's evidence that larger, older trees — sometimes called "mother trees" or "hub trees" — serve as particularly well-connected nodes in these networks, with fungal connections reaching dozens of neighboring trees.

 

 

What the Research Actually Shows (and What It Doesn't)

This is where responsible science writing requires a pause.

The wood wide web metaphor is compelling, and it's grounded in real data. But the public narrative has, in places, outrun the science. Trees have been described as "talking," "caring for their young," "making decisions," and "feeling pain." These are anthropomorphisms that make the research more relatable but less accurate.

What the evidence supports is that chemical and resource transfer occurs between trees through fungal networks, that this transfer can be directionally biased, and that trees respond to airborne chemical cues from damaged neighbors. What the evidence does not clearly support is that trees have anything resembling awareness, intention, or emotion in these processes.

The distinction matters — not because the science is less interesting without the anthropomorphism, but because it's actually more interesting. A system that distributes resources and chemical information across a forest without any central coordination, without any individual awareness, without any plan — just through the accumulated physics of fungal growth and chemical gradients — is more remarkable than a forest full of trees that chose to be generous. It's cooperation without a cooperator. Sharing without a decision to share.

Some researchers have pushed back on the strongest claims of the wood wide web narrative. A 2023 review questioned whether the scale of carbon transfer through mycorrhizal networks is large enough to meaningfully affect tree survival, and whether some of the observed transfers might be better explained by fungal self-interest (the fungus moving resources for its own benefit, with trees as incidental recipients). The debate is ongoing, which is exactly what healthy science looks like.

 

 

 

What It Means to Stand in a Forest Knowing This

None of this changes what a forest feels like. The quiet is still quiet. The shade is still shade. The particular calm that comes from standing among trees — the phenomenon that the Japanese practice of shinrin-yoku (forest bathing) is built around — doesn't require understanding the chemistry underneath it.

But knowing changes the texture of the experience. Knowing that the air between the trees carries information. Knowing that the ground beneath your feet is threaded with fungal networks that have been transferring resources between root systems since before the first human walked upright. Knowing that the forest you're standing in is, in a chemical and physical sense, one connected system rather than a collection of individual trees that happen to be growing near each other.

The forest doesn't need you to know this. It was doing it before anyone understood it, and it will continue long after the research papers yellow. But there's something about standing in a place and understanding, even partially, what's happening beneath the surface — a kind of respect that comes from knowledge rather than projection.

The trees aren't talking. They're doing something older and stranger than talking. And the fact that we're only beginning to understand it — after living among forests for the entirety of human existence — is its own kind of humility.

 

 

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