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ecological relationship

Mycorrhizal networks

Mycorrhizal networks are connections formed when fungi link the roots of different plants. Carbon and other substances can move between trees through the soil, but the popular picture of forests as cooperative networks run by "mother trees" is not supported by the evidence.

This is the clearest case in NatureHQ of a story travelling much further than its evidence. The underlying science is real: fungi form intimate partnerships with plant roots, and field experiments have detected carbon moving between trees of different species, including mature ones. From there, popular books and documentaries built a picture of forests as cooperative communities in which old trees deliberately feed their own seedlings through a fungal internet. In 2023, two independent reviews examined the primary literature and found that three specific headline claims — that these networks are widespread in forests, that they transfer resources in quantities that matter, and that trees preferentially nourish kin — are not supported by it. That does not make the fungi imaginary. It makes this a good place to see how a modest result becomes a settled fact in the public mind without the intervening evidence.

Developed record · 86% complete · reviewed 2026-08-09

Quick facts

What it is
Fungal hyphae linking the roots of two or more plants
How common
Mycorrhizal fungi are near-universal in plants; linked networks between trees are much less well established
Carbon movement
Detected between trees in field experiments
Mother tree hypothesis
Not supported by two independent reviews

What is actually established

Mycorrhizal fungi colonise plant roots and trade mineral nutrients for sugars. That partnership is ancient, near-universal and uncontroversial. The disputed part is what happens when the same fungal individual connects two plants.

Carbon does move between trees below ground

Well supported

Good evidence backs this, though some details remain open.

Isotope-labelling experiments in the field have detected movement of carbon between trees of different species, including between mature trees, with mycorrhizal fungi the most likely route.

Who this applies to
the temperate forest tree species tested so far
Studied in
Betula papyrifera, Pseudotsuga menziesii, Picea abies, Fagus sylvatica
Why we rate it this way, and what the caveats are
Well supportedModerate confidence

That carbon moves is well evidenced by two independent field experiments. What is far less certain is how much, by which route, and whether the receiving tree benefits at all.

How far it can be extended

Detected independently in North American and European forests, in seedlings and in mature trees, using different labelling approaches.

Caveats

  • Carbon found in a neighbour's roots may have been used by the fungi rather than by the tree.
  • Net transfers measured were small relative to a tree's total carbon budget.
  • Labelling designs struggle to exclude movement through soil rather than through fungi.

Still unanswered

  • How much of the transferred carbon is actually used by the receiving tree?
  • Is the fungus a conduit, a trader, or the main beneficiary?

Last reviewed 2026-08-09

The evidence (2 studies)

In pot experiments, plants connected by fungi respond to a neighbour being attacked

Emerging evidence

Real findings exist, but too few or too recent to be settled.

Broad bean plants connected by intact mycorrhizal mycelium produced aphid-repellent and parasitoid-attracting volatiles when a connected neighbour was infested; plants whose fungal connections were severed did not.

Who this applies to
broad bean plants with one fungal species, in pots
Studied in
Vicia faba

You may have heard

“Plants talk to each other through the wood wide web.”

A controlled pot experiment showed defensive chemistry appearing in a connected neighbour and not in a disconnected one, which is a real and careful result. Turning that into forests holding conversations skips several unanswered questions, starting with what the signal is.

Why we rate it this way, and what the caveats are
Emerging evidenceModerate confidence

The mesh design cleanly separates fungal connection from soil chemistry, which makes the result credible. It is one crop species, one fungus, in pots, with the signal itself unidentified.

Caveats

  • A pot experiment with a single crop species and a single fungus.
  • The nature of the transmitted signal is unknown.
  • No demonstration that this operates at meaningful scales in a wild ecosystem.

Still unanswered

  • What is the signal?
  • Does anything comparable happen in a forest, where networks are far more complex?

Last reviewed 2026-08-09

The evidence (1 study)
Words used here
Mycorrhiza
A partnership between a fungus and a plant root. The fungus supplies water and minerals; the plant supplies sugars.
Hypha
A single fungal thread. A mass of them is called mycelium.

What the reviews found

Two independent critiques, and why they matter.

The idea that "mother trees" deliberately feed their own seedlings is not supported by the evidence

Contested

Researchers actively disagree, and the disagreement is substantive.

Systematic and critical reviews find that three widely repeated claims — that common mycorrhizal networks are ubiquitous in forests, that they transfer resources to seedlings in quantities that matter, and that mature trees preferentially supply related seedlings — are not supported by the primary literature, and that citation patterns have amplified positive results.

Who this applies to
the temperate forest systems where the idea originatedDo not extend this beyond the taxa listed — the popular version over-reaches.
Studied in
Pseudotsuga menziesii, Betula papyrifera, Picea abies

You may have heard

“Forests are connected by a wood wide web through which mother trees feed their young.”

The underlying observation — carbon moving between trees below ground — is real. The elaboration into deliberate, kin-directed nurture came from popular books and documentaries rather than from the measurements, and two independent reviews have now found the specific claims unsupported. It is an unusually clear case of a story travelling faster than its evidence.

Why we rate it this way, and what the caveats are
ContestedModerate confidence

Two independent reviews reached similar conclusions, which is significant. They are reviews rather than new data, researchers in the field dispute their framing, and absence of strong evidence is not proof the phenomena are absent.

How far it can be extended

The reviews concern the specific systems the original claims were built from. Extending either the claim or its rebuttal to forests generally would repeat the error being criticised.

Caveats

  • This does not mean fungal networks are fictional, or that carbon does not move between trees.
  • The reviews are literature analyses, not new field measurements.

Where researchers disagree

  • Researchers associated with the original work dispute the reviews' framing and argue that the evidence base is stronger than the reviews allow.
  • Field experiments do detect below-ground carbon movement, so the disagreement is about scale, direction and function rather than about whether anything moves at all.

Still unanswered

  • How common are common mycorrhizal networks in real forests?
  • What experiment could show whether transferred resources actually benefit a receiving seedling?

Last reviewed 2026-08-09

The evidence (3 studies)

The 2023 review did something unusual and useful: as well as assessing the evidence, it traced how the studies had been cited. Positive results were cited far more often than negative ones, and several claims had drifted well beyond what the original papers reported. That is a mechanism worth understanding on its own, because it is not specific to forests.

Full answer

Words used here
Citation bias
The tendency for results supporting an appealing conclusion to be cited more often than results that do not, which makes a body of evidence look more one-sided than it is.

What is still unknown

  • How common are linked networks in real forests?

    Why it matters: Almost every downstream claim depends on this, and it is much harder to establish than it sounds — mapping which fungal individual connects which trees is genuinely difficult.

  • Does carbon that reaches a seedling actually get used by the seedling?

    Why it matters: It is the difference between trees sharing and fungi taking a cut. Current labelling methods struggle to tell them apart.

    What would settle it: A labelling design that can track carbon into plant tissue rather than into the root zone.

Claims about this, checked

Things people have heard, and what the evidence actually supports.

The research behind this page

12 studies, newest first. Each one has a page explaining what it found and what it could not show.

You may also find this interesting

What this page is still missing

NatureHQ publishes its own gaps. This record is at 86% completeness against what we would call a finished subject.

  • Arbuscular mycorrhizas, which dominate in grasslands and most crops, are not covered.
  • The response from researchers whose work the 2023 reviews criticised deserves fuller treatment.

Last reviewed 2026-08-09 · 7 claims · 12 search questions answered on this page