Under the Forest, a Fungal Network Enables Trees to Exchange Carbon, Water, and Nutrients

Just a few centimeters beneath our feet, roots and fungi weave connections capable of moving carbon and nutrients between plants. This mysterious “Wood Wide Web” has fascinated biologists for decades. But what does it actually transport, and how far can trees benefit from it?

Long before modern trees, plants had already struck a pact with fungi

The story begins long before the first forests. Roughly 450 million years ago, the ancestors of terrestrial plants were already forming close relationships with fungi. Studies published in Science even suggest that this ancient alliance may have helped plants conquer the continents.

The deal is surprisingly productive. Fungi spread tiny filaments, called hyphae, through the soil to explore volumes that roots alone cannot reach. They scavenge mineral elements in particular. In return, the plant supplies them with carbon from photosynthesis, turning the mycorrhiza into a genuine mutualistic partnership.

And that’s where the story gets stranger. A single fungus can colonize the roots of several plants, creating what researchers call a common mycorrhizal network. Multiple plants become physically connected underground, sometimes with no surface signs at all.

In 1997, a Canadian experiment revealed that carbon really does move from one tree to another

In a Canadian forest, Suzanne Simard and colleagues sought to trace the invisible. Their experiment, published in Nature in 1997, used carbon isotopes as tracers. The study focused on paper birch and Douglas fir trees linked by ectomycorrhizal fungi. The result would popularize a fascinating idea.

Carbon taken up by one tree was indeed found in its neighbor, with transfers varying notably with the lighting conditions. In other words, carbon-based resources can circulate between plants. The forest floor suddenly ceased to look like a mere reservoir of soil and became a remarkably active space for biological exchanges.

Attacked plants can broadcast an astonishing underground alarm signal

Not only nutrients travel. In 2013, an Ecology Letters study connected bean plants through fungal networks. When some plants were attacked by aphids, their neighbors linked through the network altered their defensive volatile compounds in turn.

The phenomenon resembles an underground alert system, but with a crucial caveat: the study involved beans and aphids, not a forest-wide dialogue. The exact mechanisms remain under study. Between chemical signaling, fungal response, and plant reaction, the network still holds many shadows to illuminate.

The alluring “Internet of Trees” hides a reality far more subtle than the metaphor

The term “Wood Wide Web” is irresistible. It suggests trees exchanging resources and warnings like connected computers. Yet scientists today urge greater caution. A 2023 analysis suggests that some popular claims about these networks go beyond what forest experiments actually demonstrate.

The case of the famous “mother trees” is particularly debated. The idea that older trees would voluntarily redistribute their resources, or even favor their descendants, remains far less solidly supported than its popularity would suggest. Researchers also note that an observed carbon transfer does not automatically mean that one tree is actively “feeding” another.

That does not make the underground world any less fascinating; quite the opposite. Fungi do participate in carbon and nutrient cycles, linking roots and influencing how forest ecosystems function. But beneath every forest walk may lie something more interesting than a vegetal Internet: a biological network whose rules remain largely to be discovered.