Earth's Fungal Highways
A Living Web Beneath Our Feet
Scoop up a teaspoon of healthy soil and you might be holding something astonishing: as much as ten meters of delicate fungal thread, quietly trading with plant roots. Scale that up, and the picture becomes almost cosmic.
An international team has now produced the first global maps of arbuscular mycorrhizal fungal networks—the underground partnerships that link fungi to roughly 70 percent of plant species on Earth. Published in Science, the work estimates that topsoils hold about 110 quadrillion kilometers of these tubular cells, called hyphae. That length is nearly a billion times the distance from Earth to the sun. Their living mass comes to roughly 300 megatons of carbon—several times the carbon locked in every human body alive today.
The numbers feel abstract until you remember what the networks actually do. They ferry water and nutrients to plants in exchange for carbon the plants fix from the air. In healthy soils they can expand a root system’s foraging reach by up to a hundredfold and supply more than 80 percent of a plant’s phosphorus. They are, in effect, a planetary circulatory system we have only just begun to see whole.
How Do You Weigh a Hidden Kingdom?
Lead author Justin Stewart of the Society for the Protection of Underground Networks (SPUN) and colleagues assembled density measurements from more than 16,000 soil cores drawn from 322 studies spanning nine biomes. Machine-learning models then folded in environmental layers—climate, soil type, vegetation—to estimate network density in the vast unsampled stretches of land. To turn length into living biomass, the team collaborated with biophysicists at the research institute AMOLF, using robotic imaging of more than 300,000 living hyphae grown in the lab.
The result is a kilometer-by-kilometer portrait of fungal infrastructure across ice-free terrestrial Earth, paired with an interactive visualization designed with data artist Moritz Stefaner. Governments and land managers can already download the underlying layers.
“It is hard to overstate the importance and enormity of these fungi,” Stewart said. “There could be up to 10 meters of mycorrhizal network in just a teaspoon of soil.”
Co-lead Corentin Bisot, an AMOLF biophysicist, added that new imaging, robotics, and machine learning are finally letting researchers watch how these network-forming fungi move nutrients and help regulate climate.
Where the Networks Thrive—and Where They Thin
Grasslands emerge as quiet champions, holding an estimated 40 percent of the planet’s arbuscular mycorrhizal infrastructure. Flooded grasslands of South Sudan, Florida’s Everglades, and the Tibetan Plateau stand out for especially high predicted density. Forests, deserts, and tundra each carry their own signatures; the map makes those differences visible for the first time.
The same models flag a clear pressure point. Large-scale croplands are predicted to host roughly half the network density of wilder ecosystems. Researchers are careful not to pin the drop on any single practice yet; more work is needed to link specific farming choices to fungal health. Still, thinner networks raise practical questions. Soils with sparser hyphae may store less carbon, cycle nutrients less efficiently, and weather stress less gracefully.
That matters because these fungi move an estimated 4 billion tons of CO₂-equivalent into soils each year—about 11 percent of current human-related carbon-dioxide emissions. Last year, several of the same researchers showed that carbon can race through individual hyphal highways at speeds that would feel, scaled up, like hundreds of kilometers per hour. The new global maps begin to place those microscopic flows in planetary context.
Grasslands, despite their outsized fungal wealth, remain among the least protected biomes and are being converted to farmland faster than forests. Earlier SPUN work found that 95 percent of predicted biodiversity hotspots for these fungi lie outside protected areas. The density maps sharpen that picture without claiming the story is finished; large regions of Earth are still unsampled, and the authors treat those gaps as open invitations rather than dead ends.
Working With What We Can Now See
For Toby Kiers, evolutionary biologist and SPUN’s executive director, the practical next step is clear: bring fungi into climate and conservation planning that long overlooked them. Biologist and co-author Merlin Sheldrake frames the same moment as both wonder and responsibility. Mycorrhizal fungi have shaped life for hundreds of millions of years; understanding how their living transport systems are distributed is a step toward working with them on food security and climate challenges alike.
The maps do not pretend to be the final word. They are a high-resolution first draft of an infrastructure that has always been there—thread by thread, teaspoon by teaspoon—holding plants, soils, and carbon in conversation. With the outline finally drawn, the invitation is simply to look closer, protect smarter, and keep learning how the quiet highways underfoot keep the surface world alive.
“With the emergence of new technologies in high-resolution imaging, machine-learning and robotics, we are starting to reveal what has long been hidden under our feet.” — Corentin Bisot
