Beneath the ground, vast networks of fungi quietly support plant life and play an important role in regulating the planet's climate by helping move carbon into soils. Now, researchers have created the first global maps showing where these underground fungal networks are found and how much of them exist worldwide.
The study, published in Science , focuses on arbuscular mycorrhizal fungi, a group of fungi that form partnerships with most plants on Earth. Alongside the research, scientists released an interactive visualization that allows users to explore the remarkable scale of this hidden underground infrastructure. The maps are expected to help researchers and policymakers identify areas where these fungal networks are thriving and where they may be under threat.
The Hidden Partnerships Supporting Plant Life
Arbuscular mycorrhizal fungi, commonly called AM fungi, form mutually beneficial relationships with approximately ~70% of plant species worldwide. Plants provide the fungi with carbon produced through photosynthesis, while the fungi supply plants with nutrients and water.
These underground networks function as living infrastructure that helps sustain ecosystems and move carbon into the ground. In 2025, researchers published a global analysis of underground mycorrhizal fungal diversity in Nature and launched a digital platform called the Underground Atlas to help identify likely biodiversity hotspots beneath the surface. Until now, however, scientists had not attempted to estimate and map the physical density and worldwide distribution of AM fungal networks themselves.
Mapping 110 Quadrillion Kilometers of Fungal Networks
To build the new maps, researchers compiled measurements from more than 16,000 soil cores collected around the world. They then used machine-learning models that incorporated environmental data from deserts, tundra, forests, and other ecosystems to predict fungal network density in regions where direct measurements were unavailable.
Working with the Physics of Behavior group at the AMOLF research institute, the team also used robotic imaging to analyze more than 300,000 living AM fungal hyphae grown in laboratory conditions. Combining all of these data sources allowed researchers to estimate both the total length and mass of the global network.
Their analysis suggests that AM fungal networks extend for approximately ~110 quadrillion kilometers and contain roughly ~300 megatons of carbon (4-6x the mass of all living humans).
"It is hard to overstate the importance and enormity of these fungi," said lead author Dr. Justin Stewart, with the Society for the Protection of Underground Networks (SPUN). "There could be up to 10 meters (32 feet) of mycorrhizal network in just a teaspoon of soil."
Scientists often describe mycorrhizal networks as one of Earth's circulatory systems because they transport carbon, nutrients, and water throughout underground ecosystems.
In healthy soils, these fungal networks can expand the effective foraging area of plant roots by up to 100 times and provide > 80 percent of a plant's phosphorous needs.
"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" said co-lead author, Dr. Corentin Bisot, an AMOLF biophysicist. "We are learning how the complex bodies of network-forming fungi transport nutrients and help regulate the climate."
To help visualize the results, the researchers collaborated with award-winning data visualization designer Moritz Stefaner to create the Mycorrhizal Infrastructure Map .
The project offers the most detailed global view yet of Earth's fungal infrastructure. Estimates were calculated for every 1km 2 of terrestrial land, excluding ice caps and regions where data were insufficient for reliable predictions.
The data behind the maps are publicly available, giving governments and other decision-makers new tools for monitoring the health of underground fungal communities.
The work builds on previous research published by several of the same authors in Nature . That study examined how mycorrhizal fungi and plants create highly efficient systems for exchanging carbon and nutrients. Researchers measured carbon movement through these living networks at speeds reaching 120 um/sec (if one was inside the network, these speeds would feel like ~400km/hr). The new study extends that work by exploring how these flows operate at a planetary scale.
Threats to Underground Fungal Ecosystems
The researchers also identified areas of concern.
Network densities in croplands are predicted to be about half those found in wild ecosystems. At the same time, wild grasslands contain roughly ~40% of the world's arbuscular mycorrhizal biomass.
Despite their importance, grasslands remain among the least protected ecosystems on Earth and are being converted to agricultural land four times faster than forests.
These findings support previous S…