Mapping the Unseen: The First Global Atlas of a 110-Quadrillion-Kilometer Fungal Web

For the first time, scientists have visualized the physical infrastructure of one of the planet’s most vital yet overlooked living systems. An international team, led by the Society for the Protection of Underground Networks (SPUN), has published the first global map estimating the distribution and mass of arbuscular mycorrhizal (AM) fungal networks . These subterranean webs, composed of microscopic tubular hyphae, form symbiotic partnerships with the vast majority of land plants and function as a massive, largely invisible scaffold for terrestrial life. The findings, published in Science on June 11, 2025, reveal a network of staggering scale—and a conservation crisis that threatens to unravel it.

The Scale of a Hidden Kingdom

The research synthesizes data from 322 studies covering over 16,000 soil cores collected across nine major biomes . Using machine learning to bridge data gaps, the team produced the first high-resolution (1 km²) estimate of global hyphal density . Their calculations place the total length of AM fungal filaments in the top 15 centimeters of Earth’s soils at roughly 110 quadrillion kilometers (68 quadrillion miles) .

This means that if the delicate, tubular threads were placed end to end, they would stretch approximately 730 million to one billion times the distance from Earth to the sun, a span that could cover roughly 10 percent of the width of the Milky Way galaxy . This living, branching network does not merely occupy space; it actively stores carbon. The study estimates the total hyphal mass holds around 300 megatons of carbon, a reservoir four to six times larger than the annual carbon emissions from global transportation .

Where the Web Is Strongest—and Where It’s Fraying

The new maps reveal that the densest fungal networks do not follow patterns of above-ground biodiversity. While tropical and subtropical forests are major hubs, the research identified wild grasslands and savannas as disproportionately critical reservoirs . In regions like the flooded grasslands of the Florida Everglades or the Cerrado savanna in Brazil, the top layer of soil holds an outsized portion of the world’s mycorrhizal biomass . These grassy ecosystems contain roughly 40 percent of the total global AM fungal network .

This revelation underscores a dangerous blind spot in global land management. Large-scale croplands present a stark picture of degradation. Fungal network densities in intensively farmed areas are roughly 50 percent lower than in wild ecosystems, a decline driven by tillage, synthetic fertilizers, and pesticide use . Compounding this loss, wild grasslands—now known to shelter some of the densest fungal webs on Earth—are being converted to farmland at four times the rate of forests, an acute threat to a major terrestrial carbon sink . The lowest densities of fungal networks are concentrated in arid deserts, arctic tundra, and heavily managed agricultural belts, revealing a map of both natural limits and human-induced scars.

Why These Networks Are Ecologically Non-Negotiable

The ecological importance of AM fungi cannot be decoupled from the very existence of most plant life on Earth. These fungi form obligate symbiotic relationships with the roots of roughly 80 to 90 percent of all land plant species . The partnership is foundational: the fungi deliver essential water, phosphorus, and nitrogen to their plant hosts, and in return, the plants supply the fungi with carbon fixed from the atmosphere .

This carbon economy extends far beyond individual plants. By shunting carbon into the soil and binding it into stable forms, the mycorrhizal network acts as a massive climate regulation engine . The physical presence of the hyphae also literally knits the soil together, reducing erosion, improving water retention, and creating a porous architecture that sustains entire ecosystems . The concept of a “wood wide web” is rooted in this biology, as the network can connect multiple plants, enabling the transfer of resources and chemical warning signals between them .

A Conservation Crisis Hidden Underground

The most alarming finding from this mapping effort is the near-total absence of protection for the ecosystems where these fungi are most diverse and abundant. Less than 10 percent of predicted mycorrhizal fungal biodiversity hotspots fall within any form of legally protected area. This means approximately 90 percent of the world’s richest hubs of underground fungal life are entirely outside existing conservation zones, exposed to agricultural expansion, urbanization, and climate change with no protective framework .

This is not merely a gap; it is a systemic failure of terrestrial conservation, which has historically focused almost exclusively on what is visible above ground. The conversion of grasslands, now identified as fungal treasure troves, at a rate quadruple that of forests represents one of the most urgent and unaddressed conservation challenges of our time .

What This Means for Policy and Practice

The high-resolution, interactive maps produced by this study are designed to be tools for action, not just academic curiosities . They make a concrete case for a fundamental reorientation of environmental policy:

• Redesigning Protected Areas: The existing global network of conservation areas is nearly blind to underground biodiversity. The new maps, with their 1 km² resolution, provide a guide for designating new reserves specifically designed to safeguard subsurface ecosystems and carbon stores .
• Reforming Agriculture: Farming practices that decimate fungal density are effectively dismantling a free, natural carbon sequestration system. Policies that incentivize no-till farming, cover cropping, and a sharp reduction in fungicide and synthetic fertilizer use are no longer just about soil health—they are about climate infrastructure repair .
• Integrating Soil Carbon into Climate Frameworks: With 300 megatons of carbon at stake, the argument for including soil carbon preservation as a verifiable mitigation strategy under international climate agreements like the Paris Agreement is irrefutable . The monitoring infrastructure to do so now exists.
• Reframing Grassland Priorities: Land-use planning and corporate supply chain commitments must acknowledge that grasslands are not just inferior forests. They are first-tier global assets for below-ground biodiversity and carbon storage, and their current rate of conversion is a planetary-scale risk .
• Investing in the Underground: This scientific breakthrough was achieved by a dedicated research organization, SPUN, and highlights a persistent funding gap. Sustained investment in large-scale soil DNA sequencing and robotic monitoring is necessary to move this from a one-time snapshot to an ongoing planetary health monitoring system .