The Hidden Web: Global Maps Reveal Mycorrhizal Fungi Hotspots — and a Glaring Protection Gap

According to MONGABAY

Beneath Our Feet: The Living Tapestry We Never See

Every step we take, whether through a city park or a rainforest trail, presses against one of the most vital ecosystems on Earth—yet one we’ve scarcely understood. Mycorrhizal fungi, the delicate threads beneath the soil surface, form an ancient, underground network that connects plants, regulates climate, and stores carbon.

Now, for the first time, scientists have charted these life-sustaining webs on a global scale—and what they found is both breathtaking and alarming.

Published in Nature and spearheaded by the Society for the Protection of Underground Networks (SPUN), the study reveals vast fungal biodiversity hotspots that are largely unprotected, despite their foundational role in Earth’s ecological and climate systems.

This is the fungal equivalent of mapping rainforests or coral reefs for the first time. Only this time, the forest is invisible.

Mapping the Invisible: 25,000 Soil Samples, 2.8 Billion DNA Sequences

The study represents a monumental data effort. Scientists analyzed 2.8 billion DNA sequences from nearly 25,000 soil samples across 130 countries to create what they call the Underground Atlas—the first high-resolution global maps of mycorrhizal fungal biodiversity.

Using machine learning, they identified regions of high fungal richness and endemism, particularly in ecosystems like:

• Ethiopia’s Simien Mountains
• Brazil’s Cerrado savanna
• West African rainforests
• Tasmania’s cool forests

Yet, less than 10% of these hotspots fall within legally protected areas. That statistic has raised red flags across the conservation community.

Why Mycorrhizal Fungi Matter So Much

Mycorrhizal fungi form mutualistic relationships with over 80% of plant species, wrapping around or penetrating plant roots and exchanging nutrients for sugars. Their filaments—called hyphae—extend far beyond root zones, linking plants into vast “communication and trade” networks.

Some of their key roles include:

• Transporting nutrients like phosphorus and nitrogen
• Distributing water in times of drought
• Sharing resources and warning signals between trees
• Storing carbon in stable underground forms

Plants send an estimated 13 billion metric tons of CO₂ to these fungal partners each year—about a third of global fossil fuel emissions. That carbon is often locked in soils for centuries, making these networks vital players in climate stability.

Diversity in the Dark: Arbuscular vs. Ectomycorrhizal Patterns

The study distinguishes between two major types of mycorrhizal fungi:

• Arbuscular Mycorrhizal Fungi (Glomeromycota): Found in tropical and subtropical regions, including rainforests and savannas. Richest near the equator, their presence mirrors patterns in animal and plant diversity.
• Ectomycorrhizal Fungi (Basidiomycota, Ascomycota): More common in temperate and boreal regions, especially in coniferous forests. These fungi show peak richness in the northern hemisphere and southern parts of South America and Australia.

Each group supports different ecosystems, but both are equally crucial to global ecological resilience.

A Protection Crisis: Conservation Stops at the Surface

While the world has long invested in protecting charismatic megafauna and sweeping landscapes, underground life has been left behind. SPUN’s findings highlight a major oversight: existing conservation strategies largely ignore fungal diversity, even though ecosystems cannot function without it.

Some examples of the disparity:

• In Asia, only 2.2% of arbuscular richness hotspots are protected.
• In Europe, the best-protected region, the number reaches just 19.6%.
• Coastal erosion is expected to wipe out fungal hotspots in Ghana within decades.

These gaps suggest conservation efforts are dangerously incomplete, potentially undermining food systems, water cycles, and carbon storage capacity.

The Underground Atlas: A Tool for Tomorrow

To address this invisibility, SPUN created the Underground Atlas, a public, interactive tool that allows users to view fungal diversity patterns anywhere on Earth with 1-kilometer resolution. Conservationists can now overlay these maps with existing protected areas, land use changes, or restoration plans.

“This isn’t just a map,” says Michael Van Nuland, SPUN’s lead data scientist and the paper’s co-author. “It’s a call to realign our conservation strategies with how life on Earth actually works.”

Fungal Futures: Solutions Beneath the Soil

Recognizing the role of fungi in global challenges could shift how governments and organizations approach:

• Climate action: Soils rich in fungi store more carbon and resist erosion.
• Agriculture: Mycorrhizal networks reduce the need for fertilizers, boosting sustainability.
• Biodiversity conservation: These fungi support plant and insect diversity aboveground.
• Ecosystem restoration: Restoring fungal networks accelerates reforestation and water retention.

Rebecca Shaw, WWF’s chief scientist, emphasized their value:

“Mycorrhizal fungi need to be recognized as a priority in the ‘library of solutions’ to biodiversity decline, climate change, and food insecurity.”

Cultural and Scientific Blindness: Why We Missed This

Part of the problem lies in what Toby Kiers, SPUN’s executive director, calls “fungus blindness.” While forests and rivers inspire awe, fungi are seen as rot, disease, or just dirt. But that misperception has cost us dearly.

“Disrupt these ecosystems,” Kiers warns, “and forest regeneration slows, crops fail, and biodiversity begins to unravel.”

From colonial forestry to industrial agriculture, land-use decisions have long prioritized visible, profitable outputs—ignoring the fungal scaffolding that sustains them.

What We Can Do Now

The solutions aren’t high-tech—they’re strategic:

• Integrate fungal data into conservation planning
• Fund more fungal biodiversity research
• Include soil biodiversity in international agreements like the Convention on Biological Diversity
• Involve Indigenous and local communities, who often understand underground dynamics through traditional knowledge

SPUN is expanding its soil-sampling network and working with policymakers to turn data into action. The goal is to mainstream fungal conservation within the broader environmental movement.

From Hidden to Heroic: A New Conservation Story

This isn’t just a scientific discovery—it’s a narrative pivot. Fungi are no longer just background organisms in the grand ecological theater. They are lead actors.

Merlin Sheldrake, study co-author and SPUN’s director of impact, put it simply:

“These maps help alleviate our fungus blindness. They’re a lens into the vast, connected world beneath our feet—a world that holds the solutions we’re desperately seeking.”

Fungus as Foundation

It took four years, 25,000 soil samples, and billions of DNA sequences to make something clear: the most important ecosystem engineers are the ones we can’t see. Mycorrhizal fungi don’t just live underground—they uphold everything above it.

Protecting them is no longer optional. It’s foundational.

As the climate shifts and biodiversity dwindles, the path to resilience may be not in the skies above—but in the soil beneath.

References

• Society for the Protection of Underground Networks (SPUN): spun.earth
• Convention on Biological Diversity (CBD): cbd.int

According to MONGABAY

Frequently Asked Questions

What do global maps of mycorrhizal fungi actually show us?

Global mycorrhizal distribution mapping—combining soil sampling surveys, root tip observations, metagenomic soil DNA analysis, and remote sensing of forest composition—has revealed several major patterns in how mycorrhizal fungi are distributed across the earth’s terrestrial ecosystems. The most fundamental pattern is the divide between arbuscular mycorrhizal (AM) fungi, which are globally distributed but dominate tropical and warm-temperate forests and most agricultural land, and ectomycorrhizal (ECM) fungi, which dominate boreal and temperate coniferous and deciduous forests of North America, Europe, and Asia. This distribution is primarily driven by climate (temperature and precipitation) and the tree species composition these climates produce—ECM associations are particularly common in the families Pinaceae, Fagaceae, and Betulaceae, which dominate temperate and boreal forests. A third type—ericoid mycorrhizal fungi—dominates heathland and arctic tundra ecosystems where ericaceous plant families (heather, blueberry, cranberry) are the dominant vegetation.

Which regions have the most mycorrhizal fungal diversity?

Mycorrhizal fungal diversity peaks in forest ecosystems with long evolutionary histories of plant-fungal coevolution and stable environmental conditions. In terms of ectomycorrhizal richness, old-growth temperate forests of the Pacific Northwest of North America, the ancient broadleaf forests of Europe (particularly in regions with high tree species diversity), and old-growth boreal forest in Scandinavia and Russia are among the richest communities. For arbuscular mycorrhizal fungi, tropical forests show high diversity, though AM fungal biodiversity is less well-characterised globally due to the historical difficulty of detecting AM fungi (which cannot be cultured) without molecular techniques. The most significant data gaps for mycorrhizal diversity are in tropical Africa and Southeast Asia—regions with high plant endemism but low soil biodiversity sampling effort, likely harbouring substantial undescribed mycorrhizal diversity.

How does climate change affect mycorrhizal fungal distributions?

Climate change is altering mycorrhizal distributions through several mechanisms. Direct temperature effects: warming allows range expansion of mycorrhizal species adapted to warmer climates while potentially contracting the ranges of cold-adapted species; some ECM species associated with boreal trees are already showing phenological shifts (earlier fruiting) consistent with warming trends. Host plant range shifts: as tree species migrate in response to warming, their obligate mycorrhizal partners must either co-migrate (if dispersal limitations allow) or give way to different fungal communities colonising the new arrivals; tree-fungal migration mismatches could disadvantage forest expansion at leading edges. Altered precipitation and drought: increased drought frequency in many regions affects soil moisture content, which directly constrains hyphal growth and sporulation; drought-intolerant mycorrhizal species lose abundance; drought-tolerant species may expand. Nitrogen deposition: atmospheric nitrogen pollution from combustion and agriculture is increasing soil nitrogen in previously nitrogen-limited forest soils, shifting conditions from ECM-favouring (low nitrogen) toward AM-favouring (higher nitrogen).

Why does mycorrhizal type matter for forest carbon storage?

The mycorrhizal type of a forest ecosystem fundamentally influences how much atmospheric carbon is captured and retained in soil over time. ECM fungi produce recalcitrant (chemically resistant) organic compounds during hyphal turnover that persist in soil for longer periods—ECM-dominated forest soils tend to accumulate more stable organic matter. ECM fungi also suppress decomposition by saprotrophic (free-living decay) fungi through competition for nitrogen, slowing the breakdown of organic matter and allowing carbon to accumulate. AM-dominated ecosystems tend to have faster nutrient cycling with more carbon returned to the atmosphere more quickly. The Steidinger et al. 2019 study estimated that ECM-dominated forests store approximately 70% more carbon per unit area than AM-dominated forests, though this figure is debated and the causal mechanisms are complex. The implication is that shifts in mycorrhizal composition—driven by nitrogen deposition, climate change, or forest management—could significantly affect terrestrial carbon sequestration capacity at global scales.

Can we map mycorrhizal fungi from satellites or is soil sampling required?

Direct detection of individual mycorrhizal fungal species from remote sensing is not currently possible—satellites cannot resolve or distinguish soil microbial communities. However, remote sensing can map the distribution of mycorrhizal type at forest ecosystem level by tracking the distribution of tree species with known mycorrhizal associations (since tree identity is the strongest predictor of the dominant mycorrhizal type). Multispectral and hyperspectral satellite imagery can distinguish forest types at species level in some conditions; combined with trait databases identifying the mycorrhizal associations of tree species, this allows mycorrhizal type maps to be generated at large spatial scales. These indirect maps require ground-truthing with actual soil samples and molecular analysis, but allow comprehensive global coverage impossible with soil sampling alone. The Global Forest Biodiversity Initiative and the SPUN (Society for the Protection of Underground Networks) project are advancing global mycorrhizal mapping using combined satellite and soil metagenomic approaches.