Appraisers already know how to price dirt. Soil class, irrigation, comparables, a view. None of those columns is the living trade under the land — mycorrhizal fungi swapping plant carbon for nutrients and water through threads thinner than hair.
That trade is an underground network. It is not a metaphor. It is not a soil-health invoice. It is not a carbon receipt. It is the production system most land plants already run, whether or not the market has a line item for it.
what an underground network actually is
An underground network is a living system of mycorrhizal fungi connected to plant roots, trading plant carbon for nutrients and water through hyphae — tubular cells, often ten to fifty times thinner than a human hair — that forage in soil the root itself cannot reach.
The working definition is a trade, not a story. The plant photosynthesizes. It pays a share of that carbon into the fungus. The fungus returns phosphorus, nitrogen, water, and access to a foraging area that can dwarf the root system. Most land plants run some version of this partnership. Arbuscular mycorrhizal fungi associate with about 70% of land plant species, including the grasses. Ectomycorrhizal fungi associate with many trees. They are not the same underground — that difference gets its own post. The job on this page is the living connection itself.
Growers, foresters, and Indigenous nations who work living ground did not need a map product to know the land is more than dirt. The maps are new. The relationship is not. This page is for the landowner, the agency, and the foundation who inherited a ledger that only saw the surface.
the trade under the land
Carbon moves one way. Nutrients and water move the other. Hyphae are the pipes.
Hawkins, Kiers, and colleagues estimated in Current Biology in 2023 that terrestrial plants allocate about 13.12 gigatonnes of CO₂-equivalent a year into mycorrhizal mycelium — roughly 36% of 2021 fossil-fuel CO₂. That number is allocation, not a vault. Carbon moving through living hyphae, at least temporarily. It is not a 100-year storage claim, and it is not a credit.
A separate paper, Stewart and colleagues in Science in 2026, measured the arbuscular infrastructure that carries part of that trade: about 1.10 × 10¹⁷ kilometers of living hyphae in the top 15 centimeters of soil — roughly 110 quadrillion kilometers — weighing about 300 ± 60 million tonnes, on the order of four to six times the biomass of all humans. SPUN's public explainer for that arbuscular-only map cites roughly 4 billion tonnes of CO₂, about 11% of fossil emissions. Keep the two papers apart. Hawkins is a global allocation into arbuscular, ectomycorrhizal, and ericoid mycelium. Stewart is the size of the arbuscular pipes.
The valuation literature almost skipped the biome. In the 2024 Ecosystem Services Valuation Database synthesis — more than 9,400 monetary records — the subterranean biome is 0.08% of the sample. That is a hole in the books. It is not a license to invent a dollars-per-acre figure here. Price is a bridge. It is never the worth of the fungi.
dirt, a practice, and a network
Three objects get called "the underground." They are not substitutes.
| dirt price | soil-health practice | underground network | |
|---|---|---|---|
| what it is | The surface the market already knows how to sell | A completed action — cover crop, reduced till, a payment | Living hyphae trading carbon for nutrients and water with plants |
| what you hold | An appraisal, a comparable, a soil class | An invoice, a practice code, a cost-share | The connection itself — condition of a living system |
| what gets priced | Dirt, timber, water, views | The practice, not the fungi | Usually nothing |
| when it thins | The number still prints | The file still closes | Forage, drought recovery, and nutrient cycling get worse while the ledger looks fine |
A soil-health program can be the reason a network stays. NRCS practices, inoculants, and conservation easements are cousins, not villains. The contrast is the object you hold when the work is finished. A practice payment holds a completed action. An appraisal holds dirt. Neither is the living network.
Soil as a body system is a different argument, and it already has a home: dirt is a health system. This series is the named fungal network under the land.
the maps, not the product
The Society for the Protection of Underground Networks — SPUN, a science and mapping nonprofit — did not mint a product. They mapped physical infrastructure.
Two maps to name.
The Underground Atlas (Van Nuland and colleagues, Nature, 2025) is the first global, roughly 1-kilometer map of arbuscular and ectomycorrhizal richness and endemism. Training data: more than 2.8 billion fungal DNA sequences, about 25,000 soil samples, 130 countries. About 9.5% of predicted richness hotspots sit in protected areas — about 5.1% for arbuscular hotspots, about 13.9% for ectomycorrhizal. Vascular plants, trees, and vertebrates are on the order of three times better covered. About 90% of the richest underground is unprotected.
A Hidden Infrastructure (Stewart and colleagues, Science, 2026) is the first global map of arbuscular hyphal density and biomass. Same kilometer scale. Grasslands hold about 40% of that arbuscular biomass and are poorly protected — the living-cover case for grass is what grasslands actually are. Do not restage the prairie here.
Those maps are regional screens, not parcel surveys. A kilometer on a side is about a hundred hectares. They tell capital where to look. They are not a diligence report on your forty acres, and they are not a certificate.
A biological soil crust is a different underground job — the surface glue in dry country — already written: the crust that holds the desert together.
the network is the asset
The underground network exists whether or not anyone buys a certificate. It was trading before the appraisal, before the map, before the registry. It does not need us to be real. What it needs is for someone to fund the land it lives in while it is still living.
That is the only job the instrument has. Beneficiaries already absorb the cost of a thinning network — weaker forage, slower drought recovery, fertilizer replacing a partnership the land used to run. ensurance lets them fund that land as a present-tense asset: condition priced, routed to a named place. Mechanically, a certificate funds one named place directly and a coin funds protection across the protocol indirectly. Both route proceeds to an account that represents a place or a purpose. Neither is the fungi. That is the entire technical content of this page.
Popular talk of a wood-wide web oversold how trees share through common mycorrhizal networks. The base mutualism was never the part that needed a story.
Our own stage, stated honestly: subterranean.ensurance is live and volumes are small. healthy-soils.ensurance is a related door. The mechanism works and the market for it is early. That is a different sentence from "this is solved."
And the price is a bridge, never the worth. An underground network is not worth a land gap, a carbon flow, or a missing valuation row. Those numbers exist so capital can see the fungi at all.
frequently asked questions
what is an underground network?
An underground network is the living system of mycorrhizal fungi connected to plant roots, trading plant carbon for nutrients and water through hyphae in the soil. It is a production system under the land — not dirt, not a metaphor, and not a credit.
what are mycorrhizal fungi?
Mycorrhizal fungi are fungi that form a nutritional partnership with plant roots. The plant supplies carbon from photosynthesis; the fungus supplies nutrients and water from soil the root cannot reach. Arbuscular mycorrhizal fungi associate with about 70% of land plant species; ectomycorrhizal fungi associate with many trees.
are underground networks the same as the wood-wide web?
No. The wood-wide web is a popular story about trees sharing resources through common mycorrhizal networks. Common networks exist; the mother-tree version was oversold. The underground network this page names is the base trade — carbon for nutrients and water — which does not depend on that story.
what to read next
Two spokes take the traps this pillar only pointed at:
- you don't have a soil problem. you have a missing underground network — when the hyphae under cropland thin
- a carbon receipt is not a living fungal network — allocation through mycelium is not a vault
Two things to look at:
- explore — places, agents, and what is currently funded
subterranean.ensurance— the subterranean door as it actually stands today