Global Mapping Reveals the Vast Underground Web of Mycorrhizal Fungi

Scientists have produced the first global map of mycorrhizal fungal networks—microscopic filaments that attach to plant roots and transport nutrients through soil. The map, created by a team led by ecologist Justin Stewart, quantifies the extent of these networks and identifies where they are most and least dense.

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Mycorrhizal fungi have partnered with plants for roughly 450 million years, exchanging nitrogen and phosphorus for carbon derived from photosynthesis. This long-term symbiosis underpins the flow of carbon deep into the soil column.

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• Justin Stewart – lead ecologist, Society for the Protection of Underground Networks (SPUN)

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• Adrian Florido – NPR reporter who conducted the interview

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• Society for the Protection of Underground Networks – coordinated data collection and analysis

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• New York Times – reported on dense fungal networks under grasslands, providing additional context

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Using a combination of soil samples, satellite observations, and artificial-intelligence algorithms, the team estimated the total length of fungal threads at approximately 68 quadrillion miles—about 730 million times the distance from Earth to the Sun. A single teaspoon of soil can contain up to 100 meters of fungal filaments. Spatial analysis shows the highest densities in wetland ecosystems such as the Everglades, while desert regions like the Sahara exhibit the lowest concentrations. Grasslands also display “particularly dense” networks, a finding highlighted by the New York Times.

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Mapping these subterranean pathways provides a baseline for protecting an ecosystem component that has previously been invisible to most conservation strategies. Stewart emphasizes that knowledge of distribution is a prerequisite for effective stewardship: without it, policymakers cannot target protection measures where they are most needed.

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• Justin Stewart described the network as “vast” despite the absence of visible mushrooms, underscoring its hidden nature.

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• He reiterated the project’s guiding principle: protecting an ecosystem element requires first knowing its location and extent.

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• “There's no mushroom, but it's a vast network,” — Justin Stewart, Ecologist, SPUN

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• “You can't protect what you don't know.” — Justin Stewart, Ecologist, SPUN

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The research team plans to refine the map with additional field data and to integrate the findings into land-management policies. By expanding the dataset, they aim to monitor changes over time and to inform conservation priorities for ecosystems where fungal networks are most critical.

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