The Forest Beneath the Forest
Walk through an old woodland and you see trees — but what you cannot see is arguably more extraordinary. Beneath your feet, a dense web of fungal threads (called mycorrhizal networks) connects the roots of neighbouring trees, enabling them to exchange nutrients, water, and even chemical signals. Researchers have nicknamed this the "wood wide web."
What Are Mycorrhizal Networks?
Mycorrhizae are symbiotic partnerships between fungi and plant roots. The fungi colonise tree roots and extend far into the surrounding soil as ultra-thin threads called hyphae. In exchange for sugars produced by the tree through photosynthesis, the fungi dramatically increase the tree's ability to absorb water and minerals — particularly phosphorus and nitrogen, which are often scarce in forest soils.
When a single fungal network links multiple trees, it becomes a common mycorrhizal network (CMN) — the basis of the wood wide web.
What Do Trees Share Through These Networks?
Research has revealed that connected trees can transfer a surprising range of resources and signals:
- Carbon (sugars): Larger, established trees (sometimes called "mother trees") can send photosynthetically derived carbon to seedlings growing in low-light conditions under the canopy.
- Phosphorus and nitrogen: Nutrients can move between trees depending on need and availability.
- Water: During drought, networks may help distribute moisture more evenly.
- Defence signals: When a tree is attacked by insects or pathogens, it can release chemical signals that travel through the network, priming neighbouring trees to boost their own defences.
The Role of "Mother Trees"
Ecologist Suzanne Simard's research in Canadian forests identified large, old trees as hub trees — highly connected nodes in the mycorrhizal network. These mother trees support dozens of younger trees, especially their own offspring seedlings, by sharing carbon resources. When mother trees are removed, the wider network can weaken significantly, affecting forest regeneration.
Which Trees Are Connected?
Mycorrhizal networks are widespread but not universal. There are two main types:
- Ectomycorrhizal networks: Common in temperate and boreal forests — oaks, beeches, pines, spruces, and birches. The fungi form a sheath around the outside of the root tip.
- Arbuscular mycorrhizal networks: More common in tropical forests and grasslands. The fungi penetrate root cells directly.
Interestingly, the networks are often species-specific to some degree — trees of the same species are more likely to be well-connected, though cross-species linkages do occur.
Implications for Forest Conservation
Understanding mycorrhizal networks has changed how many ecologists think about forest management:
- Clear-cutting destroys the network entirely, making reforestation much harder.
- Selective logging that retains mature hub trees helps maintain network integrity.
- Monoculture plantations support far simpler networks than biodiverse natural forests.
- Protecting old-growth woodland is not just about individual trees — it is about preserving the entire underground ecosystem.
A New Way of Seeing the Forest
The concept of the wood wide web invites us to rethink what a "forest" actually is. Rather than a collection of individual competing plants, a forest is better understood as a deeply interconnected community — one where cooperation and resource sharing are as important as competition. It is a perspective that makes spending time among trees feel even more profound.