Mycorrhizal networks
The Forest's Hidden Internet Has a Billing System
Beneath every forest floor runs a living network that trades nutrients for sugar — and occasionally cuts off neighbours who don't pay up.
The Idea
The relationship between fungi and plant roots — mycorrhizae — is one of the oldest alliances on Earth, stretching back roughly 450 million years to when plants first colonised land. But calling it a 'wood wide web' (as the popular press loves to do) undersells how strange and commercially precise the arrangement actually is. Fungi can't photosynthesise, so they tap into plant roots to collect sugars. In return, their thread-like hyphae extend far beyond what roots could reach alone, scavenging phosphorus, nitrogen, and water from pockets of soil too fine for roots to access. The plant gets minerals; the fungus gets carbon. So far, so mutually agreeable. What makes mycorrhizal networks genuinely surprising is the directionality and conditionality of the exchange. Carbon doesn't just drift through the network — it flows, and recent research suggests fungi actively regulate that flow based on which plant partners are delivering the best return. Some species appear to withhold nutrients from plants that aren't photosynthesising enough to pay their share, and favour those that are. This isn't conscious behaviour, but it's not simple osmosis either. It's a biochemically mediated negotiation happening in real time, across a network that might connect dozens of trees in a single hectare. The forest floor, in other words, is running something closer to a market than a commune.
In the World
In 2016, ecologist Suzanne Simard published findings from decades of fieldwork in the forests of British Columbia that changed how many scientists talked about trees. Using radioactive carbon isotopes as tracers, she demonstrated that carbon moved from mature Douglas firs through mycorrhizal networks into the roots of younger seedlings growing in their shade — seedlings that weren't photosynthesising enough to sustain themselves. The older trees weren't just coexisting with the young ones; they appeared to be subsidising them. Simard called the large, well-connected trees 'mother trees', a term that generated as much controversy as it did headlines. Critics argued the language implied intentionality that the data couldn't support, and that some of her conclusions were overstated. The debate is genuinely unresolved: subsequent studies have produced mixed results about how consistently and how much carbon actually transfers between trees in ways that benefit the receiver. What's not in dispute is that mycorrhizal networks do move resources between plants, and that the topology of the network — who's connected to whom, and how richly — shapes which trees thrive. Whether that constitutes 'communication', 'cooperation', or simply elegant chemistry operating at scale is a question that keeps forest ecologists productively at odds.
Why It Matters
Most of us move through forests — or past houseplants, or through farmland — with a rough mental model of plants as individual organisms competing for light and space. The mycorrhizal picture complicates that cleanly. Plants are, in a meaningful sense, embedded in networks they didn't choose, trading with partners they can't see, in exchanges governed by biochemical rules that look almost economic in their logic. That reframe has practical stakes. Agriculture has spent decades breeding crops and treating soils in ways that disrupt or destroy mycorrhizal relationships — heavy tillage, phosphorus-rich fertilisers (which reduce a plant's incentive to invest in fungal partnerships), and fungicides all degrade the network. As researchers look for ways to grow food with less synthetic input, restoring mycorrhizal function is increasingly part of the conversation. But beyond the practical, there's something worth sitting with here: the boundary of what we call an 'individual' organism is blurrier than it looks. A tree is also, partly, its fungal partners, its microbial collaborators, its network position. That's a quiet challenge to how we tend to draw lines around living things — including, perhaps, ourselves.
A Question to Ponder
If the health of a tree depends partly on a network it didn't build and can't control, what does that suggest about how we think of resilience — in ecosystems, or in anything else?
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