If you walk a paddock at Mangaroa in late autumn, kneel down, and pull back a tussock of grass, you’ll see white threads. They’re fine, almost cobwebby, and they sit in the layer where the roots end and the soil begins. Those threads are mycelium — the body of soil fungi — and on a healthy pasture there are kilometres of them in every cubic metre of ground.
We talk a lot about cattle and sheep in regenerative farming. They’re visible. They’re charismatic. They’re the part of the system you can photograph. But the largest livestock at Mangaroa, by living biomass, isn’t on the surface at all. It’s the soil mycelium network beneath it — what we’ve come to call our underground livestock — and it does most of the work that makes the rest of the farm possible.
This post is about that network. What it is, what it does, why it matters for the carbon conversation, and what we try not to do as farmers in order to keep it alive.
What mycelium actually is
Most people meet fungi as mushrooms. The mushroom is the fruit. The body of the organism — the much larger part — is mycelium: a branching network of cell-thick filaments called hyphae, threading through soil, leaf litter, wood, and roots. A single mycelial individual can occupy hectares. The largest known organism on Earth is a mycelial network in Oregon that covers nearly ten square kilometres.
Inside a working pasture, two main groups matter. The first is saprotrophic fungi — the recyclers. They break down dead plant material, manure, fallen wood, and dead roots into forms other organisms can use. Without them, paddocks would slowly fill up with un-decomposed grass.
The second is mycorrhizal fungi — the partners. These form a literal physical connection with plant roots. The plant gives the fungus sugars (made from sunlight via photosynthesis) and the fungus gives the plant water and minerals it can’t reach by itself. Phosphorus is the headline nutrient mycorrhizal fungi deliver, but the list is long: nitrogen, zinc, copper, sulphur, and trace elements that grass roots simply can’t access on their own.
A pasture grass without a fungal partner is a plant with a much smaller effective root system. A pasture grass with one is, in effect, hundreds of times more rooted than it looks.
The cattle-mycelium loop
Here’s the part that’s easy to miss: the relationship between a grazing animal and the mycelium under its feet is not separate. It’s a single loop.
When a Coopworth ewe takes a bite of grass and moves on, several things happen at once. The plant is stimulated to regrow. To regrow, it has to spend energy, and it gets that energy by photosynthesising and pulling sugars down into the roots. Some of those sugars — researchers estimate up to 30% on healthy soils — leak out through the roots into the surrounding earth as root exudates. The exudates feed the mycorrhizal fungi attached to the roots. The fungi multiply, extend their reach, and bring back more water and more minerals to the plant. The plant grows back faster, bigger, and more nutrient-dense than before.
Multiply that loop across a paddock, a year, and a herd, and you start to see why grazing — done well — can build soil rather than degrade it.
The catch is in the phrase “done well.” The same loop, run badly, eats itself. Continuous set-stocking, where animals are left in one place for months, never gives the grass time to regrow, never lets the mycelium re-extend, and slowly converts living soil into compacted dirt. Adaptive grazing — short, high-intensity grazings followed by long recovery — is the management practice that lets the loop stay productive.
That’s the practice we work with at Mangaroa. Our sheep and cattle move through paddocks in a rotation that varies with the season: shorter recoveries in spring when grass is racing, longer ones in late summer and winter when growth slows. The mycelium gets the same chance to recover as the grass does.
Glomalin: where the carbon actually goes
If you’ve heard “regenerative agriculture sequesters carbon,” you’ve probably also seen the eye-rolls that come with it. Some of that scepticism is fair — the carbon-credit conversation has produced a lot of hand-wave estimates that don’t survive a soil core. So it’s worth being specific about the actual mechanism.
The most interesting part of the mycelium-carbon story is a glycoprotein called glomalin. It’s produced almost exclusively by mycorrhizal fungi (specifically the arbuscular kind, which dominate pasture systems). When mycelium dies and decomposes, glomalin doesn’t break down quickly. It’s sticky, water-resistant, and persistent. It binds soil particles together into the small crumbly aggregates you can crumble in your fingers when you pick up healthy topsoil.
Two things follow from that. First, glomalin is itself a carbon-rich molecule — by some estimates it accounts for 27% of the carbon in some soils. Second, because it stabilises soil aggregates, it traps other organic carbon inside those aggregates and keeps it from being respired back to the atmosphere.
In other words: the mycelium isn’t just sequestering carbon directly through its own glomalin. It’s also building the physical structure that lets the rest of the soil hold onto carbon for decades.
This is the part of the story that disappears when you swap a perennial pasture for an annual cropping system, plough the ground, or apply enough synthetic nitrogen that the plant stops needing the fungal partner. The glomalin stops being made. The aggregates fall apart. The carbon goes back up.
We’re honest about the fact that we don’t have our own glomalin lab data yet. What we do have is a partnership with Eco-index (Navigator X) for ecosystem mapping, and visible signs in the field: soil structure that holds together when wet, water that infiltrates instead of running off, dung that disappears within days, and native bush regenerating into pasture edges where we’ve stopped pushing. Those are the kind of indicators that show up before any soil-core number does.
What kills mycelium
If grazing well builds the underground network, it’s worth knowing what tears it down. The list, in roughly the order it matters:
- Tillage. Ploughing physically breaks the hyphae and exposes them to UV and air. Heavy cultivation will collapse a mycorrhizal network in a single pass.
- Synthetic nitrogen. When a plant has free nitrogen handed to it, it stops trading sugars for nutrients. The fungal partnership breaks down because it isn’t needed. Long-term studies show mycorrhizal density falls dramatically on heavily fertilised paddocks.
- Broad-spectrum fungicides. They don’t distinguish between the fungus on the leaf and the fungus on the root.
- Continuous overgrazing. No regrowth means no exudates. No exudates means a starved fungal community.
- Compaction. Heavy machinery and concentrated stock pressure on wet soil destroys the air pockets the network depends on.
We don’t till our pasture. We don’t apply synthetic fertiliser. We don’t use broad fungicides. We try not to have stock on wet ground. None of that is virtuous — it’s just the management that keeps the underground livestock alive.
The pasture is part of the ngahere
The piece we keep coming back to is that a Mangaroa paddock isn’t a field of grass with some animals on it. It’s an above-ground / below-ground system where the most active part is the part you can’t see.
This is the same logic that runs through the rest of the farm. The 500+ acres of native old-growth forest we steward, and the 700+ acres of pine being transitioned back to native ngahere, run on the same fungal infrastructure that runs the pasture. The mycelium under a pasture grass is genetically related to the mycelium under a tōtara. The same network is doing the same work, in different parts of the same valley.
When we talk about restoring the mauri of the whenua, this is a lot of what we mean. The mauri isn’t a metaphor sitting separately from the science. It’s the same thing the soil ecologists are pointing at when they talk about “intact fungal community structure” — the felt-sense version of the technical observation. A paddock with a working mycelium network feels different to walk on. The grass smells different. Water moves through it differently. The animals graze it differently.
You can pick up either language. The whenua is the same whenua.
What this means for what’s on your plate
You don’t need to hold any of this in your head to enjoy a piece of Mangaroa lamb or beef. The animal does its part of the loop without our explanation. The grass does its part. The mycelium does its part.
But if you’ve ever wondered why grass-fed meat from a regenerative farm tastes different to grass-fed meat from a conventional one — both animals ate grass, after all — a lot of the answer is in the ground neither of them can see. The grass on a pasture with a working fungal network grows differently. It’s denser in trace minerals. It’s longer in the secondary plant compounds — the polyphenols, the terpenes, the flavour molecules — that pass through the animal and into the meat. The same paddock, sprayed and tilled and conventionally fertilised, would grow grass that looks similar and tastes nothing like it.
The cattle and the sheep are the visible part. The mycelium is the part that makes them what they are. Both are our livestock. We try to look after them in the same spirit — in service to the soil, the seasons, and the future.
If you’d like to come and put your hands in the ground, the Farm Shop / Kete Kai is open Tues–Sun, and we run open days and Community Harvest Days through the seasons. Bring a kid. Pull back a tussock. The threads are right there.