The underground forest
Buried in the soil are the lattices and networks of another kingdom of life, one that’s inextricably connected with what grows above the ground. Fungi determine the types of trees that thrive, and change the quality and health of soil. So, what exactly are they up to down there—and what powers do fungi have that humans could harness?
Piano Flat, Waikaia Valley, northern Southland.
Autumn’s long sigh is on the land, the beech forest flush with mushrooms after recent rain. I’m on my knees, my gaze drifting along the side of the heavy root buttress of a big red beech. Slimy cream-grey mushrooms, slippery as fish, shoal along its base. Tiny white ones teeter above the forest floor. Everywhere I look, mushrooms sprout from the leaf litter. I’m here with David Orlovich, a mycologist from the University of Otago. He and his team have come south from Dunedin in the hope of adding to the scant repository of research that exists into these fungi. Expeditions like this can be hit-and-miss affairs—if there hasn’t been just the right combination of cool temperatures and rainfall, you might walk through a patch of forest like this and find very little.
Today, though, we’ve struck it lucky. There are little armies of gold mushrooms and dark-red conical ones, clusters of little gnome hats and branching coralline fungi, all in the earthy, nostalgic colours of old New Zealand: the browns and creams of Crown Lynn ceramics, the tan of suitcase leather and old armchairs, the pale pink found inside a conch shell.
Orlovich reckons this patch of forest has perhaps 50 to 100 species of mushrooms in an area the size of a tennis court. And what we can see is only the surface detail—mushrooms are just the reproductive parts of fungi. The rest of the fungus lives underground.
At the base of a large mustard-yellow mushroom, Orlovich digs his pocketknife into the soil and levers out a fistful of mycelia, a dense clump of fine threads the same yellow as the mushroom. These fungi attach themselves to the root tips of plants in symbiotic relationships called mycorrhizae. Orlovich pulls out a beech root and shows me the little white shoots at the end. “The tree is sending carbon, from photosynthesis, down into the roots,” he says. “And the fungus is sucking that sugar out.”
In return, mycorrhizal fungi help the trees they live beneath, supplying them with nutrients such as phosphate and nitrogen drawn from the soil. (Trees often can’t extract enough of these by themselves.) Mycorrhizal fungi create vast, intricate networks of those fine, clumped threads Orlovich just showed me which enable the trees of a forest to exchange carbon with each other. Some researchers describe this carbon exchange as a form of social welfare, with stronger trees providing resources to weaker ones for the overall benefit of the forest. Others see it as a form of parasitism. As always in nature, the truth is likely to be a complex combination of the two.
But what if there’s more going on than meets the eye? “We always focus on the trees, as if the fungi are in the service of the trees,” Orlovich says. “But the fungus is fertilising the tree and harvesting the products of the tree. If the fungus wasn’t there, the tree wouldn’t be able to grow. So, in a way, the trees are being farmed by the fungi.”
New Zealand’s beech forests are spectacularly rich in mycorrhizal fungi, but it’s thought that we’ve catalogued less than a third of the species that live here. In fact, there are so few people studying our fungi that even just figuring out what we’ve got would be the work of several lifetimes. And that’s without understanding what is going on under the soil.
“The big unknown thing in my mind,” says Orlovich, “is what do they all do? Why are there so many species?
What drives them to differentiate from each other and evolve? So at the very basic level, we don’t know how they’re working or exactly what they’re doing. My head just kind of explodes at this point when you start to think about the reality of it.”
Oban, Rakiura. About 50 people from all around New Zealand have gathered in the Stewart Island Community Centre for the 34th national Fungal Foray, an annual event in which the most devoted amateur and professional mycologists get together to collect and describe as many fungi as they can in a new area.
As everyone scatters across the island’s network of paths, I tag along with Kent Jacobsen and Stephanie da Silva, a young couple from Whakatāne. The pair, amateur mycologists, have driven down the country for the Fungal Foray, stopping to look for mushrooms along the way.
We plunge into the forest, our eyes locking onto the little clusters of mushrooms that pop up here and there. Da Silva shows me one with a shimmering lime-green stipe, or stalk. I’m intrigued to see Entoloma hochstetteri, the little blue mushrooms that adorn our $50 note, throughout the forest. Occasionally, da Silva passes me a mushroom to sniff. One smells like crayons, another like a swimming pool with too much chlorine in it, and yet another like baby powder. The couple carefully remove the most prized specimens, placing them in a little wooden box they share.
One of the big advantages of an official event such as this is the ability to collect native fungi, as to gather them from conservation land without a Department of Conservation (DOC) permit is illegal.
“I’m going to be picky about what I collect today,” says Jacobsen. “At the last foray we collected about 600 species. The amount of processing and writing down was just too much. I just want to relax a bit this time.”
This, he tells me, is their fourth foray. “It’s like opening a box of presents,” says da Silva. “You never know what you’re going to find. I always find something different.”
“No two mushroom hunts are the same,” says Jacobsen.
The chance of discovering a new species, he tells me, is part of what keeps them coming back. “A hundred times we’ve walked out of the forest thinking we’ve found a new species. We’ve both found mushrooms that we’ve been told are only the second reported specimen. So we’re very close to getting a first record.”
The decision to hold this year’s Fungal Foray on Rakiura was somewhat controversial among the regulars, because the island has no beech forest. Rather, the forests here are dominated by rimu, miro and southern rātā, and these trees’ fungal partners don’t produce mushrooms. (Almost 80 per cent of plants host non-mushroom-producing mycorrhizal fungi.) That means mushrooms are scarcer, and most of those we do see are the type that grow on rotting plants, not living tree roots. Still, it’s the first foray on Rakiura, and there’s plenty to find.
Walking on ahead, I find Eric McKenzie looking at rust—a plant disease caused by fungi—on the leaves of a native shrub. He passes me a hand lens, allowing me to see the tiny white bugs that are eating the microscopic fungal spores. Native rusts, he tells me, don’t do too much harm to native plants. Over millions of years, they’ve found an equilibrium between parasite and host. But when foreign fungi arrive and begin to grow on plants that haven’t evolved defences, the results can be disastrous—as in the case of myrtle rust, which threatens to kill native myrtle species such as pōhukutawa, rātā and mānuka.
This rust could easily be a new species. McKenzie pulls off a couple of leaves and puts them in his bag to identify it back at home base. These, along with everyone else’s most interesting fungal finds, are due for an appearance on the table later in the day.
The table is the business end of any Fungal Foray. As the foragers drift back to the community centre from the bush, today’s table quickly becomes covered in mushrooms and fungi-speckled leaves.
Here on the table is where you learn whether a beautiful mushroom you collected was also found by ten other people or is in fact a rare species—perhaps even one that hasn’t been described. And if you want a mushroom identified, this is the place to get it done. Around the room, microscopes are working overtime as everyone gets down to the hard grind of identifying, cataloguing and storing their finds. I tune in to some of the beautifully descriptive common names. Waxgills. Inkcaps. Earth tongues. Dead man’s fingers. Stinkhorns.
The foray participants are a diverse bunch. Around a third are amateur collectors, while the rest are students or professional mycologists employed by crown research institutes such as Manaaki Whenua–Landcare Research or Scion. Many of these scientists study fungal pathogens such as rusts, applying their skills to biosecurity measures to protect the country from invasive species. (McKenzie’s rust turns out to be a new species.) A few here are trained taxonomists, their chief aim being to collect, document and formally describe our native fungi. Taxonomy—the hard graft of cataloguing species—is already an endangered profession but, when it comes to fungi, it’s almost an extinct art, with funding and collecting opportunities painfully rare.
Given how little we know about our fungi, this is of major concern, says Peter Buchanan from Manaaki Whenua. “We only know about a quarter to a third of the fungi New Zealand holds,” he tells me.
“We’ve only recorded about seven or eight thousand different species, and we think there’s 20,000 to 25,000, at a conservative estimate, based on what other countries have.”
(Others I talked to put this figure closer to 40,000 species.)
Recently, 30 native New Zealand fungi were added to the International Union for Conservation of Nature (IUCN) Red List of Threatened Species. Among those are three critically endangered species: Hypocreopsis amplectens, or tea tree fingers; Deconica baylisiana, an alpine pouch fungus that was recently rediscovered in the mountains of Otago, having not been seen for 50 years; and Abstoma purpureum, a sand-dune puffball that may already be extinct.
Establishing a basic knowledge of what we actually have living here is crucial. “We can’t adequately conserve a species unless we know it exists,” says Buchanan.
Getting to know our fungi is also of vital importance to biosecurity. “Documenting what actually occurs here natively helps our understanding of which fungi are invasive and do not belong here,” he says.
For many professional mycologists, the annual Fungal Foray is one of their few chances to do what they’ve trained for. As organiser Renee Johansen, an ecologist at Manaaki Whenua, tells me, “This event is really important because people get a chance to go out and collect, hone their skills, share their knowledge and add to the New Zealand collection.”
It’s also about moral support. “Science can be quite isolating,” she says. “You can spend a lot of time alone in the lab or in front of your computer, reading the research, writing the papers and wondering, ‘What’s the point? Does anyone even care if I give this fungus a name?’ And then you come to an event like this and realise, ‘Oh, yeah, these people care.’”
Fungi are mostly invisible, but they’re essential—to plants, to forests, and thus to human existence.
“Very few plants grow without mycorrhizal fungi,” says University of Canterbury ecologist Ian Dickie. “It’s an essential and fundamental part of the plant. This is equally true of a human. You are not just the human cells in your body. It’s also all the bacteria in your gut and the fungi and bacteria growing on your skin that create the organism that’s you. For a plant, that just happens to be mycorrhizal fungi.”
It’s a partnership thought to go back to the earliest days of plant evolution, more than 400 million years ago. The first land plants, which evolved from marine algae, had no roots. They may have only been able to get established on land with the help of mycorrhizal fungi.
Here in New Zealand, our beech forests and their fungi have been through a lot together. During the last ice age, when the South Island was covered in glaciers, beech species were almost wiped from the land by the advancing ice. The trees probably clung to existence in warm pockets like the one I visited at Piano Flat. When the ice retreated, it left denuded land—and in order for the forest to grow back, beech seeds and fungal spores had to find their way out onto the exposed land at pretty much the same time.
Most fungi rely on wind to spread their spores, but some—such as New Zealand’s pouch fungi—possibly rely on animals to do the job. Pouch fungus mushrooms look like berries, perhaps in order to trick birds into eating them. Another theory is that they rely on insects to spread their spores. Either way, as soon as fungi spores and beech seeds found themselves in the same place at the same time—for instance, in the dung of a browsing moa—new seedlings sprouted.
When humans arrived in New Zealand, the beech forest was again forced back, this time by fire. In its place grew tussock grasslands with their own complement of fungi. Research shows that as soon as you go a couple of tree lengths away from the forest edge, none of the beech forest’s favourite fungal partners are in the soil.
What you will find, however, are intruders.
Last autumn, during the nationwide COVID-19 lockdown, I found myself taking daily walks across my local golf course. I marvelled at the sight of hundreds, perhaps thousands, of Amanita muscaria mushrooms sprouting beneath the pines.
Ask anyone to draw a toadstool and the most likely result will be a colourful sketch of Amanita muscaria—a big, bright-red mushroom with white spots.
These days, it’s found all around New Zealand. It’s also one of the most important mycorrhizal fungi for pine trees. As such, it is a leading conspirator in the spread of invasive pines (see sidebar)—and now, Amanita is moving into native bush.
Amanita is highly visible, but it’s probably not the only imposter. There are likely other, less conspicuous exotic fungi also creeping into our forests—and we’re inviting them in.
Dickie is most concerned about soil movement, and what we might be shifting, unseen, with that soil. He mentions the government’s One Billion Trees Programme, which aims to plant a billion trees throughout the country by 2028. There has been talk of eco-sourcing the plants—harvesting seed from the same location as they will be replanted in—but Dickie believes we should be doing the same thing with the soil, “so that you’re not taking soil from one site and moving it to another site. That’s going to spread pathogens. It’s going to spread non-native fungi.”
These fungi could facilitate the invasion of weeds into native bush. Douglas fir is much more shade-tolerant than pine trees, which has allowed it to creep into native forest in some places around New Zealand, especially where the understorey has been disturbed. It is also adept at forming new relationships with a wide range of fungi. A recent study by Holly Moeller from the University of Canterbury showed that Douglas fir was using non-native fungi to invade beech forests—where it was also helping itself to our native fungi.
The effects of this invasion on our native forest are yet to be studied. Like everything else in the fungi world below ground, what little we do know only raises many more questions.
New Zealand’s fungi have evolved in isolation from their counterparts overseas. That means we’ve got many species that are similar to, but slightly different from, well-known species elsewhere. Shiitake and oyster mushrooms are eaten all round the world, and we have native versions in our own forests. Māori ate them, and research is currently under way into reestablishing edible species such as tawaka (Cyclocybe parasitica) and native lion’s mane (Hericium novae-zealandiae) as staple food sources, or even commercial crops.
But fungi have many uses outside of the culinary. Current research is looking at the use of fungal mycelia in 3D printing as a replacement for plastic, and in cleaning up agricultural waste (mycelia produce enzymes that dissolve the waste into a form the fungi can eat). An Auckland company called BioFab is currently manufacturing packaging out of the mycelia of native fungi. Molecular tools such as gene sequencing are allowing us for the first time to really see what’s going on in our soils.
“The whole field has just exploded,” says Dickie. “We’ve never been able to see below ground and understand who’s who and where they are. And suddenly we can.”
It also looks like we might be able to turn the destructive tendencies of some native fungi to our advantage.
The Armillaria family of fungi are found around the world, and can grow to cover huge areas—a single Armillaria fungus in Oregon stretches almost 10 square kilometres and is thought to be the largest living organism on the planet. (This fungus could be more than 8000 years old, which would also make it one of the oldest living things on Earth.) In New Zealand, we have our own Armillaria species, Armillaria novae-zelandiae, known to Māori as harore.
Harore is a hunter of trees, with a root-like structure that snakes up to 60 metres through the soil in search of new food sources.
It’s very common in the New Zealand bush. “If you’ve ever gone tramping and seen a log or tree or stump covered in great big, shiny, honey-coloured mushrooms, that’s probably what you’re looking at,” says University of Canterbury masters student Genevieve Early.
In native forests, harore breaks down decaying wood, recycling nutrients into the understorey. “In native forests it tends to behave pretty well,” says Early. “But if you give it a forestry plantation, it rips through it.”
When harore gets into commercial pine forest, she tells me, it kills seedlings and stops trees growing. She’s now looking at how we might set harore loose in areas infested with wilding pines.
Inoculating wood with Armillaria spores in the areas where wilding pines have been felled, says Early, will provide a buffer against a resurgence of the weeds, preventing pine seedlings from regenerating, and killing any remaining pines. “I think on its own it would be unlikely to provide a solution to the entire problem, but I think it could definitely be part of the toolbox.”
Harore could be our fungal avenger, slaying pine trees in the name of biodiversity. A native, edible, pine-killing mushroom with tentacles half the length of a rugby field, which glows in the dark. If that’s not enough to get people excited about fungi, I’m not sure what is.