Chapter 1

An Underground Tapestry of Give and Take

As we leave the gravel road and step into the forest, it seems more like a dream of a forest than a real place. Or maybe it’s real but we aren’t. We can’t hear our footsteps because the forest floor is deep and muffled with fallen needles and branches and other debris, all silently acquiescing to the hidden hungers of microscopic life. We can’t hear our voices — at least, I can’t hear their voices when they disappear from view, and I startle at the sudden and complete silence. I walk faster to catch up and not be the pain in the ass who interferes with their work by getting lost. Because I talked myself onto this research trip and offered to help set up the site, and I’d hate to make them regret saying yes.

The forest floor is so soft and springy that I feel a little seasick. I follow a will-o’-the-wisp of laughter to a cluster of young trees, and then the pitch of the land changes and I’m plunging downhill. I don’t worry about falling because all the hard edges of the forest seem so padded with either greenery or rot that I don’t think a tumble would hurt. I pass great humped shapes among the trees — boulders or maybe fallen trunks, although they look like whales surfacing, velveted in brown and green. I finally catch sight of University of British Columbia ecologist Suzanne Simard’s blonde hair, which might be the brightest thing in the entire Malcolm Knapp Research Forest, and rush to catch up.

We’re still surrounded by living trees, but here and there are ageing stumps that are all around the same height. Some still have patches of bark, most are slicked with white and green lichen, and some are encrusted with charcoal. A few have a little fright wig of splinters on top. All have a gaping hole a few feet from the ground that’s about as big as my two fists put together — a hole that’s flat on the bottom and frowning down on top. The stumps look like many things — small statues of the Easter Island mo‘ai, eyeless tiki gods, the unhappy ghosts of trees, all shrieking soundlessly about the massacre they suffered and the upcoming harvest scheduled for this very spot.

‘Why do they have such sad faces?’ I ask Simard and Jean Roach, her long-time friend and forestry colleague.

‘This forest was harvested by hand back in the 1940s,’ Simard tells me. ‘The men made those holes so they could stick in a piece of wood called a springboard. They’d stand on that to make the cut higher up the stem, away from the curvature of the base.’

‘Eighty years ago!’ I say. ‘I’m amazed these stumps are still here after all that time.’

She looks around. ‘This was an old-growth cedar forest. Now it’s cedar mixed with hemlock and Douglas fir, but if we let it go for 500 years the cedar would retake it.’

She and Roach continue tramping down the slope, following their GPS to the centre of the research site. I take a few pictures of the sad-sack stumps before I follow them, feeling a little silly about my rush to anthropomorphise. But screw it, I decide: if Canada’s timber industry didn’t want the odd wanderer to read these stumps as an indictment of humanity’s harsh hand in the forest, they should have whittled those holes into smiley faces.

After I heard Simard speak at the Urban Soil conference in 2015, she seemed to be in the news more and more. The science media were paying lots of attention, and there were several of her TED Talk videos bobbing around on the internet, as well as an audio interview on Radiolab. By the time I was ready to visit her for a second time in 2017, I was afraid she was so inundated with requests from people like me that she wouldn’t have the time or the bandwidth for my questions. And that seemed to be the case for a while, as my emails and calls went unanswered. When I finally heard from her, she was apologetic: family complications and weeks spent deep in the forest had intervened. She invited me to spend a few days with her in British Columbia in the fall, helping her and Roach set up plots for a huge, multisite study she had launched called the Mother Tree Project. And if I wanted to get a better idea of what the project was about, I could drive up the day before the work began in Malcolm Knapp and hear her explain it to a group of commercial foresters near Merritt, British Columbia.

I arrived in Merritt to meet up with Simard and her postdoc, Teresa (Sm’hayetsk) Ryan, whose research focuses on increasing the understanding of how the Indigenous people of North America cared for the land. I had been wondering if Simard’s work might seem either threatening or irrelevant to men and women who make a living cutting down trees, but the foresters were friendly as we trooped into the woods. There, Simard and Ryan offered a quick summary of the Mother Tree Project, Simard’s biggest research effort yet, with support from several universities, First Nations, and government. It focuses Simard’s lifetime of research on the question of how to harvest trees in a way that allows forests to regenerate more quickly — an urgent question during this period of climate change, in which wet forests are becoming drier and forests are stressed as never before. Many people agree that the conventional practice of clear-cutting — logging all trees in a section of forest — and replanting them with seedlings grown in sterile, nursery soil needs urgent reassessment: clear-cutting is not only a body blow to the forest, but also burps a big pulse of carbon formerly stored in forest soil into the air. Forest soil loses half its carbon in a clear-cut. According to Greenpeace, the carbon emissions from deforestation comprise a fifth of global emissions, higher than those from transportation. However, it’s unclear which logging practices are better for long-term forest and climate health. The Mother Tree Project hopes to answer that.

In six forests dominated by Douglas firs across a climate gradient, the project will test four different harvesting strategies: conventional clear-cutting, single-tree retention (in which single trees will be spared every twenty to twenty-five yards, with preference for the larger and older Douglas firs that Simard calls Mother Trees), retention of 30 per cent of the forest in patches centred on Mother Trees, and retention of 60 per cent of the forest in patches centred on Mother Trees but with some of the smaller trees within the patch removed for harvest. In each site, they will also leave an unharvested plot as a control. In each of the harvested areas, they will test various replanting and seeding treatments. In the coming years and decades, researchers will return to these sites to assess forest regeneration, productivity, soil-carbon levels, and resilience.

The foresters had many questions, but none expressed any of the scepticism I anticipated about Simard’s basic premise that trees are engaged in a daily dialogue more vigorous than that among my neighbours. One forester asked, ‘Why do you call them Mother Trees?’ and Simard answered, ‘Because they nurture their young and they’re big and old!’ That got a laugh, presumably because several of the women there, including Simard, are mothers but are not big or old.

Simard had an easy time engaging with the foresters, at least in part because her French-Canadian family has a long connection to the hard work of harvesting trees. Her great-grandfather and his brothers, her grandfather and his brothers, and her father and uncles were all loggers. She adored her grandfather, who lived at the edge of a cedar-hemlock forest and cut small cedars for later use as telephone poles, removing them from the forest by horse and floating them across a lake to be milled. ‘He logged, but he had a light touch,’ she told me. ‘He was always trying to make the forest his home.’

Simard began following in her family’s footsteps in the 1970s, heading off to the University of British Columbia to get a degree in forestry. She worked summer jobs in the bush and began noticing that forestry had changed dramatically since the days of her ancestors. Clear-cutting was common. The vast empty spaces left behind were replanted much like the megafarms that were replacing small family farms across North America, where crop diversity had given way to hundreds of acres of only one crop. Where there had once been great diversity in the native forest — a mixture of conifers like Douglas fir, lodgepole pine, hemlock, and spruce, plus broadleaf trees like birch, aspen, cottonwood, alder, and willow — the forestry companies were replanting a single, highly marketable variety of conifer in rows, much like a giant cornfield. As the conifer seedlings started to grow, some of the broadleaf varieties would try to stage a comeback, only to be sprayed to death with herbicides. The assumption behind this approach in both forestry and agriculture is that the crop — whether conifers or corn — will grow better without competition for water, nutrients, and sunshine from non-crop plants.

After Simard graduated and began working for a private timber company in the 1980s, her initial revulsion at the ugliness of these plucked forests deepened to concern about their long-term health. ‘The great thing about that job was that I was in the forest all the time and really got to know it,’ she says of her work, which included laying out roads, planning the cuts and surveying afterward, planning the replanting, and even firefighting. ‘But I was horrified by what was going on. There had always been outbreaks of the mountain pine beetle, but they became massive. Industry responded by clear-cutting whole valleys.’

In the end, she concluded, ‘I had a good understanding that all was not well in the woods.’

Even though she still assumed that the prevailing wisdom was correct — that it made economic and maybe even ecological sense to replant the harvested forests in monocrops of pine, spruce, or fir — she started doing her own research to try to improve the health of the plantations. She had started grad school by the late 1980s and, still working for the timber company, set up hundreds of research plots in which she tested that wisdom. In plantations where native plants were starting to come back, she weeded them out in various combinations and degrees, looking for the point at which the conifers grew best as a result of reduced competition.

But that’s not what happened.

‘It was amazing,’ she says. ‘I was taking out alder and willow and birches and all these beautiful plants, and the conifers started dying. They kept dying. There was more disease and insect infestations. I kept looking at these plants and thinking something wasn’t right.’

She went on to get a job as a government forestry scientist, tasked with figuring out how to make the plantations more successful. She told her new employer that based on her research, the plantations should be planted with a mixture of trees — and not just a mixture of conifers, but also with a sprinkling of the native broadleaves. ‘That was anathema, the opposite of what they wanted to do,’ she says. ‘The government wanted industrial plantations with single-species rows like carrots and to produce two-by-fours, on and on into perpetuity.’

But her direct supervisor was interested in her research and urged her to get a doctorate so she could learn more about forest interactions. Still a government scientist, she enrolled at Oregon State University to study with ecologist Dave Perry, who had also come up with evidence that the presence of native broadleaves helped the conifers grow better. He was looking into the possibility that the trees were helping each other underground, perhaps via the long, silky strands of fungi. When we see mushrooms in the forest or elsewhere — I see hundreds in my Portland, Oregon, neighbourhood, especially after it rains — most of us don’t realise that these are just the fruits of an organism that weaves a vast underground tapestry of fine threads called hyphae. There is an almost-inconceivable density of these hyphae: every time we take a step in the forest, Simard says, there are around 300 gossamer miles of them under each footprint.

At around the time Simard began her PhD work, British scientists had found that grassland plants in pots could be connected underground by mycorrhizae — meaning ‘fungus roots’, a composite structure formed by the fungi and the roots. Some 90 per cent of land plants are colonised by these mycorrhizae. In forests and other areas, conifers and some other trees associate with ectomycorrhizal fungi, which cover their root tips. Other trees and nonwoody plants associate with arbuscular mycorrhizal fungi, which pierce their roots. Although scientists originally thought that fungi were stealing the sugary carbon fuel that plants make during photosynthesis, they’ve known since the 1880s that in many cases plants are trading their carbon fuel to the fungi — which cannot make carbon through photosynthesis — in exchange for water and nutrients. Beneficial partnerships like this between different species are called mutualisms, and they occur in all ecosystems and probably involve every species on Earth. And they are hugely important, influencing everything from nutrient cycles throughout the biosphere to individual cells.

Simard wondered if the reason the conifers in her research plots failed when she removed the broadleaves was that they were not only connected through the soil, but also provided some benefit to one another through their fungal support systems. As part of her doctoral research, she tested this idea, injecting a radioactive form of carbon into young Douglas firs and birches — two of the ‘early succession’ trees that together colonise a bare or disturbed landscape — growing next to each other in a forest clear-cut. She mimicked fluctuations in sunlight and found that the birch shared carbon fuel through its ectomycorrhizal connection to the fir based on the amount of shade the birch cast on the fir: the more the fir was shaded, the more carbon the birch transferred to it. On the other hand, the western red cedar she had planted nearby and which connects to other plants via arbuscular mycorrhizae instead of ectomycorrhizae only received a tiny portion of the birch’s largesse.

Later, one of her graduate students repeated this experiment over different seasons. As in the first experiment, when the birches leafed out in midsummer and the firs were shaded so much that they had a hard time photosynthesising, some of the birch’s carbon flowed to the fir. Early in the spring and later in the fall, when the birch had no leaves and could not photosynthesise, some of the growing fir’s carbon flowed to the birch. It isn’t clear which organism — tree or fungus — orchestrates the transfer, but it is obvious that they cooperate to maintain a diverse, healthy forest community. As in the original experiment, western red cedars planted nearby received very little carbon from either the birch or the fir, because cedars are not part of the ectomycorrhizal network joining those other trees.

Simard’s original experiment wound up being published in the prestigious scientific journal Nature in 1997 and set off an excited international clamour about this evidence of the ‘wood-wide web’. Implications of Simard’s work even reached Hollywood and inspired some of the thinking that led to director James Cameron’s film Avatar, in which the roots of the revered Tree of Souls offer simultaneous connection to members of the Na’vi clan. Shortly after the publication in Nature, a reporter from the Vancouver Sun called the now-somewhat-famous Simard to ask her opinion of the Canadian Ministry of Forestry’s practice of spraying broadleaf trees with herbicide in an effort to help the plantation conifers grow. Simard was still working for the ministry, finishing her PhD, and about to have a baby. She wearily replied, ‘For all the good it does, they might as well be painting rocks.’ That comment wound up on the paper’s front page, and she almost lost her job. She decided government was the wrong place for her and moved on to academia, where she’s been ever since.

Simard and an enthusiastic band of students — as well as a handful of other scientists around the world — continue to focus on the connections among trees and the underlying mycorrhizal networks and the implications these connections have for forests, especially given the hotter, drier climate to come. Scientists now think fungi have been building these water- and nutrient-distributing networks among themselves for a billion years and began extending them to plants a half-billion years ago, allowing plants to move onto the land from the waters and thrive there. Plants can’t move around to search for food or water, but an individual fungus can snake its tiny hyphae far and wide, poking into the gaps between soil particles for water and siphoning it into the network. The hyphae also wrap around those soil particles to enzymatically snap off minerals and make them quickly available to both themselves and the plants in their networks — without that enzymatic action, those nutrients would only become available to plants through a slow soil-weathering process. When the seeds of trees drop into the forest duff and start to sprout, they indicate their eagerness to join in this mycorrhizal feast by exuding a chemical into the soil through their roots, inviting the fungi to connect.

What are the advantages for these young trees? Simard and her students began studying this by planting seedlings in a forest near a Mother Tree. Some of the seedlings had fine-mesh bags around their roots that didn’t let the hyphae get through — so, they were prevented from joining the mycorrhizal network — and others had no mesh bags or other impediments to connection. They found that the linked-in seedlings were healthier, so much so that they survived at a higher rate than the solitary seedlings. They flourished even in the shadow of the Mother Tree, where it was hard to catch enough light to photosynthesise — and the lab determined that this was because the Mother Tree was pulsing extra carbon toward the seedlings.

Simard and other researchers around the world keep trying to tease out the value of these fungal connections: what are the benefits flowing through both ectomycorrhizal underground networks (root-like structures comprising fungus plus conifers and some other trees) and arbuscular mycorrhizal networks (comprising fungus plus most other plants)? Some of their studies are conducted in greenhouses with plants growing together in pots so the scientists can observe interactions away from the massive complexity of the real forest and eavesdrop on at least some of the dialogue among plants. Not a spoken language, but ‘a language that is chemical,’ explained Julia Maddison, a former student in Simard’s lab. ‘We don’t know how a language that is not based on sound or sight works, but we know it’s almost certainly more direct. When the chemical message arrives, it does something, without the need for a brain or other organ to interpret.’ When they want to compare plant communities not connected to a mycorrhizal network with communities that are connected, researchers grow one group in pots with each individual plant wearing a fine-mesh sheath around its roots to prevent connection; in the other group, plants within the pots are allowed to connect normally. To prevent plants from communicating with each other via airborne volatile chemicals — and plants do this regularly — they cover the tops with bags.

These accumulated studies show that the mycorrhizal networks offer trees and some other plants more than just carbon, water, and mineral nutrients. They also function as a forest early-warning system: when attacked by insect or fungal pests, trees emit a sort of chemical scream into the underground networks, prompting other plants to produce chemicals that make them less appetising targets for the pests. Other benefits are still shrouded in mystery. A study by Swiss scientist Florian Walder of flax and sorghum grown together showed that the flax shared very little of its carbon with the network and withdrew huge amounts of nitrogen and phosphorus, whereas the sorghum dumped in a lot of carbon but didn’t seem to be taking much of anything. Still, both plants grew better together than either did when growing only with its own kind, so they were clearly getting something from each other via the network — the science just couldn’t pinpoint what it was.

‘We just haven’t looked hard enough,’ Simard told me. ‘All these interactions are fluid, changing all the time, happening all at once. If we could look at the whole suite of interactions, we’d find out there is something else they’re getting out of the relationship.’

As tree seedlings grow, they keep adding mycorrhizal connections to the forest at large. They might associate with only twenty species of fungi when they’re young, but as they mature into large trees, they can build underground partnerships with hundreds of fungal species. Simard’s student Kevin Beiler came up with an ingenious method of tracing the fungal connections among Douglas firs in a thirty-by-thirty-yard plot containing sixty-seven trees in an old-growth forest near Kamloops, Canada. Beiler took DNA samples from the Douglas firs, then drilled into the soil to track the distribution on tree roots of two sister species of fungi from the genus Rhizopogon. The study revealed mycorrhizal networks that linked trees old and young, although the younger trees had far fewer connections than the older trees. One standout elder was connected to forty-seven other trees through its mycorrhizal connection with eleven individual fungi from the two species. That elder is presumably connected to more trees of other species and to another 100–200 species of fungi that weren’t being tracked by the study, all operating their own pipeline of goods, services, and news — in the form of chemical messages — from the forest at large.

To make an analogy to humans, this tree in Beiler’s study is like my friend Lori here in Portland, or my friends Linda and Karen back in Cleveland, where I used to live. None of them can go anywhere in their respective cities without seeing someone they know — someone they taught, or worked with, or lived near, or dated the brother of. Through those women, you can probably find anything or anyone in those cities. You connect with its history and life and current moment. But the comparison is meagre, because the trees and fungi are engaged in an ongoing dialogue that also sustains life. We can’t do that, despite our many tech-facilitated links.

Just as there are many tree species in a forest, there are also many species of fungi — at least fifty different kinds per acre, Simard says, even in a modest urban forest like the ones not far from my house in Portland. There are thousands of fungal species that can associate with Douglas fir, and they likely all offer a slightly different partnership to the tree. Just as trees can be early- or late-succession participants in an ecosystem — some find their niche early, like Douglas firs and birches; others only find their niche later, after those early colonisers have begun turning a bare, burned, or degraded landscape into a functioning biological community — there are also early- or late-succession fungi, which tend to associate primarily with the oldest trees in the landscape. The Rhizopogon of Beiler’s study is a late-succession fungi genus associated with the bigger, older Douglas firs that Simard is focusing on for the Mother Tree Project. While Simard and her lab staff don’t know everything this fungus does, they know it’s especially great at taking up water. Thus, the Mother Tree connected to those forty-seven other trees from Beiler’s study can keep offering them sips of water in a drought. And of course, that tree is likely connected to individuals from another 200 fungal species and is also connected to other tree species and their mycorrhizal networks. They are all whispering to each other in chemical sentences, giving to the forest community and taking from it in ways scientists may never be able to figure out.

The overlapping layers of connection are staggering and possibly infinite. ‘Everything is connected to everything else,’ Simard says. ‘We find nested networks that could cover the landscape. When we lay down a pipeline or make a road or some other cut into the earth, then we sever the networks. But minus those disruptions, it’s hard for me to imagine that it’s not all linked.’

Simard and her lab have been primarily studying the interactions among trees and fungi, but the web of forest relationships is much bigger than that, of course. Animals are part of every landscape, part of the symphony of interactions that create an ecosystem, but too much of our science is siloed into looking at all these living things in isolation from each other. While I was writing this book, Allen Larocque, one of Simard’s students, was investigating the impact of the Pacific salmon on these northwest forests.

Every year, millions of sexually mature salmon leave salt water for fresh water, returning to the rivers and streams where they hatched and spent the first part of their lives. This mad dash to spawn takes the salmon hundreds and sometimes thousands of miles from the ocean, even into mountain streams high above sea level. Most don’t make it: some starve on the way there, some sicken in polluted waters near cities, some are caught by fishermen, and many are seized and devoured by bears, otters, and eagles.

We’re used to thinking of salmon as a gift to eager inland creatures, but few of us realise that the salmon runs are also a huge nutrient pulse to forests and other landscapes. The primary nutrient they confer upon the land is nitrogen, which is essential to every living thing. Animals need it to make protein, DNA, and other important compounds; plants use it for all that plus it’s a major component of chlorophyll; we’re all hungry for it and dwindle without it. Nitrogen is the major gas in our atmosphere, but neither animals nor plants can use it in that form — it has to be ‘fixed’ in another chemical form, which happens naturally via bacteria or lightning strikes. Forests in the Pacific Northwest accumulate nitrogen in a variety of ways. Some are dotted with plants like the red alder tree that curry relationships with certain kinds of bacteria, forming special nodules in their roots where these bacteria fix nitrogen for themselves and the plant — an energetically demanding task that creates a form of nitrogen that lasts 400 years — and the trees provide them the energy to do this in the form of carbon fuel. Sometimes nitrogen drops to the forest floor from the branches of trees, where lichen host bacteria that fix nitrogen. But often the forest’s biggest single source of nitrogen is from the dead bodies of salmon. Scientists call their contribution the salmon shadow.

‘Kind of sounds like something from Mordor, this shadow spreading over the land,’ laughs Larocque. ‘It affects the whole landscape, even kilometres from the river. But the biggest effect seems to be 100 to 200 metres away.’ That deeper salmon shadow changes the forest dynamics and influences what kinds of vegetation, insect, and bird communities thrive there.

Larocque had been working on this project for three years when I talked to him and had taken several trips to streams where the salmon were leaping. Where there are salmon, there are also bears. During one trip, Larocque and his colleagues rounded a bend in the river to see a salmon lying on a rock, newly gashed open by powerful claws, its heart exposed and beating. They stepped away for a few minutes and while their heads were turned, the bear snatched away its prey. ‘The whole forest smells like a slaughterhouse when the salmon are running,’ Larocque says. ‘There are carcasses everywhere.’

And those carcasses are loaded with nitrogen. All plant and animal bodies contain nitrogen, which clusters in the proteins — meaning that protein-rich food is also nitrogen rich. In plants, proteins are concentrated in the most biologically active parts, like the root ends and the fast-growing shoots. ‘This is why herbivores prioritise fresh green foliage over the older foliage,’ Larocque explained. ‘The fresh green tips have higher nitrogen content, as well as being tastier, I imagine.’ Nitrogen thus accumulates in the food chain, and the animals that eat other animals — which are protein rich — have more nitrogen in their bodies than strict plant eaters. Even humans who are carnivores have more of a certain form of nitrogen — an isotope called 15N, which is heavier than ordinary nitrogen — than do humans who are vegan. Salmon are carnivores that accumulate a lot of 15N over their lifetimes. Thus, the salmon shadow on the land has a specific signature — that of 15N — making it easy for scientists to measure.

Some of this salmon-derived nitrogen makes its way deeper into the forest via bears and wolves that drag their prey to their favourite picnic sites, eat parts of the fish, and discard the rest. Teresa Ryan — who’s also working on the ‘salmon forest’ project — says that these carnivores can carry as many as 150 fish per day into the woods during the salmon run. But the Simard lab suspects there is a larger nitrogen-spreading mechanism at work — namely, the forest’s many overlapping mycorrhizal connections.

Larocque has begun to test this by first measuring the natural abundance of 15N in the soil, fungi, and vegetation at his test site — it’s there as the result of aeons of salmon bringing nitrogen upstream. He first deposits a fresh load of 15N onto the ground, simulating a rotting salmon. Then he takes samples of soil, fungi, and vegetation over time to see if he can catch this wave of heavy nitrogen moving through the forest’s many webs of relationships.

Miles from the forests of British Columbia, a University of Washington scientist stumbled upon another relationship that provides nitrogen to plants, including trees in a forest. ‘This was not a eureka moment,’ says ecologist Sharon Doty. ‘It was a “what the hell?” moment.’

Back in 2001, Doty was studying the stems of poplar trees as part of a project to conduct genetic engineering that would help the trees degrade environmental pollutants. But every time she’d prepare stem tissue for the first step of the process, what she describes as ‘slimy bacteria’ leaked out. She sequenced the DNA of the bacteria because she figured that if she knew exactly what it was, then it would be easier to kill. She was astonished when the bacteria turned out to be rhizobia — the best known of the bacteria that enter the root nodules of leguminous plants like clover and peas and produce nitrogen in exchange for carbon fuel. Until Doty’s discovery, scientists overwhelmingly believed that these particular bacteria only performed this nitrogen-fixing service in such nodules. The editors of scientific journals were hard to convince otherwise; it took her more than three years to publish a paper on her discovery.

The rhizobia and other nitrogen-fixing bacteria were clustered thickly inside the poplars’ branches, leaves, and roots. ‘Trees can defend themselves against pathogens, but they’re letting these microbes colonise them at a high density,’ Doty says. ‘We sometimes find millions of microbial cells per gram of tissue.’ The rhizobia enter through cracks in the roots and migrate throughout the tree through its vascular system. Doty thinks the rhizobia may also land on a leaf surface via a breeze, or in drops of rain, or be conveyed by insects. Once there, the bacteria gain access to the inside of the leaves through the stomata, tiny holes in the leaves that suck in the carbon dioxide needed for photosynthesis and expel unneeded oxygen.

Doty and her colleagues went on to study whether the nitrogen-fixing microbes found in the poplar leaves would do the same job in other plants. Using a solution made from the poplar rhizobia, they soaked the seeds and sprayed the roots of a wide range of other plants — from crop plants like tomatoes, maize, and rice to forest plants like Douglas firs and western red cedars — and found that all got a growth boost from these nitrogen-fixing bacteria. ‘I think this is a very ancient symbiosis,’ Doty says. ‘Conifers like Douglas fir diverged evolutionarily from flowering plants like tomatoes many millions of years ago. The fact that both of these plants allow the microbes to colonise and provide these profound growth impacts suggests that this is a way plants always got nutrients, not from primates like us providing them with chemical fertilisers.’

Some plants may need a boost from nitrogen-fixing microbes in their tissues more than others. Poplars tend to live in rocky areas with almost no soil, so they’re unlikely to benefit as much from the kind of underground sharing that trees in the thick of the forest get. Poplars are also an early coloniser that can flourish in rocky, sandy landscapes that don’t have a lot of other trees and, thus, not a lot of mycorrhizal pathways between them; it seems possible that they are able to do this because they’re especially good at attracting microbial partners to provide their nutrients instead. Another researcher, Christopher Chanway from the University of British Columbia, has found an abundance of nitrogen-fixing microbes in the needles of lodgepole pine, another early coloniser. Doty finds it plausible that these early colonising trees may make it easy for other trees to get a start in the forest by sharing some of their nitrogen through the emerging mycorrhizal networks.

Doty also found that the bacteria living in the poplar tissues can do far more than just provide nitrogen to the plant. The bacteria cluster inside the leaves near the stomata, producing a hormone that closes them during a drought, thus helping the plant save water. Even with the stomata closed, the plant doesn’t starve for carbon dioxide: as the microbes eat the plant’s carbon fuel, they release carbon dioxide as a waste product, just as we do, and that keeps the plant fed until the drought crisis passes. When Doty soaked the seeds of rice and other plants in the rhizobia solution, they, too, became more drought tolerant. Other researchers have done similar work with salinity tolerance, which is a huge problem in agriculture as irrigation tends to make croplands become saltier, and found that the microbes made plants more salt tolerant.

‘Microbes have this incredible power to help plants,’ Doty says. ‘It’s a huge untapped resource.’

A huge untapped resource for us as we try to manage the environments we’ve disrupted and continue to disrupt for our food, water, wood, living spaces, and so on — but business as usual for the rest of nature, where living things engage in constant, complicated interactions without our notice. As I plunged into the Malcolm Knapp Research Forest with Simard and Roach back in September 2017, I couldn’t help but believe that every quivering twig, every lip of fungus curling away from a fallen tree, every sprightly tuft of moss — everything — was throbbing with a dance of life carried on by multiple partners. Science is just barely beginning to catch on.

Not that we can fault the scientists. There is only the time and the money and the technology and the skills to address a sliver of what’s going on in the natural world — more of our science is directed elsewhere, often toward the kind of science that leads to product development — and it’s hard work. During my two days of participation, a lot of gear had to be schlepped into and out of the woods. Simard and Roach gave me a few things to carry, but Simard herself carried a bulging clown-car backpack stuffed with tools and fell more than once from the lopsided load. When we got to the site, they set their instruments down and looked dismayed. ‘That’s a lot of trees,’ Simard said.

‘A lot of trees,’ Roach agreed.

I was confused. They’re forest scientists — shouldn’t they be glad to see a lot of trees?

We got to work ‘taming the site’ — getting a baseline of what actually is there before woodcutters come in and conduct one of the four harvesting methods. First, Simard and Roach determined the exact centre of the circular site — it was right near a 1,000-year-old cedar that still towered fifty feet above us even though it was broken and burned — then began dividing the site into big pie-shaped wedges with white tape. We had to account for all the trees within the wedges — their general health, their girth and height, their species, and much more data — and it became my job to nail small, numbered metal tags into each one, just below where the tree would be cut. Thanks to the numbers — each of which corresponded to a slew of statistics Roach entered on the study paperwork, along with our initials as the source of the data — Simard, Roach, and future researchers would understand the variety and distribution of trees that had formerly covered the site. We would also estimate the amount of other vegetation at the site and carry away samples of soil and mosses.

As I started measuring and tagging the trees, wedge by wedge, I cottoned on to their dismay at the number of trees on the site. There were a lot of trees, mostly slender Douglas firs, hemlocks, and cedars that took root in the aftermath of the harvest nearly eighty years ago, plus a handful of bigger trees that had escaped it. I banged my fingers more than once as I tried to get the tags close to the ground, all facing in the same direction, and tried to keep the numbers sequential, although every once in a while, I’d realise I had missed a tree and would lope over to bang a tag into it. One of Simard’s students, Katie McMahen, followed behind me, calling out data about each tree to Roach, who jotted it down. I was just thinking I had the hang of this modestly challenging task when I heard McMahen call out, ‘I can’t find number 543!’ I went back and helped her look and together we found it — several yards from 542 and 544, and hard to locate in the maze of trees.

Simard was watching this from the side of a soil pit she was digging twenty feet away, laughing. ‘You know, Kristin,’ she called out, ‘those tags are still going to be here in a hundred years and the researchers are going to be saying, “Who was this KO that pounded in the tags?”’

It was funny but also a little dazzling. Simard’s old research plots from more than thirty years ago are still protected and studied. This, her biggest study of all, would be visited over and over again by scientists long after we were gone.

Later, I sat and watched Simard work on the soil pit, one of four for this site. She had laid a twenty-by-twenty-centimetre square on the ground and began removing the forest floor below. First, she pulled away the loose duff on top, then the so-called fermentation layer — where branches and needles and recognisable chunks of biology are decomposed by microorganisms — then the humus layer below, where those chunks are so decomposed that they’re unrecognisable. She kept digging until she reached the hard layer of mineral soil at the bottom. In a pit dug earlier that day, the mineral layer was more than a yard below the surface. This one was about two feet down. She picked at some chalky material in the hard soil. ‘Sometimes there are tiny shells, because all of this was once covered by seas,’ she mused. Then she pulled a tiny yellow branch from the fermentation layer and dropped it in my hand. It looked like a piece of coral but bendable and fragile.

‘Piloderma, one of the forest fungi,’ she announced. ‘It’s one of the showier ones. There are probably a hundred species of fungi in this forest, but most are hard to see.’

Later, McMahen told me how she and Simard met. She’d been working at the Mount Polley mine in British Columbia for five years. During her tenure, the dam to a big tailings pond — containing the ground-up rock left over from mining — broke and spilled a ‘slurry of toxic water and mud into Quesnel Lake, once renowned for being the cleanest deepwater lake in the world’, according to a local paper. Simard was brought in to consult about degradation of the nearby forest, and the two met and found a common interest in landscape restoration.

McMahen’s research isn’t only applicable to catastrophic mine disasters; it could address the more ordinary disasters that cause degraded landscapes the world over. ‘We’re testing some methods that use ecosystem legacies and memories,’ she told me. ‘Those are pieces of the environment before it was disturbed. Many things survive — fungal spores, seeds — and all those little memories help the system recover to where it was.’

It’s such a simple project. Part of it echoes the Mother Tree work: little trees will be planted near the edge of the forest in the midst of the spilled tailings, which she says are so degraded they’re hardly even soil. Some of the trees will be planted behind a trench that will cut off their access to the mycorrhizal networks operating in the forest, and some will not be blocked. McMahen and others will see how much the networks can reach past the edge of the living forest into the dead zone to breathe vitality into the new trees. Other trees will get a handful of forest soil as they’re planted. The idea is that some of the forest’s memory might endure in that soil and give the seedlings a boost.

‘Yeah, forest memory — that’s anything biological with a blueprint in it,’ Simard said when I asked her about the project. ‘Anything that provides DNA to the next living community.’

Is there living memory and DNA for wholeness everywhere, even in our most degraded landscapes? Even in our most degraded relationships, including those with each other?