Finding the Mother Tree: Discovering the Wisdom of the Forest

by Suzanne Simard

By October, I had the foliar nitrogen data in my hands. Pine seedlings growing among alder were rich in nitrogen, and those without it were depleted.

Policymakers, I thought, saw only the data of depletion. The short-term, the first roadside glance. Alder preempting resources that otherwise would be available to pine seedlings. But once I stood back and took in the longer sweeps of time and season and scene,

Where I’d eliminated all of the alder, I also lost far more pine seedlings to voles and rabbits, which had made a beeline for the needles. The critters Robyn and I had worried about had reproduced like crazy in the clipped alder piles.

I worried that in the long haul, in the decades to come, the reduction in soil nitrogen would reduce the growth rates of the open-grown pines that remained. Eventually I would learn that these alderless pines would become so malnourished that they’d be infested by the mountain pine beetle, and most of the rest would die. Three decades later, only 10 percent of the original seedlings planted in the bare-earth treatment would remain.

They missed what we could not yet fully see: how the symbiotic bacteria and mycorrhizas in the roots of the alder, and the other invisible creatures in the soil, helped the pine.

interactions over resources isn’t a winner-take-all thing; it’s about give-and-take, building more from a little and finding balance over the long term.

I was terrified of public speaking. “I keep having this nightmare where I spill my slides and have to speak off the top of my head.” The only time I’d given a talk cold like that, I’d frozen and almost passed out from embarrassment.

“Yeah, that’s why I’ll always be a technician,” he said. “But you can’t hide if you want change.”

her tears were never far away as she got older.

I remembered Dad telling me to imagine an audience as a bunch of cabbages.

Though we missed our home in the woods, he hadn’t mixed easily with the small-town, working-class culture of the pulp-mill crossroads,

half the free-to-grow pines now have some infection or injury that will eventually kill or maim them.”

productivity of century-old pine forests would dwindle by half where alders were no longer present to add nitrogen back to the soil.

In these high-elevation forests, a lot of cash was spent to grow seedlings in open spaces where they didn’t naturally exist. True enough that 20 percent more seedlings survived where the non-cash-crop shrubs were weeded than where they were left untouched—but only for the short term. In the same subalpine environments, spraying ferns into pincushions did not improve the long-term survival rate of spruce, but the short-term height growth of the prickly seedlings was a quarter more than where the ferns were left alive. These minimal, temporary yields were enough to satisfy the policymakers.

“Well, we need to better understand what we are winning and what we are losing at the same time,” I said. “Maybe there are better ways to improve the plantations than raking away the forest floor. It doesn’t bode well for long-term health when we remove organic matter and compact the soil. We need better data before applying these treatments over the whole landscape.”

“But we have to be careful, because the more birch removed, the more firs die from root disease,” I said. “Cutting and girdling stresses the birch and makes them vulnerable to root infections. As soon as we cut the birch, the infection overwhelms their roots and spreads to the roots of the firs, causing seven times the infection rates of untreated stands. I’m worried that we’re trading increased early growth for lower survival in the long run.”

forests structured mainly by competition, or is cooperation as or even more important?

changes the climate scientists were predicting. The ponderosa-pine woodlands were turning to grasslands, while the Douglas-fir forest was being overtaken by the ponderosas.

the very weeds and insects that were killing the forests might be the ones with the genes to persist as the temperatures rose and the rains changed.

principal question of my research program: How do mycorrhizal

networks affect the regeneration of trees in our changing climate?

The Douglas firs that Yuan Yuan and I had infested with western spruce budworm had dumped half of their photosynthetic carbon into their roots and mycorrhizas, and 10 percent of it had traveled straight to their ponderosa-pine neighbors. But what had me banging out an email to Yuan Yuan, now a professor at the Fujian Agriculture and Forestry University, was that only those pines connected by a mycorrhizal network to the dying firs, not those whose connections were restricted, were recipients of this inheritance.

I’d written back with an idea that had been germinating since the insect outbreaks had transformed our forests into oceans of dead trees: If dying trees communicate with incoming species, we might use this knowledge to better assist the migration of tree species as the old forests become maladapted to their native places. A warning-and-aid system—those infested Douglas firs telling pines to upgrade their defense arsenal, for instance—might be important for the growth of the new species or races (genotypes) as the old forests were dying back. As the injured Mother Trees slowly folded their cards, did they transmit their remaining carbon and energy to their offspring? As part of the active dying process. Like senescing grasses, handing over their remaining photosynthates to boost the next generation. Maybe they just dispersed the content of their dying cells randomly to the rest of the ecosystem, since energy is neither created nor destroyed.

The firs had increased defense-enzyme production with the budworm infestation, which was normal, but within a day, the ponderosa pine had done the same thing. “But look,” I wrote, “none of this happens unless the two tree species are linked in a network.”

Even slight injury to the firs elicited an enzyme response in the pine. The firs were communicating their stress to the pines within twenty-four hours.

Mother Trees Connect the Forest film

Could Mother Trees distinguish kin from stranger seedlings?

“Many of the kin are alive, but the strangers are dead.” Unrelated and unconnected to the Mother Tree, the strangers had perished in the summer drought.

The thirty-year battle over the entrenched dogma that competition was the only interplant interaction that mattered in forests

Under this Mother Tree, just as with the first, more kin seedlings were alive than strangers, especially in bags that allowed them to connect to the network.

That health depends on the ability to connect and communicate. This cancer diagnosis was telling me I needed to slow down, grow a backbone, and speak out about what I’d learned from the trees.

“Do you think it’s important that we’re seeing that Mother Trees are also bigger when they’re next to their kin?” Amanda asked. “It makes sense if they’re passing signals back and forth.” Of course it did. Being connected and communicative affects the parents as much as the kids.

“The amounts are small,” Amanda said, “but the Mother Trees are sending more carbon to the mycorrhizal fungi of their kin than the others! Kin-recognition molecules seem to have carbon and micronutrients.”

Of course, not all families are the same. Forests are mosaics too. That’s what makes them thrive. Birch and fir transmitted carbon to each other, even though they were different species, and to the cedars in their unique arbuscular mycorrhizal network. These old trees were not only favoring their kin, they were also ensuring the community in which they were raising their kin was healthy.

Maybe society should keep old Mother Trees around—instead of cutting most of them down—so they can naturally shed their seed and nurture their own seedlings. Maybe clear-cutting the old, even if they’re not well, wasn’t such a good idea. The dying still have much to give.

My unfinished business—my main lingering question—centered on this: Were the old Douglas-fir Mother Trees that were unhealthy—sick with disease,

using their last moments to transfer their remaining energy and substance to their offspring?

Our modern societies have made the assumption that trees don’t have the same capacities as humans. They don’t have nurturing instincts. They don’t cure one another, don’t administer care. But now we know Mother Trees can truly nurture

Grown intimately together, this forest had almost twice the productivity of the stands where we’d trenched between the species two decades earlier. This was the opposite of the usual foresters’ expectations. They figured that fir roots free of birch interference would obtain more of the resource pie, as though the ecosystem worked as a zero-sum game—the adamant belief that greater total productivity cannot possibly emerge from species interactions.

“Why are the plants so sweet under the birches, Auntie Suzie?” she asked.

Their roots and fungi draw water from deep in the soil, I told her, and with it bring calcium, magnesium, and other minerals, and this feeds the leaves so they can make sugars. The birches, with their cables of fungi, knit the other trees and plants together, and through their web share the nutritious soup drawn from the soil and also the sugars and proteins made by their leaves.

Mary Thomas had even called the birches Mother Trees—long before I had stumbled onto that notion. Mary’s people had known this of the birches for thousands of years, from living

The word “equal” is where Western philosophy stumbles. It maintains that we are superior, having dominion over all that is nature.

apart the ecosystem, to reduce it into its parts, to study the trees and plants and soils in isolation, so that I could look at the forest objectively. This dissection, this control and categorization and cauterization, were supposed to bring clarity, credibility, and validation to any findings.

for a study of the diversity and connectivity of a whole ecosystem to get into print. There’s no control! the reviewers cried at my early papers. Somehow with my Latin squares and factorial designs, my isotopes and mass spectrometers and scintillation counters, and my training to consider only sharp lines of statistically significant differences, I have come full circle to stumble onto some of the indigenous ideals: Diversity matters. And everything in the universe is connected—between the forests and prairies, the land and the water, the sky and the soil, the spirits and the living, the people and all other creatures.

high-density plots—where the planted firs were only a few meters apart—the understory was dark. The floor looked bare except for rusty needles, their acidity slowing down the cycling of nutrients.

Some of these new trees were toddlers, others kindergartners, still others juniors, this patch of forest starting to look like a schoolhouse, with diversity and kinship. The mycorrhizal network, I imagined, was becoming more complex as the forest aged, the biggest trees becoming the hubs—the Mother Trees.

I had learned so much more by listening instead of imposing my will and demanding answers.

In making the mycorrhizal-network map, I thought we might see a few links. Instead we found a tapestry.

that lingering question since my illness still haunted me: If we are equal to everything in nature, do we share the same goals in death? To pass the wand as best we can. Passing onward to children the most crucial material.