July 1993, somewhere in a British Columbia forest. Young trees planted in groups of three, fifty centimetres apart, are sealed one by one inside bags. Some are capped with a conical tent of varying opacity, put in place four weeks earlier, to give them an artificial sky, full sun, partial shade, deep shade. Then gas is injected. Into the paper birch bag, carbon dioxide labelled with carbon 14. Into the Douglas fir bag, carbon 13. A two-hour pulse, tents removed, in full light. Then you wait nine days, pull everything up, separate foliage, stems, coarse roots and fine roots, grind, burn, and read what the tissues contain. The question fits on one line: does the carbon of one tree end up in the body of another.
That scene, repeated in August 1994, produced the Nature paper of 7 August 1997, and the whole book is built around it.
A structure that is a life
Finding the Mother Tree (French edition: À la recherche de l’arbre-mère) is not a lecture, it is an autobiography moving at the pace of a demonstration. Prologue, fifteen chapters, epilogue, and a strictly chronological order. It opens in the Monashee Mountains with the family’s horse loggers, “Hand Fallers”, then come the drought, the shelter trees, the move to the Ministry of Forests and the first professional dissonance, “Killing Soil”, “Alder Swales”. The experimental core occupies chapters 7 to 9, with “Bar Fight”, “Radioactive”, “Quid Pro Quo”. What follows mixes the hostile reception from the profession, “Painting Rocks”, private life, illness, and the handover, “Passing the Wand”. The epilogue launches the Mother Tree Project.
Every chapter starts from a scene of her life and brings an experiment back to it. The device can grate, yet it holds, because the biographical order is also the logical order of the discovery.
The anomaly at the start
The starting point is not an intuition, it is a number that does not add up. As a young researcher at the Ministry of Forests, Simard finds that up to 10% of planted young Douglas firs sicken and die once the aspens, paper birches and cottonwoods around them have been carefully removed. Yet those seedlings have everything silviculture promised them, more space, more light, more water than a seedling wedged in a dense old forest. They die anyway. The whole book comes out of that.
The detail of the protocol, which is worth reading
The 1997 experiment deserves to be told, because its strength lies in how it is put together. Three species growing naturally together on the site, paper birch and Douglas fir, both ectomycorrhizal, plus western redcedar, which forms vesicular-arbuscular mycorrhizas and serves as the control. The redcedar cannot be wired into the same fungal network. So whatever it does receive measures what simply travelled through the soil.
Simard first checked that the connection was plausible, seven ectomycorrhizal morphotypes shared by the first two species, covering more than 90% of their root tips. Then the reciprocal labelling, which is the real invention. Each partner receives its own isotope, 7.4 MBq, and in the first year the scheme is reversed between replicate groups to cancel out differences in fixation between the two labels. You do not follow one flow, you follow both at once.
The results have a sobriety that surprises anyone who knows the book’s reputation. First run, on two-year-old seedlings, the exchanges go both ways and balance out, so the net is zero, and the total amounts to 4% of the isotope fixed. What passes through the soil to the redcedar stays under 1%. Second run, on three-year-old seedlings, this time the Douglas fir is a net receiver under all three light regimes, on average 6% of the total isotope fixed, and the effect doubles in the shade. Net transfer goes from 2.7% in full sun to 9.5% in deep shade. The redcedar takes up only the equivalent of 18% of what moves between the other two, which means that most of it goes through the fungal filaments and not through the soil.
The authors’ interpretation is cautious and purely physical. The birch photosynthesises 1.5 times more than the fir in full sun and 4.3 times more in deep shade, its leaf nitrogen content is twice as high, so the carbon runs down a gradient. A source-sink relationship, not generosity. Nature put the subject on its cover under the title “The Wood-Wide Web”, and it is that phrase, not the caution of the paper, that travelled around the world.
What the book adds on top of 1997
Then comes everything Simard accumulated over twenty-five years, and that she tells here for the first time in one sequence. The direction of the flow reverses with the seasons, in summer carbon goes from the birch to the shaded fir, in autumn, when the birch drops its leaves and the fir is still growing, the net runs the other way. Across six stands of about 930 m², almost every tree is linked by no more than three degrees of separation, and one very old individual is connected to 47 others, with a projection beyond 250. Seedlings with full access to the network have a 26% better chance of survival. Mycorrhizas supply up to 40% of the nitrogen and up to 50% of the water a tree needs, and the tree trades through its roots between 10 and 40% of the carbon it stores there.
Two episodes stand out. Defoliated Douglas fir seedlings, doomed as a result, transfer stress signals and a substantial amount of carbon to neighbouring ponderosa pines, which immediately step up their production of defence enzymes. And kin recognition, worked on with the doctoral student Amanda Asay and the ecologist Brian Pickles, related Douglas firs tell the root tips of their own offspring from those of stranger seedlings, and favour them with carbon. Simard writes that she does not know by what mechanism. That honesty counts in her favour.
The mother tree, finally, is not female. The technical term in her papers is hub tree, the biggest, the oldest, the most connected, whose deep roots bring up water that shallow-rooted seedlings would never reach. When the neighbours suffer, the flow increases.
The claims, including the one that does not hold
Four ideas hold up solidly. Trees exchange in a real forest and not only in pots. The direction of the flow obeys a gradient, not an intention. A hub tree is worth more standing than its value as timber, since cutting it makes the survival of the young ones drop. And clearcutting combined with complete brush removal is a mistake even in yield terms, which is the most effective argument in the whole book because it speaks the foresters’ own language.
The fifth claim is more fragile and Simard knows it, that Western science is too reductionist to grasp a system of interdependencies, and she explicitly ties that criticism to a masculine model of reality and to Indigenous knowledge. In an interview with Richard Grant she puts it very well: “We don’t ask good questions about the interconnectedness of the forest, because we’re all trained as reductionists. A teaspoon of forest soil contains several miles of fungal filaments.” You can follow her there or not. The fact is that half her book recounts what it costs to ask those questions. A young researcher, she tells Ferris Jabr, would hear the old hands answer, “Why don’t you study growth and yield instead? I was more interested in how these plants interact. They thought it was very girly.” And on the reception of her early work, this sentence from the book: “A shadow was growing over my work.”
All of these quotations come from English-language interviews and are given here in the original. I have not checked their wording in the French text published by Dunod.
The quarrel, and what it teaches
In 2023, Justine Karst, Melanie Jones and Jason Hoeksema published three papers challenging the strength of three claims that have become commonplace, that mycorrhizal networks are everywhere, that they benefit seedlings, that old trees favour young ones. They diagnose a positive citation bias. Simard replied in 2025. The biologist Toby Kiers sums up the objection in a way worth hearing: “Where some scientists see a big cooperative collective, I see reciprocal exploitation.”
That dispute teaches something, and that is why I am reporting it. It is not about the 1993 measurements, which nobody contests, it is about the gap between what a measurement establishes and what a story makes it say. You can see that gap very clearly by reading Simard herself. In her papers, cautious language, gradients, percentages, standard deviations. In public, species “as interdependent as yin and yang” and veteran trees passing on messages of wisdom. She never wrote that trees are conscious. The way she says it does suggest as much, and a reader who hears that is not wrong to hear it.
The prose, the longueurs, the clearings
454 pages, and the review in La Vie des idées puts its finger on it, the book is “dense” and “rich”, sometimes redundant, the inner monologues keep coming back, the dialogues smack of late reconstruction. The cancer, the divorce, the ceremonies, all that intimate material I was afraid I would find cumbersome in fact works like clearings, places where the light comes in and where the concept becomes legible. The same review speaks of “a summation of a life and of science seen through human and natural ecology”, which is exactly it.
The epilogue leaves the narrative to break ground. The Mother Tree Project, launched in 2015 at the University of British Columbia, covers Douglas fir, ponderosa pine, lodgepole pine and western larch, and it is designed to run for a hundred years. The closing scene is almost too good to be true and it is true, in the Harrop-Procter community forest near Nelson, about 11,300 hectares, the manager Erik Leslie marked the oldest and healthiest trees with blue paint before the cut, at Simard’s request. “I crossed a line, I suppose. It’s a way of giving back what the forests have given me.”
What I keep from it for my own work comes down to one point of method. Simard did not start by claiming that trees communicate, she started from a number that did not add up, 10% of seedlings dead when they had everything, and she spent four years building a setup where the answer could not come from anywhere else. The redcedar control is what carries the demonstration, not the carbon 14. The lesson is useful to anyone who plugs electrodes into a leaf.
Read in March 2022. Entry written in 2026.
