8-minute read

The idea that trees communicate and exchange nutrients with each other via underground networks of fungi has captured the popular imagination, helped along by the incredibly catchy metaphor of a “wood-wide web”. Suzanne Simard, a Professor of Forest Ecology at the University of British Columbia, has developed this idea more than anyone else and happily talks of mother trees nurturing their offspring. This idea has not been without controversy in scientific circles, if only for its anthropomorphic language. I was both sceptical and curious about her ideas. High time, therefore, to give her scientific memoir Finding the Mother Tree a close reading.

First, a quick biology lesson to get you up to speed. At the heart of this story are not just trees but foremost fungi. Except for their above-ground fruiting bodies that we call mushrooms, fungi largely weave their way unseen through soil, decaying wood, and other substances. Here, they form mycelium: networks of fine tubular cells. Many fungi live in symbiosis with plant roots, forming mycorrhizas (combining the Greek words for fungus and root). Mycorrhizas connect plants and fungi into sprawling networks that play a role in plant nutrition and soil chemistry, though not all interactions are necessarily mutualistic (i.e. beneficial to both partners). There are various types of mycorrhiza, but important to this book are ectomycorrhizal fungi. They are predominantly associated with woody plants and envelop plant roots in a sheath of fungal cells. By the 1980s, researchers such as David Read (and others before him) had shown that chemicals can pass between plants via these fungal pathways. Simard would pick up on this discovery and run with it.

Interestingly, Simard was born in a family of loggers and, before entering academia, worked for a logging company and later the Forest Service of British Columbia. She thus experienced up close the government’s standard forestry practice, their free-to-grow policy. This means that plantations are actively cleared of native plant species using herbicides and mechanical means so that Douglas fir and other lucrative trees are “free to grow” without competition. Why, then, were so many seedlings failing?

“Easily the strongest suit of Finding the Mother Tree is the story of the uphill struggle of a young woman in the masculine world of Canadian forestry […]”

Easily the strongest suit of Finding the Mother Tree is the story of the uphill struggle of a young woman in the masculine world of Canadian forestry to try and convince them that their approach is misguided. Simard excels at describing her experiments and the rationale behind them in an understandable way. Some of her main findings are that removing native trees such as birch only provides short-term benefits to fir but leaves them more vulnerable in the long run. Starting from her suspicion that fungi have something to do with this, she discovers how birch and fir exchange carbon and nitrogen via mycorrhizal networks and can swap roles as source and sink over the seasons. Allowing fir and birch to grow together results in richer fungal communities and protects fir from pathogenic fungi. Digging deeper into fundamental aspects of mycorrhizal fungi, she notices that older and younger firs are connected underground, and hits on the idea of mother trees nurturing their offspring. Further work shows how fungal networks allow for warning signals to be communicated, kin to be recognized, and how dying trees might even off-load nutrients to younger trees. In an industry that sees trees as a commodity and focuses on short-term benefits and maximizing profit, her findings are not particularly welcomed and heavily scrutinized. She has faced plenty of abuse in the process.

The other, perhaps less expected part, is that Finding the Mother Tree is also a memoir in which Simard writes openly of her personal life. It is not until chapter 5 that you get to the first research, the preceding chapters telling of her family and childhood. In later chapters, the science sometimes takes a backseat to her life story, which is a shame as this is when her findings become more open to interpretation.

“Take the phrase “mother tree”. Beyond masking a biology quite unlike our own […] in scientific publications […] she instead talks of “hub trees” which evokes network topology. Quite the difference, no?”

My beef with this book is three-fold. First is its tone. Though she does not go as far as Peter Wohlleben did in The Hidden Life of Trees (and for which he was criticized)* some of Simard’s language and metaphors are emotive and value-laden. The introduction is full of words such as “ancient”, “wisdom”, and “healing”. No doubt her message will resonate with readers of Braiding Sweetgrass and Lessons from Plants, but when she concludes that “the forest is wired for wisdom, sentience, and healing” (p. 6), I cringed. Why, yes, I do have a giant chip on my shoulder regarding overt spirituality—I cannot deny my bias. In all seriousness, though, take the phrase “mother tree”. She admits that they are “mother and father trees, since each Douglas-fir tree has male pollen cones and female seed cones. But… it felt like mothering to me” (p. 228). Beyond masking a biology quite unlike our own, you would not get away with such emotive language in scientific publications. There, she instead talks of “hub trees” which evokes network topology. Quite the difference, no? But it is not a word you will find in this book. It contributes to my impression that this is Simard’s platform to share her beliefs and speculate to her heart’s content, unhindered by peer review.

This leads to my second objection: I have no issue with her experiments and results (I think she has done amazing work over the years), but I question some of her interpretations. For example, having explained concepts such as turgor pressure, source–sink gradients, and pressure-flow in chapter 8, she then mentions how birch transfers carbon to fir. Birch transfers more carbon when shading the fir and hindering its photosynthesis, i.e. when there is a steeper concentration gradient between the two. Can we really conclude from this that “birch was detecting and staying attuned to the needs of fir” (p. 160), or is this just simple physics? What she does insufficiently, in my opinion, is discuss how her ideas have been received by the wider scientific community, how she has defended them, and what other interpretations are possible. Furthermore, there is not much here in the way of signposting where her ideas become speculative, such as her brainwave that mycorrhizas resemble neural networks and the chemicals zipping around them resemble neurotransmitters. These are interesting ideas, but my concern is that lay readers will unquestioningly accept them as established facts, Simard’s track record as a publishing scientist giving them an air of legitimacy. One of the best critiques I have read is the chapter on the wood-wide web in Sheldrake’s Entangled Life that raises numerous objections. For example, he points out how this plant-centric metaphor downplays the role of fungi and mentions David Johnson, who cautions against extrapolating from laboratory findings on potted seedlings to whole forests. Unfortunately, Finding the Mother Tree left me with the impression of a scientist so enamoured with how her findings align with her values and beliefs that she cannot take sufficient distance to critically interrogate them.

“The reason I object to [anthropomorphic metaphors] is not that I think animals and plants are automatons devoid of agency [but because] comparing them to us introduces a new straitjacket.”

Finally, Simard freely uses anthropomorphic metaphors and assigns agency to trees. The reason I object to this is not that I think animals and plants are automatons devoid of agency. If anything, I am convinced that we routinely underestimate them, as I hope my reviews of books such as Safina’s Beyond Words and Mancuso’s The Revolutionary Genius of Plants have shown. But comparing them to us introduces a new straitjacket. In Entangled Life, David Read argues that “utopian visions of the soil are a shameless projection of human values onto a non-human system” (p. 180). Sheldrake, I think, captures best the objection to anthropomorphism: “Are we able to stand back, look at the system, and let the polyphonic swarms of plants and fungi and bacteria […] be themselves, and quite unlike anything else? What would that do to our minds?” (p. 193).

Above criticism is not intended to pooh-pooh Simard’s work. Though I might disagree with some of her interpretations, what she has uncovered about plant–fungi interactions is truly amazing and shows there is so much more happening below-ground than we ever realised. Her book successfully shows how aggressive forestry policies do not produce the desired results and she points the way toward better practices. Indeed, understanding mycorrhizal networks can have many applications. Whether or not her concept of mother trees resonates with you, I recommend this book simply because it is a first-hand account from the woman who pioneered this research. I would, however, recommend you read it in tandem with Entangled Life for a fuller picture.

---

* A 2023 publication in Nature Ecology & Evolution further critically reviewed the portrayal of mycorrhizal networks in popular media.

Disclosure: The publisher provided a review copy of this book. The opinion expressed here is my own, however.

Finding the Mother Tree

Other recommended books mentioned in this review:

__________________________________________________________________

__________________________________________________________________