The forest, the trees, and the fungal ties that bind

A view up a forested mountain valley to clear skies dotted with clouds
Forested mountainsides in the Mount Baker-Snoqualmie National Forest (Photo by Jeremy Yoder)

The following is a guest post by Erin Zess, a Postdoctoral Researcher with the MOI Lab in the Department of Plant Biology at the Carnegie Institution for Science. Erin is on Twitter at @ZessingAround.

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The Menominee Tribe of Wisconsin, whose ancestral lands extended over 10 million acres across the Great Lakes region, call themselves “Maeqtekuahkíhkíw Kew Kanâhwíhtahquaq,” which translates to “The Forest Keepers.” The land ethic of the Tribe — articulated by Chief Oshkosh over two centuries ago, before the arrival of professional forestry in North America — is to: “Start with the rising sun and work towards the setting sun, but take only the mature trees, the sick trees, and the trees that have fallen. When you reach the end of the reservation, turn and cut from the setting sun to the rising sun and the trees will last forever.” Living by this dictum, the Menominee Tribe has sustainably managed their remaining Tribal lands, 235,560 acres, for over 150 years. In that time, they have harvested the entire volume of the forest twice over and, today, the forest volume is greater than when timber harvesting began. 

Suzanne Simard, a professor of forest ecology in the University of British Columbia’s Faculty of Forestry, is another kind of forest keeper. Simard’s research focuses on the function, distribution, and ecological impact of the belowground fungal networks that connect trees in robust forests, and her work has helped shift the mainstream Western perspective on forest systems towards understanding them as cooperative and connected. In her new book, Finding the Mother Tree: Discovering the Wisdom of the Forest (Knopf, $28.95 in hardback), Simard recounts her journey from her family’s homestead in British Columbia, through her early career at a timber company and in the Canadian Forest Service, to her current position in academia, describing how her work has brought her, “full circle to stumble onto some of the indigenous ideals: diversity matters.” 

Simard begins her story in a place with a conspicuous absence of diversity — a plantation forest, where trees are grown in rigid monoculture. Simard noticed that the plantations she was tasked with evaluating were full of sickly seedlings. She also observed that, unlike neighboring seedlings that had naturally regenerated, which had actively growing roots, the roots of the introduced seedlings were withered and dead. This observation provided the genesis for Simard’s research career, and in Finding the Mother Tree, she narrates the many years she spent unpicking the mystery of why some seedlings thrived while others died, and what their roots had to do with it. 

During her earliest experiments, Simard studied how the density of certain plant species — birch and alder — impacted the survival and growth of more lucrative tree species, including larch, cedar, fir, and pine. The Canadian forestry policy was to clear-cut undesired plant species in order to allow desirable trees to be “free to grow,” based on the assumption that these species were in competition for resources and that their interactions were a zero-sum game. Simard’s work provided evidence that, in some cases, undesired plant species could significantly enhance the growth and survival of desirable species over longer timespans. Simard observed that the roots of healthy seedlings were “bearded in gossamer,” and she found that these delicate threads were a special type of fungi — mycorrhizas — that seemed to connect trees to their compatible neighbors.

Simard’s thesis work, honing in on the relationship between paper birch and Douglas fir, showed that mycorrhizas mediate cooperative interactions between plant species in the context of a healthy forest system. In these experiments, conducted with seedlings in the forests of British Columbia, Simard labelled birch with the radioactive isotope carbon-14 to follow sugars that may travel to fir, and labeled fir with the stable isotope carbon-13 to trace sugars that may travel in the opposite direction. By measuring how much of each isotope ended up in each seedling, Simard could calculate the reciprocal exchange of photosynthetic carbon between the species, as well as the net transfer. In a landmark paper published in Nature in 1997, Simard shared her remarkable findings about ‘the wood-wide web.’ She described how paper birch and Douglas fir were trading photosynthetic carbon back and forth through the mycorrhizal network, and that the balance of trade could be tipped depending on resource availability, with relative resource-richness leading to greater levels of resource donation. Follow-up experiments have substantiated these results, as well as shown that other types of compounds are exchanged between tree species through mycorrhizal networks.

The unifying theme of the research in Simard’s current lab at the University of British Columbia is to understand how mycorrhizal networks affect the regeneration of trees in our changing climate. In 2010, Simard contributed to a study that mapped the architecture of the mycorrhizal network in a multi-age, old-growth Douglas fir forest, finding that larger trees serve as hubs and play an important role in facilitating regeneration and stabilizing the entire system. Simard refers to these larger, older, well-connected trees as ‘Mother Trees,’ and subsequent studies have shown that these trees use the fungal network to nourish disadvantaged seedlings, including their offspring. As part of her ongoing Mother Tree Project, Simard has found that the retention of Mother Trees helps forests regenerate by supporting seedling health, and argues that sustainable forestry management should prioritize maintaining these trees.

Throughout Finding the Mother Tree, Simard uses metaphors to describe her work, including the eponymous ‘Mother Tree’. Simard claims that forest mycorrhizal networks have the signatures of intelligence — that they learn and remember. For a certain kind of scientist, these conclusions represent a sensational overinterpretation of the data, recalling the debate over the field of ‘plant neurobiology’ (eg. herehere). In other ways, too, Simard has a strong perspective on her results. Where Simard sees mycorrhiza-mediated interactions as a model of socialism, other scientists see evidence of reciprocal exploitation or fungal self-promotion. Either interpretation involves an imposition of intentions; the politics of plants are, obviously, just our politics in disguise and, ultimately, not that interesting. Simard’s claim that a forest behaves as though it is a single organism is more open to genuine scientific critique, bringing up long-standing disagreements about the prevalence and importance of natural selection operating at the level of a group. I accept Simard’s use of slippery language, and her penchant for metaphor, as a strategy to engage non-scientists and communicate a sort of ecstatic truth about nature as she sees it. I understand that some precision must be sacrificed at the altar of general interest, and I think that Simard strikes an admirable balance.

Simard argues for “expanding our modern ways, our epistemology and scientific methodologies, so that they complement, build on, and align with Aboriginal roots.” Simard acknowledges that her discovery that forests are cooperative and connected was not new, but rather “the ancient wisdom of many Aboriginal people.” Her prescriptions for the ills of modern forestry, too, emulate what the Menominee Tribe of Wisconsin have been practicing for hundreds of years, centering the intrinsic value of the forest as a community and as a life-sustaining force. Simard credits the simple act of listening as transformative, and she makes it obvious that she has been profoundly influenced by indigenous wisdom. I wish that Simard delved more into how her worldview has evolved over time, and what the process of listening has really entailed. Finding the Mother Tree would be a more impactful and thought-provoking book if Simard shared more of her perspective on where Western science and indigenous wisdom overlap, similar to Robin Wall Kimmerer’s masterful Braiding Sweetgrass and Gathering Moss.

Finding the Mother Tree succeeds as a work of science communication, giving life to Simard’s experiments and results, but it falters as a memoir. The narrative nonfiction style of the prose, where events are described from the perspective of Simard as she imagines herself in the past, makes all of the characters opaque, Simard included. Her life story is undeniably interesting and compelling, but I never got a sense of what Simard thinks or feels about any of her formative experiences. The more personal parts of Finding the Mother Tree felt superficial, and, at times, stilted. Simard seemed to be caught between wanting to share some biographical details, and not wanting to disclose too much of herself, and the result is a play-by-play narrative that reads like a movie script. 

In Finding the Mother Tree, Suzanne Simard makes a convincing case that forests are “wired for wisdom, sentience, and healing,” and she implores us to learn from them. I’m left wondering, though, beyond scientific lessons, what has Simard herself learned from the forest? What has the forest taught her about our — Western scientists, settler colonists, humans in the 21st century — culpability and complacency; about learning and unlearning; about hope and life and the future? Simard writes that, “This is a book about how the trees might save us,” but Finding the Mother Tree provides little insight into what that process looks like on an individual level. 

Reviewed

Simard S. 2021. Finding the Mother Tree: Discovering the Wisdom of the Forest. New York: Knopf, 368 pages. Publisher website

References

Alpi A, Amrhein N, Bertl A, Blatt MR, Blumwald E, Cervone F, et al. Plant neurobiology: no brain, no gain? Trends Plant Sci. 2007 Apr;12(4):135–6. doi: https://doi.org/10.1016/j.tplants.2007.03.002.


Beiler KJ, Durall DM, Simard SW, Maxwell SA, Kretzer AM. Architecture of the wood-wide web: Rhizopogon spp. genets link multiple Douglas-fir cohorts. New Phytol. 2010 Jan;185(2):543–53. doi: https://doi.org/10.1111/j.1469-8137.2009.03069.x.

Brenner ED, Stahlberg R, Mancuso S, Vivanco J, Baluska F, Van Volkenburgh E. Plant neurobiology: an integrated view of plant signaling. Trends Plant Sci. 2006 Aug;11(8):413–9. doi: https://doi.org/10.1016/j.tplants.2006.06.009.

Kiers ET, Duhamel M, Beesetty Y, Mensah JA, Franken O, Verbruggen E, et al. Reciprocal rewards stabilize cooperation in the mycorrhizal symbiosis. Science. 2011 Aug 12;333(6044):880–2. doi: https://doi.org/10.1126/science.1208473.

Klein T, Siegwolf RTW, Körner C. Belowground carbon trade among tall trees in a temperate forest. Science. 2016 Apr 15;352(6283):342–4. doi: https://doi.org/10.1126/science.aad6188.

Mausel DL, Waupochick A, Pecore M. Menominee Forestry: Past, Present, Future. J For. 2016 Nov 24;115(5):366–9. doi: https://doi.org/10.5849/jof.16-046.

Pickles BJ, Wilhelm R, Asay AK, Hahn AS, Simard SW, Mohn WW. Transfer of 13 C between paired Douglas-fir seedlings reveals plant kinship effects and uptake of exudates by ectomycorrhizas. New Phytol. 2017 Apr;214(1):400–11. doi: https://doi.org/10.1111/nph.14325.

Simard SW. Mycorrhizal Networks Facilitate Tree Communication, Learning, and Memory. In: Baluska F, Gagliano M, Witzany G, editors. Memory and Learning in Plants. Cham: Springer International Publishing; 2018. p. 191–213. doi: https://doi.org/10.1007/978-3-319-75596-0_10.

Simard SW, Perry DA, Jones MD, Myrold DD, Durall DM, Molina R. Net transfer of carbon between ectomycorrhizal tree species in the field. Nature. 1997 Aug;388(6642):579–82. doi: https://doi.org/10.1038/41557.Song YY, Simard SW, Carroll A, Mohn WW, Zeng RS.

Defoliation of interior Douglas-fir elicits carbon transfer and stress signalling to ponderosa pine neighbors through ectomycorrhizal networks. Sci Rep. 2015 Feb 16;5:8495. doi: https://doi.org/10.1038/srep08495

About Jeremy Yoder

Jeremy B. Yoder is an Assistant Professor of Biology at California State University Northridge, studying the evolution and coevolution of interacting species, especially mutualists. He is a collaborator with the Joshua Tree Genome Project and the Queer in STEM study of LGBTQ experiences in scientific careers. He has written for the website of Scientific American, the LA Review of Books, the Chronicle of Higher Education, The Awl, and Slate.
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