When the Forest Breathes

This narrative nonfiction work weaves together findings from a vast forestry field experiment, personal experiences of loss and renewal, and collaborations with Indigenous communities across British Columbia and beyond, spanning roughly 2015 to 2023.

Suzanne Simard opens with the premise that renewal in forests depends on dying, and that the life cycles of forests mirror those of humans. She reflects on the public's embrace of her discovery that the biggest, oldest trees, which she calls mother trees, are the energetic keystones of the forest, connected through underground mycorrhizal fungal networks, or webs formed by soil fungi. These fungi form symbiotic relationships with tree roots, trading soil nutrients for photosynthetic carbon and linking trees and seedlings in extensive webs. Indigenous peoples have long recognized this interconnectedness, Simard notes, but their knowledge systems are routinely dismissed by Western science. Determined to find better ways to manage forests amid climate change and industrial clearcutting (the practice of harvesting every tree in a large area), Simard launched the Mother Tree Project (MTP), a vast field experiment across nine experimental Douglas fir forests in British Columbia's interior. Her longtime colleague and best friend Jean Roach managed the project, while postdoctoral fellow Teresa Ryan, a member of the Ts'msyen Nation, helped Simard see that colonial forestry required a transformation from exploitation to a regenerative worldview valuing reciprocity.

The MTP compares five logging treatments: clearcutting, retaining 10 percent of the largest trees as seed trees, retaining 30 percent in clustered patches, retaining 60 percent with selective understory thinning, and leaving the forest untouched as a control. Graduate student Amanda Asay's research reveals that Douglas fir seedlings recognize kin and grow larger near relatives than strangers, with greater mycorrhizal colonization. Another student, Eva Snyder, studied mycorrhizal connections among western redcedar, Pacific yew, and Douglas maple. Simard connected with Dave Walkem, a member of the Nlaka'pamux Nation and the first person with status Indian designation (a legal recognition under Canada's Indian Act) registered as a professional forester in British Columbia. Dave agreed to host the ninth MTP site but insisted the clearcut treatment be excluded, explaining that old trees regenerate the forest. After four years of preparation, the crew planted 225,000 seedlings across the nine sites in spring 2019, testing seven Douglas fir genotypes from warmer and cooler climates to investigate assisted migration as a strategy for adapting to climate change.

Wildfire is a recurring presence. In August 2018, lightning ignited a fire near the Cariboo Mountains MTP plot while Simard, Jean, and Simard's daughters Hannah and Nava were measuring trees; they fled as flames climbed into the canopy. Simard connects these fires to decades of mismanagement: fire suppression, elimination of deciduous firebreaks with herbicides, and replacement of diverse forests with flammable conifer plantations. When she returned to the burned plot a year later, she found resilience: liverwort colonizing charred earth, new seedlings germinating, fireweed blooming, and the mother trees mostly alive, their thick bark having protected them. Threaded through the research is Simard's family life: Her daughters joined fieldwork crews, while her mother, whom she calls Mum, had Alzheimer's disease and grew increasingly anxious about the fires that surrounded them.

Simard's collaborations with Indigenous communities deepen throughout the book. Teresa demonstrated the Ts'msyen practice of harvesting cedar bark, always asking the tree's permission and offering tobacco. In Heiltsuk territory, Simard and Teresa explored ancestral stone-trap fishing weirs and root gardens, evidence of sophisticated agrarian systems predating European contact. Doctoral student Allen Larocque's research finds that salmon-rich riparian (streamside) forests contain dramatically higher soil carbon, approximately 600 metric tons per hectare. On Haida Gwaii, an archipelago off British Columbia's northern coast, Simard met Lisa White-Kuuyang, a Haida cedar weaver who described watching ancient forests disappear. Simard demonstrates how cedar reproduces through layering, with lower branches rooting in the soil and growing into saplings that the Haida and Ts'msyen call "sister cedars." A proposal to fund MTP research on Haida Gwaii was rejected by the provincial government. Later, hereditary chief Rande Cook (Makwala) of the Ma'amtagila Nation invited Simard to document clearcut damage in his people's territory. The Ma'amtagila were forced from their land in 1886 and never ceded their territory; 150 years of industrial logging had since replaced diverse forests with dense monoculture plantations at roughly one-quarter the productivity and biodiversity of old growth.

Among the MTP's findings, the most striking concerns forest floor carbon. Simard and Jean discovered that logging caused a 61 percent reduction across the experimental sites, over five times the losses found in previous studies. The losses were equally severe whether some trees were retained or all were cut, because massive logging machinery ground and compacted the forest floor regardless. First-year seedling data reveals similarly stark contrasts: At the driest site, only five percent of planted seedlings survived in clearcuts compared with 33 percent under 60 percent retention, while wildlife cameras captured diverse fauna in retention treatments nearly matching unlogged controls.

In summer 2021, Simard and Nava joined the Fairy Creek blockade in Pacheedaht territory on Vancouver Island, the largest act of civil disobedience in Canadian history, where activists defended one of the last pristine watersheds from Teal-Jones Group's logging. Simard visited Titania, a 2,000-year-old yellow cedar matriarch in the path of a proposed road, and spoke on the legislature steps alongside hereditary chiefs. Weeks later, a defender emailed Simard a video of the ancient cedar being felled. The provincial government paused logging while First Nations collaborated on a stewardship plan, but permanent protection remained uncertain.

Personal losses compounded throughout this period. In January 2022, Amanda Asay died at 33 after falling into a tree well while skiing. Mum's application for MAID (medical assistance in dying), Canada's end-of-life program, was approved. On August 15, 2022, Mum died on her own terms after a ceremony with family. Around the same time, scientists submitted a paper critiquing Simard's mycorrhizal network research, and attacks on her work escalated. Simard draws strength from Mum's reassurance: "You come from the forest. The trees are in your blood. No one can destroy the knowledge and understanding inside of you" (201).

Eva Snyder's Septuplets experiment, in which seven seedlings were planted in a wagon-wheel pattern with cedar at the hub, confirms that cedar, maple, and yew share arbuscular mycorrhizal fungi (root-penetrating fungi that link neighboring plants) and are likely connected belowground. Carbon flows from cedar and maple to yew, with more flowing when yew is shaded, suggesting that larger trees supplement the energy needs of shade-tolerant species.

In the penultimate chapter, Simard traveled to the Amazon rainforest, visiting the ancestral territory of the Achuar people near the Ecuador-Peru border, where the intact forest, a protected Indigenous reserve, stores 140 billion metric tons of carbon. Guide Ramaro introduced a kapok tree as his grandfather, explaining that his ancestors are buried among its roots. Simard resolves never to give up her work.

In the conclusion, Simard summarizes the MTP's chief finding: Temperate forests store at least half their carbon belowground, some of it thousands of years old. She advocates for stopping further logging of old-growth forests, demechanizing logging in secondary forests, and embracing Indigenous knowledge systems. Hopeful developments include the Haida Nation's 2024 ratification of title to Haida Gwaii and the dismissal of Teal-Jones Group's 2023 lawsuit against the province seeking $75 million in compensation for logging restrictions on Haida Gwaii. The book closes with the teaching that forests demonstrate interdependence as an essential feature of thriving living systems: When the forest breathes out, we breathe in.