Dr. Suzanne Simard’s logging background inspired her forestry career and her lifelong research in the connections and communications of trees. Her 2021 book “Finding the Mother Tree: Discovering the Wisdom of the Forest” is partly a memoir and partly an engaging description of her research and its implications for the health of our forests. She combines the scientific methods and results of her research with emotional descriptions of nature that appeal to anyone who has ever loved a piece of forest or a backyard tree.
Trees are connected to each other by a dense underground network of mycorrhizal (root) fungi. This network transports water, photosynthetic sugars, signaling chemicals, and essential nutrients like nitrogen and phosphorus. This molecular transportation is necessary for growth of seedlings, and especially for regeneration of the forest in the wake of severe stresses such as logging, fire, or insect infestation.
Dr. Simard’s experiments demonstrate the wide extent of this network and how critical it is to the health of the forest, especially in the context of replanting after logging. Radioactive labeling of carbon dioxide in one experiment allowed her to trace the paths of the sugars created by photosynthesis in birch and Douglas fir trees which were connected by the mycorrhizal network. She found that “the more shade that birch cast, the more carbon it donated to fir,” by measuring the amount of radioactive carbon that moved between the trees. “Birch and fir were trading carbon,” she writes. “They were communicating. Birch was detecting and staying attuned to the needs of fir. Not only that, I’d discovered that fir gave some carbon back to birch too. As though reciprocity was part of their everyday relationship. The trees were connected, cooperating.”
In the past century, forestry practices have been based on a theory of competition for resources. Canadian policies mandated a “free-to-grow” strategy. In theory, if all other competition for water, light, and nutrients was removed, the desired trees would grow fast and strong. Logging companies clear-cut large areas of forest, and then replanted fast-growing “cash crop” trees while removing all other trees and shrubs from the area. Little consideration was given to species diversity or even preferred growing conditions.
Simard describes her experiences in replanting clear-cuts as a young logging employee. She had been tasked to find out why the young spruce saplings planted in fungi-less mineral soil of the clear-cuts kept turning yellow and dying. It wasn’t until years later that her experiments showed that it was the absence of the mycorrhizal fungi (and the subsequent networks with other trees) that had killed the saplings.
One of her first experiments was spraying herbicide in different amounts, in order to see what concentration most effectively killed all plants except the desired Douglas fir seedlings. She reports that “all but one of the treatments would end up failing to improve conifer growth and, no surprise, native plant diversity was lowered. In the case of birch, killing it improved the growth of some of the firs but caused even more to die.” This was because healthy birch roots helped to keep down a pathogenic fungus that otherwise infected and killed both the birch and the desired fir trees.
Simard compares these logging practices to those of her grandfather. “My grandfather had reaped harvests while leaving the forest vibrant and regenerative, the mothers intact. He was never wealthy, but he lived in rich peacefulness with the forest, taking only what he needed, leaving gaps so the trees could come back.”
One set of experiments tested the growth of pine seedlings grown with different amounts of “weed” plants, specifically alders. After years of data collection, she presented her work at an industry conference and received significant (and sometimes sexist) pushback from her fellow foresters, loggers, and policymakers.
“It turned out that getting rid of alder so pines could be free to grow provided only a fleeting advantage in water uptake,” Simard writes. “Not only that, its side effect was loss of soil […] Policymakers […] saw only the data of depletion. The short-term, the first roadside glance […] The bare-earth treatment had traded a short-term gain — fleeting water, light, and nutrient increases — for long-term pain, a long-term decline in fixed nitrogen additions.”
She repeated these experiments with multiple types of cash crop trees and weed trees, with the same results. Removing the weed trees does not help the desired trees to grow, and often leaves them vulnerable to disease, sunburn, nutrient deficiencies, and other issues.
This theme of collaboration is reinforced by her descriptions of working alongside and learning from relatives, friends, coworkers, and scientific collaborators — all experienced outdoorswomen or scientists committed to discovering and learning from the natural world.