Scientist Susan Simard is a professor of Forest Ecology at the University in Vancouver, British Columbia, who has been studying the below-ground fungal networks that connect trees and facilitate underground inter-tree communication and interaction. Over a period of more than thirty years this field scientist and her students have learned how fungi networks move water, carbon and nutrients such as nitrogen between and among trees as well as across species. Her research has demonstrated that these complex, symbiotic networks in our forests — at the hub of which stand what she calls the “mother trees” — mimic our own neural and social networks. This groundbreaking work on symbiotic plant communication has far-reaching implications that include developing sustainable ways to ‘manage’ forests, and to improve tree and plant resistance to pathogens.

Other scientists who study these networks (like Dr. Merlin Sheldrake) agree with Susan who suggests that the forest behaves as though it’s a single cohesive organism.

Susan grew 80 replicates of three species: paper birch, Douglas fir, and western red cedar believing the birch and the fir would be involved in two way communication underground while the cedar would not. To test her idea she injected two isotopes of carbon into the trees (in plastic bags) and within an hour the birch and fir exchanged carbon through their root systems.

During the summer birch was sending more carbon to fir than fir was sending back to birch, especially when the fir was shaded. And then in later experiments, she found the opposite. Fir was sending more carbon to birch than birch was sending to fir, and this was because the fir was still growing while the birch was leafless. The two species were interdependent.

Douglas fir and birch were conversing not only in the language of carbon but also exchanged nitrogen, phosphorus, water, defense signals, allele (gene) chemicals and hormones.

Fungal threads called mycelium connect different individuals in the forest below the ground, not just individuals of the same species but also work between species, like birch and fir. Hub or “mother trees” nurture their seedlings by sending excess carbon etc. to their kin. They even reduce their own root competition to create space for their seedlings to grow. When mother trees are injured or dying, they also send carbon and defense signals to the next generation of seedlings helping the youngsters to resist future stresses. Through back and forth conversations, trees increase the survival rate of the whole community.

What makes the forest so resilient is that there are many hub or mother trees and many overlapping networks.

It is possible to remove one or two hub trees but not many of them; there is a tipping point after which the whole system collapses.

Trees may not have nervous systems but they can feel what is happening and can experience something analogous to pain. When a tree is cut it sends out electrical signals like wounded human tissue does.

Massive disturbance at this scale affects hydrological cycles, degrades wildlife habitat, and emits greenhouse gases back into the atmosphere, which creates more disturbance and more tree diebacks.

Worse, foresters continue to plant one or two species of trees for harvesting and weed out other trees like aspens and birches. These simplified forests lack complexity, and they’re really vulnerable to infections and insect infestation.

Simard explains her frustrations with Western science. “We don’t ask good questions about the interconnectedness of the forest, because we’re all trained as reductionists. We pick it apart and study one process at a time, even though we know these processes don’t happen in isolation. When I walk into a forest, I feel the spirit of the whole thing, everything working together in harmony, but we don’t have a way to map or measure that.”

In her view her research and that of others is exposing the limitations of the Western scientific method itself.

The one hope is that forests as complex systems have an enormous capacity to self-heal. Simard has demonstrated this capacity with recent experiments in which retention of hub trees, and careful patch cutting can lead to regeneration and recovering species diversity.

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