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General · 12th December 2016
Ray Grigg
Suzanne Simard, a forest ecologist from UBC, has been studying the intelligence of trees for about 25 years. When you walk in a forest, she says, you see trees, but “underground there is... a world of infinite biological pathways that connect trees and allow them to communicate, and allow the forest to behave as if it's a single organism. It might remind you of a sort of intelligence.”

Simard has documented this intelligence using tracer isotopes such as carbon-13, to show how “birches and Douglas fir supply each other with carbon and nutrients, while taking turns as the dominant partner in the exchange” (Maclean's, Sept. 19/16). This interdependence is often so strong that felling one tree can cause the other to die.

Such interdependence is even interspecies. The mycorrhizal networks that form the living body of fungi — their fruiting bodies are mushrooms — have no photosynthesis to produce the sugars they need, so they get this essential nutrition from trees in exchange for elements such as nitrogen, phosphorus and carbon. “The connection runs so deep that from 20–80% of the tree's sugars can be transferred to the fungi, while the transfer of nitrogen to trees is such that without the swap, trees would be toy-sized” (NewStatesman, Oct 26/16).

The fungi, in addition to assisting the roots absorb water, also manufacture complex chemicals that increase the trees' resistance to diseases. “The mycorrhizal fungi are now known to have a bond of mutualism with the roots — a symbiotic connection from which both parties benefit” (Ibid.). As Simard explains, “plant communities are driven not only by competition, but by cooperation,” adding that, “Forests may be more socialist than we thought.” The boundary between tree and fungus is so indistinct that the fungi's tiny hyphae tubes — hundreds of kilometres of them under a single footstep — are fully integrated into the cellular structure of tree roots.

Furthermore, as Simard has discovered, the thin threads of the fungal mycelium form a kind of underground internet now called the Wood Wide Web, allowing trees to pass nutrients and electro-chemical signals over distances from 20 to 200 metres among hundreds of trees. "These plants are not really individuals in the sense that Darwin thought they were individuals competing for survival of the fittest," she says. "In fact they are interacting with each other, trying to help each other survive."

But this complex communication system is something we might have suspected since learning that trees and fungi have co-existed for 450 million years, Indeed, no communication or cooperation would be unlikely.

These interactions are now quite easy to document, thanks to the work of scientists such as Simard. Isotopes of carbon can be added to only one tree, then its distribution and proportions can be measured in the surrounding trees and fungi. Reversing the process will indicate the degree of nutrient exchange in the opposite direction.

Forests, Simard has proven, “are complex systems with hubs and networks that overlap.” Old trees are located at these hubs. Take out too many of them, then the forest loses the feedback, adaptation and genetic wisdom that gives it resilience, “and the whole system collapses.” Part 4 of 4 next week.