Trees have long existed in folklore and literature as benevolent and sentient beings. But ascribing any human-like intentionality to plant behavior raises the hackles of many a bioscientist.
With the accumulation of more than two decades of credible research, however, many in the scientific community acknowledge that trees are able to transmit information and communicate among each other in ways that help in their collective survival.
There’s a lot happening under the surface of the forest floor. The work of University of British Columbia eco-scientist Christine Simard and other researchers indicates that trees use an underground “wood-wide web” to exchange food and water with each other. The underground lattice of fungal pathways—called a mycorrhizal network— enables a beneficial tree-to-tree sharing system.
Plant biologists have long recognized the phenomenon known as mycorrhizae: Fungi grow along the root system of a host plant, which increases the plant’s ability to absorb water and life-sustaining nutrients. In turn, the plant gives the fungi the carbohydrates formed from photosynthesis (fungi need those sugars to survive, but cannot make them for themselves). It’s the proverbial win-win.
The key aspect of mycorrhizal networks in trees is in the “network.” Studies suggest that a tree uses mycorrhizae not only to feed itself, but to give water and nutrients to other trees in its vicinity.
Simard’s work has revealed the existence of “hub trees” within a forest. Her team found that while most trees were linked to some other trees in the mycorrhizal network, it was the biggest, oldest trees whose root systems were most highly connected—sometimes to hundreds of other trees of their own, or different, species.
The hub tree used the network to transfer its excess carbon to other trees that needed it, such as smaller saplings in the forest undercanopy that were starved of sunlight. Simard’s team has credited these “mother-to-child” carbon transfers with increasing the seedling survival rate by 400 percent.
Dozens of research studies conducted in North America and Europe have created compelling evidence that trees protect themselves against external threats in novel ways.
A tree’s leaves recognize the saliva of plant-eating animals and insects, and telegraph the danger to the rest of the tree via electrical impulses. This causes the tree to release unpleasant
chemicals on its leaves that repel the intruders. What’s more, it appears the volatile chemicals the damaged tree emits to protect itself are also detected in the air by the as-yet unharmed neighboring trees and plants, which respond by pumping out repellent chemicals to defend against an imminent attack.
Our understanding of the complex and cooperative systems by which trees and plants protect themselves from environmental threats can inform smart conservation and agricultural practices.
Discoveries about hub trees suggest forest management that preserves old-growth forests, such as less clearcutting in favor of more patch-cutting. The evidence about how trees and other plants defend themselves against insect attack can guide agro-scientists in preserving, or restoring, these natural defensive traits in food crops, thus reducing the need for pesticides.
Whether collective altruism, or simply evidence of the wonders of natural selection, the ways trees communicate with each other could help us better preserve and replenish our greenspace in years to come.
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