The next time you’re hiking in the foothills, stop and listen. The trees around you are talking.
By Amanda McCracken
“The tree which moves some to tears of joy is in the eyes of others only a green thing that stands in the way.”
— William Blake
You may not hear them, but trees communicate messages to each other via air and roots, and scientists are proving what poets have known for years: There is wisdom in the trees.
Some call it the “wood-wide web,” says German author and forester Peter Wohlleben in his bestseller, “The Hidden Life of Trees: What They Feel, How They Communicate.” While we gaze up at their magnificent crowns, below our feet trees engage in sophisticated communication.
Trees and other plants communicate via a fungal network of mycorrhiza, which literally means “fungus root.” Through ‘nature’s Internet,’ trees share resources like water, and nutrients like nitrogen, carbon and other minerals. Trees’ hairlike root ends entangle with microscopic fungi filaments to create the mycorrhizal network. The relationship is symbiotic—fungi feed off sugars produced by the trees, while the trees benefit from minerals supplied by the fungi.
According to the National Forest Foundation, each tree in a healthy forest is connected to others via this network. A study on Douglas firs at England’s University of Reading says trees recognize the root tips of their relatives, and favor them when sending carbon and nutrients through the network.
Trees even “mother” other trees via the network. Older, more seasoned trees—called mother or hub trees—have well-established root networks that recognize distress signals. These trees nurse sick trees by sending them vital nutrients. Mother trees also send water and carbon to saplings to help them thrive when sunlight can’t penetrate the canopy deeply enough to shine on shorter seedlings.
In her viral TED Talk, “How Trees Talk to Each Other,” Canadian forest ecologist Suzanne Simard says, “Mother trees colonize their kin with bigger mycorrhizal networks. They send them more carbon belowground. They even reduce their own root competition to make elbow room for their kids. When mother trees are injured or dying, they send messages of wisdom on to the next generation of seedlings.”
Simard used isotopic tracing to track carbon moving through a mycorrhizal network from a mother tree to her seedlings. She observed that this process builds resilience within younger trees and further strengthens the forest community.
Bark, Beetles & Bacteria
Nurturing isn’t the only way trees communicate with each other. By releasing chemicals, hormones and even electrical pulses, trees alert others to danger, particularly pests.
However, these distress signals can backfire in certain cases, like the mountain pine beetle epidemic. Forest entomologist Dan West, of the Colorado State Forest Service, studies interactions between local pine trees and beetles. “Each tree has its own combination of terpenes—these are mostly ten-carbon-chain compounds that make trees smell like trees,” he explains. Trees release terpenes when distressed, which bark beetles recognize. The beetles oxidize terpenes in their gut and release them into the air as a waste byproduct. This acts as a signal to other beetles that says, “This species of tree is weak enough to attack; it has released its distress signal.”
“The silver bullet is water,” West says. Pine trees infested with beetles release pheromones to warn other pines in the area to ramp up their defenses. As a result, alerted trees take up water and turn it into resin, which is toxic to bark beetles. If beetles manage to burrow into trees, trees in turn cover them with resin so they can’t communicate. In drought years though, “trees have to pull on water to grow instead of to defend themselves,” West says.
Trees aren’t the only plants that communicate with each other, says biology professor Dr. Kathryn Morris of Xavier University. Bacterial attacks prompt certain plants to make salicylic acid. “They know to produce this acid because a message was sent as a plant hormone through the fungal network to warn other plants to start producing a chemical to protect themselves,” she says.
Companion plants also utilize fungal networks. Companions to tomatoes—calendula, garlic, parsley and basil—release herbicidal chemicals through the network that detrimentally affect tomato hornworms. Horticulturist Jason Shimmel of Sturtz & Copeland Flowers & Plants says garden tilling destroys most fungal networks, but some companions don’t need them to ward off pests. For example, nasturtiums are great companions to cucumbers, squash and tomatoes, he says, as they repel cucumber beetles, whiteflies and aphids. And their bright orange and yellow flowers are edible. Chives and radishes function similarly to deter destructive bugs.
So the next time you hike through the trees or stroll in your garden, pause to consider the remarkable conversations going on right beneath your feet. As William Blake said, “…nature is imagination itself.”