How Do Trees Communicate?

How Trees Communicate with Each Other

The whisper-soft rustling of leaves, the creaking of branches, the slow, groaning shift of trunks in the wind: sometimes it can feel like the very forest is dancing together in some secret conversation that we with our limited human senses are not privy to.

And while trees speaking might sound like something straight out of the Lord of the Rings, groundbreaking research from scientists like Dr. Suzanne Simard and Peter Wohlleben has proven that trees communicate in a variety of ways.

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Forests Are More Than Just a Collection of Trees

Trees are fascinating, and there’s so much more to them than meets the eye. Decades of scientific research has confirmed what early humans instinctually knew — that forest trees are engaged in whispered conversations, working together to grow and flourish in a harsh world filled with predators, changing climatic conditions, and more.

That’s right: contrary to what Darwin would have you believe, trees are not selfish individuals forever toiling against each other to claim their own piece of the sky, but rather members of an ancient society connected through a vast and intricate network of hair-thin fungal filaments called mycorrhiza — all just a few inches beneath the soil surface.

In fact, by analyzing the DNA in root tips and tracing the movement of molecules through underground conduits, groundbreaking scientist Suzanne Simard has discovered that in a healthy forest, these tiny fungal threads link the roots of nearly every tree — and that “one teaspoon of forest soil contains several miles of fungal filaments.”

Trees Communicate Without Words

Sure, there’s plenty of conflict in forests, but there’s also negotiation, reciprocity, and even altruism. And not just within the same species: scientists have found that certain trees — especially conifers and deciduous tree specieslike Douglas Fir and Birch — will form mutually beneficial associations. Through these networks, trees can send chemical, hormonal and even slow-pulsing electrical signals, which scientists are only just beginning to interpret.

Edward Farmer at the University of Lausanne in Switzerland studies these electrical pulses and has identified a voltage-based signaling system bearing a striking resemblance to animal nervous systems. Although the accepted knowledge is that plants don’t have neurons or brains, it’s clear that even without nervous systems, trees on some level know what’s happening and even feel something akin to pain: when one is cut, it sends out electrical signals and healing compounds  — similar to wounded human tissue.

One example of this is when pine trees are cut or wounded, they send sap to the affected area to seal it off and begin the healing process. As natural healers know, pine sap contains antiseptic, anti inflammatory compounds. 

Monica Gagliano at the University of Western Australia has gathered evidence that some plants may also emit and detect sounds, in particular a crackling noise in the roots at a frequency of 220 hertz. Other studies have even suggested that roots grow toward the sound of running water and that certain flowering plants sweeten their nectar when they detect a bee’s wing beats.

Sending Danger Signals

They also communicate through the air, using pheromones and other powerful scent signals to warn each other of danger. In one stunning example, the wide-crowned umbrella thorn acacia, which happens to be a favorite food of giraffes, has developed a unique survival technique. When a giraffe starts chewing acacia leaves, the injured tree emits a distress signal using ethylene gas. Neighboring acacia trees pick up on this and begin pumping tannins into their leaves. When consumed in large quantities, these tannins can sicken or even kill giraffes.

But the system certainly isn't foolproof: since giraffes have evolved with acacia trees, they know to eat facing the wind so that the warning gas won’t reach the trees ahead. Absent wind, they’ll simply travel beyond the reach of ethylene gas (around 100 yards) to avoid the tannins that way.

Trees can also detect scents through their leaves and even taste danger. When elms and pines come under attack by leaf-eating caterpillars, for example, they detect the caterpillar saliva, and release pheromones that attract parasitic wasps, a natural predator for caterpillars.

Although alarm and distress seem to be the main reasons trees communicate, these networks allow them to do more than just warn each other of danger. The healthiest trees growing in the best conditions are able to share life-saving nutrients with their less fortunate friends, keeping each other alive — oftentimes against all odds.

Mother Trees Support Their Offspring

For young saplings in a fully shaded area of forest, for example, this network is literally a lifeline as bigger trees (often Mother Trees) pump sugar, water and other lifesaving resources like carbon, nitrogen and phosphorus into their roots.

They’ll even increase their flow of sharing in response to distress signals from neighboring trees. Simard’s research shows that mother trees are a vital defense against threats big and small, and that when the biggest, oldest trees are cut down in a forest, the survival rate of younger trees is reduced.

Simard’s research has found that mother trees act as hubs, and that the bigger and older a tree is, the more connections it has — sometimes hundreds! These Mother Trees seem to recognize their own kin, colonizing them with bigger mycorrhizal networks, sending them more carbon and other nutrients, and even reducing their own root competition to make elbow room for their “kids”.

Their presence increases seedling survival by as much as 400% and when too many are cut down, entire tree networks can collapse. When they’re injured and dying, they’ll send a substantial share of their carbon and even messages of wisdom with the next generation of seedlings. It’s clear: without Mother Trees, many seedlings and forest trees simply wouldn’t make it.

Trees Look Out For Each Other

But trees don't just help their young — in some cases, they’ll also keep some remnant their elders alive for hundreds of years after they’ve been felled. Bestselling author and forester Peter Wohlleben speculates that they’re “reluctant to abandon their dead, especially when it’s a big, old, revered matriarch.” This of course just hints at the importance of Mother Trees to forest societies.

All of this is made possible by the incredible mutualistic fungi that essentially act as an extension of each tree’s root system. In addition to exchanging nutrients, the fungi are able to explore the soil by growing into tiny crevices and accessing nutrients that would otherwise be unavailable to the tree.

What’s in it for the fungi? Well, they’re not performing this service for free — you might even say they charge a fee, as they consume around 30% of the sugar that trees photosynthesize from sunlight. This sugar is their fuel and allows them to scavenge the soil for nitrogen, phosphorus and other mineral nutrients that the trees need. In short: working together with trees allows the fungus to secure its own livelihood with a steady source of food and carbon dioxide.

As you can see, forests are so much more than just a collection of trees. And while we have the feeling we’ve only discovered the tip of the iceberg when it comes to forests and trees, the verdict is clear: connected forests are more resilient, heathy, diverse, and able to stand the test of time. In that way, they’re more like us than we might think. Feeling inspired? Plant a tree with us today!