The social life of forests

Trees are much more than what they are to us. Trees can and do “talk” to each other. How is this possible? What are they sharing with each other? Watch to find out! #STEMinASL

[Video Description: Barbara, a white woman, is wearing a black V-neck long-sleeved shirt and a pair of silver hooped earrings.

0:02 – A photo of adult trees with green leaves and trunks in the background and the sun peering through them. There are green shrubs in the foreground.

1:30 – A photo shows an African savannah with tan grasses. There is an umbrella thorn acacia tree on the right and a giraffe, on the left, eating the leaves off the tree.

4:28 – Top photo: A close-up photo of a leaf with a parasitic orange wasp on the top of a brown/tan caterpillar.

4:33 – Bottom photo: A close-up photo of a green caterpillar climbing on a green stem with white oval-shaped eggs on its back.

5:09 – A drawing of trees with their underground roots connecting to each other through green lines.

5:33 – A cross-section photo showing three plants and their roots connected in a spider-like web by white filamentous mycelium.

7:03 – A photo showing a giant tree with a brown circular patch (no grass) surrounding the tree and some green grass further away from the tree.

7:46 – A photo showing a trail through a dense forest with sunlight peeking through the trees.]

*Text excerpts from several sources and modified for Atomic Hands

Transcript: When we walk in a dense forest, trees might move some of us to tears of joy while others might see them only as a green thing that stands in their way. But trees are much more than what they are to us.

Yes, trees are the foundation of forests, but a forest is much more than what you see… It is a whole other world — a world of infinite biological pathways that connect trees and allow them to communicate and allow the forest to behave like a single organism. Trees can and do “talk” to each other. How is this possible? What are they sharing with each other?

Trees communicate in different ways. Scent is one. Scientists observing the African savannah discovered one of the ways trees communicate is through scent. The giraffes in the savannah were feeding on the leaves of umbrella thorn acacias, and the trees didn’t like this one bit. It took the acacias mere minutes to start pumping toxic substances into their leaves to rid themselves of the large herbivores. The giraffes got the message and moved on to other trees in the vicinity. But did they move on to trees close by? No, for the time being, they walked right by a few trees and resumed their meal only when they had moved about 100 meters away.

The reason for this behavior is astonishing. The acacia trees that were being eaten gave off a warning gas (specifically, ethylene) that signaled to neighbor trees of the same species that a crisis was at hand. Right away, all the forewarned trees also pumped toxins into their leaves to prepare themselves. The process might feel very familiar to you… It is similar to our bodies mounting an immune response to combat unwanted intruders entering our bodies. Although the trees were armed with pumped toxins, the giraffes were too wise to this game and moved farther away to a part of the savannah where they could find trees that were oblivious to what was going on. Or else the giraffes moved upwind. Because the scent messages are carried to nearby trees on the breeze, and if the animals walked upwind, they could find acacias close by that had no idea the giraffes were there.

Similar airborne communication processes exist in other tree species. When it comes to some species of insects, trees can accurately identify which bad guys they are up against. The saliva of each insect species is different, and trees can match the saliva to the insect. Indeed, the match can be so precise that trees can release pheromones in the air that summon specific beneficial predators. These predators help trees by eagerly devouring the insects that are bothering them. For example, elms and pines call on small parasitic wasps that lay their eggs inside leaf-eating caterpillars. As the wasp larvae develop, they devour the larger caterpillars bit by bit from the inside out, thus saving the trees from bothersome pests and allowing them to grow with no further damage.

Trees don’t rely exclusively on aerial communication through scent. Dr. Suzanne Simard of the University of British Columbia has discovered that they also warn each other using an underground network – also known as “wood wide web.” This complex network connecting trees is dependent on a symbiotic relationship with microbes in the soil like fungi and bacteria. Fungi can cover a large surface area by developing white fungal threads known as mycelium and they connect to trees around their root tips. Mycelium receives sugars from the tree and provides vital minerals back to the tree, such as nitrogen and phosphorus. 

Over centuries, a single fungus can cover many square kilometers and network an entire forest. Scientists believe all trees have a mycorrhizal network, but trees only communicate with each other if the fungal and bacterial species that constitute their mycorrhizal networks are the same.

Mycorrhizal networks are extremely important for tree health during times of danger. Certain species of fungi can facilitate tree resilience to certain environmental stressors such as predators, toxins, and pathogenic microbes that invade an ecosystem. Through the mycorrhizal network, trees can warn their neighbors about an invasive predator or inhibit the growth of invasive plant species. Using a technique called allelopathy, the surrounding trees can then defend themselves by releasing chemicals to deter predators or pathogenic bugs. It was even found that trees can send a stress signal to nearby trees after a major forest disturbance, such as deforestation.

The next time you take a walk in the forest, take a moment to realize that trees are social beings and they have ways to communicate, support, and nurture with one another. And, there remain so many more discoveries to learn the ancient wisdom of our forests. Perhaps talking to plants is the first step!



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