The Biosemiotics Debate: What Did One Tree Say to the Other?

Growing up in Mesa, Arizona, my personal ecological experience has been limited by variations of desert. Because of this, any opportunity I had to head up north to forest-blanketed Flagstaff was treasured. My first trip to Northern Arizona was during autumn when I was eleven. On the drive up there, I remember being awe stricken by the miles of greenery I could see as I peeked out the window. My first step out of the car was met by a quick breeze that sent goosebumps down my spine. I began to walk while feeling the pine needles give a satisfying crunch beneath my shoes. I remember crossing my arms trying to keep the cold out. Clearly regretting not wearing a jacket, I glanced around me at the towering conifer trees. They were quite a sight to be taken in. I breathed deeply, noticing the fresh pine smell, and thought about the entirety of this forest and all of its wonders. How long have these trees been here? How do they survive each season? Today, with my continuing love for forests, I am able to more confidently answer these questions. The interactions that trees have with the environment and with each other is often misunderstood.

Is it deliberate how far they make you go
especially if you live in the city to get far
enough away from home to see not just trees
but only trees?
Leaves by Lloyd Schwartz, 1941

In my recent analysis in Part II of this blog of the film Avatar, by James Cameron, I was able to learn more about the biosemiotic processes and relationships between the trees and their environment. Even though the fictional ecosystem was presented in a mystical way, the film  nevertheless resembled our own planetary ecosystems and how we exploit them.

Exploitation of forests is often based on misconceptions involving the livelihood of trees. However, today, it is well known that trees are connected to each other by their roots, and that nearby fungi help transmit nutrients between the individuals. Did you know that trees can actually talk to each other? No, I do not mean that trees will tap their neighbor on the shoulder and say “Wonderful CO2 we’re having today!” There are other methods in which trees can transmit signals to their neighbors as a form of communication. German forester Peter Wohlleben, in his New York Times best selling book, The Hidden Life of Trees, explained many different processes on how trees are able to communicate through chemical signaling, scent, and sound vibrations. Wohlleben explained these processes as “…news bulletins are sent out via the roots not only by means of chemical compounds but also by means of electrical impulses…” (10).

Photograph by Dominicus Johannes Bergsma, distributed under a CC BY-SA 4.0 license., via Wikimedia Commons.

As many scientists are confirming, fungi in the soil helps to transmit chemical signals between the roots of trees. “The fungus not only penetrates and envelopes the tree’s roots, but also allows its web to roam through the surrounding forest floor” (Wohlleben 51). When a stimulant has been detected by the fungi, that information travels through the tree like electricity through cables. The main difference is the speed in which this occurs. Wohlleben explains that these chemical signals travel at about one third of an inch per second, much slower in comparison to what we are used to. 

These stimulants are often detected from local insect predators. For example, bark beetles are known for killing conifer trees by attacking in large numbers (Kolosova & Bohlmann 85). Increasing bark beetle activity in Flagstaff has been a problem since 2011. A devastating wildfire named “Wallow Fire” affected the White Mountains in Northern Arizona. This is a problem because bark beetles are known to thrive in disturbed environments (Bonnie Stevens). The trees have two ways to combat these invasions: through the protection of fungi, or through defense services found in the inner bark.

Photograph by Katja Schulz from Washington, D. C., USA, distributed under a CC BY 2.0 license., via Wikimedia Commons.

In addition to fungi assisting the trees through their vast neural-like network, they offer protection against insects and other potential predators. Scientists at Northern Arizona University in Flagstaff have been utilizing a native fungus that is known for killing bark beetles. Exposure to the white powdery spores found on the surface of the fungi is what kills the beetles. Another line of defense from the tree is the production of resin in the inner bark. When there is damage done to the tree, lesion formation influences the accumulation of toxic chemicals in the area that will then kill the invader (Kolosova & Bohlmann). This signal-and-response system aids in the tree’s survival.

In fact, trees are able to utilize a “sense of smell.” Pheromones are often released when an individual tree is under attack. If, for example, a deer approaches a tree to munch on its leaves, the individual tree will pump toxins into its leaves making it unpalatable to the deer. Additionally, as Wohlleben states, the tree will release chemicals into the air warning surrounding trees of the same species to pump the same toxins into their leaves. This signal allows them to be protected as a community from any harm coming their way. 

Photograph by Ryan Hodnett, distributed under a CC BY-SA 4.0 license., via Wikimedia Commons.

Acorns and pinecones are probably the first thing to come to mind when tree seeds are mentioned. The young seedlings from trees can always be seen scattered all over the forest floor. When the seeds are buried in the soil and are given enough water and nutrients to finally sprout, their roots begin to vibrate at approximately 220 Hz. Nearby tree roots are able to “hear” this frequency and direct their roots to grow in the direction of their newest addition (Wohlleben 13). The frequency is a signal sent out to the other trees to alert them of a newcomer. Trees are able to utilize their “senses” in similar ways to us. It is because of their sound, and scent receptors that trees can keep in close contact.

We see these processes at work in James Cameron’s film. The trees are portrayed in Avatar like they are just another character. Through one of the trees, which they refer to as “Hometree,” the Na’vi can listen to the stories of their ancestors. In this film, the trees actually could talk. I believe James Cameron intentionally included this to better display a close biosemiotic relationship between trees and people. By showing this, it helps the audience to reflect on their own relationship with nature and how it can be improved. The trees around us are not so much inanimate objects, but a thriving community with fluid communication.

Photograph by Elaine Trias; Flagstaff, Arizona

As I have continued my education in ecology, my love and curiosity of the natural world has grown. I have taken a particular interest in trees and forests because that is the environment I have been exposed to the least. It has become useful to me to observe biosemiotic processes within a single ecosystem to gain a better understanding of its presence. Biosemiotics are the semiotic processes (signs and signals) that are found in biological organisms and systems. It helps in explaining the interactiveness trees have with each other to proliferate as an ecosystem. Forests are able to collectively survive in their community because of this. They relate to biosemiotics through their own systems of communication. Fungal networks, chemical signals, pheromones, and vibrations are all signs and signals that allow for communication between the trees in their ecosystems. It is because of these processes that trees can be perceived as being able to talk to each other.