For some of us it comes as no surprise that the forests of this earth are alive and fully communicative. Yet their means of communication are still to complex for us simple humans to understand. Some researchers do however have qualified guesses:
Forests are essential ecosystems for life on earth. They cover 30% of the surface of the earth, serving as the habitat of an enormous variety of living beings and they play an essential role in the cycling of water, carbon, oxygen, nutrients and soil formation. Some of the biggest and longest-living organisms on the planet live there: trees, with some individuals that manage to survive for hundreds and thousands of years.
Owing to their large size and longevity, trees are exposed to many natural enemies. Throughout their lives, they undergo countless attacks from herbivores, mainly insects and vertebrates, as well as other harmful organisms such as bacteria and fungi, against which they must defend.
Trees that are capable of overcoming such attacks and obtain the necessary resources (light, water and nutrients) will survive and successfully reproduce. To cope with the constant aggressions, plants have developed complex and varied defensive systems that prevent or delay their aggressors’ advances, or diminish their performance. Until recently, the reaction of trees when confronted with their enemies was seen as a simple and passive process. However, we now know that their defence mechanisms are much more active than previously imagined.
Trees, just like other plants, are able to control their defences according to the risk of attack and the existing environmental conditions. The effort they make to protect themselves is not constant; in the same way that the immune system of human beings responds to an infection, trees react to threats by producing more and new chemical and physical defences.
The synthesis of defensive substances is highly costly for plants, and for this reason they usually produce defences only when it is strictly necessary. In this way they achieve a maximisation of growth and reproduction when the risk involved is low. This strategy is especially relevant in trees which, owing to their longevity and size, must deal with countless dangerous situations.
Trees, like other plants, feel the damage caused by their enemies, identify the organisms causing the damage, and react accordingly. The damaged parts send out a message of danger using chemical signals to the rest of the tree and warn of the need to prepare and increase defences. Upon receiving such a signal, plants may stop growing and devote their resources to producing chemical and physical barriers, accommodating their anatomy and physiology to the risk. But these responses are not always the same. They depend on other factors such as the enemy that is causing damage, the intensity of the damage, and environmental factors such as availability of light, water and nutrients.
Recent studies in this field show that one of the most characteristic defensive mechanisms is a change in the emission of volatile organic compounds that are constantly released to the atmosphere by plants and, in particular, by trees. The alteration in the relative concentrations of these substances could be an effective system of internal communication for the tree, warning of the presence of an attack to parts that are far away from it. With these subtle variations in the emission of volatile substances, trees may attract other insects that are the natural predators and parasites of their herbivores; and also insectivorous birds, which approach the tree in search of food. They thereby manage to indirectly reduce the pressure of their enemies, establishing a network of relations with other inhabitants of the forest which, as if a language was involved, interpret the messages issued by the trees. But, do they use this particular code of volatile substances as a communication system between neighbouring trees? If this is so, then plants that have not yet been attacked, upon receiving the warning messages in the volatile substances released, could get ready for a possible attack.
Research in this field is now focused on resolving these and other uncertainties about the various forms of communication between different parts of the same tree, among different trees, between trees and insects and even between trees and beneficial fungi. We now know that trees can perceive changes in the surrounding environment, they can detect the presence of damaging organisms, they can identify them, code them, activate their defences and change the concentration and composition of the volatile substances released. A new and complex world of interactions is now open, where there are many organisms involved in this language of forests. Understanding the flow of information and who the members involved in this singular community are is an ambitious challenge for science and, from the research point of view, we could say that we have entered the era of the communication of the plants.
And if you want to learn more, here is an excellent documentary on plant communication and intelligence:
This film investigates the notion that plants are intelligent, evolved biological forms through interviews with researchers across the globe that are exploring the boundaries between animal and plant. Researchers in the Savannah desert find that populations of Kudu are mysteriously dying off, and make a surprising discovery – Acacia trees have developed a survival technique in response to dense herds of Kudu overgrazing.
When the trees sense that they are being overtaxed they defensively release a toxic gas, eliminating the threat to their population. In examining the predatory nature of plants such as the Venus Fly Trap, the narrator explains that plants have learned to adapt to their environments. In the case of the Venus Fly Traps and other carnivorous flora, the plants compensate for nutritional deficiencies by eating insects, further demonstrating that they are capable of reacting to their environment.
Scientists at Bonn University in Germany focus their studies on the exploration of plants’ ability to recognize and respond to environmental stimuli. Using peas and beans as an example for their use of tendrils to seek out air and light, the researchers demonstrate their point by stimulating pea plants with sticks, causing the tendrils to react. They suggest that pea seedlings exhibit the capacity for memory and perception in their ability to grow upwards regardless of how they are positioned, i.e. a plant on its side reorients itself to continue vertical growth.
Japanese researchers investigate the way plants function at the molecular level, asking how plants sleep, if they need sleep and what happens if they don’t sleep? By recreating day and night cycles in artificial conditions, they manipulate their botanical test subjects in the hopes of proving that sleep and rest are not purely animal behaviors.
A small but growing area of research, the study of plant intelligence is considered somewhat controversial and met with skepticism by the larger scientific community, but is no less important to our understanding of intelligent life be it human, animal or botanical. In the Mind of Plants provides valuable insight into this developing area of investigation and inspires viewers to consider our relationship with the botanical cohabitants of the world.