Do trees talk to each other?

July 31, 2018 12:00 am | Updated 03:32 am IST

Yes they do, all the time, to help a neighbour or to save their community from an infestation. Explore their secret network in this week’s Eco-logical.

Animal communication is an often-discussed topic. We get the idea of communication taking place from observing their body language and their responses to calls typical to each animal and bird. But can immobile and silent plants communicate with each other? Yes they can and they do, in the language of the forest.

A tree may appear like a loner, a solitary being. But it is interacting with fellow trees all the time, say experts who have studied the concept. It has now been widely accepted that forest trees are communal, living in a co-operative and inter-dependent relationships, maintained by communication. Read on to know more about this secret social network of the flora.

How do trees talk?

Above ground, plants and trees engage in airborne communication. Plants / trees pass on their messages through sound and smell. Underground, they do so using a special fungal network nicknamed by scientists -- the Wood Wide Web.

Airborne communication

Trees not only exchange information among themselves but also with other organisms such as insects.

Smell a problem

Think of the scent of a tree that is cut. Chemicals emitted by this tree, that contribute to the smell, signal to other plants to prepare for an attack. These warning signals are of great help when there is an infestation risk. The tree under attack by insects releases a range of volatile molecules into the air alerting the trees around. After exposure to these chemicals, other trees produce toxins or substances that make themselves harder to digest for insects.

Through sound

It was discovered in 2013 that plants and trees communicate with each other and with insects through sound. Monica Gagliano from the University of Western Australia discovered that the roots of plants make a clicking sound as they grow, which can be detected using highly sensitive laser microphones. Through a series of experiments, Gagliano and her team found that the roots of young corn plants made regular clicking noises. They also found that the roots, when suspended in water, ‘leaned’ towards the source of any sound with frequency of 220Hz that was emitted in the region. This frequency falls within the range that the roots themselves emit. She hypothesised that plants may use sound waves to detect water at a distance.

Plant-insect communication

When bees buzz, they are not just flying, they are communicating to the flower to release the pollen. The sound of buzz (at a particular frequency) make tomato flowers to release their pollens, studies have found. Similarly, bark beetles may pick up the air bubble pops inside a plant, which is a hint that trees are experiencing drought stress. Bark beetles often attack trees that are already weakened by drought.

The Wood Wide Web

Not all transfer of information happen above the ground. A majority of the networking happens underground.

The vast majority of land plants live in symbiotic relationships with soil fungi. The fungi cannot photosynthesise, as they have no access to light and have no chlorophyll, whereas the trees photosynthesise. Trees use the sun’s energy to refashion carbon dioxide and water into sugar. Fungi get sugar and carbon from trees, and in return release nutrients such as phosphorous and nitrogen, as well as water (collected from their environment) to the trees.

The vegetative part of the soil fungi is called mycelium. Mycelium is made up of long white fibres called hyphae. The roots of trees and mycelium join together to form the mycorrhizal networks. It is through the mycelium that fungi absorb nutrients from their environment.

Fungi also colonise several hosts at once, creating a large fungal network that ferries nutrients and signalling chemicals (communication) between trees. They even connect trees that are miles away.

How does the communication happen?

The tree-to-tree communication happens for various purposes and in many forms. It may not be a typical ‘Hello’. But it is definitely a network of sharing and caring and that ensures the survival of the community.

Warning signals

Trees send distress chemical signals about drought and disease or an insect attack. Other trees pick up these signals and increase their own resistance to the threat.

This communication is comparable to the airborne communication. But such warnings are more precise in terms of source and recipient when sent by means of the mycorrhizal networks, say experts.

Love thy neighbour

A dying tree might divest itself of its resources to the benefit of the community through this network. A ‘parent’ tree use the fungal network to feed the seedlings that have sprouted under its shade. Researchers have found how old trees were able to survive with resources from younger ones.

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