Branching out: is communication possible between trees and people?


Why can’t we communicate with trees the same way we communicate with, say, elephants? Both live in social groups and look after not only their young but also their elders. That famous elephant memory is also found in trees, and both communicate in languages that we didn’t even recognise at first. Trees communicate through their interconnected root systems, and elephants communicate using low-frequency rumbling below the range at which we can hear. We get a feeling of wellbeing when we run our fingers over the rough skin of both creatures, and what we would love above all is to get a reaction from them.

Is such communication possible between people and trees? First we have to take a closer look at what we mean by “communicate”. It is not enough that we consciously or subconsciously eavesdrop, so to speak, on the scents trees use to communicate among themselves. We have a physical reaction when we breathe them in, but for communication to happen, the trees also need to react to our signals.

Epping Forest ... ancient woodland on the eastern border of London.
Epping Forest … ancient woodland on the eastern border of London. Photograph: Adrian Jones/Alamy

Trees transpire chemical compounds. We are subconsciously aware of these compounds and we respond with changes in blood pressure. The tree, for its part, is unaware of our response – after all, we are not in contact with the tree in any way. And even if we hug the tree and talk of electric fields, which is one way we could mutually affect each other (because plants, like us, function partially by transmitting electric signals), there is still one huge obstacle: time. Trees, as we all know, are awfully slow. You can multiply the time it takes you to make contact with the tree by 10,000 to find out when you can expect a response.

Trees store memories, respond to attacks and transfer sugar solution, and perhaps even memories, to their offspring. All these abilities suggest that they must also have a brain. But no one has yet found any such thing. Professor František Baluška at the University of Bonn has recently been looking into this. For some time now, he has been of the opinion that plants are intelligent – after all, they can process information and make decisions – but consciousness takes the discussion to a different level.

Baluška and his colleagues sedated plants that feature moving parts, such as Venus flytraps. The anaesthetics the scientists used deactivated electric activity so that the traps no longer reacted when they were touched. Sedated peas showed similar changes in behaviour. Their tendrils, which usually move in all directions, stopped searching and started to spiral on the spot. After the plants broke the narcotics down, they resumed their normal behaviour.

Did the plants wake up as we do when we come to after a general anaesthetic? This is the critical question, because in order to wake up, you need one thing above all others: consciousness. And it was exactly this question that a reporter posed to Baluška. I really liked his answer: “No one can answer this because you cannot ask [the plants].”

When you hug a tree, nothing electric happens, because your voltages are the same. But might the tree be aware of your touch in some other way? All you have to do, for example, is stroke your tomato plants for a few minutes each day and they slow their upward growth and put their energy into growing thicker stems instead. This, however, is not the plant saying it loves you too, but rather the plant reacting to what it likely experiences as a breeze blowing by, because the wind elicits a similar response. If you were hoping to hug a tree and get a hug back, this information must be disappointing.

We do, however, find a great deal of sensitivity in a completely different part of the tree: its roots. At this level, the tree works its way through the ground with its root tips, which contain brain-like structures. The root tips feel, taste, test and decide where and how far the roots will travel. If there is a stone in the way, the sensitive tips notice and choose a different route. The sensitivity to touch that tree lovers are seeking is therefore to be found not in the trunk but underground. If it is possible to make contact, the roots would be the first place to try. However, they like neither pressure nor fresh air – and so there’s no point exposing these tender structures, because even 10 minutes in the sun spells death for their tissue.

The most recent scientific discoveries, however, offer something completely different: the heartbeat of trees.

What blood is to people, water is to trees. I have written a lot about how water is transported up into the crown of the tree; exactly how that happens has not yet been adequately explained. But Dr András Zlinszky at the Balaton Limnological Institute in Tihany, Hungary, is shedding some light on the matter. Some years ago, he and colleagues from Finland and Austria noticed that birch trees appear to rest at night. The scientists used lasers to measure trees on calm nights. They noticed the branches hung up to 4in (10cm) lower, returning to their normal position when the sun rose. The researchers started talking about sleep behaviour in trees.

Zlinszky could not get this discovery out of his head, and he decided he needed to investigate further. He and a colleague, Professor Anders Barfod, measured another 22 trees of different species. Once again, they documented the rise and fall of the branches, but this time some of the cycles were different. The branches changed position not only morning and night, but also every three to four hours. Was it conceivable that the trees were making pumping movements at these regular intervals? After all, other researchers had already determined that the diameter of a tree’s trunk sometimes shrinks by about 0.002in (0.05mm) before expanding again. Were the scientists on the trail of a heartbeat that used contractions to pump water gradually upward? A heartbeat so slow that no one had noticed it before? Zlinszky and Barfod suggested this as a plausible explanation for their observations, nudging trees one step further toward the animal kingdom.

Redwood forests.
Redwood forests. Photograph: James Yu/Getty Images

A heartbeat every three to four hours is, unfortunately, too slow for even the most sensitive person to feel when they hug a tree. But there is one last possible way to connect with trees: our voices. Can plants hear? I can answer without hesitation in the affirmative. This was tested years ago with Arabidopsis, a genus of rockcress beloved of scientists. Beloved because it grows well, it reproduces rapidly, and it’s easy to keep track of its genes. Scientists discovered that the roots of Arabidopsis oriented themselves toward clicks in the frequency of 200Hz and then grew in that direction.

Arabidopsis also seems to react to the nibbling of caterpillars, an ominous sound to plants of all species. Researchers at the University of Missouri put caterpillars on samples of the plants. The vibrations caused by the caterpillars munching were enough to shake the plants’ stems, and the researchers used laser beams to record the vibrations. When researchers then played these vibrations to plants that were not being eaten, they produced particularly large quantities of defensive chemicals when they were later attacked. Wind and other sounds with the same frequency did not elicit a reaction. Arabidopsis, then, can hear, and this makes perfect sense. Thanks to acoustic warnings, it is able to recognise danger some distance away, so it can make appropriate preparations to defend itself. What is particularly important here is that the plants ignore noises that pose no threat to them. These noises probably include human voices. What a shame.

I can well understand people’s desire to communicate with trees. To sit under these giants, run your hands over their bark, and feel secure – all this would be even more special if there were an active, positive response to your presence or, even better, to your touch. I am not going to deny that something like that might be possible, but conservative science at least has no proof that it could happen. And even if this were the last word on the subject, does the tree have to respond? Could it not be that people and trees live in completely different worlds? After all, our species has existed for only 0.1% of the time that trees have been around. For the time being, it should be enough that we feel good around trees – and I hope we can then be content to allow them to live their own wild lives.

Although trees may feel nothing of our attempts to communicate, we, for our part, definitely experience a physical reaction. I encourage you to experience this for yourself. Make a plan to go outside and immerse yourself in nature. If there is a forest near you, make that your destination. If you live in a city, find a park or even just a tree-lined street where you can take a walk. Stand and feel the air on your skin. What can you smell? The gentle, earthy aromas of old leaves gently decomposing on the ground or the tangy, brisk scents of new growth? What can you hear? The scratching of squirrels scuttling up trunks or the rustle of leaves as birds turn them over to find insects underneath? Shut your eyes and feel that this is a place where you belong.

Take a moment to just sit – on a stump or a log or a carpet of leaves. Does that bring you even closer to feeling part of the forest? Run your fingers through the crispness of leaves or over the softness of moss. What do you know about the trees and plants around you? Do you know their names? Do you know if they are safe to eat and, if they are, how they taste? What more would you like to learn about their lives, what would you hope to find in guide books and what do you hope scientists will explore in the future so we can really get to know the amazing creatures that are trees in all their biological complexity? We share a world and if they thrive, so do we.

Edited extract from The Heartbeat of Trees: Embracing Our Ancient Bond with Forests and Nature by Peter Wohlleben, translated by Jane Billinghurst, published by Greystone (£18.99) on 5 June. To support the Guardian order from guardianbookshop.com. Delivery charges may apply.



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