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Do trees have brains and talk to each other?
Do trees have brains and talk to each other? They are intelligent, express emotions and make friends, claims a new book. Barking? Judge for yourself
By Peter Wohlleben
• Some research claims trees are able to communicate with each other
• Forester Peter Wohlleben believes they are able to transmit information
• Scientists are starting to ask whether trees possess intelligence and brains
There's increasing evidence to show that trees are able to communicate with each other. More than that, trees can learn.
If that's true — and my experience as a forester convinces me it is — then they must be able to store and transmit information.
And scientists are beginning to ask: is it possible that trees possess intelligence, and memories, and emotions? So, to cut to the quick, do trees have brains?
It sounds incredible, but when you discover how trees talk to each other, feel pain, nurture each other, even care for their close relatives and organise themselves into communities, it's hard to be sceptical.
There's increasing evidence to show that trees are able to communicate with each other
I didn't always feel this way. In fact, when I began as a civil servant with the German forestry commission in the Eighties, I knew next to nothing about the hidden life of trees.
It was my job to look at hundreds of spruces, beeches, oaks and pines every day, to assess their readiness for the lumber mill and their market value.
About 20 years ago, while organising survival training and log cabin breaks for tourists, I began to rediscover the love of nature I'd had as a six-year-old.
Next, I noticed that visitors were enchanted by crooked, gnarled trees — ones that I would have dismissed because of their low commercial value.
Forester Peter Wohlleben believes trees must be able to store and transmit information
I began to pay attention to more than just the quality of the trunks. I noticed bizarre roots, strangely intertwined branches, mossy cushions on bark . . . all kinds of wonders. Including, unbelievably, evidence of tree friendships.
In the forest that I manage (near the village of Hümmel, east of the Belgian border), I stumbled on a ring of mossy stones, arranged in a circle about five feet across. They were an unusual shape, gently curved with hollowed-out areas.
Scratching at the moss with a knife, I discovered a layer of bark — these were pieces of wood, not stone. But they were hard as rock, and at first I couldn't understand why they were not decomposing, until I tried to move one . . . and discovered it was rooted into the ground, still alive.
What I'd found was the remains of a tree stump, the vestiges of an ancient forest giant. The moss-covered 'stones' had grown where the outer ring had been, and the interior had long rotted away completely. This tree must have been felled at least 400 years ago, perhaps much more, but it was not completely dead.
HOW TREES DRINK 200 GALLONS IN A STORM
During a heavy storm, a mature deciduous tree can 'drink' a couple of hundred gallons of water, which is funnelled to its roots. This water is stored in the surrounding soil, to help the tree through future dry spells. Trees think ahead.
A single tree contains millions of calories in the form of sugar, cellulose, lignin (which helps to make the structure 'woody') and other carbohydrates. But to insects and birds, a tree isn't so much a grocery store as a guarded warehouse, because the food is surrounded by a thick protective wall of bark. Trees think about security.
Every day in summer, trees release about 29 tons of oxygen into the air per square mile of forest. A person breathes in nearly two pounds of oxygen each day, so that's the daily requirement for tens of thousands of people. Trees don't care about us — but we should care about them.
It had no leaves, however. Without leaves, a tree cannot absorb nourishment from the sunlight.
Living cells must have food in the form of sugar, and they must breathe. The roots of the stump ought to have suffocated and starved to death long ago.
One possible answer existed. The other beeches around the stump had been pumping sugar into it for centuries to keep it alive, through their tangled roots.
Most individual trees of the same species growing in the same copse or stand will be connected through their root systems. It appears that helping neighbours in times of need is the rule, which leads to the conclusion that forests are super-organisms, much like ant colonies.
But the support they give each other is not random. Research by Professor Massimo Maffei at the University of Turin shows trees can distinguish the roots of their own species from other plants, and even pick out their own relations from other trees. Some are so tightly connected at the roots that they even die together, like a devoted married couple.
Diseased or hungry individuals can be identified, supported and nourished until they recover.
When the thick silver-grey beeches in my forest behave like this, they remind me of a herd of elephants. Like the herd, they look after their own, helping the sick and the weak back onto their feet.
And as those mossy wooden 'stones' revealed, they are even reluctant, like elephants, to abandon their dead. Of course, this cannot be done for every stump. Most rot and disappear within a couple of hundred years — which is not very long for a tree. But a few are maintained on life support for centuries. It appears to be the closeness of connection, or even affection, that determines how helpful the other trees will be.
It seems many species do this. I have observed oak, fir and spruce stumps as well as beeches that have survived long after the tree was felled. But it's not just silent support that trees offer each other.
Dr Suzanne Simard of the University of British Columbia in Vancouver has discovered that they can also send warnings using chemical signals and electrical impulses through the fungal networks that stretch under the soil between sets of roots — networks known as the 'wood wide web'.
These fungi operate like fibre-optic internet cables. Their thin filaments penetrate the earth, weaving through it in almost unbelievable density. One teaspoon of forest soil contains many miles of these tendrils.
Over centuries, if left undisturbed, a single fungus can cover many square miles and create a network throughout an entire forest. Through these links, trees can send signals about insects, drought and other dangers.
News bulletins are transmitted by chemical compounds and also by electricity, travelling at an inch every three seconds.
In comparison with the lightning impulses in mammal bodies, that is extremely slow. But there are species, such as jellyfish and worms, whose nervous systems conduct impulses at similar speeds.
Scientists are beginning to ask whether it is possible that trees possess intelligence
This might help to explain how swarms of insect pests are able to identify trees becoming weak. It's conceivable that some caterpillars and beetles tune in to the warnings flowing from tree to tree, then test which individuals are failing to pass on the message, by taking a bite of their leaves or bark.
A tree's silence might indicate that it is cut off from the fungal network, perhaps because it has lost its ability to communicate, and so is unable to prepare for attack or call for help. So not only do trees talk, insects eavesdrop.
Communication between trees and insects isn't all about defence and illness. There are also the feelgood messages, the perfumed invitations issued by sweet smelling blossom.
These lovely scents are not to please us but to attract bees, which come for the sugar-rich nectar and take away a dusting of pollen, to fertilise other trees.
And it's not just the smells: blossoms are vivid, gaudy splashes of colour. So trees are using displays of erotic perfume and dazzling adornment for sexual purposes — just like many animals and birds.
There's one more way that animals communicate, through sound. I was dubious at first that trees could deliberately make noises, but the latest scientific research is persuading me otherwise.
Dr Monica Gagliano from the University of Western Australia has been monitoring roots with highly sensitive apparatus, and believes they crackle at a frequency of 220 hertz, which the human ear hears as a low A note.
When this note was played back to seedlings, their roots tilted towards the sound. It appears they could hear it, and were responding.
You might wonder, if trees can talk to each other in so many ways, what they have to discuss.
Among beech trees, at any rate, the conversation might be about when to feed the deer.
Deer are extremely partial to beechnuts, which help them put on a protective layer of fat for winter.
The nuts contain up to 50 per cent oil and starch, making them more nutritious than any other food source. And trees make a lot of them — every beech produces at least 30,000 nuts in a year. It has to, because the odds of a beechnut growing into an adult tree are nearly two million to one. Do the maths: a beech isn't sexually mature until it's between 80 and 150 years old, depending on how much light it gets while growing.
Assuming it lives to be 400, it will fruit at least 60 times and produce a total of about 1.8m nuts . . . the minimum number it needs to be sure of spawning one new tree.
But why produce nuts only 60 times in 400 years? Why not every year? The answer is that the trees don't want to overfeed the deer, because big, hungry herds will strip the forest bare.
No sapling will stand a chance if the deer population explodes.
So the trees must co-operate, to ensure that they all withhold their nuts for several years at a time, and then simultaneously come into fruit together. The deer will have a feast, it's true, but the herds won't be able to rely on an annual bounty. Early human farmers spotted this
thousands of years ago. Like the deer, wild pigs gorge on beechnuts, too. Their bodies adapt so their birth rate triples, because they're getting enough nutrition for big litters of piglets. When the nuts arrive and the boars get fat, it's known as a 'mast' year.
The farmers would release their domestic pigs into forests during mast years.
The porkers gobbled the beech nuts, piled on plenty of meat, and had lots of chubby piglets. Then the farmers would round them up, and there'd be pork on the table throughout winter.
If you think that needs clever communication, think about how umbrella thorn acacias on the African savannah defend themselves against giraffes.
When they start picking at foliage, the acacias begin pumping foul-tasting toxins into the leaves to deter them. It happens in minutes, which for a tree is instantaneous. The giraffes get the message and move on.
But they don't go to the next acacia. They wander at least 100 yards before trying their luck again. The reason is astonishing. As they come under attack, the acacias give off a warning gas called ethylene that signals a crisis to neighbouring trees.
That triggers other acacias to dump toxins into their own leaves, as a defensive measure.
And the giraffes have learned that when one tree tastes bad, others in the vicinity will, too.
The exception is when the wind picks up and only trees downwind detect the ethylene in the air, and react. Giraffes know it too, and head upwind.
Elms and pines use a different tactic. When an insect eats a leaf, electrical signals travel from the damaged area to the roots — just as human tissue sends pain signals along the nervous system.
It takes at least an hour for the roots to react and unleash the defences, by flowing bitter compounds into the leaf to send the attacker packing. But something even more amazing is also happening: the tree identifies the attacker by its saliva. Armed with this, the tree releases phero-mones to summon specific predators, to prey on the insects. For example, elms and pines call on parasitic wasps that lay their eggs inside leaf-eating caterpillars, condemning them to slow, painful deaths. Trees are prepared to wait for revenge.
The main reason humans cannot perceive how clever and complex they are is because we exist in such short time scales by comparison. There's a tree in Sweden for instance, a spruce, that is more than 9,500 years old. That's 115 times longer than the average human lifespan.
A tree's childhood lasts ten times as long as ours. Activities that take us moments — waking up or stretching our limbs, can last months for a tree.
It's hardly surprising that most of us see trees as practically inanimate, nothing more than objects. But the truth is very different. They are just as intensely alive as we are . . . and for much, much longer.
Do trees have brains and talk to each other? They are intelligent, express emotions and make friends, claims a new book. Barking? Judge for yourself
By Peter Wohlleben
• Some research claims trees are able to communicate with each other
• Forester Peter Wohlleben believes they are able to transmit information
• Scientists are starting to ask whether trees possess intelligence and brains
There's increasing evidence to show that trees are able to communicate with each other. More than that, trees can learn.
If that's true — and my experience as a forester convinces me it is — then they must be able to store and transmit information.
And scientists are beginning to ask: is it possible that trees possess intelligence, and memories, and emotions? So, to cut to the quick, do trees have brains?
It sounds incredible, but when you discover how trees talk to each other, feel pain, nurture each other, even care for their close relatives and organise themselves into communities, it's hard to be sceptical.
There's increasing evidence to show that trees are able to communicate with each other
I didn't always feel this way. In fact, when I began as a civil servant with the German forestry commission in the Eighties, I knew next to nothing about the hidden life of trees.
It was my job to look at hundreds of spruces, beeches, oaks and pines every day, to assess their readiness for the lumber mill and their market value.
About 20 years ago, while organising survival training and log cabin breaks for tourists, I began to rediscover the love of nature I'd had as a six-year-old.
Next, I noticed that visitors were enchanted by crooked, gnarled trees — ones that I would have dismissed because of their low commercial value.
Forester Peter Wohlleben believes trees must be able to store and transmit information
I began to pay attention to more than just the quality of the trunks. I noticed bizarre roots, strangely intertwined branches, mossy cushions on bark . . . all kinds of wonders. Including, unbelievably, evidence of tree friendships.
In the forest that I manage (near the village of Hümmel, east of the Belgian border), I stumbled on a ring of mossy stones, arranged in a circle about five feet across. They were an unusual shape, gently curved with hollowed-out areas.
Scratching at the moss with a knife, I discovered a layer of bark — these were pieces of wood, not stone. But they were hard as rock, and at first I couldn't understand why they were not decomposing, until I tried to move one . . . and discovered it was rooted into the ground, still alive.
What I'd found was the remains of a tree stump, the vestiges of an ancient forest giant. The moss-covered 'stones' had grown where the outer ring had been, and the interior had long rotted away completely. This tree must have been felled at least 400 years ago, perhaps much more, but it was not completely dead.
HOW TREES DRINK 200 GALLONS IN A STORM
During a heavy storm, a mature deciduous tree can 'drink' a couple of hundred gallons of water, which is funnelled to its roots. This water is stored in the surrounding soil, to help the tree through future dry spells. Trees think ahead.
A single tree contains millions of calories in the form of sugar, cellulose, lignin (which helps to make the structure 'woody') and other carbohydrates. But to insects and birds, a tree isn't so much a grocery store as a guarded warehouse, because the food is surrounded by a thick protective wall of bark. Trees think about security.
Every day in summer, trees release about 29 tons of oxygen into the air per square mile of forest. A person breathes in nearly two pounds of oxygen each day, so that's the daily requirement for tens of thousands of people. Trees don't care about us — but we should care about them.
It had no leaves, however. Without leaves, a tree cannot absorb nourishment from the sunlight.
Living cells must have food in the form of sugar, and they must breathe. The roots of the stump ought to have suffocated and starved to death long ago.
One possible answer existed. The other beeches around the stump had been pumping sugar into it for centuries to keep it alive, through their tangled roots.
Most individual trees of the same species growing in the same copse or stand will be connected through their root systems. It appears that helping neighbours in times of need is the rule, which leads to the conclusion that forests are super-organisms, much like ant colonies.
But the support they give each other is not random. Research by Professor Massimo Maffei at the University of Turin shows trees can distinguish the roots of their own species from other plants, and even pick out their own relations from other trees. Some are so tightly connected at the roots that they even die together, like a devoted married couple.
Diseased or hungry individuals can be identified, supported and nourished until they recover.
When the thick silver-grey beeches in my forest behave like this, they remind me of a herd of elephants. Like the herd, they look after their own, helping the sick and the weak back onto their feet.
And as those mossy wooden 'stones' revealed, they are even reluctant, like elephants, to abandon their dead. Of course, this cannot be done for every stump. Most rot and disappear within a couple of hundred years — which is not very long for a tree. But a few are maintained on life support for centuries. It appears to be the closeness of connection, or even affection, that determines how helpful the other trees will be.
It seems many species do this. I have observed oak, fir and spruce stumps as well as beeches that have survived long after the tree was felled. But it's not just silent support that trees offer each other.
Dr Suzanne Simard of the University of British Columbia in Vancouver has discovered that they can also send warnings using chemical signals and electrical impulses through the fungal networks that stretch under the soil between sets of roots — networks known as the 'wood wide web'.
These fungi operate like fibre-optic internet cables. Their thin filaments penetrate the earth, weaving through it in almost unbelievable density. One teaspoon of forest soil contains many miles of these tendrils.
Over centuries, if left undisturbed, a single fungus can cover many square miles and create a network throughout an entire forest. Through these links, trees can send signals about insects, drought and other dangers.
News bulletins are transmitted by chemical compounds and also by electricity, travelling at an inch every three seconds.
In comparison with the lightning impulses in mammal bodies, that is extremely slow. But there are species, such as jellyfish and worms, whose nervous systems conduct impulses at similar speeds.
Scientists are beginning to ask whether it is possible that trees possess intelligence
This might help to explain how swarms of insect pests are able to identify trees becoming weak. It's conceivable that some caterpillars and beetles tune in to the warnings flowing from tree to tree, then test which individuals are failing to pass on the message, by taking a bite of their leaves or bark.
A tree's silence might indicate that it is cut off from the fungal network, perhaps because it has lost its ability to communicate, and so is unable to prepare for attack or call for help. So not only do trees talk, insects eavesdrop.
Communication between trees and insects isn't all about defence and illness. There are also the feelgood messages, the perfumed invitations issued by sweet smelling blossom.
These lovely scents are not to please us but to attract bees, which come for the sugar-rich nectar and take away a dusting of pollen, to fertilise other trees.
And it's not just the smells: blossoms are vivid, gaudy splashes of colour. So trees are using displays of erotic perfume and dazzling adornment for sexual purposes — just like many animals and birds.
There's one more way that animals communicate, through sound. I was dubious at first that trees could deliberately make noises, but the latest scientific research is persuading me otherwise.
Dr Monica Gagliano from the University of Western Australia has been monitoring roots with highly sensitive apparatus, and believes they crackle at a frequency of 220 hertz, which the human ear hears as a low A note.
When this note was played back to seedlings, their roots tilted towards the sound. It appears they could hear it, and were responding.
You might wonder, if trees can talk to each other in so many ways, what they have to discuss.
Among beech trees, at any rate, the conversation might be about when to feed the deer.
Deer are extremely partial to beechnuts, which help them put on a protective layer of fat for winter.
The nuts contain up to 50 per cent oil and starch, making them more nutritious than any other food source. And trees make a lot of them — every beech produces at least 30,000 nuts in a year. It has to, because the odds of a beechnut growing into an adult tree are nearly two million to one. Do the maths: a beech isn't sexually mature until it's between 80 and 150 years old, depending on how much light it gets while growing.
Assuming it lives to be 400, it will fruit at least 60 times and produce a total of about 1.8m nuts . . . the minimum number it needs to be sure of spawning one new tree.
But why produce nuts only 60 times in 400 years? Why not every year? The answer is that the trees don't want to overfeed the deer, because big, hungry herds will strip the forest bare.
No sapling will stand a chance if the deer population explodes.
So the trees must co-operate, to ensure that they all withhold their nuts for several years at a time, and then simultaneously come into fruit together. The deer will have a feast, it's true, but the herds won't be able to rely on an annual bounty. Early human farmers spotted this
thousands of years ago. Like the deer, wild pigs gorge on beechnuts, too. Their bodies adapt so their birth rate triples, because they're getting enough nutrition for big litters of piglets. When the nuts arrive and the boars get fat, it's known as a 'mast' year.
The farmers would release their domestic pigs into forests during mast years.
The porkers gobbled the beech nuts, piled on plenty of meat, and had lots of chubby piglets. Then the farmers would round them up, and there'd be pork on the table throughout winter.
If you think that needs clever communication, think about how umbrella thorn acacias on the African savannah defend themselves against giraffes.
When they start picking at foliage, the acacias begin pumping foul-tasting toxins into the leaves to deter them. It happens in minutes, which for a tree is instantaneous. The giraffes get the message and move on.
But they don't go to the next acacia. They wander at least 100 yards before trying their luck again. The reason is astonishing. As they come under attack, the acacias give off a warning gas called ethylene that signals a crisis to neighbouring trees.
That triggers other acacias to dump toxins into their own leaves, as a defensive measure.
And the giraffes have learned that when one tree tastes bad, others in the vicinity will, too.
The exception is when the wind picks up and only trees downwind detect the ethylene in the air, and react. Giraffes know it too, and head upwind.
Elms and pines use a different tactic. When an insect eats a leaf, electrical signals travel from the damaged area to the roots — just as human tissue sends pain signals along the nervous system.
It takes at least an hour for the roots to react and unleash the defences, by flowing bitter compounds into the leaf to send the attacker packing. But something even more amazing is also happening: the tree identifies the attacker by its saliva. Armed with this, the tree releases phero-mones to summon specific predators, to prey on the insects. For example, elms and pines call on parasitic wasps that lay their eggs inside leaf-eating caterpillars, condemning them to slow, painful deaths. Trees are prepared to wait for revenge.
The main reason humans cannot perceive how clever and complex they are is because we exist in such short time scales by comparison. There's a tree in Sweden for instance, a spruce, that is more than 9,500 years old. That's 115 times longer than the average human lifespan.
A tree's childhood lasts ten times as long as ours. Activities that take us moments — waking up or stretching our limbs, can last months for a tree.
It's hardly surprising that most of us see trees as practically inanimate, nothing more than objects. But the truth is very different. They are just as intensely alive as we are . . . and for much, much longer.