The Hidden Life of Trees: Peter Wohlleben

Trees live for a very long time, oldest tree being 9500 yrs old.

Trees have electrical impulses in the root, used for communication, also have a sense of smell and taste among many others. when a giraffe eats an acacia tree’s leaves, the tree quickly releases bitter toxins to make them unappetizing. Even more amazing, the acacia emits chemical signals into the air that warn nearby trees, which then start producing their own defenses before the giraffes reach them. Similarly, when insects eat, they can taste the saliva, then the trees emit scents that attract the insects’ predators.

In forests, They can communicate with other beings in the wild - other trees, they help nourish the stumped trees, fungi etc. when in isolation or in farms they seem to have lost this ability of theirs. The ecosystem tightly depends on each type of animal living in it. Lets say wolves disappear, they preys would thrive and vegetation would decline effecting other species living in the ecosystem.

Introduction

While author was travelling he came across a beech stump, and looking at its stump, it was felled centuries ago. The underneath of the bark was still green meaning it still had chlorophyll and alive. It could have been the neighbour trees via interconnected roots or via the system of fungi, helping give nutrients to this stump.

1. Friendship

Trees can distinguish their own roots from other roots even when interconnected. Then why give food/nutrients to others, their competitors? It’s like humans where working together is more beneficial for them. Trees together can help moderate the climate, stores water reserves and regulates humidity; and not at the mercy of wind etc. this way they can live old together. If trees were not working together, they would die more randomly and there would be holes in the canopy; causing even more issues.

But not all stumps are taken care of — some are simply left to die, eventually decaying into humus. Trees seem to support only those that were once part of an interconnected relationship(author calls them as friends), with intertwined roots, usually among trees of the same species.

2. Language of trees

They use scent as a means of communication. To relate, humans use deodorant, perfumes and our own smell “tells” something to other people. The example about acacia tree and specific scents being released based on the insects saliva in the starting, illustrates this too. This though depends on wing to help disperse and warn the neighbours.
When the trees get hurt, leaves get eaten, they also do feel pain - the tissue around it changes. It’s just that the electrical impulse travels at a much slower speed, for the defense mechanism to reach the site.

They also send electrical signals through the fungal network around their root tips, helping them know about all kinds of dangers.

If the trees are sick(cannot sense the smell) and have lost the fungal network, they cant participate in the network and are cannot fend off the disaster.

The plants which we grow for vegetation have lost the ability to communicate both below and above ground, more like deaf and dumb; becoming easy prey for insects and pests. The author says farmers can consider growing some wildness alongside so that the plants become more “talkative”.

The colourful flowers, and the scent they release also invite bees and others to help pollinate.

There was an experiment done in regard to sound too. Researchers noticed the roots giving from cracking sound at 200 hz frequency. When young sapling were grown in lab alongside the sound waves, the roots were growing towards that direction, as if they heard it.

3. Social security

Trees struggle to grow when different species grow nearby, as they fight for resources. But it’s a different story if they are of the same species.
Each tree ca have varying conditions, different soil, different sunlight reaching etc. but the sugar per leaf is still the same (the same chlorophyll) because they sync their nutrients and water store vis roots.
So it’s actually in vain that people worry about closely packed trees in forests and culling them to evenly space them. You may worry about survival of the fittest for trees but thats not really the case here. The strong trees can also fall sick, and this when the other trees help it survive at that time. The chain is only as strong as its weakest link.

4. Love

Wind is the primary source of pollination, insects and others help but they aren’t the primary ones always.

Deciduous trees are those that shed their leaves each autumn and regrow them in spring. Examples: oak, maple, beech, birch.

Evergreen (Non-Deciduous) Trees keep their leaves year-round, like pines, firs, and spruces.

Trees want to avoid self- pollination as they weaken. To tackle this some trees keep a gap between the male and female flower blossom period, while some trees have entirely different male/female trees. Usually the male ones are brighter so insects visit them to collect pollen and then go for the female trees where pollination happens.

Some trees like bird cherry, have a biochemical recognition system — their flowers can detect their own pollen and reject it.

5. The tree Lottery

Blossoming, producing nuts and seeds takes a lot of energy so at this period they are usually defenseless and produce less sugar, more vulnerable to insects. Most trees endure but sick trees have a chance of dying out.

Most seeds never grow into trees due to shade, animals eating them, or poor soil. Some trees employ strategy where the seeds wont germinate right away but after some time like few years, as it spreads the risk.

6. Slowly does it

Very less sunlight comes to the new plants after passing through the canopy, making them grow very slowly.
This is actually beneficial, as their wood would be much stronger and they become more resistant to fungi, storms etc. The author calls this the upbringing from the mother trees. When the mother tree is sick or end of its life, then the tree would grow up to cover the canopy. The other trees who could not make it in time, would become the crown prince/princess and wait for their turn.

7. Forest Etiquette

when growing up the plans have their branches sideways to grab as much sunlight as they could. When they go up, their old branches are gone and replaced by wood, the new branches point to the sky, making it like a crown. These actually help lighten the load of snow and rain when they travel down to the roots.

Sometimes, heavy snowfall or uneven conditions (like sunlight) cause trunks to grow at an angle. In such trees, the pressure and strain are greater on the wood than on the roots. Some trees even split into forks, but if one side of a forked crown breaks, the wound often doesn’t heal properly, allowing rot to set in and gradually weakening the tree.

8. Tree school

If trees were to keep pumping water everyday to all of its branches without restraints, the soil would dry up, especially in summer. Nature teaches this the hard way, to not do that and force to adapt.

When this happens, the tension inside the tree’s water system becomes extreme.
This excessive pressure can cause tiny internal tears in the trunk and branches — like stress fractures inside the wood. These tears can’t easily heal because trees don’t have a way to close internal wounds completely.
Through these openings, fungi and other pathogens can enter, spreading rot inside the trunk and weakening the tree from within.

Some trees decide to just lean over and take support of already strong neighbours, but then again learn the hard way to grow themselves when the neighbours are cut down or eventually die.

Mimosa trees leaves fold inward on pressure. There was an experiment where water droplets were dripped on them in regular intervals. The leaves seem to realise that water was harmless and stopped closing.

The question rises - How do trees learn? They don’t have any brain.

When trees are thirsty, scientists noticed vibrations along their trunk - as if warning their neighbours for the water scarcity, just as humans talk using vibrations in larynx.

9. United we stand, divided we fall

Some Fungi co-exist and help the trees absorb more water and nutrients - like phosphorus and nitrogen, than just their root hairs.
They actually grow into the root hairs, as well as surroundings. Also help connect to other trees, and help pass information such as impending insect attack. They also help filter out heavy metals etc, from the soil.

Fungi though in return take upto a third of the produced sugar and carbs from the trees.

Fungi also can live for 100s of years but environmental factors can kill them. Still trees usually have multiple options, for fungi unless there are none left.

Fungi help other trees also, as a way for stability. Some pathogen might affect a variety of trees so diversity helps.

10. Mistress of moving water

Water goes up the tree with the help of capillary action and transpiration. As the water vapour is exhaled by the tree, the suction helps pull the water up. Another factor is osmosis, water flows from cells with low sugar to cells with higher sugar content, until same relative water content

11. Trees aging gracefully

Just like humans have skin to protect their inner organs, trees have bark that shields them from injury and disease. As they grow, they shed old layers of bark to allow new growth. When trees age — sometimes over hundreds of years — they slow their growth and can no longer pump water to their highest branches, which gradually die and fall away. Over time, fungi enter through old wounds and help decompose inner wood, sometimes leaving the trunk hollow. The tree still remains alive, since only the outer layers are vital. The inner layer just gives it support. Thats actually still fine for the tree, as it makes the tree lighter and more flexible in strong winds.

12. Mighty oak or mighty wimp

Oak trees have tannins which slow down fungal breakdown or help against insects, have a thick bark and have great fortitude to grow against multiple adversities when growing alone. But they are easily overgrown by other specific like beech tree and outcompetes them for light and space, eventually resulting in them dying. Every trees strength lies in its adaptability in environments and not their own raw strength.

13. Specialists

This is why only certain trees dominate specific habitats. Spruce grow in snowy areas.
Oaks can grow well in very hot/sunny places as they are more light demanding.
Beeches can grow in shades, then can overgrow once some light comes in the canopy.

14. Tree or not tree

According to dictionary, Tree needs to have a woody trunk from which branches grow. Main shoot should grow up or the plan is classified as a shrub. There are Dwarf trees in tundras, which grow below eye level.
Some trees even though are stumps now aren’t dead as we saw in chapter start and there are trees which grow over the old stump, what about those?

The key lies in the underground, the roots. As long as they are alive, the stump can become a tree again, or can raise multiple shoots off of it, like a bush. Or a shrub can become a tree if the roots could support it.

Earlier, We have established that trees can learn, generate electrical impulses, have warning systems to notify other trees. The author calls that the roots are probably the brain equivalent of the tree (though thats not really proven).

Perhaps humans would pay more attention to trees once they realise how similar they are to animals .

15. In the realm of darkness

The soil is home for countless beings.
Mites help decompose dead leaves, wood. Weevils go into dead roots to help decompose. Then various microorganisms like bacteria, fungi help break them down into humus.
The soil basically lives and it’s not just dirt. Even slight disturbances like removing fallen leaves, etc can disrupt the balance and some soil animals may die.

16. Carbon dioxide vacuums

Trees store large amounts of CO2 in their body. When fungi etc decompose, they all are emitted back to atmosphere. Thats why it doesn’t make much difference even when we burn them - on account of CO2 emission.

But the rate it is released back into the air, is very slow, if it takes the fungi path. Some of the carbon might become humus, which can help store it for centuries and eventually become coal.

The coal we see, is actually carbon deposit from millions of years ago which were permanently removed from the carbon cycle. We are actually reintroducing it back by burning them.

It is argued than rate at which new forests are being added is more than before, but we discussed before that ideally trees would grow slower, so this extra addition of fertilisers etc is actually unhealthy for it to grow a long life.

Forests and commercial lumber associations say that after 60-80yrs, the trees don’t process much CO2 as before so they need to be cleared to add fresh saplings. This is misleading as old trees have greater biomass additionally. Commercially though they might have less wood, because fungi could rot the inner wood as discussed earlier.

If we want them to use against climate change, they need to be left untouched.

17. Woody climate control

Trees can change the environment slowly. We can see some clear changes like temperature or water changes etc, gradually.
Trees help evaporate and also drink water from heavy downpours.

But this is true for right trees at right places.
Some trees haven’t adapted in other places like spruce, which are umbrella shaped. Which means water doesn’t even get to go to the roots from rains, and in cold places which is where they thrive, there is hardly any evaporation so the ground water stays intact, their major source for water. Humans mis-plant trees for their specific wood needs etc, but we need to put the right trees too.

18. The forest as water pump

Trees help make clouds via transpiration. Conifer trees keep transpiring water all year round, unlike deciduous trees(which drop their leaves). This constantly adds moisture, giving more clouds and more sunlight gets reflected, causing lower temperatures.
Even the ground water is put into circulation, helping filter it in the process too. This water is cooler and helps cool the temperature too in this process.
Surface water freezes during winters too, unlike the ground water which is still in circulation.

19. Yours or mine

Animals innately learnt to give back to the ecosystem in one way or other, for not giving back would mean over exploiting and then dying out.

Aphids gorge on the sap from the leaves, take the protein and excrete out the sugar. This makes them popular with other animals, for their sugar excreta - ants, lady bees, honey bees etc.
Wasps take the outer parts of leaves, barks etc and mix with their saliva to form nests for their larvae.
Caterpillars on the other hand eat up all leaves, and frequently doing so across seasons might kill the tree. The trees release scents which attract wasps who act as bodyguards and kill the caterpillars.

Young trees are used as scratching posts to shed animals’ skin, such as by deers for their antlers. They are left in a state where they would die out. Deers also eat up barks when they don’t have other food options. Thats why animal populations should also be controlled, which nature does via their predators. Human intervention can offset the balance.

When the tree bark is removed and the tree is exposed, it is vulnerable to fungi. But forest trees rings are so small and dense, it’s hard for fungi to fully penetrate and trees can try to close up before long term effects. This is another story for commercial trees which grow too quickly and have wide and sparse rings.

20. Community housing projects

Birds, bats etc especially like thick trunks as they provide insulation.
Woodpeckers usually drill starting part of the bark, and let fungi do the rest. They come back after a while(months) to clear out the damp mush of wood fibres. The fungi would still continue to wreak havoc, and the birds keep clearing them away. As the holes get bigger, it gets too large for the baby birds, so these birds keep drilling away new holes.
On these old holes, new animals like bats, beetles, ant colonies move in, which usually cant take out bark by themselves.

21. Motherships of bio-diversity

There are various types of species dependent on trees.
There are many species which depend on dead decomposing trees. So clearing dead trees, isn’t required in forests.
Even trees can get the nutrients from their dead parents via fungi etc, and for example young spruce grow especially well on dead trees. As the trees decomposition is a slow process they eventually grow into the soil from the dead trees while the dead tree becomes humus.

22. Hibernation

Even trees prepare for winters. Trees try to fill their tissues with food - the sugars.
They reduce their water content, which is why the leaves die and falloff as the water from them is pumped out, branches closing their connection. Water inside tree would be bad in winters, if they freeze, water would expand and the tree would burst out. They would usually keep deep inside, where it wont easily freeze. Sugars also lower the freezing point.
Conifers follow a different strategy, their needles have thick waxy coating, and have high sugar concentrations. The stomata in leaves are also inside dents/pits, making it harder to transpire.

The branches are also flexible and they can bend under weight so they don’t snap off on winter winds and snow.

Trees also deposit any waste that they don’t want into these dead leaves, before they drift off. The chlorophyll is usually broken down too.
Conifer trees can also shed their needles if required and deposit wastes there.

The young trees wake up earlier than the mother trees and start taking in sunlight to grow up and spread out. The warm temperatures on ground give it away for these young tree thats its time, while the mother trees crowns still are put against cold winds.

A big risk is late frost, the frost which occurs after trees wake up and warmed up. The water could freeze and kill them. Some trees like beech trees choose to wake up very late, to tackle this.

23. A sense of time

They understand the concept of time. Light receptors in leaves help know if it is dawn, midday or dark. They know to drop leaves in autumn, and infer via temperatures on season.

24. A question of character

Trees also have individuality. Two species of same tree right next to each other can grow at different speeds, and have different responses to seasonal change, drought etc.
Due to climate changes, the fall keeps getting delayed and some risk-taking trees hold on to their leaves a while longer. This can very well go south, if winds do come and blow over everything.

Trees usually don’t grow thick branches at the bottom. If they broke it would take longer for them to close and fungi could wreak havoc until then. Smaller branches and their holes can be easily closed in few years and the fungi isolated. These branches are then not replaced.
Some trees though go against this. When neighbouring tree does, they could grow thick branches to go sideways, and absorb that share of sunlight. While this is beneficial in the start, it isn’t eventually. The sounding trees eventually cover the canopy, then - no sunlight falls on these thick lower branches and they die out. Now they have to pay a price for it.