Yale Environment
360: You write in your book:
"When I began my life as a
forester, I knew as much about the hidden life of trees as a
butcher knows about animals."
Peter Wohlleben: Forestry students are taught how to
harvest wood, what machines to use, how to sharpen the blade of
a chainsaw, how to sell the timber, what price to expect -
that's about it.
As a young forester I was told to make
clear-cuts, to use insecticides, and so on...
I thought,
"Wait, I
am someone who wants to protect nature, and here I am being
asked to destroy it!"
I visited some other districts that were operating in an
eco-friendly way, and I thought, that's the way woods should be
managed.
But the problem is I was still thinking of
trees as a
commodity, as something to sell, not as living beings. I had to
learn from the people of the community where my forest is
located how to take a closer look at trees, to see them as
unique individuals.
I also started reading the latest scientific
research that began to present me with a new picture of trees as
highly sensitive and social beings.
e360: Social beings...?
Wohlleben: We all learn in school that evolution advances by
pitting each individual against every other in the struggle for
survival.
As a forester, I learned that trees are competitors
that struggle against each other for light, for space. But we
are now learning that individuals of a species are actually
working together, they are cooperating with one another.
e360: How exactly do trees cooperate with one another?
Wohlleben: One thing is that mother trees suckle their children,
they feed the young tree just enough sugars produced by its own
photosynthesis to keep it from dying.
Trees in a forest of the
same species are connected by the roots, which grow together
like a network.
Their root tips have highly sensitive brain-like
structures that can distinguish whether the root that it
encounters in the soil is its own root, the root of another
species, or the roots of its own species.
If it encounters its
own kind, I don't know if scientists yet know how this happens,
but we have measured with radioactive-marked sugar molecules
that there is a flow from healthy trees to sick trees so that
they will have an equal measure of food and energy available.
"Parts of the forest that grew naturally
were 3 degrees C cooler
than those managed by humans."
e360: How do the healthy trees that feed their sick companions
benefit?
Wohlleben: If sick trees die, they fall, which open gaps in the
canopy.
The climate becomes hotter and drier and the environment
becomes worse for the trees that remain. In the forest I manage,
students from Aachen University did a study that shows that the
parts of the forest that grew naturally were 3 degrees C cooler
than those that are managed and disturbed by humans.
The world is trying to limit warming from climate change to 2
degrees, but undisturbed forests can do even better than that.
Forests create their own microclimate.
When we thin forests, the
temperature rises, the humidity goes down, evaporation
increases, and all the trees begin to suffer.
So trees have a
stake in supporting one another to keep all members of the
community healthy.
e360: You tell one amazing story in the book about trees keeping
neighboring stumps alive.
Wohlleben: This one beech tree was cut four to 500 years ago by
a charcoal maker, but the stump is still alive - we found green
chlorophyll under the thick bark.
The tree has no leaves to
create sugars, so the only explanation is that it has
been
supported by neighboring trees for more than four centuries.
I
made this discovery myself, and later learned that other
foresters have observed this happening as well.
e360: Are there other ways that trees help each other?
Wohlleben: We know that trees also exchange information.
When
one tree is attacked by insects, we can measure electrical
signals that pass through the bark and into the roots and from
there into
fungi networks in the soil that alert nearby trees of
the danger.
The trees pay for this service by supplying the
fungi with sugars from their photosynthesis.
And the fungi in
turn protect their host trees from attacks by other dangerous
species of fungi and contamination by heavy metals.
Trees also send chemical signals through the air when they are
attacked by insects. Nearby trees receive these messages and
have time to prepare their defenses.
Scientists like Suzanne Simard [who teaches forestry at the University of British
Columbia in Vancouver] have labeled this amazing web of
communication the
Wood Wide Web.
e360: You have also written that trees remember their
experiences?
Wohlleben: We had a heavy drought here.
In subsequent years, the
trees that had suffered through the drought consumed less water
in the spring so that they had more available for the summer
months.
Trees make decisions. They can decide things.
We can
also say that a tree can learn, and it can remember a drought
its whole life and act on that memory by being more cautious of
its water usage.
e360: You've said that there are "friendships" between trees.
What is the evidence for that?
Wohlleben: In about one in 50 cases, we see these special
friendships between trees.
Trees distinguish between one
individual and another. They do not treat all other trees the
same. Just today, I saw two old beeches standing next to each
other.
Each one was growing its branches turned away from the
other rather than toward each other, as is more usually the
case. In this way and others, tree friends take care of each
other. This kind of partnership is well known to foresters.
They
know that if you see such a couple, they are really like a human
couple; you have to chop down both if you chop one down, because
the other will die anyway.
"Plants process information
just as animals do,
but for the most
part
they do this much more slowly."
e360: You speak about trees as if they had personalities.
Wohlleben: Trees have just as much character as humans do.
They
also exercise independent judgments, which can differ. If trees
lose their leaves too early, they many not produce enough food
for a long winter.
If they keep them on too long, they may get
caught in an early snowstorm and the weight of the snow can
break their branches.
Some trees of the same species and age
living right next to each other shed their leaves weeks before
their neighbors.
I'm not sure why some choose to do this earlier
and others later, but it shows that there really are differences
of character that we can't easily account for.
e360: You have been criticized for attributing 'emotions' to
trees. Scientists usually avoid such language.
Wohlleben: We humans are emotional animals. We feel things, we
don't just know the world intellectually.
So I use words of
emotion to connect with people's experience. Science often takes
these words out, but then you have a language people can't
relate to, that they can't understand.
That's one reason most
scientific research has so little impact on people.
If you only
write technically about "biochemical processes," people would
quickly get bored and stop reading. We have been viewing nature
like a machine.
That is a pity because trees are badly
misunderstood.
e360: How so?
Wohlleben: We just see them as oxygen producers, as timber
producers, as creators of shade.
I always ask people,
"Who would
think of, say, elephants in such terms?"
We don't look at
elephants just as commodities or as mechanical and insentient
objects. We recognize them as marvelous beings.
On the other
hand, nobody thinks about the inner life of trees, the feelings
of these wonderful living beings.
e360: Plants are not generally thought to possess consciousness.
Wohlleben: We have this essentially arbitrary caste system for
living beings.
We say plants are the
lowest caste, the pariahs
because they don't have brains, they don't move, they don't have
big brown eyes. Flies and insects have eyes, so they are a bit
higher, but not so high as monkeys and apes and so on.
I want to
remove trees from this caste system.
This hierarchical ranking
of living beings is totally unscientific.
Plants process
information just as animals do, but for the most part they do
this much more slowly. Is life in the slow lane worth less than
life on the fast track?
Perhaps we create these artificial barriers between humans and
animals, between animals and plants, so that we can use them
indiscriminately and without care, without considering the
suffering that we are subjecting them to.
e360: How would understanding trees better change the way we
manage forests?
Wohlleben: Humans are weakening ecosystems by indiscriminately
cutting timber.
We destroy tree social structures, we destroy
their ability to react
to climate change. We end up with
individuals that are in a bad shape and susceptible to bark
beetles, which can only infest trees that are already sick.
A
tree that is healthy can get rid of them. So the beetle is
winning because we have degraded ecosystems to the point where
they are unable to respond effectively to threats.
Here in
Germany, we have planted spruces to replace the beech trees. It
is now too dry and warm for spruce, so those forests are failing
in large parts of our country. It's because we have planted the
wrong species for the climate.
We need to let nature heal itself
and come back to balance with broadleaf species that are natural
to our region, like oaks and beeches, which will help to cool
the forests down and can survive climate change without too much
harm.
"Faster growth
makes trees less healthy
and more susceptible to
illnesses."
e360: Do we need to manage forests at all?
Wohlleben: We are told that forests and woodlands need
management, but it is just plantations that need management
because they are unstable systems that can be destroyed by
storms, by insects, by fire.
It's like a farm with hundreds of
acres of corn. It is highly likely that insects or fungi will
kill these plants because there is just one species.
It's the
same thing with monoculture tree plantations.
Natural systems,
with a variety of species, are much more resilient.
e360: Managed forests and planted forests tend to space trees
farther apart to encourage growth and prevent competition
between the trees.
Is this a good idea?
Wohlleben: Well, that is one mistake introduced by foresters.
While it is true that trees may grow faster when we remove their
comrades, because more sunlight means more photosynthesis, they
actually grow too quickly for their own good.
Trees should grow
very slowly in the first 200 years, which we can call their
youth. If they grow too fast in the beginning, they will waste
all their energy in the rapid growth and will be out of breath,
exhausted, and die early.
It is similar to industrial meat
production where a pig, for example, is fed too much so that it
grows prematurely and in five or six months it can be sold and
slaughtered.
But the animals are unhealthy...
People on their home plots make the same mistake:
They cut down
some trees to encourage the growth of others...
That would be like
a family where they shoot the parents to give the kids more
space.
You slaughter their mother and the young trees will grow
very fast, but they will be unhealthy and have short lives.
e360: Trees are growing faster now because of more CO2 in the
air. Is that a good thing?
Wohlleben: Not at all.
In Germany now, for example, trees are
growing 30 percent faster than decades ago. But as I've said,
faster growth makes trees less healthy and more susceptible to
illnesses.
The wood is also of lower quality, so the price we
get for it is going down.
The cells of these fast growing trees
actually become bigger and more susceptible to fungi. A little
wound can open them to rot, which kills them.
e360: Can foresters help protect forests from climate change and
other environmental threats? I understand that in your forest,
you still do things the old fashioned way.
Wohlleben: That's right, we use horse-drawn carts to remove the
wood.
In between the trees, we don't use any heavy machinery,
which compresses the soil up to two meters deep and pushes the
air out and makes it less able to soak up the water in winter
that the trees need to use for growth in the spring.
e360: So the low-tech methods are actually more cost effective?
Wohlleben: Yes, they are working well all over the world; in
the Amazon, even in the U.S., some forest owners are working with
these methods.
We recommend growing only
tree species that are
natural to the area. I also advise not to make any clear cuts,
don't kill the mother trees that are protecting their children,
leave the families intact.
Don't use heavy machinery and cut out
pesticides and other toxic chemicals that kill off beneficial
insects and microorganisms in the soil.
These are the keys to
maintaining a successful and long-lived forest.
