The Secret Life of Trees (2025) s01e02 Episode Script
Adulthood
MICHAEL PALIN: Three trillion trees
blanket our world.
From spectacular cherries
in spring
..to the golden maples
of North America
..and the strange-looking
baobab trees of Madagascar.
They can bring us joy
..and even keep us alive.
All these amazing trees around us
give us the air that we breathe.
But what do we really know
about their hidden world?
As you get closer to the tree,
it just gets
more and more remarkable.
In this series, we'll follow
their incredible life spans
There are trees alive on Earth today
that are as old
as the Great Pyramids.
..discover how trees communicate
This whole wood is interconnected,
and that opens up
so many possibilities.
..and learn how they survive in some
of the toughest places on Earth.
This time, we're following trees
as they reach adulthood
..when they do
the most extraordinary things
But what's really incredible
is that they're actually talking
to each other.
It's just amazing
to see these exposed roots.
..in the face of incredible odds.
THUNDER RUMBLES,
LIGHTNING CRACKS
Unfortunately,
it's been struck by lightning twice.
You had chimneys
belching out smoke, soot,
and this tree
managed to deal with that.
You'll never look at a tree
in the same way again.
Arriving at adulthood
is a major milestone
in a tree's life.
Some trees get there quickly.
Apple
..pear
..and cherry trees bear fruit
as young as five years old.
It's a visible sign
that they've reached maturity.
Others, like the slow-growing
hemlocks of North America,
can take up to 300 years
to become an adult.
And once they're mature,
some species, like this olive tree,
can be in their prime
for a thousand years or more.
These adult years
are the busiest of a tree's life.
ROBIN CHIRPS
Tree guru Tony Kirkham
spent 40 years
working at Kew Gardens.
He's visiting
one of his favourite trees
..an English oak.
This is a lovely oak tree.
It's probably around 75 years old.
It's gone through the teenage mode.
It's gone through adolescence,
and it's coming into adulthood now.
And rather than slowing down at 75,
this tree is just getting going.
Unlike us people, where we get to
a certain age and we stop growing,
we may put a little bit
more weight on as we get older,
a tree is dead opposite to that.
Trees continue to grow,
so it's putting on
about 50 centimetres a year
in height and spread,
and with that, more leaf.
So, this is all this year's growth.
So, it's fresh. Fresh shoots.
This is growing pretty fast,
this tree.
Tony is visiting
at the beginning of the day,
an especially important time
for a tree.
To prepare for the day ahead,
this oak is doing something
surprisingly familiar.
It's stretching.
It's early in the morning,
and so it's waking up,
it's stretching, it's flexing,
and it's getting ready
for a hard day's work.
Those branches lift
by about ten centimetres
in preparation
for catching that sunlight.
Experts have only recently
discovered
that trees sleep at night,
relaxing their branches down.
Then, just before dawn,
they raise them up
..and angle their leaves
towards the sun
..ready to create the food they need
to grow taller
and stronger through adulthood.
As this oak wakes up,
so do more than 2,000 other species
of living things that call it home.
The oak plays host to
the most different living organisms
of any other tree in Britain.
From mosses, lichens,
insects, mammals, birds.
A whole range of living things.
It's a high-rise zoo
for all these species.
It's in pretty good condition,
and hopefully, this tree will be
around for several hundred years.
Every tree on Earth has lodgers.
Countless creatures who live
amongst their leaves and branches.
Many just want
a safe place to stay the night.
But some need the tree
for their survival.
Beetles burrow
beneath a tree's bark.
Woodpeckers may look beautiful,
but they inflict serious damage
in their search for food.
Unable to run away
from these pesky pests,
trees have developed some
ingenious ways to defend themselves.
And one of the most remarkable
is communication.
Incredibly,
trees can talk to other trees
and warn them
when they're under attack.
Professor James Logan
is at Broadwoodside near Edinburgh.
He's an expert
in how living things communicate.
Anytime that I'm around trees,
I'm in absolute awe.
They're the geniuses of nature
in many ways,
and they do it in such a secret way.
I'm in this fantastic avenue
of hornbeam trees.
These trees are about 24 years old,
and there couldn't be
a better place to come
to explore how trees
communicate with each other.
When we think about communication
as humans,
we think about everything
that we're seeing
or that we're hearing around us.
Now, trees don't have eyes,
and they don't have ears,
but what they do have is the ability
to produce smells,
chemicals in the air.
And as I'm standing here
under this tree,
this tree is producing
loads of chemicals.
It's like an aerial soup
of chemicals around me
that this tree is using
to communicate with.
The smelly messages from the tree
start when a caterpillar
or larger animal
chomps on one of its leaves.
Remarkably, the tree knows
it's an animal disturbing its leaf
rather than just the wind,
because it's able to detect
the attacker's salvia as it chews.
When they start to get munched,
what's happening inside the tree
is it initiates a defence system.
So, the tree
starts to produce chemicals
that actually taste really bitter
to put off the insects.
What's really incredible is that
when this leaf is being attacked,
it's sending a signal
to the rest of the tree.
So all the leaves on the tree
start to produce
the same types of chemicals
that make it taste really bitter
to protect the entire tree.
But it doesn't stop there.
The alarm call is carried
even further on the breeze.
When this tree
is being attacked by insects,
not only is it sending out signals
to protect itself,
but it's actually sending out
signals to the tree next door.
Now, these two trees might be
metres and metres apart,
but actually, that tree
is communicating with this tree.
They're actually talking
to each other.
This tree is sending out
a chemical signal
telling this tree
that it's being attacked.
So, this tree
actually receives that signal
and starts to produce
the same chemicals
as if it was being attacked
to protect it as well.
Every tree in this avenue
will be picking up
on the same signals.
It's almost like a highway
of information.
And sometimes,
we can smell the signals ourselves.
If you walk into a pine forest,
you know,
you're hit
with this amazing smell of pine.
The familiar scent is in fact
our noses
detecting the chemical alarm calls
released by the trees.
And without even realising it,
we could be benefiting from them.
We've all heard about getting out
into nature to do us some good.
And if you walk into a forest,
you know, there's something
quite pure about the smell.
It feels like it's cleansing you.
But there is actually
some scientific evidence to this,
because some of those chemicals
have been shown
to have a really good effect
on our health.
Lowering our stress.
Being good for our mental health.
And I'll tell you what,
this is good for the soul.
Trees in the prime of adulthood
may look static,
but they're buzzing with activity.
BEE BUZZES
And they're flourishing
in landscapes across the globe,
even in our cities.
But how do some of the eight million
trees in London
beat the odds to thrive
for 300 years or more?
Trees can flourish
in some truly remarkable places
..including our very busiest cities.
In America,
around five and half billion trees
line its streets and parks,
providing shade and colour
amidst the urban grey.
One of the world's
leafiest cities is London.
The UK's capital has nearly
eight and a half million trees.
Almost as many as there are people.
In spring, its streets erupt
in pastel pinks
..and reds and golds
brighten up an autumn day.
But what does it take for a tree
to thrive in the urban jungle?
Historian and Londoner Josh Levine
is tree hunting on Cheapside,
one of the capital's oldest streets.
Here, emerging out of
the City of London, is a tree.
And it's much older
than all of these buildings
that are stretched down here.
This is a London plane tree,
known as the Cheapside plane.
Josh thinks it's the oldest tree
in the City of London.
And he has the pictures to prove it.
This is going back
to the 19th century,
and it gives you a real sense
of how this must have been
going way back.
With the tree looming over,
as the tree still does,
you can see the horse and carriage,
you get a sense of just
how different everything was.
The images date back
over two centuries,
so Josh believes the plane tree
was planted around 300 years ago.
It is from some time
in the 18th century.
We don't know when exactly.
But we know that by 1841,
people were talking about it
as though it was a venerable tree,
a magnificent landmark.
What's amazing about this tree
is that it's endured everything
London has thrown at it,
especially the city's grime.
If you think about Victorian times,
you had the most
polluted atmosphere, you know.
You had chimneys
belching out smoke, soot,
and this tree
managed to deal with that.
Three centuries ago,
Londoners discovered
that plane trees
can thrive in places
where pollution chokes other trees.
Josh can reveal
how they flourished for so long.
And here we are,
really close up to it.
I mean, you can look at it
in all its gnarled glory.
And what was so great about them,
the reason they survived,
was because of this.
Their bark.
The bark comes off.
So, in an area like London,
which was, think about it, you know,
in Victorian times,
absolutely filthy.
What could survive it? I mean,
people could barely survive here.
A tree that could survive
was this one
because the impurities would go
into the bark, into the covering,
and then it would fall off,
and it could rejuvenate.
It could live again.
All year round,
plane tree bark flakes away,
taking the pollution with it
and revealing fresh growth beneath.
This process
allowed the Cheapside plane
to survive
the 65-year-long Victorian era
when pollution was at its peak.
But another challenge came
four decades later.
To explain, Josh needs to climb
to the height of the tree's canopy.
I've got a view
that you just don't normally see.
It's a great way to see the tree.
I mean, there's the tree down there.
And then
there's this astonishing sight.
This is St Paul's Cathedral.
During the Second World War,
this area was devastated
by German bombers.
Aerial photographs taken in 1945
reveal the aftermath of the Blitz.
And you can see
the total devastation.
You can see things
have been flattened. Everywhere.
So, what's left?
St Paul's. It survived.
And the other thing here
to have survived is just below us.
It's the tree.
St Paul's is a famous symbol
of London's wartime resistance.
But the Cheapside plane
is an equally lucky
and special survivor.
Today, it's one of more than
100,000 London planes
that line the capital's streets.
From Westminster
..to Wembley.
It's believed that every year,
London's trees combine
to remove nearly 2.5 million tonnes
of pollution from the air.
Let's face it, living in London
has always been difficult.
But a tree that's able to adapt
to the circumstances,
a tree that's able
to rejuvenate itself,
that's the one
that's gonna do well in London.
There are 70,000 different species
of tree on the planet.
And many of them
have found remarkable ways
to adapt to their landscapes.
On the edge of the Arctic circle,
the temperature can drop
to minus 45 degrees.
But this icy world is still home
to willows and birches.
And they've found
a special way to survive.
These are dwarf willows
and dwarf birches.
There are entire forests where
no tree is more than a metre tall.
Being close to the ground
protects them
from the worst of the freezing winds
and helps them to survive.
At the opposite extreme, in the dry,
dusty plains of North America,
the roots of jacaranda
and juniper trees
spread up to 30 metres away
from their trunks
in the hunt for water.
So, remarkably,
these trees can grow flowers
even in the middle of a desert.
Even the more hospitable
landscape of Italy
is home to a tree
that has adapted to survive.
The elegant Italian cypress.
Nestled in the rolling landscape
of Tuscany
is a vineyard that produces
the world famous Chianti wine.
It's owned
by Count Sebastiano Capponi
..the 20th generation of his family
to look after this land.
The cypress trees have become kind
of an icon of the Tuscan landscape.
People, when they come to Tuscany
and they see
the cypress-lined drives,
they fall in love with it.
The drive was planted by
my great grandfather, Piero Capponi,
around the end of the 19th century,
beginning of the 20th century.
Every time I come home
and I see these beautiful trees,
it's definitely a wonderful
and warm welcoming for me.
Cypress trees have been planted
in Italy
since before the Romans,
2,000 years ago,
to mark boundaries
and to protect buildings
from the wind.
Adult cypresses are long-living.
They can survive
up to a thousand years
..and they have a remarkable ability
to protect themselves
from a particular enemy.
Wildfire.
We had a couple
of fires two years ago
due to the drought, and
we have to be careful, you know.
Have to be careful
because a single spark,
in a matter of minutes and hours,
it will burn down
acres and acres of woodland.
But the clever Italian cypress
uses fire to its own advantage.
Like pine or fir trees,
they grow cones to hold their seeds.
But the cypress has two
different types of seed cone.
The first opens to release its seeds
as soon as they're ready.
You see all the cypress cones,
the mature ones are the brown ones.
Yeah, this is the open ones.
This is the typical ones you find
on the floor in woods, you know.
Once they open, the birds will come,
and they will spread
the seed around,
and then new saplings will grow.
But there's second special cone
that has developed
to deal with wildfires.
The fire ones are the closed ones.
They can stay shut like that
for many, many years.
You can see this
is a mature one over here.
And they will open up only
at very, very high temperatures.
As our summers get hotter,
this landscape
is increasingly vulnerable
to the threat of wildfire.
Whilst the trees themselves
will die in a fire,
the intense heat opens up
the special cones.
So the seeds usually sealed inside
are released,
and new cypress trees
can grow tall in the landscape.
I think the major ability
of Italians is to create beauty,
and this is a part of that beauty.
These trees are part
of that beauty, and
and Tuscany would be a very
different thing without them.
Trees in the prime of adulthood
really do
the most extraordinary things.
But what we can see above ground
is just the beginning.
We'll discover
that it's below the surface
where the tree is hiding
its greatest secrets.
The rolling countryside
of southern England
is home to majestic oak,
ash, and beech trees,
many hundreds of years old.
Like most trees,
we can only see them above ground.
But this seemingly normal hedgerow
holds something intriguing
beneath it.
Tree expert Tony Kirkham is entering
a mysterious underworld
to understand what's happening
below the surface of a tree.
This is Hell Lane in Dorset.
It's a holloway.
And, basically, it's a sunken lane.
The trees line either side.
They're growing over,
and they join in the middle,
creating this secret tunnel.
It's very atmospheric.
It's mystical. It's magical.
This ancient pathway
was created over centuries
as thousands of people walked
across the land,
pushing the soft, sandy soil
in between the trees
lower into the landscape.
The great thing about this place
is that you can see tree roots.
I think they fascinate me so much
because they're underground.
They're out of sight.
We don't see them.
It's a hidden life of a tree.
A tree's roots defend it
from one of its great enemies
..the wind.
All trees can flex and bend in
a breeze, but as they grow taller,
they become more vulnerable
to the impact of the wind.
So, here we have a tree
that's about 15 to 20 metres tall.
And these are ash trees.
And everybody would believe that
below ground would be a mirror image
of what we see above ground,
in order to support that height
and stop it blowing over
on a windy day like today.
But, actually, that's a myth.
And tree roots are very shallow.
Surprisingly, most tree roots grow
sideways, just below the surface.
It's about the tree roots
gripping the soil.
So, you can this amazing root,
this amazing lateral anchor root.
That's an anchor root.
And the primary objective of a root
is to support that tree,
to stop it blowing over
and for it to
to be able to grow tall
and reach up into the sky.
Even as adults,
trees keep growing taller.
And they continue to grow new roots
exactly where they need them.
As the trees move in the wind,
like on a windy day like today,
as they move, the tree sends signals
down to the root system,
saying, "I need more roots
on this side.
"I need more roots on this side."
The different parts of the tree
talk to each other and
and create these roots.
But roots aren't just anchors.
A growing tree has
up to 13 miles of them
to take up water and nutrients
from the soil.
The thirstiest trees can suck up
3,500 litres of water a day
..enough to fill nearly 20 bathtubs.
So, this is a lateral root
coming off the main anchor root.
We have these laterals coming down.
They will produce
these more fibrous roots
that have the ability
to absorb moisture.
Most trees, their root systems
are a maximum of a metre deep.
In fact, about 90% of tree roots
are in that top ten centimetres
where there's lots of water,
oxygen, nutrients.
And as the tree grows, that lateral
root system will grow with the tree.
Some adult trees can have as many
as five million fibrous root tips
to nurture them.
And whilst the parts of the tree
we see above the surface
weigh five times more
than their roots,
it's these hidden underground heroes
that are performing
the most incredible feats.
It blows my mind all the time.
Even though I've been working
with trees for 50 years,
it still fascinates me
how they stand up.
Trees in their prime can thrive
in many varied landscapes.
Some stand tall
as magnificent loners.
Others grow
in long, majestic avenues.
And perhaps the most atmospheric
of all, in vast woodlands.
The Woodland Trust's
Kylie Jones Mattock
looks after a collection of trees
near the North Wales coast.
It's a rare piece of forest that
really comes to life in the autumn.
It's an amazing place.
It's a place full of life.
It's an ancient place too.
I really love this time of year.
In October, the leaves
are just starting to turn.
These individual trees
on their own,
each tree isn't that old.
But there've been
trees growing together here
for hundreds,
if not thousands, of years.
And when a woodland
has been that well-established,
really special things
start to happen.
When trees grow together
in a woodland,
they can do
something extraordinary -
use their roots to share
water and food with one another.
But this act of generosity
only happens
with the help of a go-between.
And it's in the autumn
that it starts to reveal itself.
Just as the trees are starting
to close down for the autumn,
the fungi show their true colours.
They bring us this splash of colour,
and they come in purples and reds,
colours that you don't see
in nature as often.
You get this glimpse
into the hidden world of the forest.
Whether they're toadstools
..mushrooms
..or puffballs
..fungi can seem otherworldly.
But what we see is just
the tip of the iceberg.
Beneath the surface,
there's a much larger part
of the fungi
that spreads far and wide
across the forest floor.
Just by lifting a rock,
you can really lift the lid
on the hidden world of the forest.
Intertwined with all these roots
are a network
of microscopic fungal threads.
They intertwine with the roots, wrap
round them, even penetrate them.
This whole woodland here
is absolutely riddled with fungi,
twisting and interconnecting
beneath our feet.
And these tiny threads
enable the trees
to get to places
they couldn't otherwise reach.
The fungal threads attach themselves
to a tree's roots
and help it gather the nutrients
it needs from the soil.
But experts like Kylie are only
just beginning to fully understand
how much trees rely on
this incredible fungal network
..because the threads also connect
the trees to each other.
They link one tree's roots
to the roots of its neighbours
..binding hundreds
of trees together.
What makes those links between
all the trees in this forest,
over a vast area,
is this fungal network,
which means
this whole wood is interconnected.
A bit like
a complex web of cables,
connecting
the whole of this woodland.
This whole wood is
part of a wood-wide web.
Some experts believe
the trees could make use
of this incredible hidden connection
to support one another
in times of need.
To help us visualise
this wood-wide web,
I'm going to have a little go
at recreating it
with some low-budget tech.
So, these lights represent
all the things that pass within
the network between the trees.
Because the fungal strands link
the roots of different trees,
the fungus could move nutrients
from one tree that's doing well
to a neighbouring tree that
can't find enough food on its own.
For example, a small oak seedling
like one of these,
growing under the shade,
it's going to struggle to survive.
But the parent tree can actually
channel nutrients, sugars,
to that young sapling so it can
survive and thrive in the forest,
just waiting for its chance
to grow up into the canopy.
One cubic inch of soil can hold
as much as eight miles
of fungal threads.
And the connections
could spread for miles.
So if a tree on the far side of the
woodland is struggling for water,
trees with plenty on the other side
could share what they have.
The other trees in the forest
could be using their fungal network
to support that tree
to ensure it survives.
It's a fantastic system,
and we're really
just on the verge of understanding
all the things
that this wood-wide web achieves.
This woodland is a community.
An entire forest of trees that could
potentially be sharing resources,
allowing each other to thrive, all
by hidden connections we never see.
We just have no idea
what the potential is.
But we do know
that these connections
are going to be incredibly important
to the health, the resilience,
the survival of our woodlands
as they face challenges
in the future.
Trees have astonishing ways
to flourish,
even in our changing world.
And when they're harmed
by forces they can't control
THUNDER RUMBLES,
LIGHTNING CRACKS
..they can even heal themselves
in the most surprising
and ingenious ways.
Have you ever been among birch trees
and looked closely at their trunks?
They're dotted
with what look like eyes
..that follow you
through the forest.
These are scars,
reminders of whole limbs
that have been lost in the past.
And they are the perfect example of
how adult trees can heal themselves.
It happens as trees get taller.
When new branches grow higher up,
their leaves block sunlight
from reaching those
on the older branches below.
So the tree deliberately amputates
the old branches
by cutting off their food supply,
and they fall away,
leaving behind the eyes.
But what happens when trees are
harmed by forces they can't control?
THUNDER RUMBLES,
LIGHTNING CRACKS
Whether it's a violent storm
ELEPHANT ROARS
..a run-in with a grumpy elephant
..or even a bear
with an un-scratch-able itch.
Injuries are
an inevitable part of a tree's life.
BEAR GRUNTS
If there's one place to be
a wounded tree,
it's at the Royal Botanic Gardens
at Kew.
This world-famous sanctuary
in London
looks after
2,000 different species of tree
..from all over the planet.
Cecily Withall is
a member of Kew's Tree Gang
..the equivalent
of an on-call doctor service.
This morning,
she's doing her daily rounds.
Things like lightning,
wind or even human intervention
can harm a tree.
It's really important
for us as a unit in the Tree Gang
to really make sure that these trees
are, one, safe for the public
to be looking at them
and being around them,
but also maintaining them
so that they have huge longevity
in front of them.
Make sure that
they can outlive our time here,
which is the most important thing.
First stop on Cecily's round
is a rather extraordinary patient.
This tree was planted
in 1814 and is a Corsican pine
..classed here at Kew
as one of our unluckiest trees.
At 30 metres high, this pine
towers over the trees around it.
But its height means it acts like a
lightning rod for any passing storm.
Unfortunately,
it's been struck by lightning twice.
Trees don't really have
a defence mechanism
to stop them being struck
by lightning.
If a tree is struck,
it can die instantly.
50% of strikes will kill a tree.
When lightning hits a tree,
the water internally
in the trunk and the stems
will completely turn to gas
instantly.
THUNDER RUMBLES,
LIGHTNING CRACKS
The extreme power
of a lightning strike,
up to 300 million volts,
can split an entire tree in two.
Luckily, the Corsican pine survived.
The lightning only travelled
down the outer edge of the tree.
What we can see from the damage
on this tree is just bark.
You can see on the front of the bark
where it's exploded
off of the main trunk.
Like human skin, a tree's bark
is its first line of defence.
A tough outer layer that shields
the vulnerable wood beneath.
And when a wound does go deep,
the tree seals around it,
stopping any infection
before it can cause more damage.
They might not be able to completely
get rid of the wound itself,
but fortunately for us,
the tree stops
that wound becoming any larger.
The tree really is its own doctor
and can heal
and seal those wounds away
so they don't spread
throughout the rest of the stem.
But this unlucky tree hasn't
just survived two lightning strikes.
Nearly 100 years ago,
it was hit by a small aeroplane.
The aircraft itself was seen
to remove the top of the tree.
Hit the canopy, and a limb came down
and ripped the bark off.
Luckily, the pilot survived
..and the tree
sealed off the injury.
At 211 years old, this Corsican pine
is a true survivor.
Like so many trees
across our planet,
it's doing extraordinary things
to thrive in its prime.
So, the tree is named
the unluckiest tree at Kew,
but I really don't think so.
I think that if it's managed
to survive two lightning strikes
and a plane hitting the canopy
It's still here, growing strong.
I think it's pretty special.
In the final episode,
we'll discover what happens
when trees reach old age.
Like this yew, which is almost
as old as the Tower of London.
This could easily be 900 years old.
They look ancient,
and they are ancient.
A time when surprising things
start to happen
I can see two here
that are actually burrowing -
oh, my goodness - into the holes.
..as ancient trees give away
their deepest secrets.
That last third of a tree's life is
when they get really interesting.
For more information about
the secret life of British trees,
go to the Woodland Trust at
blanket our world.
From spectacular cherries
in spring
..to the golden maples
of North America
..and the strange-looking
baobab trees of Madagascar.
They can bring us joy
..and even keep us alive.
All these amazing trees around us
give us the air that we breathe.
But what do we really know
about their hidden world?
As you get closer to the tree,
it just gets
more and more remarkable.
In this series, we'll follow
their incredible life spans
There are trees alive on Earth today
that are as old
as the Great Pyramids.
..discover how trees communicate
This whole wood is interconnected,
and that opens up
so many possibilities.
..and learn how they survive in some
of the toughest places on Earth.
This time, we're following trees
as they reach adulthood
..when they do
the most extraordinary things
But what's really incredible
is that they're actually talking
to each other.
It's just amazing
to see these exposed roots.
..in the face of incredible odds.
THUNDER RUMBLES,
LIGHTNING CRACKS
Unfortunately,
it's been struck by lightning twice.
You had chimneys
belching out smoke, soot,
and this tree
managed to deal with that.
You'll never look at a tree
in the same way again.
Arriving at adulthood
is a major milestone
in a tree's life.
Some trees get there quickly.
Apple
..pear
..and cherry trees bear fruit
as young as five years old.
It's a visible sign
that they've reached maturity.
Others, like the slow-growing
hemlocks of North America,
can take up to 300 years
to become an adult.
And once they're mature,
some species, like this olive tree,
can be in their prime
for a thousand years or more.
These adult years
are the busiest of a tree's life.
ROBIN CHIRPS
Tree guru Tony Kirkham
spent 40 years
working at Kew Gardens.
He's visiting
one of his favourite trees
..an English oak.
This is a lovely oak tree.
It's probably around 75 years old.
It's gone through the teenage mode.
It's gone through adolescence,
and it's coming into adulthood now.
And rather than slowing down at 75,
this tree is just getting going.
Unlike us people, where we get to
a certain age and we stop growing,
we may put a little bit
more weight on as we get older,
a tree is dead opposite to that.
Trees continue to grow,
so it's putting on
about 50 centimetres a year
in height and spread,
and with that, more leaf.
So, this is all this year's growth.
So, it's fresh. Fresh shoots.
This is growing pretty fast,
this tree.
Tony is visiting
at the beginning of the day,
an especially important time
for a tree.
To prepare for the day ahead,
this oak is doing something
surprisingly familiar.
It's stretching.
It's early in the morning,
and so it's waking up,
it's stretching, it's flexing,
and it's getting ready
for a hard day's work.
Those branches lift
by about ten centimetres
in preparation
for catching that sunlight.
Experts have only recently
discovered
that trees sleep at night,
relaxing their branches down.
Then, just before dawn,
they raise them up
..and angle their leaves
towards the sun
..ready to create the food they need
to grow taller
and stronger through adulthood.
As this oak wakes up,
so do more than 2,000 other species
of living things that call it home.
The oak plays host to
the most different living organisms
of any other tree in Britain.
From mosses, lichens,
insects, mammals, birds.
A whole range of living things.
It's a high-rise zoo
for all these species.
It's in pretty good condition,
and hopefully, this tree will be
around for several hundred years.
Every tree on Earth has lodgers.
Countless creatures who live
amongst their leaves and branches.
Many just want
a safe place to stay the night.
But some need the tree
for their survival.
Beetles burrow
beneath a tree's bark.
Woodpeckers may look beautiful,
but they inflict serious damage
in their search for food.
Unable to run away
from these pesky pests,
trees have developed some
ingenious ways to defend themselves.
And one of the most remarkable
is communication.
Incredibly,
trees can talk to other trees
and warn them
when they're under attack.
Professor James Logan
is at Broadwoodside near Edinburgh.
He's an expert
in how living things communicate.
Anytime that I'm around trees,
I'm in absolute awe.
They're the geniuses of nature
in many ways,
and they do it in such a secret way.
I'm in this fantastic avenue
of hornbeam trees.
These trees are about 24 years old,
and there couldn't be
a better place to come
to explore how trees
communicate with each other.
When we think about communication
as humans,
we think about everything
that we're seeing
or that we're hearing around us.
Now, trees don't have eyes,
and they don't have ears,
but what they do have is the ability
to produce smells,
chemicals in the air.
And as I'm standing here
under this tree,
this tree is producing
loads of chemicals.
It's like an aerial soup
of chemicals around me
that this tree is using
to communicate with.
The smelly messages from the tree
start when a caterpillar
or larger animal
chomps on one of its leaves.
Remarkably, the tree knows
it's an animal disturbing its leaf
rather than just the wind,
because it's able to detect
the attacker's salvia as it chews.
When they start to get munched,
what's happening inside the tree
is it initiates a defence system.
So, the tree
starts to produce chemicals
that actually taste really bitter
to put off the insects.
What's really incredible is that
when this leaf is being attacked,
it's sending a signal
to the rest of the tree.
So all the leaves on the tree
start to produce
the same types of chemicals
that make it taste really bitter
to protect the entire tree.
But it doesn't stop there.
The alarm call is carried
even further on the breeze.
When this tree
is being attacked by insects,
not only is it sending out signals
to protect itself,
but it's actually sending out
signals to the tree next door.
Now, these two trees might be
metres and metres apart,
but actually, that tree
is communicating with this tree.
They're actually talking
to each other.
This tree is sending out
a chemical signal
telling this tree
that it's being attacked.
So, this tree
actually receives that signal
and starts to produce
the same chemicals
as if it was being attacked
to protect it as well.
Every tree in this avenue
will be picking up
on the same signals.
It's almost like a highway
of information.
And sometimes,
we can smell the signals ourselves.
If you walk into a pine forest,
you know,
you're hit
with this amazing smell of pine.
The familiar scent is in fact
our noses
detecting the chemical alarm calls
released by the trees.
And without even realising it,
we could be benefiting from them.
We've all heard about getting out
into nature to do us some good.
And if you walk into a forest,
you know, there's something
quite pure about the smell.
It feels like it's cleansing you.
But there is actually
some scientific evidence to this,
because some of those chemicals
have been shown
to have a really good effect
on our health.
Lowering our stress.
Being good for our mental health.
And I'll tell you what,
this is good for the soul.
Trees in the prime of adulthood
may look static,
but they're buzzing with activity.
BEE BUZZES
And they're flourishing
in landscapes across the globe,
even in our cities.
But how do some of the eight million
trees in London
beat the odds to thrive
for 300 years or more?
Trees can flourish
in some truly remarkable places
..including our very busiest cities.
In America,
around five and half billion trees
line its streets and parks,
providing shade and colour
amidst the urban grey.
One of the world's
leafiest cities is London.
The UK's capital has nearly
eight and a half million trees.
Almost as many as there are people.
In spring, its streets erupt
in pastel pinks
..and reds and golds
brighten up an autumn day.
But what does it take for a tree
to thrive in the urban jungle?
Historian and Londoner Josh Levine
is tree hunting on Cheapside,
one of the capital's oldest streets.
Here, emerging out of
the City of London, is a tree.
And it's much older
than all of these buildings
that are stretched down here.
This is a London plane tree,
known as the Cheapside plane.
Josh thinks it's the oldest tree
in the City of London.
And he has the pictures to prove it.
This is going back
to the 19th century,
and it gives you a real sense
of how this must have been
going way back.
With the tree looming over,
as the tree still does,
you can see the horse and carriage,
you get a sense of just
how different everything was.
The images date back
over two centuries,
so Josh believes the plane tree
was planted around 300 years ago.
It is from some time
in the 18th century.
We don't know when exactly.
But we know that by 1841,
people were talking about it
as though it was a venerable tree,
a magnificent landmark.
What's amazing about this tree
is that it's endured everything
London has thrown at it,
especially the city's grime.
If you think about Victorian times,
you had the most
polluted atmosphere, you know.
You had chimneys
belching out smoke, soot,
and this tree
managed to deal with that.
Three centuries ago,
Londoners discovered
that plane trees
can thrive in places
where pollution chokes other trees.
Josh can reveal
how they flourished for so long.
And here we are,
really close up to it.
I mean, you can look at it
in all its gnarled glory.
And what was so great about them,
the reason they survived,
was because of this.
Their bark.
The bark comes off.
So, in an area like London,
which was, think about it, you know,
in Victorian times,
absolutely filthy.
What could survive it? I mean,
people could barely survive here.
A tree that could survive
was this one
because the impurities would go
into the bark, into the covering,
and then it would fall off,
and it could rejuvenate.
It could live again.
All year round,
plane tree bark flakes away,
taking the pollution with it
and revealing fresh growth beneath.
This process
allowed the Cheapside plane
to survive
the 65-year-long Victorian era
when pollution was at its peak.
But another challenge came
four decades later.
To explain, Josh needs to climb
to the height of the tree's canopy.
I've got a view
that you just don't normally see.
It's a great way to see the tree.
I mean, there's the tree down there.
And then
there's this astonishing sight.
This is St Paul's Cathedral.
During the Second World War,
this area was devastated
by German bombers.
Aerial photographs taken in 1945
reveal the aftermath of the Blitz.
And you can see
the total devastation.
You can see things
have been flattened. Everywhere.
So, what's left?
St Paul's. It survived.
And the other thing here
to have survived is just below us.
It's the tree.
St Paul's is a famous symbol
of London's wartime resistance.
But the Cheapside plane
is an equally lucky
and special survivor.
Today, it's one of more than
100,000 London planes
that line the capital's streets.
From Westminster
..to Wembley.
It's believed that every year,
London's trees combine
to remove nearly 2.5 million tonnes
of pollution from the air.
Let's face it, living in London
has always been difficult.
But a tree that's able to adapt
to the circumstances,
a tree that's able
to rejuvenate itself,
that's the one
that's gonna do well in London.
There are 70,000 different species
of tree on the planet.
And many of them
have found remarkable ways
to adapt to their landscapes.
On the edge of the Arctic circle,
the temperature can drop
to minus 45 degrees.
But this icy world is still home
to willows and birches.
And they've found
a special way to survive.
These are dwarf willows
and dwarf birches.
There are entire forests where
no tree is more than a metre tall.
Being close to the ground
protects them
from the worst of the freezing winds
and helps them to survive.
At the opposite extreme, in the dry,
dusty plains of North America,
the roots of jacaranda
and juniper trees
spread up to 30 metres away
from their trunks
in the hunt for water.
So, remarkably,
these trees can grow flowers
even in the middle of a desert.
Even the more hospitable
landscape of Italy
is home to a tree
that has adapted to survive.
The elegant Italian cypress.
Nestled in the rolling landscape
of Tuscany
is a vineyard that produces
the world famous Chianti wine.
It's owned
by Count Sebastiano Capponi
..the 20th generation of his family
to look after this land.
The cypress trees have become kind
of an icon of the Tuscan landscape.
People, when they come to Tuscany
and they see
the cypress-lined drives,
they fall in love with it.
The drive was planted by
my great grandfather, Piero Capponi,
around the end of the 19th century,
beginning of the 20th century.
Every time I come home
and I see these beautiful trees,
it's definitely a wonderful
and warm welcoming for me.
Cypress trees have been planted
in Italy
since before the Romans,
2,000 years ago,
to mark boundaries
and to protect buildings
from the wind.
Adult cypresses are long-living.
They can survive
up to a thousand years
..and they have a remarkable ability
to protect themselves
from a particular enemy.
Wildfire.
We had a couple
of fires two years ago
due to the drought, and
we have to be careful, you know.
Have to be careful
because a single spark,
in a matter of minutes and hours,
it will burn down
acres and acres of woodland.
But the clever Italian cypress
uses fire to its own advantage.
Like pine or fir trees,
they grow cones to hold their seeds.
But the cypress has two
different types of seed cone.
The first opens to release its seeds
as soon as they're ready.
You see all the cypress cones,
the mature ones are the brown ones.
Yeah, this is the open ones.
This is the typical ones you find
on the floor in woods, you know.
Once they open, the birds will come,
and they will spread
the seed around,
and then new saplings will grow.
But there's second special cone
that has developed
to deal with wildfires.
The fire ones are the closed ones.
They can stay shut like that
for many, many years.
You can see this
is a mature one over here.
And they will open up only
at very, very high temperatures.
As our summers get hotter,
this landscape
is increasingly vulnerable
to the threat of wildfire.
Whilst the trees themselves
will die in a fire,
the intense heat opens up
the special cones.
So the seeds usually sealed inside
are released,
and new cypress trees
can grow tall in the landscape.
I think the major ability
of Italians is to create beauty,
and this is a part of that beauty.
These trees are part
of that beauty, and
and Tuscany would be a very
different thing without them.
Trees in the prime of adulthood
really do
the most extraordinary things.
But what we can see above ground
is just the beginning.
We'll discover
that it's below the surface
where the tree is hiding
its greatest secrets.
The rolling countryside
of southern England
is home to majestic oak,
ash, and beech trees,
many hundreds of years old.
Like most trees,
we can only see them above ground.
But this seemingly normal hedgerow
holds something intriguing
beneath it.
Tree expert Tony Kirkham is entering
a mysterious underworld
to understand what's happening
below the surface of a tree.
This is Hell Lane in Dorset.
It's a holloway.
And, basically, it's a sunken lane.
The trees line either side.
They're growing over,
and they join in the middle,
creating this secret tunnel.
It's very atmospheric.
It's mystical. It's magical.
This ancient pathway
was created over centuries
as thousands of people walked
across the land,
pushing the soft, sandy soil
in between the trees
lower into the landscape.
The great thing about this place
is that you can see tree roots.
I think they fascinate me so much
because they're underground.
They're out of sight.
We don't see them.
It's a hidden life of a tree.
A tree's roots defend it
from one of its great enemies
..the wind.
All trees can flex and bend in
a breeze, but as they grow taller,
they become more vulnerable
to the impact of the wind.
So, here we have a tree
that's about 15 to 20 metres tall.
And these are ash trees.
And everybody would believe that
below ground would be a mirror image
of what we see above ground,
in order to support that height
and stop it blowing over
on a windy day like today.
But, actually, that's a myth.
And tree roots are very shallow.
Surprisingly, most tree roots grow
sideways, just below the surface.
It's about the tree roots
gripping the soil.
So, you can this amazing root,
this amazing lateral anchor root.
That's an anchor root.
And the primary objective of a root
is to support that tree,
to stop it blowing over
and for it to
to be able to grow tall
and reach up into the sky.
Even as adults,
trees keep growing taller.
And they continue to grow new roots
exactly where they need them.
As the trees move in the wind,
like on a windy day like today,
as they move, the tree sends signals
down to the root system,
saying, "I need more roots
on this side.
"I need more roots on this side."
The different parts of the tree
talk to each other and
and create these roots.
But roots aren't just anchors.
A growing tree has
up to 13 miles of them
to take up water and nutrients
from the soil.
The thirstiest trees can suck up
3,500 litres of water a day
..enough to fill nearly 20 bathtubs.
So, this is a lateral root
coming off the main anchor root.
We have these laterals coming down.
They will produce
these more fibrous roots
that have the ability
to absorb moisture.
Most trees, their root systems
are a maximum of a metre deep.
In fact, about 90% of tree roots
are in that top ten centimetres
where there's lots of water,
oxygen, nutrients.
And as the tree grows, that lateral
root system will grow with the tree.
Some adult trees can have as many
as five million fibrous root tips
to nurture them.
And whilst the parts of the tree
we see above the surface
weigh five times more
than their roots,
it's these hidden underground heroes
that are performing
the most incredible feats.
It blows my mind all the time.
Even though I've been working
with trees for 50 years,
it still fascinates me
how they stand up.
Trees in their prime can thrive
in many varied landscapes.
Some stand tall
as magnificent loners.
Others grow
in long, majestic avenues.
And perhaps the most atmospheric
of all, in vast woodlands.
The Woodland Trust's
Kylie Jones Mattock
looks after a collection of trees
near the North Wales coast.
It's a rare piece of forest that
really comes to life in the autumn.
It's an amazing place.
It's a place full of life.
It's an ancient place too.
I really love this time of year.
In October, the leaves
are just starting to turn.
These individual trees
on their own,
each tree isn't that old.
But there've been
trees growing together here
for hundreds,
if not thousands, of years.
And when a woodland
has been that well-established,
really special things
start to happen.
When trees grow together
in a woodland,
they can do
something extraordinary -
use their roots to share
water and food with one another.
But this act of generosity
only happens
with the help of a go-between.
And it's in the autumn
that it starts to reveal itself.
Just as the trees are starting
to close down for the autumn,
the fungi show their true colours.
They bring us this splash of colour,
and they come in purples and reds,
colours that you don't see
in nature as often.
You get this glimpse
into the hidden world of the forest.
Whether they're toadstools
..mushrooms
..or puffballs
..fungi can seem otherworldly.
But what we see is just
the tip of the iceberg.
Beneath the surface,
there's a much larger part
of the fungi
that spreads far and wide
across the forest floor.
Just by lifting a rock,
you can really lift the lid
on the hidden world of the forest.
Intertwined with all these roots
are a network
of microscopic fungal threads.
They intertwine with the roots, wrap
round them, even penetrate them.
This whole woodland here
is absolutely riddled with fungi,
twisting and interconnecting
beneath our feet.
And these tiny threads
enable the trees
to get to places
they couldn't otherwise reach.
The fungal threads attach themselves
to a tree's roots
and help it gather the nutrients
it needs from the soil.
But experts like Kylie are only
just beginning to fully understand
how much trees rely on
this incredible fungal network
..because the threads also connect
the trees to each other.
They link one tree's roots
to the roots of its neighbours
..binding hundreds
of trees together.
What makes those links between
all the trees in this forest,
over a vast area,
is this fungal network,
which means
this whole wood is interconnected.
A bit like
a complex web of cables,
connecting
the whole of this woodland.
This whole wood is
part of a wood-wide web.
Some experts believe
the trees could make use
of this incredible hidden connection
to support one another
in times of need.
To help us visualise
this wood-wide web,
I'm going to have a little go
at recreating it
with some low-budget tech.
So, these lights represent
all the things that pass within
the network between the trees.
Because the fungal strands link
the roots of different trees,
the fungus could move nutrients
from one tree that's doing well
to a neighbouring tree that
can't find enough food on its own.
For example, a small oak seedling
like one of these,
growing under the shade,
it's going to struggle to survive.
But the parent tree can actually
channel nutrients, sugars,
to that young sapling so it can
survive and thrive in the forest,
just waiting for its chance
to grow up into the canopy.
One cubic inch of soil can hold
as much as eight miles
of fungal threads.
And the connections
could spread for miles.
So if a tree on the far side of the
woodland is struggling for water,
trees with plenty on the other side
could share what they have.
The other trees in the forest
could be using their fungal network
to support that tree
to ensure it survives.
It's a fantastic system,
and we're really
just on the verge of understanding
all the things
that this wood-wide web achieves.
This woodland is a community.
An entire forest of trees that could
potentially be sharing resources,
allowing each other to thrive, all
by hidden connections we never see.
We just have no idea
what the potential is.
But we do know
that these connections
are going to be incredibly important
to the health, the resilience,
the survival of our woodlands
as they face challenges
in the future.
Trees have astonishing ways
to flourish,
even in our changing world.
And when they're harmed
by forces they can't control
THUNDER RUMBLES,
LIGHTNING CRACKS
..they can even heal themselves
in the most surprising
and ingenious ways.
Have you ever been among birch trees
and looked closely at their trunks?
They're dotted
with what look like eyes
..that follow you
through the forest.
These are scars,
reminders of whole limbs
that have been lost in the past.
And they are the perfect example of
how adult trees can heal themselves.
It happens as trees get taller.
When new branches grow higher up,
their leaves block sunlight
from reaching those
on the older branches below.
So the tree deliberately amputates
the old branches
by cutting off their food supply,
and they fall away,
leaving behind the eyes.
But what happens when trees are
harmed by forces they can't control?
THUNDER RUMBLES,
LIGHTNING CRACKS
Whether it's a violent storm
ELEPHANT ROARS
..a run-in with a grumpy elephant
..or even a bear
with an un-scratch-able itch.
Injuries are
an inevitable part of a tree's life.
BEAR GRUNTS
If there's one place to be
a wounded tree,
it's at the Royal Botanic Gardens
at Kew.
This world-famous sanctuary
in London
looks after
2,000 different species of tree
..from all over the planet.
Cecily Withall is
a member of Kew's Tree Gang
..the equivalent
of an on-call doctor service.
This morning,
she's doing her daily rounds.
Things like lightning,
wind or even human intervention
can harm a tree.
It's really important
for us as a unit in the Tree Gang
to really make sure that these trees
are, one, safe for the public
to be looking at them
and being around them,
but also maintaining them
so that they have huge longevity
in front of them.
Make sure that
they can outlive our time here,
which is the most important thing.
First stop on Cecily's round
is a rather extraordinary patient.
This tree was planted
in 1814 and is a Corsican pine
..classed here at Kew
as one of our unluckiest trees.
At 30 metres high, this pine
towers over the trees around it.
But its height means it acts like a
lightning rod for any passing storm.
Unfortunately,
it's been struck by lightning twice.
Trees don't really have
a defence mechanism
to stop them being struck
by lightning.
If a tree is struck,
it can die instantly.
50% of strikes will kill a tree.
When lightning hits a tree,
the water internally
in the trunk and the stems
will completely turn to gas
instantly.
THUNDER RUMBLES,
LIGHTNING CRACKS
The extreme power
of a lightning strike,
up to 300 million volts,
can split an entire tree in two.
Luckily, the Corsican pine survived.
The lightning only travelled
down the outer edge of the tree.
What we can see from the damage
on this tree is just bark.
You can see on the front of the bark
where it's exploded
off of the main trunk.
Like human skin, a tree's bark
is its first line of defence.
A tough outer layer that shields
the vulnerable wood beneath.
And when a wound does go deep,
the tree seals around it,
stopping any infection
before it can cause more damage.
They might not be able to completely
get rid of the wound itself,
but fortunately for us,
the tree stops
that wound becoming any larger.
The tree really is its own doctor
and can heal
and seal those wounds away
so they don't spread
throughout the rest of the stem.
But this unlucky tree hasn't
just survived two lightning strikes.
Nearly 100 years ago,
it was hit by a small aeroplane.
The aircraft itself was seen
to remove the top of the tree.
Hit the canopy, and a limb came down
and ripped the bark off.
Luckily, the pilot survived
..and the tree
sealed off the injury.
At 211 years old, this Corsican pine
is a true survivor.
Like so many trees
across our planet,
it's doing extraordinary things
to thrive in its prime.
So, the tree is named
the unluckiest tree at Kew,
but I really don't think so.
I think that if it's managed
to survive two lightning strikes
and a plane hitting the canopy
It's still here, growing strong.
I think it's pretty special.
In the final episode,
we'll discover what happens
when trees reach old age.
Like this yew, which is almost
as old as the Tower of London.
This could easily be 900 years old.
They look ancient,
and they are ancient.
A time when surprising things
start to happen
I can see two here
that are actually burrowing -
oh, my goodness - into the holes.
..as ancient trees give away
their deepest secrets.
That last third of a tree's life is
when they get really interesting.
For more information about
the secret life of British trees,
go to the Woodland Trust at