All language subtitles for Oak Tree Natures Greatest Survivor BBC 2015 HDTV 720p EN Sub_Subtitles01.ENG

One tree is an icon of
the British countryside.

It is, of course, the oak.

Today, we begin an
extraordinary experiment -

we want to understand this species
as never before and to do that,

we will film this one remarkable
specimen for an entire year.

Armed with the latest technology,
we will investigate how our oak

battles to survive through
four very different seasons.

In autumn, we go underground
to see how its root

stocks up on precious resources.

What we're looking at is
a highly dynamic system.

In winter, we discover
the sophisticated strategies

our tree uses to take on everything
the elements can throw at it.

In spring,
we find out how it senses the world

and how it even has its own
form of language. It talks to itself.

There's a chattering that
goes on across the whole canopy.

And in summer,
we'll see it fight predators

hellbent on eating it alive.

Over the next 12 months, I want to
see the world as our tree does

and tell its amazing story.

Wow!

In the coming year, I can't predict
exactly how well it will fare,

badly or well,
but I can promise you one thing -

you will never look at an oak
tree in the same way again.

The oak we've chosen to follow
for our year-long experiment

stands in Wytham Woods,
just outside Oxford.

It's a rather special tree.

For a start,
it's almost 400 years old.

That means it was a sapling during
the battles of the English Civil War.

It was laying down its roots as
Isaac Newton described gravity.

And it matured as Britain underwent
its Industrial Revolution.

What's more,
our oak is in a rather special place.

In 1942, the University of Oxford

acquired Wytham Woods,
our oak's home,

specifically so scientists could
research British woodland.

And I know these woods
extremely well.

I taught biology at Oxford
for 20 years

and my students
and I used to come and study

the countless insects that live here.

The climate,
bird populations, the soil -

scientists know a lot about Wytham

and this will help us better
understand our tree

and how it changes as we follow it
through the year.

Our year-long experiment
begins in late August

and the first task is to
assess our tree's condition.

To do this, forestry scientists
Dr Mat Disney and Dr Eric Casella

will create an incredibly accurate
three-dimensional map of our tree.

This is done by firing
almost two billion pulses

of laser light at our oak.

The end result is this beautiful
image - a virtual oak.

A year from now, it will help us
find out how our oak has fared,

how much it's grown
and how much new wood it's made,

even how much oxygen it's released.

We get some information
straight away.

Our tree is some 19 metres tall
and 30 metres wide.

But for me,
there's another quite astonishing

and quite unexpected detail.

One of the really interesting things
that we can get from these data

is we can estimate the total
number of leaves on the tree

and then from that...
Without counting them?

Without counting them
manually and I tell you,

I have manually counted leaves on
an oak tree just recently

and it's not a fun job and being
able to do it in an automatic way

without having to get your hands
dirty is far preferable.

Come on, tell me, how many?

Well, we think there are around
700,000 leaves on this tree.

To me, the fact that you can tell how
many leaves this tree has got

is just incredible.
It's amazing, isn't it?

The total area of those leaves
is about 700 metres squared so,

to put that in a bit of context,

that's about three tennis courts
worth of leaf area.

Our oak needs all these leaves
because they capture sunlight,

the source of all its energy.

But now, in late August, our tree
is acutely aware that sunlight

will soon become a precious
commodity.

As autumn approaches,
the days shorten

and the temperature begins to drop.

To survive,
our oak must transform itself.

Well, it may look as
if not much is happening,

but all across our tree,
a dramatic process is taking place.

Our oak is beginning a colossal
redistribution of its resources.

Well, it's been through this process
hundreds of times before,

but each time is no less challenging.

To see what our oak is really up to,

we need to see what is going on
beneath its bark.

BUZZING

As autumn begins, throughout
all of the branches and leaves,

a hubbub of chemical messages are now
being sent and received.

These chemicals are known as hormones
and our tree is producing them

to prepare itself for the autumn.

Well, it may seem odd, but just
like us, trees have hormones.

These chemical messengers flow
through the body of the tree,

controlling and managing all
sorts of important processes.

In us, these hormones are responsible
for some of the biggest changes

we'll go through in life,
like pregnancy and puberty.

In our tree, they're responsible
for an equally crucial change.

As autumn gets underway,
driven by hormonal signals,

trees begin to break down pigments
and nutrients in their leaves

to store over the winter.

They begin to eat themselves.

The result is a spectacular change
in the colour of the leaves.

Once the nutrients
have been extracted,

trees like our oak will start to
shed their leaves to conserve water

and energy in the coming months.

But how exactly does our tree know

when it's time to begin this
huge change?

For a very long time,
people assumed changes in autumn

were triggered simply by a drop
in temperature.

But what happens if there's
an unusually cold spell in summer?

How does our tree know not
to drop all its leaves?

It turns out that trees rely on a far
more sophisticated method

than temperature alone to sense
the changing seasons.

In their own way,
they can SEE what's going on.

Well, this should give you an idea
of how most plants see the world.

While you and I can perceive
a wide range of colours,

trees like our oak are only able
to sense the red light

in the spectrum and they can do this
thanks to an incredible

chemical pigment in their leaves
called phytochrome.

Phyocrome, a substance
in our oak's leaf cells,

is incredibly sensitive
to the red light

that makes up part of the sun's rays.

It's a kind of chemical stopwatch

that is also able to measure
the hours of sunlight and darkness.

So, as the nights get longer,
the phytochrome acts like a signal,

telling the tree that
autumn has begun.

This means that all the hormones that
prepare the tree for the cold months

kick in at exactly the right time.

It's now October and our tree is not
only dropping leaves,

it's also time for our oak to
release its most precious cargo.

Autumn is not just
a time for preparing for the cold,

it's also when our oak releases
its offspring out into the world.

We're all familiar with acorns,

but this really is
a masterpiece of evolution.

Inside this little capsule is not
only the genetic code

to make one of these, it also comes
packed with food

and protection from the elements,

meaning this seed has
all it needs to survive the winter.

To spread acorns, the tree relies
on the help of animals like jays

and squirrels,
who often store them underground

and then forget where they are.

But the oak has an ingenious trick
to improve its acorn's chances.

It varies the number of acorns it
produces from year to year.

Some years, there are thousands.

Others, like this year,
there are very few.

While acorns are the perfect
food for our friend here,

the fact that she can't
rely on oaks all the time

means she has to find
other sources of food.

But every five or ten years,
oaks have what is called a mast year.

They produce such a deluge of acorns

that all the acorn eaters simply
can't cope -

they're overwhelmed,
no matter how hard they try.

And this means that the
chances of one acorn germinating

and surviving becomes
dramatically increased.

With help from the local wildlife,
at least one of our oak's acorns

dropped this autumn is likely
to germinate next year.

And when it does,
it will be a spectacular event.

Fuelled by nutrients locked up
within the acorn,

our tree's offspring
is brought to life.

A shoot reaches upwards
to find sunlight...

..while a root
penetrates beneath to find water.

In just a few months,

this acorn has developed into an
infant oak with its very own leaves.

This tiny organism is now able
to fend for itself.

The success of the oak is largely
dependent on the animals

that help disperse its acorns.

And there's one species that,
in the last 300 years,

has been particularly helpful.

And that's us.

In the 18th and early 19th century,

there was a frenzy of oak planting
in Britain.

In just six years, it was reported
that one military officer

managed to plant 922,000 oaks.

The reason for this surge
was simple -

Britain had the world's
most powerful navy

and nearly all of our ships
were made of oak.

This is the HMS Victory,

famous for defeating the French
fleet at the Battle of Trafalgar.

The ship is a product
of almost 6,000 oak trees,

reimagined by some of Britain's
finest shipwrights.

This vessel and hundreds like it

were the reason for Britain's
insatiable demand for oak.

Climb inside and you see oak
everywhere.

This is the lower gun deck
of the HMS Victory.

Many of these sturdy oak
timbers have been here

since the ship first
set sail in 1765.

At night, hundreds of men would sleep
jammed together in hammocks

slung from oak beams
and at meal times,

they would eat together
at these oak tables.

For the crew of HMS Victory,
oak surrounded them.

It encased them and it kept them
alive against the elements.

The oak timbers of the Victory

withstood the terrifying
power of the sea.

They managed to cross the
Atlantic Ocean in hurricane season.

They survived furious battles and
innumerable volleys of cannon fire.

They saw death
and destruction on a colossal scale.

And it was an oak hull that cradled
Lord Nelson as he bled to death.

Each of these spectacular oak planks

has borne witness to
and survived the many violent

and dangerous battles on board
HMS Victory, but this wood

actually predates the building
of this ship by hundreds of years.

This wood is a product of medieval
acorns that dropped all over Britain

and, if you look closely, you can
still see the story of their lives

etched into the grain.

The way oaks live, the battles
they face in the natural world

and their incredible adaptations
are what makes this species

so uniquely useful
for building ships.

The curved boughs of the oak,

evolved to support the
vast canopies of leaves,

allow ships to be curved
yet maintain the strength

to withstand the full force
of the ocean.

By planting and cultivating oaks,

humans have been able to
travel between continents...

..and spread our species to almost
every corner of the planet.

Harnessing the strength
of this unique organism,

we have been able to overcome even
the most treacherous of oceans.

Back at our tree, it's now late
October and autumn is well underway.

Our oak is now getting six hours less
sunlight per day

than it was in peak summer

and, as the sun is
the tree's only energy source,

it must stock up
and store resources for the winter.

Crucial to how it does this is
the tree's root system -

a hidden subterranean world every
bit as complex as the world above.

I'm extremely keen to investigate how
this works, but that's no easy task.

Digging up our tree to see its roots
would kill it, so to investigate,

we're going to excavate the root
system of an oak sapling...

in its entirety.

This is East Malling Research
in Kent.

For over 100 years, they have been
experimenting with roots

and plants to help develop better
yields and they have given us

a unique opportunity
to get an insight

into what's going on
beneath the ground.

The process begins by digging
a metre-and-a-half deep trench.

It's only then the REAL
hard work can begin.

An oak's root system, even a very
young one like this,

is incredibly complex and fragile

and that means it
can only be excavated by hand.

We are trying to ensure that no root,
no matter how small, is damaged.

And that means the team must be
meticulous in their work.

It's a painstaking process

that will take ten people
almost two weeks to complete.

But once it's done,

we can begin to understand
the subterranean world of the oak.

Well, this is absolutely incredible.

Look at how much soil they've had
to remove

to expose the root system
of this tree.

It's only 15 years old

and several tonnes of earth
have had to be shifted.

This is something you'll never
see in a month of Sundays

and it's something
I haven't seen ever before.

But just look at the size of this,
look how far they go out

and as they go farther
and farther out,

these rootlets get finer
and finer and finer

until you're further out than
the tree is tall, virtually.

With the roots exposed, we can get
a glimpse into their hidden world.

Under extreme magnification,
we can see these strange threads.

They are known as mycorrhizal fungi.

They grow all over the oak's roots

and help them extract phosphates,

a vital nutrient
locked inside rocks in the soil.

Now, I've just pulled out this
little piece of rock here.

I think I can see fungal threads

that were actually
attached onto this rock.

Yes, so there's plant inaccessible
phosphate in that rock

and what the mychorriza do
is they go inside of the rock

and they pull out the phosphate

and they can transport that then
into the plant

and into the root system,

whereas the plant wouldn't
be able to do that on its own.

So the oak tree simply isn't able
to access the phosphate

in this without the fungi.

No, it's much smaller and it can
penetrate inside of the rock

and take the nutrients
back into the plant.

The tips of the fungi
can apply pressure

equivalent to the inside
of a car tyre.

And this means
they can physically penetrate

parts of the rock
to extract nutrients.

These are the hidden helpers
that allow oaks to get food

from the most inaccessible of places.

So, essentially,

what we've got here is an oak
tree like any other oak tree

which is totally dependent on a vast
army of microscopic fungal filaments,

without which it wouldn't survive
and it's a win-win for each of them,

they're helping each other. They both
require each other to survive.

If you stretched out the root
system of a mature plant,

you would expect it to have about
five miles of bare root system.

However, if you then stretched
out the mycorrhiza network,

that actually would spread around
the entire world. For a single tree?

For a single tree.
The more I see this system...

Well, you know, what I thought
of as a complex system is actually

probably 100 times more complex.

To see this root
system in its full glory,

we are going to take our sapling
out of the ground.

And put it on display in one
of the outbuildings at East Malling.

This is what an oak tree in autumn
really looks like.

At the top, we see leaves are being
drained of their nutrients.

Below, a vast branching
lattice of roots, evolved to keep

the tree standing and extract water
and minerals from the soil.

It is here that our oak will store
much of its food

over the winter months, but, laid
out like this,

the roots are not just beautiful,

they also tell us
a fascinating story.

Now, Peter, to the
untrained eye, this just

looks like a tangle of roots, but you
can tell a story about the tree now.

I think we can because what we can
see is a root, as you can see,

going down here before it heads off
out in that direction there

and this is almost certainly the
root that was inside the acorn

and it's headed on down
in this direction,

it's grown on down and then,
in the place that this was growing,

we've got some rock underneath,
some sandstone

and this root has hit that rock
and you can see, it's branched,

it's sent out many branches
to try and find

a way around the obstacle and it's
sent this one off in that direction.

Beneath our oak at Wytham,
the roots, like this sapling,

will be a kind of map,
showing the structure

and composition of the earth
in which they live.

Within the forest,

there's a very heterogeneous
distribution of nutrients.

It's not uniform

and this particular tree has
responded to that

by producing this plethora of roots,

this network of roots in this area,
to fully exploit that resource.

And presumably once that particular
patch of resource here

has been used up,
it will just go away.

Yes, these roots are ephemeral,
they'll die off fairly quickly

and the plant will
invest its resources elsewhere

so it's a highly dynamic system.
It's not just fixed and immobile.

No, absolutely not.

What we are looking at here
is something which is

sensing its environment,
responding to its environment

and utilising resources
in a very dynamic way.

At 15 years old, this sapling has
developed an amazing system of roots.

Our tree at Wytham will have roots
many times thicker,

spreading out anywhere up
to 30 metres from the trunk.

It may seem excessive,
but our tree will need them -

not just for nutrients,
but to keep itself standing.

As its last leaves are finally shed,

our oak is now fully prepared
for the difficult conditions to come.

As winter begins, our oak now
enters its most perilous season.

To survive,
it has stripped itself of leaves,

revealing an otherworldly beauty.

Our tree needs to stay alive
using almost no energy.

But in this dormant state,
our oak will have to face

everything from gale force winds
to sub-zero temperatures.

Well, it's now the depths of winter.

Our tree is bare and it's facing
some of the harshest conditions

it will have to endure all year.

At night, the temperature's going to
drop well below freezing

and out of the shelter of the forest,

the winds are going to be hitting
the top of this tree at full force.

To get some idea of what
the tree experiences,

I'm going to be sleeping
- or trying to sleep -

40 feet up there.

While our tree looks lifeless
in winter, oaks provide a home

to species ranging from spiders
and woodlice to bats and owls.

They all utilise the great size

and stability of the oak
to provide shelter.

A tree is not just a tree -
it's a home.

I think you'll be warm enough
going up there.

'I've always wanted to experience
what it might be like

'to live in an oak tree
and now I'm finally getting a chance,

'even if it is just for one night.

'Getting up to my perch
is no mean feat,

'but it gives me
a totally new perspective.'

Yes, it feels good!

Once I'm safely ensconced,
it's time to try and get some sleep.

I'll have a look out.

'At this height, you get a sense
of how big a space this really is.

'For a hibernating bat
or nesting owl,

'our oak will provide everything they
need to stay safe over the winter.

'But for me,
sleep is not coming easily.'

OWL HOOTS

I did hear a couple of noises
earlier,

which I thought might have
been deer or...

I'm sure I heard a fox.

Well, it's about three o'clock
in the morning and it's pretty cool.

It's just under three degrees and
I'm toasty in my sleeping bag here.

I've got these layers of down
and that really insulates me

pretty effectively from the cold
and that is working pretty much

like the bark of the oak tree,
which is an effective insulator.

The same principle that is keeping me
warm is also keeping our oak

and its inhabitants warm.

Its thick bark is
acting like a blanket.

But temperatures in winter
can drop below minus ten

and, in those conditions,
the bark is not enough.

CRUNCHING AND RUSTLING

Because water expands as it freezes,

if our oak were actually
to freeze solid in winter,

it could cause catastrophic damage.

So the oak has an additional
strategy.

In the lead up to winter,
it withdraws some of the fluid

from its delicate living cells.

It dehydrates itself.

What liquid is left contains high
concentrations of sugars

that act as a kind of antifreeze.

It is what allows our oak to
survive not just one cold night,

but many tens of thousands of them.

Well, I came up at night,
last night, in the dark.

And it is now apparent just quite
how high I am off the ground.

Thankfully, for me,
it was a pretty still night.

It's cold, but it's not windy.

And the view you get from here
is certainly worth it.

But it does give me
an absolutely unique experience

of life in an oak tree.

From up here you really begin to
appreciate the scale of our tree.

It is a huge habitat.

In the winter, while our tree
might look lifeless,

it is actually a vital part
of the ecosystem at Wytham.

Our oak is crucial to the survival

of countless thousands of
insects and other animals

over the inhospitable winter months.

It is now mid-January

and we are going to take a new
and very different

digital scan of our tree.

By imaging the tree without its
leaves in these still conditions

we should be able to get
a much more accurate estimate

of the weight of our oak's
wood, and this will be essential

to understanding how the tree
changes over the year.

Dr Eric Casella from the
Forestry Commission

is braving the cold for us.

And the model he is creating

will allow us to see
our tree in a totally new way.

Eric's scan reveals the
sheer complexity of our oak.

Using this model we can work out

that our tree is made up
of almost 10 tons of wood.

But the scan also reveals more.

Its branches are distinctly
clustered to one side of the tree.

Our oak has directed the growth
of its branches

away from the side shaded
by the forest

and towards the area
that receives most sunlight.

It has uniquely optimised its shape
to suit its position.

But this phenomenon
is not just above ground.

An oak's root system adapts to
help them stay standing in winter.

To see how this works,
I want to try something

that has never been done before,

I want to simulate
the effects of gale force winds

on an oak.

This is a Forestry Commission
research site just outside Edinburgh

and here they are
doing pioneering work

examining the strength and stability
of many different tree species.

They have allowed me in
for the afternoon

to come and watch
one of their experiments.

Today, for the first time,

they are going to study how an oak
tree behaves during a storm.

Some people might
be a little bit shocked

that you are just about pull
down a perfectly healthy oak tree.

What is the reason for doing it?

Well, one of the reasons
that we do this is to assess

the stability of trees and forests,

without doing this we don't know

what happens when a storm hits.

You're trying to simulate the sort
of forces

that that tree would
experience in a high wind?

Exactly.

Before we pull it, the tree must be
rigged with sensors

to monitor exactly how
it behaves under stress.

Once everything is set it is time
to get back to a safe distance

and begin the pull.

MACHINERY WHIRS

It is going.

Certainly going.

Beautiful.

With the tree down, Paul and his
team can now analyse the results.

At what angle did the tree suddenly
become sufficiently, you know,

tipped over, that it fell on its own?

Well, in this case
it was only six degrees.

That is nothing, that is like that...
That is correct, yeah.

So that tree, actually, it has
got very shallow roots,

it is not very big.

No. That is exactly what it is.

You can see, when we looked at the
roots, that it was very shallow.

While at first glance it may seem
this oak came down quite easily,

it would have taken a force 10 storm

to produce the same effect
as Paul's winch.

That size of storm can
produce 12-metre waves at sea

and has gusts of wind
anywhere up to 90mph.

This oak was, in fact, amazingly
stable given its relatively
shallow roots.

It is likely our oak has
grown much deeper roots

and with its huge spread
of branches

it is able to dissipate the
force of the winds

much more effectively.

It means that our tree can withstand
much harsher conditions.

That a large, heavy structure
like our oak can remain standing

over 400 winters is a remarkable
feat of evolutionary engineering.

And much of what has made it
so successful

at surviving the cold
and the storms of winter

has also made it useful to us.

For thousands of years, oak has been
an essential building material.

By slicing and shaping trunks of
oak into regular lengths

we are able to build
all manner of shelters

to protect us from the elements.

In the harsh winter months,
oak timbered houses

have kept us safe for centuries.

And thanks to the durability
of the wood,

many of these incredibly
old buildings still endure today.

But there is perhaps one
building above any other

that showcases the extraordinary
properties of oak timbers,

and just what
they can help us create.

Built in the 13th century,

it remains one of the most imposing
and impressive structures

in the British Isles.

And at its heart is oak.

This is Salisbury Cathedral.

It is one of the masterpieces
of British medieval architecture.

Looking at its size and scale

it is hard to believe this building
was created almost 800 years ago

and throughout its incredible
structure,

everywhere you look,
oak has been put to use.

During its construction,

an incredible 2,641 tonnes of oak

were employed to
help build the cathedral.

But it is not until you ascend
above the vaulted plaster ceilings

that you can really understand

how important this single
species of tree has been.

This building has within it
whole forests

reimagined and remoulded
by human hands.

Now, these oak beams have been
here for a very long time.

In fact these are among
the oldest of the oak beams here.

Yes, the area we are in now
is 13th century timber.

It has been tested, and it was
felled in the spring of 1222.

The roof here
can be dated so precisely

thanks to patterns in the wood.

As an oak grows it makes large
amounts of new tissue in the spring,

followed by a much smaller amount
of denser wood later in the year.

This rapid, then slow, growth
gives the appearance of rings.

If the summer weather is good,
a tree will grow a much wider ring

and that gives us a tantalising
snapshot of the past and its climate.

By looking at similar patterns
across many different samples

it is possible to date pieces of
oak with extreme precision.

It is even possible to tell where
an individual oak tree was growing.

And it turns out, to build this
amazing roof

the local craftsmen used oak
from as far afield as Ireland.

These two don't look quite the same,
to me.

No, if you look at the rings,
closely, this is Irish oak.

The tree rings
are really tight together

because the summer and the winter
almost blend into one another.

English oak,
they have hotter summers,

so they have a better growth
rate during the summer.

It makes it stronger, it is
also slightly lighter as well.

Which, when you are putting
thousands of tonnes of oak

into a roof structure, that helps.

It all adds up. Yeah.

With Salisbury's
spectacular roof completed

its builders decided to add
one extraordinary feature.

A monumental spire,

that must have filled the
medieval population

in the surrounding area
with absolute awe.

Today it still remains
the largest spire in the UK.

And inside is an incredible
lattice of oak timbers.

I tell you,
if you didn't like heights,

this would be not much
fun for somebody.

This is quite an amazing
feat of engineering, really.

And it was essentially
an afterthought,

after the cathedral was built,

and they have had to do this
ingenious framework

to help them build it.

Yeah, a thousand people
were working on it,

they were doing it to get closer
to God, if you like,

so it was their vocation, their way
of life, to be closer to heaven.

You just look up and marvel,
and you almost think,

it is divine intervention, really.

It is probably one of the most
amazing structures I have ever seen.

Well, you do get an amazing sense
of the countryside from up here.

But don't forget, it is the oak
forests growing down there,

the fact that they can withstand

all that the weather has
to throw at them,

even in the harshest winter,

and the strength and durability
and resilience

of the wood that they gave,

that made structures like
this possible at all.

Oak is an incredible
building material.

But even today we have yet
to come anywhere close

to creating structures
with the economy and beauty

of the oak tree in its natural form.

As the winter deepens
and temperatures drop down
below freezing,

our oak structure will
really be put to the test.

I want to find out exactly
how healthy our oak is

and how many more winters like this
it might be able to endure.

Thanks to some ingenious
new technology,

we now have the power to
look inside it and find out.

This is very similar to the MRI
scanner that we use of the body,

so it takes slices through the body,

we take slices through the tree,

and we're just trying to determine
whether the wood is sound or not.

As electrical currents are passed
through the tree

a map is created that will reveal
the internal structure of our oak.

Well, there is the image.
What does that show us?

Well, what it is showing us is

we have wet and dry areas,
basically, George.

And the dry areas are in red,

some of them are around
the outside of the stem,

the bulk of the stem
in the middle, is blue,

but there are breaks in that,

and that suggests there's
something wrong

with the inside of the stem,
it is not a natural picture.

Clearly something has happened,
we need to investigate that further.

This tiny gap between the roots
of our oak may look unremarkable

but inside is a hidden world.

Let's get this into position
so you can see.

That is quite a big hole, isn't it?

And we can see
all that decayed wood.

So we have got a
very, very large cavity

where the heart wood is missing,

and we can see fingers
of wood hanging down,

where the fungus has rotted out
the wood between it.

We call it the Eiffel Tower fungus.

It really only affects
the lower part of the stem

and leaves the tree effectively
standing

on its buttresses, like this,

a bit like the
Eiffel Tower on its four legs...

Hence the name. We've got
multiple legs, hence the name.

Even though that is quite a big hole

it is clearly not having a
hugely harmful effect on the tree,

it is still here, it's still
growing.

Absolutely, it has still got
these feet in the ground,

if you like, it can still
draw up nutrients and water,

and give it a firm footing
in the ground,

even though the heart is gone,

and it could still be there in
another 500 years.

It is likely our oak will still be
standing here,

alive and growing in the
landscape of the 26th century.

But after this vast
span of time has passed,

the fungus eating
away at our tree's inside,

and the age of its wood,

will mean it looks quite different.

Scattered across the UK are a select
few oaks

that have survived
over a thousand years.

And they give us clues about our
tree's ultimate fate.

This is the Bowthorpe Oak
in Lincolnshire.

And over the last one thousand years,

its insides have been almost
entirely hollowed out by fungus.

Each valley, ridge,
and peak in its wood

tells the story of the battles
this tree has faced.

Ravaged by the bitter
cold of a thousand winters,

its bark looks like the
surface of an alien world.

Sculpted by huge passages of time.

The Bowthorpe Oak is a window
into our tree's distant future.

But for now our tree is thriving.

It has endured everything
the winter has thrown at it

and is ready and waiting to
once again come to life.

As the temperature warms
and the forest is bathed in sunlight,

the countless plants and animals
in Wytham Woods come to life.

Once again, the forest is reborn
with colour, movement, and life.

And for our oak, this will be
the season of most dramatic growth.

After many months in a state
of suspended animation,

our oak is beginning
to come to life.

The buds are
finally starting to burst

and our tree is about to undergo

one of the most dramatic
changes of the year.

In the next few weeks, this oak is
going to have an epic growth spurt.

To capture this transformation,

we are setting up two
specially designed cameras.

Bolted to the spot, they will take
over 100 pictures each day,

and allow us to compress
this spectacular event

into a timescale we can appreciate.

Just like our tree, the cameras
will be powered by the sun

and will capture images continuously
for the next six months.

With everything set,
the cameras are started.

As winter ends and spring begins,

over 700,000 individual leaves
emerge across our oak.

It is a truly astonishing change.

This remarkable transformation
needs huge amounts of water.

Hidden from the naked eye,

at its peak, our tree will be
pumping 70kg of water each hour

out of the ground.

By looking at the oak wood just
beneath the bark with a microscope,

we can see how this huge quantity
of water gets moved around the tree.

These intricate pipes are
known as the xylem vessels

and they run through a layer
known as the cambium,

that carries water upwards,
from the roots to the leaves.

And thanks to some
ingenious technology,

we can now measure exactly how
much fluid is moving through them.

With the help of Dr Lucy Rowland,

I'm going to set up an experiment
that I hope will reveal

exactly how much water
our tree is taking up

and how this changes over the spring.

This is a sap flow monitor.

And as water travels up the xylem
tissue, these probes heat it up.

By measuring how quickly this heat
is carried away,

the device can calculate how
much water is flowing

through the trunk of the tree.

Over 24 hours of measurements,

we see our tree's water consumption
varies dramatically.

This is at night when we don't have
sap flowing up in the tree.

And this peak here,
this is lunchtime-ish yesterday,

when we had maximum flow up
through the stem of the tree.

And you can see here that we have
got about 10kg of water per hour,

yesterday lunchtime,
going up through the tree.

And that will increase as the
leaf area of the tree increases?

Yes, so the more leaves that come
out on this oak

over the next few weeks,

the bigger that this peak
is going to be.

As we move through the next
two weeks of spring,

our tree begins to consume ever more
water in the middle of the day.

It reaches a peak of over
60kg of water an hour,

as more and more leaves emerge.

But leaves are not all our
tree is now producing.

It is now late April

and for a precious few weeks, our oak
grows these strange new structures.

Their role is to ensure
the future of our tree,

and the continuing success
of the oak.

These fragile little objects
are known as catkins.

And they are oak's male flower,

and it is the appearance
of these every spring

that signals the start of
the oak's reproductive cycle.

And if you look carefully inside
each of these little blobs,

you will find it is completely
packed with grains of pollen.

But these pollen grains
are only half the story.

Our oak will also produce
a female flower,

but not until later in the spring.

It means that these pollen grains

will need to find a female oak flower
on another tree,

if they want to pollinate.

And that means taking to the skies.

In spring, an oak tree like ours

can release up to two billion
individual particles of pollen.

And inside each one of these tiny
grains is the unique DNA of our tree.

Blown around by the wind,
they can spread for miles,

but their mission is simple,

each grain is seeking a
chance encounter with a female flower

of one of the other 5,000 oak trees
in the surrounding woods.

Filling the air above the forest,

billions of our oak's
individual pollen grains

are scattered by the spring breeze.

Up close, we can see how complex
this tiny vessel really is.

A thick, warty shell protects
the delicate genetic cargo inside,

as gusts of wind carry it for miles.

This is the target
of our oak's pollen grains.

A female oak flower.

If the pollen is lucky enough to land
here, it will fertilise the flower.

And over the next few months,

the female oak flower will combine
its genetic material with the pollen

to create a tiny acorn.

A descendant of our oak.

The yearly act of pollination

is crucial for the long-term
future of the oak.

But at Wytham, they have been using
pollen

to open up a unique window
into its past.

This is Marley Fen.

It is an area of Wytham Woods

that has remained largely
unchanged for thousands of years.

And over that time,

as plants and trees
reproduce every spring,

the air is filled with trillions
and trillions of pollen grains

that eventually end up
in this peat here.

As pollen settles on the surface
of the fen,

plants, leaves, and other
biological matter

gradually build up on top of it.

Over time, layer upon layer of pollen
becomes preserved within the soil.

Inside this somewhat unremarkable
looking mud,

an incredible story
has been preserved,

one that records in detail

the ebb and flow of various
trees and plants in the area

for the last 12,000 years.

But to uncover the story hidden
in here, you have to dig down.

And that is what Dr Helen Walkington
and her team

have been doing
for the last ten years.

They use a long metal tube

to extract thin cylinders
of peat from the fen.

This four metre long core

can tell scientists how the landscape
and vegetation in Wytham Woods

has changed since the end
of the last ice age.

This soil, from four metres down,
was on the surface 12,000 years ago,

and shows Britain then
was a cold and barren place.

So we have got here
clay-rich material

with lots of iron
and fragments of rock.

So, I don't know if
you can see here,

but there are rock fragments
within it,

so it tells us there was lots
of erosion in this landscape,

and that's how we know that there
was not much vegetation at the time.

Without plant roots to hold
the soil in place,

the landscape of Britain
after the last ice age

was prone to rapid changes.

But as we move along the core,

more and more pollen begins appearing

as plants of all kind take hold.

As the climate warmed, it meant
oak was able to move north

and 9,000 years ago
its pollen appeared

for the first time at Wytham.

This material would represent
organic matter

that would have been moved into
Marley Fen 9,000 years ago

and at the same time,

oak pollen would be blowing
around in the atmosphere

and would settle out on the surface,

and gradually all
the material in the rest of the core

would be on top and pushed down.

I find it incredible

that I can actually put my
finger on that piece of core

and touch the exact part of
the history of Wytham

where oaks came in.

9,000 years ago.

9,000 years ago, and I can actually
physically connect with that.

And what are humans
doing at this time?

At this time, we don't have humans
at this point.

So this is it, this is pristine?

Once the humans do come into
the landscape,

things start changing very quickly.

Moving through the core to nearly
2,000 years ago,

cereal grains begin to appear
at Wytham,

and this signals a
new type of human activity.

Cereal grains are brought in
by the Romans,

and they need to completely
clear the landscape

to make space for fields,
to cultivate them.

The cereals, we don't know the exact
type of cereal they were growing,

because the shape of the pollen
grains does not unlock that for us

like it does for the trees,

which we can get down
to the species level.

But certainly the Romans would be
using this landscape to grow food,

and then as we progress up the core,

we find that oak
becomes less dominant.

But it is still here.

It is still present,
but it becomes less dominant.

And that is because humans have
set about clearing these landscapes

on a much, much greater scale.

The oak tree that we are filming
in Wytham Woods

is going to be going somewhere
about here.

Yeah, it was probably an acorn
around 0.7 metres,

something like that.

And so that represents
the period of time

that your oak tree
has been growing.

Well, at least it shows that
things change over time.

And there have been huge, huge
changes in 12,000 years,

which is a very short
piece of earth's history.

Absolutely, and in 12,000 years

those changes have been natural
and human induced.

There is a kind of interplay
of those at this site.

And I am sure that in the
next thousand years

that will be the case as well.

The oak's pollen offers us

a vivid glimpse of the challenges
trees face over vast spans of time.

But, right now, our tree is gearing
up to face

a much more imminent danger.

It's now late May,
and our tree is in full leaf.

The oak boughs visibly droop with

the weight of the new
material they have to support.

But this abundance of young,
soft leaves are extremely vulnerable.

A great threat is now emerging

and our tree must react quickly
if it wants to survive.

This is the lava of the winter moth.

It may not look very much,

but this is one of the oak's most
fearsome enemies.

This little chap will eat
an incredible amount of food

to become adult.

In fact, it will eat up to 27,000
times its own weight in young

oak leaves and, right now, there
are countless thousands of these

caterpillars infesting our tree.

But our oak isn't
powerless in the face of this attack.

After the oak's new leaves first
emerge, for a short while,

the winter moth caterpillars, amongst
others, will gorge themselves.

Unprotected from these attackers,

our oak would struggle to survive
the summer, but, incredibly,

our tree is able to recognise exactly
what's happening to it and respond.

Professor Sue Hartley has spent
much of her career

looking at the ways plants defend
themselves against insect attacks,

and was one of the first
to recognise just how sophisticated

trees like our oak really are.

How does an oak tree know
it's being attacked?

Well, that's really interesting.
This is a winter moth,

and it's about to tuck in
and you can see that when they eat

the leaf, they chew the edge,
and they are really messy eaters.

Saliva's going all over the leaf.

There's lots of dew on the leaf
surface and, within that saliva,

there are chemicals that the oak
tree can recognise.

While we might see or hear
approaching danger,

the oak senses it chemically.

It's hard to appreciate,
as we have no analogous sense,

but it's an incredibly fine-tuned
and refined system.

This chemical signalling
is really sophisticated,

so our oak tree can tell
whether it's a caterpillar

or whether it's a different
kind of herbivore like a sap sucker,

or aphid that feeds in a different
way, and it's even better than that.

The oak tree can tell the difference

between big caterpillars
and small caterpillars.

The age of the caterpillar can be
detected.

That is amazing.

Once our tree has sensed it's being
attacked in one place,

it's actually able
to signal to itself

to warn other parts of the attack.

It produces something called
wound hormones,

and those hormones move all around
the plant in the sap system and

that tells the plant to turn on its
defences in other parts of the tree.

And they also cause airborne signals
to be released that also

travel around the tree.

So the defences are ready all over
the place.

So if one branch,
if that little branch there

was suddenly
attacked by lots of caterpillars,

the tree would know and it would
protect all the rest of itself?

It would start to, yes.
It talks to itself,

and there's a sort of chattering
goes on across the whole canopy.

Once our tree knows it's
being attacked, it begins

to produce poisons that will stop its
attackers in their tracks.

The main defences of an oak

are chemicals called phenolics
and tannins.

That's what you have in your teacup.
That's what gives tea its taste.

Yes, tea contains a lot of tannin,

and it's tannin that produces that
bitter flavour in tea because

the tannin binds with
protein in your mouth,

the saliva, and gives it that
sort of bitter taste.

And that's exactly what happens
when the insects try and feed.

They find that the chemicals
in the oak leaves will bind to

the proteins in their digestive
system and stop them going so well.

So, it may look like the tree is just
a big, green heap of food,

but eating it is not that easy.

It's a real challenge to eat plants.

They're full of defences
and they're very clever,

and they're able to detect
the things that attack them.

They've had millions of years
to evolve to do that.

And they've got a very
sophisticated armoury.

After keeping the insect
hordes of early spring at bay,

our tree can continue its rapid
growth.

But now, a new danger is emerging.

An outlandish group of insects that

have hijacked our oak's
growth for their own ends.

They are, without doubt,
the strangest

and most sophisticated foe
our oak will face.

This is a gall wasp.

By laying its egg
in a female oak flower,

it causes a profound
change in the way our tree grows.

That produces a kind of tumour
known as a gall

to grow in place of an acorn.

MUSIC: Piano Concerto No 21
by Mozart

Inside the gall, a grub develops,
feeding on the nutritious

tissues within, while being given
shelter from enemies.

This bizarre structure is
the perfect nursery.

This particular structure is
known as a knopper gall

and it's the product of just
a single species of wasp.

These wasps always produce this type
of gall.

But there are many other species of
gall wasp

and they can induce very different
shaped growths.

The remarkable thing about galls
is their sheer diversity.

There are several hundred
species of gall wasp

and each one makes
a gall of a specific shape and size.

The goals are not just random
overgrowth of the oak,

the gall wasps are actually using
chemical signals in very subtle ways

to hijack the developmental machinery
of the oak at an early stage.

The exact way each species of wasp
manages to produce such

individual and unique galls is
still somewhat of a mystery.

But it seems they may be actually
altering the oak's DNA...

genetically engineering it to grow
a home for their young.

The myriad of different types of
structures these wasps create

for their offspring is
simply staggering.

But, of all the weird
and wonderful types of oak gall,

there's one that has a strange
connection with the human race.

One type of oak
gall has shaped our history.

That's because, for 1000 years,

it was the source of a special kind
of ink

with which nearly all of our
historical documents were written.

Crushed, mixed with water,
iron sulphate and gum arabic,

the humble home of the andricus
kollari wasp is transformed

into a cheap
and extremely long-lasting ink.

This is the national archives at Kew.

In the vaults of this
building are housed over 1,000 years

of British history, in the form of
millions upon millions of documents.

Stored in these unassuming
boxes is our past

and a huge amount
of it is recorded in gall ink.

So, almost any document of any
importance had to be written,

or was written using ink
made from oak gall.

That's right.

It's the most important ink
we have in Western history.

What made it so good? As an ink.

It's an indelible ink.

So it's very hard to remove.

And you can see in some of these
documents here,

these are from the trial of
Guy Fawkes.

Wow! The actual records?

Yep, these are the actual records of
Guy Fawkes' trial.

And here, you can see a nice
example of how indelible the ink is.

So here,
the scribe has made a mistake

and, to correct his error,

he's actually had to scrape
the surface of the parchment off,

remove the ink from the surface
and then rewrite over it.

And you can see this dark patch here
and the difference in the colour,

because this part of the ink was
put on much later.

This is a really good illustration.

These kinds of legal documents had
to be kept in ink that was

going to last, had to be written
in ink that was going to be lasting.

So they're written on material
parchment that is more durable

and they're written with
an ink that is not going to

just vanish before your eyes.

But oak gall ink wasn't just
used for official documents.

Everyone from poets, musicians
and mathematicians to fine artists

used this ink to record
their thoughts, feelings and ideas.

The whole of western civilisation
between from about the end

of the Roman period to the 19th
century,

our most important
texts are in iron gall ink.

It seems just a bizarre
twist of fate that all of this,

and there are how many thousands of
documents here which are written

in this ink, began
because a tiny wasp

laid an egg in oak buds
that grew into a gall,

and that provided the basis for,
essentially, our recorded history.

That's right.

What is surrounding us
is just a small fragment

of all the documents that survive
from those 1,400 years of history.

From wasp to gall to human hands.

This little quirk of evolution
has shaped human history.

This incredible ink brought us
the Magna Carta

and the American
Declaration of Independence.

It has brought us
the music of Mozart and Bach...

..and the drawings of Rembrandt
and Leonardo da Vinci.

Thanks to gall ink,
we have Isaac Newton's theories

and the letters of Charles Darwin.

Unwittingly, the oak tree has
enabled us to record our past,

to express our most profound ideas
and to share our deepest emotions.

In just three months,
our tree has gone through

a radical transformation.

It has brought out its leaves,
it has spread its pollen

for miles around, and it has repaired
the damage sustained over winter.

Now, as the insect populations
grow ever larger,

this mighty organism is finally ready
to face its most challenging season.

It's now June and,
under the intense sunlight,

trees and plants are working
at full capacity.

For the countless life forms
of the forest, it's a time of plenty.

And, at the centre of this frenetic
activity is our oak.

Right now,
it's literally being eaten alive.

There are hundreds of insects that
depend on the oak for sustenance.

But I want to see the insects us
humans do not normally come across -

the ones that live high
up in the oak's canopy.

Well, it's now the height of summer
and the tree is in full leaf.

There's even some acorns
beginning to swell.

This is just an enormous,
cathedral-like space.

What's very frustrating when you're
on the ground is that you know there

are lots of fantastic insects and
animals, but you can't reach them.

So, the only way to get to them
is to climb.

HE GRUNTS AND GASPS WITH EFFORT

If I can just find a nice
place to stand...

Oh! There we are.

Wow!

This is a very privileged
view of an oak tree

and one that only an insect
would have.

There are some insects up here that
you never see from the ground.

If I can just shake the foliage,
try and get some insects in the bag.

I'll bet there's lots of good
stuff in here.

Now, the next bit of kit
is the pooter.

That allows me
to suck insects out of the net.

Without handling them, because lots
of these things are very small.

So, let's see what we've got.

High up in our tree, there is
a wealth of life.

This is where the good stuff will be.

Hmm!

Oh!

But, to get a sense of its diversity,
and the unique

adaptations of creatures up here,
we have to take a closer look.

And we can do that under
the microscope.

Now, we've got
quite a few insects in here.

I think we'll just empty them in
there, and hope for the best. Great.

I'll just whack them in.
I'm sure it will be fine.

A big earwig there, look at that!

What is absolutely amazing with this
machine is the quality of that

image is just breathtaking.

Well, that is
the head end of a cricket,

and she's having a preen here.

The very interesting thing
about these insects is that they

have their ears on the knees
of the front leg.

You will see a little opening there,
and that is the opening of her

hearing organs, which are here
and here.

And, by having their ears
on their front legs, quite far apart,

they're able to triangulate and know
exactly where that sound is from.

Now, let's see
if we can see anything else here.

There are absolutely minute
things in here.

A tiny little thing, a mite,
absolutely minute.

And there are probably millions,
tens of millions of these up a tree.

That animal is tinier than the claw
on the hind foot of a cricket.

This spectacular variety of insects

are all at their most
active in summer,

and many of them are specially
adapted to eat our oak's leaves.

This is a plant hopper

and it's able to suck out sugary
sap from individual plant cells.

When these sap suckers
attack en masse,

it can be devastating to the
delicate leaves of our tree.

There are many, many different insect
species who call our tree home,

but there are a select few
who have a special relationship.

Species that have evolved to
specifically

take advantage of the oak.

This is one of our tree's infant
acorns, finally beginning to emerge.

It's a beautiful,
intricate structure.

Something here is not right.

This strange, black hole is
a sign that this acorn

has been tampered with.

BELLS CLANG OMINOUSLY

The culprit is one of the most
highly specialised

and bizarre species on the oak.

DISTORTED, CLANGER-LIKE NOISES

The acorn weevil.

Look at that! Ho-ho!

Is that not just
the most beautiful thing?

This is an animal that's evolved
specifically with oak trees.

It lays its eggs in acorns,

and it's got this enormously long
beak that comes out of its head

and, at the end of that
are a pair of tiny jaws,

and it drills deep into acorns
to lay its eggs in the acorn,

and she has these peculiar antennae
which are elbowed, hinged,

and, as she drills into the acorn,

she can fold them
back along the side of the head.

Our weevil also has highly
specialised bilobed feet

with which it's able to grip onto
the smooth surface

of the oak's acorns.

Being able to see them this close
brings you into their world.

You can understand the mechanics
of what they have to do,

how they have to live.

It doesn't get any better than this,
really.

That is
just evolution at its most wonderful.

The acorn weevil is just one of many
insects up our tree.

On one single branch, there's
a beautiful and deadly lacewing.

Other insect predators, such as a
damsel bug and a comb-footed spider.

And the tussock moth caterpillar,
who can feast on our oak's leaves.

All of these insects have found
ingenious ways to use the oak

for their own ends and extract
food from it in some way or other.

And it's not just insects -

us humans also consume oak.

In fact, we can drink it.

To discover more about this, I'm
going to the land of my forefathers.

Scotland.

This is the Scotch Whisky Experience
in Edinburgh.

With 3.384 different bottles,

it's the world's largest whisky
collection.

To be legally called a Scotch whisky,

the alcohol must be stored in oak
barrels for at least three years.

Whisky is, in essence,
oak-flavoured alcohol.

Does the growth of the oak tree
effect what the whisky will

eventually be?

Yes, it absolutely can do.

Generally,
what happens in quercus species is,

the tree lays down material in two
distinct parts of the year,

springtime, it lays down early wood,
which is like a sponge, very porous.

The rest of the year, late wood
which is... hard and dense.

The early wood is more
porous or spongy,

therefore it can give forth
more flavour.

So, if you're really fussy about
the type of barrel you want to use,

you will go for so-called
tight-grained oak, typically,

12-16 growth rings per inch,

if you're going to get very specific
about it!

By treating oak barrels in different
ways, by charring them

and seasoning them with other wine
and spirits, it's possible

to release multiple chemical
compounds from the oak,

leading to an incredible
diversity of whisky flavours.

So what we've got is actually a very
complicated system.

All these compounds which give
flavour to the whisky,

how many different
flavourings are there, do you think?

I would say that there is probably
between 50-100 different compounds

we can identify that have
come out of the oak wood

that can influence the character
and flavour of the whisky.

So, when you drink your mature
whisky, all these lovely,

buttery flavours, the soft texture
on the palate, the sweetness,

the vanilla, the coconut,
the almond, all of these flavours

are drawn directly
from the good-quality oak wood.

The multitude of flavours
that whiskies possess

are testament to the
complexity of the oak's wood.

From weevil to human, there are many
hundreds of species that eat

or consume the oak in some way,

but what does our tree eat?

Where does it get its energy from?

The answer is, of course, the sun,

and at the height of summer,
this process,

famously as photosynthesis,
is at its peak.

To see how the tree does this,

we need to look at its leaves
under the microscope.

These strange openings are called
stomata.

And they suck carbon dioxide
from the atmosphere into the leaves.

Then, powered by sunlight,
this carbon dioxide is combined

with water and turned into sugars
that our tree feeds on.

But, as they photosynthesise,

our oak leaves perform one final,
magic trick.

Out of the many billions of stomata
pours oxygen.

It is, perhaps,
the single most important

process in the natural world.

At the height of summer, our oak,
its magnificent structure

and its hundreds of thousands
of leaves, are able

to bask in the sunlight
and convert it into food.

In the process,

it pumps out the oxygen
that we all rely on to stay alive.

In this single act,

our oak is performing
a feat that we have yet to match.

As August begins,
it's now been a year

since we made the first
digital model of our tree.

Thanks to the detailed measurements
we've taken over the years,

and the weather data from Wytham
Woods, it's now possible to make

estimates that reveal
the ways our tree has changed.

Despite its age, our tree has grown.

Over the last 12 months,

it has been extracting carbon
dioxide from the atmosphere

through its leaves, and some
of this has been refined into carbon

and forged into new wood.

While our oak's great size
and age means that new growth

is extremely thinly spread,
it has increased in size.

In fact, our tree has
created 230 kg of new wood.

This much material has literally
been plucked from thin air.

To help it grow and photosynthesise,

our tree has had to consume
huge quantities of water.

Thanks to our sap flow data,
we can see that, over the 71 days

we recorded it, the tree drank
an incredible 58,822 litres of water.

But our oak tree hasn't just
taken from the environment around it.

As it photosynthesises,
its leaves produce oxygen.

Since we've been filming,
our tree has released

an incredible 234,000 litres of
oxygen into the atmosphere.

And that much oxygen is enough
to keep me alive for a whole year.

By spending a year looking at this
one tree, we have been

able to see just how dynamic
and complex this organism really is.

We have seen how it can create
700,000 leaves and keep them safe.

We've seen how it can withstand
the harsh winter conditions.

And we've seen how our tree
sits at the centre of a vast,

interconnected web of life.

In the face of everything
thrown at it, the wind, the rain,

freezing temperatures and constant
attacks by insects and fungi,

our tree has thrived.

In the process, it provided a home

and a source of food for millions
of individual organisms.

It's what makes this incredible
species

such an important
part of the British countryside.

The oak's endurance
and longevity have woven it

into the lives of the thousands
of creatures that rely on it.

And that includes us.

This colossus of the British Isles
has permeated our culture.

Oaks have shielded us,
protected us from danger.

They have allowed us to explore
the seas.

They have brought us pleasure.

They have helped us
express our most profound ideas.

Oaks have borne witness
to our deepest sorrows

and our most joyful moments.

This plant, perhaps more than
any other, has become part of us.