All language subtitles for E03 - Seasonal Worlds_Track7

This is the Boreal Forest.

The largest forest on Earth.

750 billion trees.

Smothered by snow
throughout the winter...

...this is
the northernmost boundary

of an extraordinary world.

I'm standing at the edge
of the Arctic Circle.

To the north of me

lies a land dominated
for most of the year

by snow and ice.

3,000 miles to the south,
the tropics,

bathed the year round
in warm sunshine.

And in between,
a very different world,

dominated by relentless change.

An endless cycle
of four distinct seasons,

each with its own challenges.

The short, freezing days
of winter

give way to the urgent
awakening of spring.

And the long, hot days
of summer

yield to the cooling of autumn.

Opportunities will be brief.

To survive these extremes,

plants have not only got to be
hardy and resilient,

but many of them have developed
special strategies

in order to meet the demands
of this seasonal world.

To succeed, they must
get their timing just right.

For months now,
this world has been asleep.

But change is coming.

Spring is on its way.

In Canada, the forests
are starting to stir.

Throughout the winter,
the sugar maples here

have kept stores of nutrients
ready for this moment.

Now, as temperatures
start to rise,

those nutrients must be
brought up from the roots.

Sap is on the rise.

Fuel for new green growth.

But just as growth reaches
full speed...

...robbers arrive.

A sapsucker.

A thief in search
of maple syrup.

The tree can tolerate
hundreds of wounds.

But if they completely encircle
the trunk,

the tree will eventually die.

The sapsucker's break-in
hasn't gone unnoticed.

Hummingbirds,

squirrels

and insects

all invade
the sapsucker's territory,

trying to steal a meal.

But unwittingly,
they help the tree.

Time spent chasing
the competition...

...means less time
to drill new holes.

The tree gets a chance
to repair its wounds...

...and the sap can rise freely
again.

So this year at least,

the tree will once more
produce its leaves.

Hundreds of miniature
solar panels

that collect energy
from the sunlight.

Each leaf is covered by
millions of microscopic pores -

stomata.

They take in carbon dioxide...

...and release oxygen
and water vapour

in a process that produces
high-energy fuel.

All the trees here can now
use that fuel to grow

over the coming months.

As spring proceeds,
the power of the sun increases.

On river banks across Europe,

many plants have been
lying dormant underground...

...waiting for the earth
to warm.

And now a race begins.

Among the first to start
are nettles.

The sprinters.

Then, only just behind,
come the brambles.

They're much more aggressive,
and have backward-pointed hooks

with which to scramble over
their rivals.

Last to come, the climbers.

Hops and bryony.

They lasso their way
towards the light.

Soon, every inch of space
and every patch of light

has been claimed.

But hidden in the shadows,

another plant has been
waiting to make its move.

This...

...is dodder.

A hunter...

...with an exceptional
sense of smell.

Moving swiftly,
it searches for its prey.

It detects the scent
of a young nettle.

The dodder punctures
the nettle's stem

and sucks out
the nutritious sap.

And it doesn't stop
at just one victim.

With its energy supply assured,
it multiplies.

It's a parasite

with an insatiable appetite.

But remarkably, its victims
can now exploit the dodder...

...when other springtime
enemies appear.

Caterpillars.

When under attack,
a leaf sends out a signal

telling the rest of the plant
to start building defences...

...foul-tasting toxins
that deter the caterpillars.

In an extraordinary twist,

the stems of the dodder
interconnecting the plants

are now being used
as lines of communication

to relay these warning signals
from plant to plant.

They respond by producing
their own protective chemicals.

Eventually,
the whole river bank

becomes one huge
defensive network,

and the one-time rivals
are now better off together.

The first warm days of spring
encourage some plants to flower

and get ahead
of the competition...

...creating beautiful displays

throughout
the seasonal world...

...from the spectacular
cherry blossoms of Japan...

...to the goldfield flowers
of California.

But spring flowering is risky.

If they flower too early,
it may not be warm enough

for pollinating insects
to be active.

But the common daisy
gives them every opportunity.

The warmer the flowers are,
the more attractive they are,

and they have
a remarkable strategy

in order to maximise this.

They were closed up tightly
throughout the night

as a protection
against the elements.

But once they feel the warmth
and the light of the sun,

they spring into action.

It's a behaviour called
heliotropism.

They turn to keep facing
the sun,

absorbing as much heat
as they can.

This is a thermal camera,

and it will tell me
the difference between

the surrounding temperature

and the temperature in
the centre of a daisy flower.

The surroundings - 12 degrees.

In the centre of a flower...

...21.

Pollinators such as
bees and wasps

prefer the warmed-up flowers

because they can get a share of
the heat for themselves.

As a consequence,
they can collect more nectar

from more flowers,
pollinating as they go.

And the daisies, with
the help of their pollinators,

are able to have a particularly
long flowering season.

But when the window
of opportunity is brief,

even more ingenious tactics
are necessary.

Here in south-west Australia,

summer temperatures can soar to
up to 40 degrees Celsius.

Now, for a brief moment
in the cooler spring,

flowering plants must get busy.

And this hammer orchid,
with its strange flower,

is doing exactly that.

It needs to attract
a pollinator,

but has no nectar,

and doesn't even
look like a flower...

...unlike these neighbouring
huge grass trees.

These produce thousands
of tiny white flowers,

all dripping with nectar.

But the orchid
has a different strategy.

It synchronises its emergence

with the brief mating season
of the thynnid wasp.

The flightless female wasp
produces pheromones

to attract males.

This male detects a scent
that seems to be hers...

...yet flies right on by.

The orchid not only has
the same shape and colour

as a female wasp,

but it sits at the same height
as she does.

It even mimics her smell.

And the beguiled male
attempts to mate with it.

It hammers against the orchid's
pollen sacs.

And the wasp leaves,
doubtless a little shaken...

...only to be duped once again.

The pollen on his back

now sticks to
this different orchid...

...and the deception
has worked.

The orchid's imitation
is even more intoxicating,

it seems,

than the real thing.

Eventually, the male wasps tire
of the orchid's enticements.

Now the wasps,
both male and female,

find the flowers
of the grass trees to feed.

And there, at long last...

...they mate.

And as for the hammer orchid...

...pollination is complete.

As summer approaches,

the need to flower
becomes more urgent.

And nowhere more so
than here...

...in South Africa.

This is the fynbos, part of
the Cape Floral Kingdom,

a great expanse
of open heathlands

just north of the Cape.

Here, there are more
different species of plant

than anywhere else
in the world -

nearly 9,000 -
many needing pollinators.

They compete with one another
for such help

by flaunting extravagant shapes

and vivid colours...

...all promising nectar
as a sugary reward.

But there is a plant here

that avoids
this crowded competition.

And the rising temperatures
of summer

bring just what it needs.

This is the first fire here
for 15 years.

Nearly all the plants
are destroyed.

Incinerated.

It might seem from the smoke

and the still-smouldering
embers that no plant

could survive such an inferno.

But just four days
after the flames...

...rising from the ashes...

...a fire lily.

It has been lying dormant
underground for 15 years,

but now, awakened by the smoke,
it flowers.

The blooms may be small
and unshowy,

but that's all they need to be.

In this charred landscape,

pollinators such as
these sunbirds

can spot these little red
beacons from great distances.

They're the only source
of nectar around.

And the more visitors
the flowers attract,

the more likely they are
to be pollinated.

It's just in time.

Within a few months, the whole
landscape is alive once more.

In fact, all these plants
need fire to survive.

And as competitors return...

...the fire lily fades.

It now returns underground,

and will rest there as a bulb
until another fire awakens it.

By the time the long, hot days
of summer arrive,

wildflower meadows
are bursting with life.

But autumn is not far away.

So now, pollinated plants must
use their remaining energy

to produce the next generation.

Seeds.

A dandelion clock contains
around 200 seeds...

...each with its own
tiny parachute.

Few seeds can
fly as far as these.

Some are known to have
travelled over 60 miles.

But to travel any distance
at all,

they need the wind
to be just right.

However, before
they can get away,

there is a risk.

Voracious hunters
live in this meadow.

Tiny harvest mice.

They love dandelion seeds.

But they don't like to share.

Finally, the sun warms
the ground

and a gentle breeze blows in,

creating an ideal updraught.

Air flowing
between the bristles

creates a vortex
that lifts the seeds up.

Heading off
on the gentle breeze,

this seed now starts
its travels.

Plants use a variety
of different techniques

to spread their seeds as far
as possible from themselves,

and one of the most
remarkable is this one.

It's called ecballium, and it's
a relative of the cucumber.

For several weeks now,

pressure has been building up
inside the pods,

until now they're as taut

as a well-pumped-up
bicycle tyre.

All they need
is just a slight nudge.

The further the plant can
fire its seeds,

the better.

If a seedling germinates
close to its parent,

the two will have to compete
for nutrients and light.

This Himalayan balsam

has seed pods that react
rather differently -

like catapults.

As they dry out,
they begin to strain

along precisely positioned
lines of weakness.

And then just the slightest
disturbance,

even a single raindrop,

is enough to trigger
the mechanism.

The east coast of South Africa.

Summer here
brings scorching temperatures.

This ceratocaryum has to
get its seeds underground

before it gets too hot.

And it has acquired
somewhat unlikely allies.

Dung beetles.

They have a particular fondness
for antelope droppings.

At this time of the year,
these beetles bury the dung

and lay their eggs on it.

And the fresher...

...the better.

Ceratocaryum's spindly stems...

...send their seeds flying.

They're the same size, shape,

and even smell remarkably like
antelope dung.

The beetles
simply can't resist them.

Dung beetles always bury
dung balls at the same depth,

and it's one which suits
the seeds very well.

So effective
is the seeds' deception

that the beetles come back
for more time and time again.

Most of the ceratocaryum's
seeds get safely buried...

...exactly where they
need to be.

As the sun begins to retreat,
so autumn arrives.

The cooler, shorter days
are the cue

for many seasonal forests

to prepare
for the winter shutdown.

The trees start to
divert their nutrients

back into their roots.

And there, other organisms
await them.

Fungi.

Mushrooms are
the familiar face of fungi.

But they are merely
the fruiting bodies.

Some of them only last
for a few days.

They are, however,
evidence of the giant organism

that lies in the soil beneath.

Just a single handful of soil

may contain
several thousand metres

of their microscopic filaments.

It's only recently
that we have discovered

the extraordinary role
that these fungi play

in a forest like this.

Their filaments plug into
the tips of the tree's roots,

and nutrients pass
between tree and fungus

throughout the year.

Some fungi have the ability

to link with
not just a single tree,

but with a whole group
of trees,

so that the entire forest

may be linked together
by these microscopic threads

to form what you might call
a wood wide web.

Hundreds of trees can be
interconnected by these webs.

Scientists call it
the mycorrhizal network.

And it might look
something like this.

They've discovered that trees

not only send nutrients
along it,

but chemical
and electrical signals,

allowing them to communicate
with one another.

But some trees
can also be selfish,

and steal from their rivals...

...or even wage war,

by sending out toxins
that will harm competitors.

It seems, however,
that most trees

do try to help each other.

They raise the alarm
when attacked by leaf-eaters,

leaving other trees time to
produce defensive chemicals.

Those that are dying

may send their food reserves
to their neighbours.

And some individuals,
known as mother trees,

recognise
their own offspring...

...and will channel resources
to them...

...so giving their young

the best possible
start in life.

As the harshness of winter
approaches...

...temperate woodlands
from Russia

to Canada...

...are now in a race
to shut down.

The green pigment in the leaves
starts to break down,

and nutrients are withdrawn
into the branches.

The chemical substances
that are left behind

then create one of the most
spectacular displays of colour

in the whole of nature.

The first freezing nights
of winter

bring with them a killer.

Frost.

Stems, when frozen, rupture...

...and flowers of ice form
in the chilly air.

For some,
winter brings dormancy.

For others, it brings death.

Another cycle of the seasons
comes to an end.

Plants all across
the seasonal world

have developed many different
strategies for success,

but they all depend on
the seasons changing reliably

year after year.

It doesn't matter whether
you live for 3,000 years

or just a few months,

everything depends on you
getting the timing just right.

But in our changing world,

this is becoming a greater
challenge every year...

...and even the most hardy
and resilient of plants

are starting to struggle.

These sequoia trees are the
giants of the natural world.

The largest living things
on the planet.

They can grow
to almost 100 metres tall

and 11 metres across.

Their bark alone can be
over a half a metre thick.

They're also
among the oldest,

some living to
over 3,000 years.

And to achieve such age
and size,

they need very particular
living conditions,

such as a farm here

in the Sierra Nevada mountains
of California.

Not only do they need energy
from the sun, but, critically,

they also require up to
4,000 litres of water a day,

so they are
almost entirely reliant

on the seasonal snowmelt.

But recent years have brought
longer, hotter summers,

and their source of water

is becoming increasingly
unreliable.

Scientists are discovering that

even these seemingly
indestructible giants

are now starting to show
signs of vulnerability.

Some are shedding their needles
and branches

as a way of conserving
precious water.

But for others, climate change
has already been fatal.

10% of them have been lost
in just the last few years.

A single giant sequoia
in its lifetime

can produce 100 million seeds.

These in my hand,
from one cone,

are more than enough to start
a completely new forest.

But they can only do
such a thing

in a world where the seasons
change with some reliability.

Today, our climate is changing,

bringing an unprecedented level
of unpredictability

all across the seasonal world.

The question is, can we curb
climate change sufficiently

to ensure that the seasons
will continue?

Only if we can do that

will the future
of seasonal plants,

including these magnificent
trees, be assured.

During
filming The Green Planet,

it wasn't only the plants

that struggled to get
their timing right.

The increasing unpredictability
of the seasons made it

frustratingly difficult
for the crew

to be in the right place
at the right time.

Whether at the height
of summer...

We are in the middle
of a biblical rainstorm.

...or a quiet autumnal
afternoon...

This is crazy!
Hurricanes are no joke.

...they were always
kept on their toes.

That's really scary!

Ooh!

Sometimes very numb ones.

It's been the most snow
they've had for 38 years.

And I think this is now
our fifth filming trip

in a row where the seasons
haven't done

what they're predictably
meant to do every year.

And these challenges continue

in attempting to find and film
an elusive plant

with a remarkable
survival strategy -

the fire lily.

Somewhere out there is a tiny,
tiny red plant...

...in all of that.

Travelling to South Africa
at the height of summer...

...the crew witnessed
many extraordinary flowers

bursting into bloom.

But if they are to see
a fire lily, they need a fire.

None of the team
have filmed wildfire before -

not something
to be underestimated.

In most cases with wildfires,

when they go wrong,
they go wrong radically.

And it's very unforgiving.

If you get caught
on the wrong side of a fire

because you want to get
that special shot,

there's a possibility
you can get killed,

that's really
what it comes down to.

And after some understandably
studious note-taking...

...it's time to put
their training to the test.

The fire's just
racing up a gully behind me.

The heat is intense.

You can't even stand to be,

like, five metres from it.
It's insane.

This is what any fire lilies
here should be waiting for.

Jeepers.

But fynbos wildfires
are starting to become

fiercer than in the past...

...something Fire Chief Reinard
Geldenhuys knows first-hand.

Nowadays,

we're experiencing more extreme
temperature conditions

and more extreme
wind conditions,

which exacerbates
a fynbos fire.

A fynbos fire in full tilt
with a strong wind behind it

is an animal
that's just running wild.

It's a very frightening sight

if you're standing
in front of it.

Guided by the experience
of the fire crew,

the team are able to
safely capture

the full fury of the blaze.

It's given me a complete,
new appreciation for fire,

how intensely it burns

and how quickly it roars
through this environment.

And the fact that any plants
can survive afterwards

is just...yeah, it's crazy.

As destructive as it seems,

the fire has been part of
this ecosystem for millennia.

Fires should refresh
and regenerate the landscape.

Worryingly, however,
this fine balance

between plant and fire
is beginning to shift.

More extreme wildfires
may spell disaster.

If you disturb the soil
in a fynbos system,

you're going to lose
a lot of species.

Bigger, hotter fires
can burn the soil layer

and burn out all the seeds.

And for the species that have

these really intricate
strategies, like the fire lily,

it really is a difficult game.

Every year is getting hotter
and potentially drier,

so it's kind of becoming
Russian roulette

for a lot of the species here.

In the fire's aftermath,

the crew must now try to find
a tiny flower.

But have any survived
the blaze?

It just looks completely dead.

The whole valley.

There's nothing for it
but to get their hands dirty.

Searching in the ash
is a grubby business.

I feel...

...disgusting.

After scouring this
mountainside just days

after it burned,

they finally find the first
signs of regeneration.

Wow.
That's what it's all about!

That's the fire lily.

It's like a proper bright red
against all the black.

I mean, that's amazing.

There's another one over there,

and there's another one
behind those.

This place hasn't burned
for 15 years,

so they've been sat underground
waiting for this precise moment

for that entire time,
and then within two weeks,

they're up and they're
flowering. It's incredible.

This time, the fire lilies here
succeeded in flowering,

but in the 15 years
since they last bloomed,

the Earth has experienced ten
of the warmest years on record.

You know, there's huge debates
about climate change,

how real is it really,
and so on.

Erm...

We experience it in the fire.

It's more intense, it burns
easier, it burns longer.

In the past, we used to have
one big fire per season,

and we said,
"Yo, that was a big one."

Now we have five to six
big ones per season.

If we don't change our ways,
we are going to reach a point

where fires are burning
with such ferocity

that it will destroy
the landscape.

And in recent times,
a rapidly changing climate

has led to some of the biggest
fires in living memory,

not just in South Africa,
but around the world.

The next five to ten years
are going to be pretty scary

to actually see what this
has done to the ecosystem.

Let's hope that the next time
this fire lily blooms,

it'll find a world
in which it can still survive.