All language subtitles for BBC.The.Green.Planet.3of5.Seasonal.Worlds.1080p.HDTV.x265.AAC.MVGroup.org

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 sap sucker.

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 sap sucker's break-in
hasn't gone unnoticed.

Hummingbirds, squirrels and insects

all invade the sap sucker'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-western 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.

He hammers against the orchid's
pollen sacks.

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.

And 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,

wild flower 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 a 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.

HE LAUGHS

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 seed's deception

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

Most of the Ceratocaryum 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 thing
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 are found 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 the height of summer...

We are in the middle of a biblical
rainstorm.

..or a quiet autumnal afternoon...

MAN: 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,
is that, 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 just...
You can't even stand to be, like,

five metres from it. It's insane.

Whoa!

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.

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 there

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 pop of bright red
against all the black.

I mean, that's amazing.
There's another one over there,

and there's another one behind us.

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, burns easier,
burns longer.

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

and we said,
"Ja, 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 will find a world in which it
can still survive.

Next time on The Green Planet...

..desert worlds.

A landscape of extremes...

..where water equals life.

It only takes a drop.

The Open University has produced
a poster

that explores the vital role
that plants have for our planet.

To order your free copy, call...

..or go to...

..and follow the links to the
Open University.