All language subtitles for E04 - Desert Worlds_Track7

The Taklamakan Desert

in northern China.

A constantly shifting
landscape of sand...

...temperatures that swing
from minus 20...

...to more than
40 degrees centigrade...

...and most critically,

almost entirely without rain.

Yet, here on the dunes...

...a Euphrates poplar tree.

And it's not alone.

Some of these trees have
lived here for 1,000 years.

They have exceptionally
long roots

with which to collect water.

And what is more,

those roots are connected to
neighbouring trees

so that if one strikes water...

...others can share it.

In every desert
across the planet,

plants have found ways to
not only survive...

...but flourish.

This is the Gran Desierto of
Mexico and the United States.

These dunes may appear to be
totally barren.

In fact, they are full of life.

In the sands beneath my feet,

there are seeds
of many different kinds.

In fact, you could say that
the dune itself

is one great seed bank,

and when it rains,

it bursts into life.

But rain may come
only once a decade,

and even then, the long-awaited
storm may be very brief.

So seeds must respond
immediately.

This is sand verbena.

It can grow from a seed to a
sweetly scented flowering plant

in just a few weeks.

Primroses and many other plants

soon join the race to flower
before the sand dries.

Desert blooms like this,
however, are rare.

This is the first year
for 20 years.

The combination of vibrant
colour and powerful scent

attracts migrating pollinators,

such as these painted lady
butterflies,

which fly into the middle
of what were only recently

barren dunes.

Everything is rushing
to complete their lives

before the moisture has gone.

Such spectacular blooms

transform deserts
all around the world...

...from the Atacama
in South America...

...to the dusty plains
of Southern Africa.

Rain in deserts, however,
never lasts long,

and all too soon, the flowers
wither and die.

But not before they've produced
the next generation...

...the seeds that will now wait
in the sand for the next rains.

In the Sonoran Desert
of North America,

the huge saguaro cacti

have a different strategy.

They store water in quantity...

...and can live to a great age.

But in their early years,

they are extremely vulnerable.

This little saguaro cactus
is about ten years old.

When they're really small
and growing out in the open,

there's a real chance that
they may shrivel up and die.

But this one has been lucky.

It's been growing in the shade
of this mesquite tree,

and it's got a very good chance
of surviving to maturity.

The young saguaro is protected
by the mesquite's branches.

They halve the amount of
scorching sunlight

reaching the cactus...

...and so keep it cool.

And the mesquite's
extremely long roots

draw up water,

bringing it within reach
of the young saguaro.

So the mesquite is known as
a "nurse plant",

and a very effective one it is,
too.

In fact,
this particular mesquite

has already nurtured seven
young saguaros

over the past 30 years.

As a young cactus grows,

it needs the protection
of its nurse plant

not only from the heat,

but from the other hazards
of desert life.

Temperatures can drop to
minus 10 degrees overnight...

...and very occasionally,

it even snows.

If the water stored inside
a young cactus should freeze,

the cactus will die.

But the nurse plant traps

a blanket of slightly warmer
air around it,

just enough to keep it alive.

Eventually, saguaros outgrow
their nurses,

but by that time,
they are robust enough

to face the elements
by themselves.

No matter how old
a desert plant is,

water is always precious,

whether gathered from
melting snow...

...or a shower of rain.

So cacti have developed
extraordinary adaptations

that enable them
to not only collect water...

...but to retain it.

Instead of leaves, which would
lose precious moisture

through evaporation,

they have spines.

Each spine has a tiny pad
at its base

where the water is absorbed...

...and then stored in
the great swollen trunk.

A large saguaro can hold
5,000 litres of water...

...and is able to do so

because it has another
special adaptation.

The ridges on its surface

are like the pleats
on an accordion.

They allow the saguaro
to change its shape.

After rain has fallen,

the pleats expand,

and the saguaro
fills up its water tank.

In the dry times,
it uses its water

to grow, produce flowers,

and, eventually, seeds.

Fully loaded with thousands
of litres of water,

this saguaro won't need
to drink a single drop

for another year.

But such valuable stores
of water attract thieves.

Now the spines' function
changes from collecting...

...to guarding.

The spines of some species
are a quarter of a metre long.

Others are needle-like barbs

that grow in clusters,

and easily break off
in the skin of any animal

that touches them.

But perhaps
the most vicious cacti

belong to a group called
the chollas.

This is called
a teddy bear cholla

because of the thick coating
of spines on it.

But don't be deceived by
the name.

There is nothing cuddly about
this particular teddy bear.

In fact, it's the most
dangerous plant in the desert,

and I wouldn't dream of putting
my hand anywhere near it

without proper protection.

Brush against it...

...this can happen. Ow!

This can happen.
Even with this glove on,

one of them has just
gone through, I can feel it.

It's quite painful.

Look closely at the spine

and you can see very clearly
why they're so dangerous.

Each is like
a splinter of glass,

sharp enough to pierce flesh.

And they're covered
with backward-pointing barbs.

So getting them out,
even with a pair of pliers,

is quite hard.

This is not pleasant at all.

They won't come off without...

Oh, look at that.

It's hard to imagine a more
aggressive defence than this.

And it makes both the plant
and its buds

virtually invulnerable.

Most animals
know to keep clear.

Cholla buds
grow like tiny barrels

from the top of the adult plant
and then drop off.

If the young cholla
put down roots here,

it would compete
with its parent for water.

Night falls...

...and this one is on the move.

A pack rat.

She knows how to
deal with a cholla.

She avoids the spines
by gripping it

at the place where it broke off
from its parent.

And she works fast.

There are pack rat hunters
here.

She uses the cholla to build
a spiny wall around her nest.

The flesh of the cholla
supplies her with water...

...and the severed spines
further reinforce the defences.

This cholla bud...

...might be next.

But one accidental nudge...

...and it escapes.

The bud starts
to put down roots...

...so the cholla,
thanks to the pack rats,

finds new territory...

...and sets about claiming it.

Few plants deal with
the problems of desert living

better than cacti.

There are almost 2,000
different species of them.

They're spread across the
deserts of the American West,

from Arizona all the way
to Mexico and beyond.

In South America,

the Andes catch virtually all
the rain-carrying clouds

that blow in
from the Pacific...

...and that has created
to the east of them

the world's driest desert -

the Atacama.

In the desert world,

water thieves
can come in many forms,

to exploit even the smallest
chink in a plant's defence.

One of the strangest
travels within the gut

of a fruit-eating mockingbird.

These are the seeds...

...of tristerix,

a kind of mistletoe.

Their goal is the water
inside this hedgehog cactus.

Using the spines as anchors,

the seeds start to germinate.

Each produces a long probe

with which to try and locate
the cactus's skin.

For most, that's a stretch
too far

and they perish.

But for this one,

the cactus's surface
is within reach.

It clamps onto it with
a special sucker...

...and then waits for darkness.

At night, the cactus
opens its pores

in order to respire.

Oxygen goes out,

carbon dioxide goes in.

And so does tristerix.

Once within,

its tissues spread throughout
the body of the cactus,

sustained by the precious store
of water that they find there.

Then, a year later,

it breaks through
the cactus's skin...

...and bursts into flower.

Hummingbirds come to drink
their nectar

and pollinate them
as they do so.

And then,
to complete the cycle,

tristerix produces hundreds of
white eye-catching seeds,

ready to be carried away
by a bird

to invade another cactus.

The Karoo Desert
in Southern Africa.

And although it may look bare,

its rocky ground contains
an unrivalled variety of plants

that, one way or another,
store water in their tissues.

They belong to
many different families,

but as a group,
they're known as succulents.

Some are small and low

and barely distinguishable from
their surroundings.

These look like little pebbles.

They resemble them so closely

that animals which might be
only too glad

to steal their water
just pass them by.

When rain does fall,
they absorb it

and quickly expand.

But even this doesn't spoil
their disguise.

They just look like
larger pebbles.

Nor are they green.

The cells on their top surface
are transparent

and allow sunlight
to pass through.

Deep within, and out of sight,

are the green cells
where photosynthesis occurs -

the process
which uses this light

to make food for the plant.

When the time comes
to reproduce, however,

the stone plant
abandons its disguise.

And now it blooms.

The flowers open and close
every 24 hours.

So, for a few dangerous days,

the plant advertises
for pollinators,

before returning to life
as a pebble.

Some desert plants have
developed a very different way

of attracting pollinators.

This is stapelia.

It produces what is perhaps the
desert's strangest disguise.

It uses water
stored in its stems

to grow buds
the size of tennis balls.

The flower, once opened,

is called a desert starfish.

Instead of releasing millions
of loose pollen grains,

as most flowers do,

the desert starfish produces
them packed in five tiny sacs.

But if its strategy
is successful,

just one of them will produce
hundreds of seeds.

And this depends on deception.

The flower
appears to have hair...

...wrinkly skin...

...and it produces a stench

like the carcass
of a dead animal.

And when a carrion fly
investigates...

...the flower clamps a tiny sac
of pollen to its proboscis.

It's not easy to feed with
such encumbered mouth parts.

But try as it might,
the fly can't get rid of it.

And it's still there
when the fly leaves

to try and feed from
another bogus cactus.

This time, however, when its
clamped-up proboscis

slots into the flower,
the pollen sac is released.

With pollination complete,

the fly is no longer needed.

And just as well!

Some deserts can be so dry

that plants must find
techniques of surviving

for long periods without
any water whatsoever.

One of them is to grow
extremely slowly,

and few plants grow more slowly
than this one -

the creosote bush.

It is inactive
for most of its life

and only wakes up and grows
for a brief period...

...if and when
there is a fall of rain.

I've seen evidence
of this grow-slow strategy

for myself.

40 years ago,

I came here to California's
Mojave Desert

to visit one particular plant.

An individual creosote bush

tends to spread not by
setting seeds

and producing a new generation,

but by sending out new stems
around its base.

This plant started growing

between 10,000 and 12,000
years ago.

That was in 1982.

Since then, careful measurement
has shown

that it has increased its size
by less than one inch.

Its ability to endure
is truly extraordinary.

So efficient is creosote

at collecting what little rain
falls here

that few other plants can
compete with it.

As a result,
over the last 12,000 years,

it's come to completely
dominate this landscape.

The Chihuahuan Desert
in north Mexico.

Here, one particular plant

plays the waiting game so well

that it spends much of its life
looking dead

and certainly not worth eating.

And it can survive like this
for a decade.

This is the resurrection plant.

It's a kind of moss.

It barely has roots

and it certainly can't store
much water.

But it can travel.

After a particularly long
drought...

...it breaks away
from its roots...

...and becomes...

...a tumbleweed.

Blowing across the desert,
it can travel a mile in a week.

With luck, it may find water.

Just a shower of rain
can bring it back to life.

As its fronds soak up
the water, they unfurl.

In its protected centre,
it still has green cells,

which absorb both the water
and sunlight,

and rapidly produce the food
it needs to resume its growth.

It will grow for just as long
as there is moisture.

But when that disappears...

...it closes up once more

and resumes its travels.

Here in the canyon lands
of Utah

lives a plant
that has developed

a finely balanced relationship

with the animals with which
it shares this dramatic desert.

Rain does occasionally
fall here

and turns dust into mud.

But that doesn't last long.

A brief window of opportunity
opens.

Seeds that have been
buried for years

may now be exposed to light...

...and come to life.

This is coyote tobacco.

In just a few weeks,
it grows a metre tall

and produces dozens of flowers.

The night air becomes heavy
with their fragrance.

Soon, they attract hawk moths,

which sip their nectar,

and in doing so,
pollinate them.

But the moths also
lay their eggs on them.

Soon, their caterpillars
have hatched

and are munching the leaves.

Their nibbles expose
the plant's sap

to the drying air.

But the tobacco plant
has a defence.

The leaves under attack
produce nicotine.

This chemical
sedates the caterpillars

and slows them down.

And what is more, it makes them
give off a particular scent...

...one that summons others
to come to the plant's aid.

Big-eyed bugs -

miniature assassins
only 2 mm long.

And whiptail lizards.

Big or small, they make
a meal of the caterpillars.

It's certainly effective.

But there's more to this
strategy than meets the eye.

When the leaf
of a tobacco plant

is attacked by a caterpillar,

all the rest of the leaves
prepare to defend themselves.

But how does this leaf
know that

that leaf there
is under attack?

Well, scientists here
in the United States

have specially genetically
modified these tobacco plants

so that under special
lighting conditions,

this microscope can show us
exactly what is going on.

I'm going to attack
one of the leaves of this plant

with these tweezers,
which, to the plant,

will seem as if it's being
nibbled by a caterpillar.

Signals are being transmitted
along the veins

that link the leaf
to the rest of the plant.

It's rather like a very simple
nervous system.

From that initial injury,
the whole of this little plant

is aware that something
had happened.

This signal warns each leaf
of the danger...

...so that it is ready
to produce nicotine

the moment it's attacked.

With this defence at the ready,
the tobacco plant

can continue to grow until,
eventually, it produces seeds.

It's particularly important
in deserts

for seeds to be distributed
as widely as possible

so that some will have a chance
of reaching moisture.

And deserts have an excellent
agent to help them do that.

The wind.

Many seeds have adaptations
to help them exploit it.

They have shells to protect
the seeds within

from abrasion...

...or wings to help them
catch the air.

As the temperature rises
throughout the day,

desert winds
increase in strength.

Here in Arizona,
the land is regularly swept by

what is known as a haboob.

It's a giant sandstorm,

but also, in effect,
a seed storm.

Countless millions of them
are swept up into the air.

Some seeds can travel

thousands of miles
on the wind...

...so that plants
may eventually reach

even the most isolated desert.

Some have landed on an island

in the middle of the world's
largest salt flat, in Bolivia.

In the Galapagos,

they sprout on fields
of recently erupted lava.

They've even reached

one of the most inhospitable
of all sites -

the tiny island
of San Pedro Mártir,

a scorched, lonely rock
off the coast of Mexico.

This is the home
of the giant cardon,

a species of huge cactus that
can weigh up to 12 tonnes.

They're able to thrive here

because of an extraordinary
partnership...

...with brown
and blue-footed boobies.

The cardons here
can become so broad

that they provide cooling shade
for nesting birds.

As the booby chicks get older,
they repay the cardons...

...with their droppings.

Guano.

The digested remains
of vast shoals of fish.

This guano is of such strength
and quantity

that most plants
would be poisoned by it.

These cardons, however, have
evolved the ability to tolerate

the toxins in the guano
and digest the nutrients.

As a result, the cacti
now grow in a dense forest

over a million strong.

But such relationships
are very finely balanced

and can only too easily
tip into catastrophe...

...as is now happening
in northern Zimbabwe.

For six months of the year,

the savannah here is kept
lush and green by daily rains.

But when the rainy season
is over,

it becomes
as dry as any desert.

So to survive here, trees
must be able to tolerate

both conditions.

And these giants
are adapted to do just that.

They are baobabs.

This one might be
over a thousand years old.

It's survived here
in part thanks to

its ability to store
thousands of litres of water

within the spongy wood
of its trunk.

But its battered surface

is evidence of a very finely
balanced relationship.

These huge trees are a focus
for animals of all kinds.

And they're particularly
important for elephants.

In the wet season,
they eat the baobabs' fruit

and disperse the seeds
in their dung.

Now, as the dry season
begins...

...they migrate
to distant watering holes.

The baobabs
have damp inner wood...

...and the elephants use it

to quench their thirst
on the journey.

This relationship can only work
because baobabs

have a remarkable ability
to heal themselves.

Between each damaging attack,

they expand their spongy wood
and grow new skin.

And they've done this
time and time again,

over centuries.

Today, however, it's harder
for the baobabs to recover,

as dry seasons
become longer and drier

due to climate change.

Not only that,
but the elephants are forced

to take ever more wood from
the trees in order to survive.

In some parts of Africa,
many of the largest

and oldest baobabs
have fallen in the last decade.

The loss of a vital species
like the baobab

strikes a blow
at all life in the desert.

In these hostile lands, few
living organisms can survive

without help from others.

You can find an extraordinary
illustration of this

in Arizona's saguaro country.

If you wander off
the beaten track here,

you may be lucky enough
to find one of these.

It might look like an old boot,

but in fact,
it's part of a saguaro cactus.

Almost every saguaro has one.

There's one up there.

It has been produced,
indirectly, by woodpeckers,

which regularly dig homes
for themselves

in the bloated trunks
of the saguaros.

In the next six months,

the cactus heals the wound,

and so creates a safe, cool
and watertight nest hole.

It's tough lining
will persist for years,

even after the cactus itself
has died and rotted away.

A single saguaro may hold

several of these
extraordinary homes.

So over its lifetime,

it may provide accommodation

for some 3,000 chicks
of several different species.

But in the long term,
the saguaro benefits,

as their lodgers repay
the cactus

by pollinating its flowers...

...and dispersing its seeds.

It's relationships like these
that enable life to flourish

in some of the world's harshest
landscapes.

Over millions of years,

plants have become
superbly adapted

to hostile desert conditions.

But it's a very finely balanced
existence,

and one that makes them
uniquely vulnerable.

However, our growing
understanding

of the complex ways by which
desert animals and plants

rely on one another
is now helping us to understand

how best we can protect them.

90 years ago, a photograph
was taken from this very spot

that shows a population
of saguaro cactus

that was very different
from what it is today.

In the last 50 years,

the population of saguaros here
has greatly diminished -

not because of a direct assault
on the cactus,

but because many of
the shade-giving nurse trees

were harvested for firewood,

leaving young saguaro
to die in the sun.

Now that this relationship
is understood

and the nurse trees
are protected,

there are already signs

that the saguaro
are recovering.

Wherever there's a desert,

plants have evolved
to meet its challenge.

But everywhere,
they need our help.

As we understand
more about them

and their intimate
and complex relationships...

...we will be better able to
protect them,

and all life,
in these beautiful

but increasingly fragile
worlds.

The most remote shoot
for the Deserts team

is to the island
of San Pedro Mártir

in the Sea of Cortez, Mexico.

They are to film
the giant cacti

that have found a unique way
to thrive here.

It takes 48 hours to travel
the 260 miles...

...over unpleasantly choppy
seas.

It's not made some of us
feel very well.

I think one of us
is quite seasick.

There is nothing
but big blue out there,

and the island is somewhere
in that direction.

Can't see it yet.

As they draw close
to the island,

there's a spectacular reminder

of how rich life in the sea
is here.

Oh, look in front of us,
look at that for a pod!

Oh, they're everywhere.

Show us the way!

Meeting them here is
desert scientist Ben Wilder.

It's through his research
that the team first heard about

the island's peculiar
residents.

I'll never forget
the first time I came to

actually exactly where
we're standing right now.

It was April of 2006,
and saw this view,

and it both settled in my heart
and captivated my mind.

And so that started a process
of trying to understand,

you know,
what can produce this?

The secret is in the
relationship between the cactus

and a type of seabird
called a booby.

All the boobies
that we need to film

are right up there
at the top of the island,

so it's going to be
a bit of a scramble.

The crew soon discover how
harsh the conditions are here.

I'm pretty tired.
It's pretty hot.

But it's a great view.

There's very few places on
Earth where you're going to see

this many cactus. I mean,
it's absolutely amazing.

I would say this is
the only place

- you're going to see this.
- Well, there you go, then.

Ben's research is uncovering
the ingenious ways

the cacti have adapted
to the conditions here.

The waters just offshore here
are some of the most productive

marine waters in the world,

and so it's kind of an ideal
habitat for seabirds to roost.

But when they do so,
they deposit tonnes of guano,

and so those nutrients,

really high in nitrogen
and phosphorus,

actually are toxic
to most plant species.

The cardons thrive because
they're uniquely able

to process the guano

and extract what they need
to fuel their growth.

One of the first shots
the crew need to get

is of the boobies
nesting under the cacti.

The lack of predators

means the birds aren't afraid
of people.

It should make filming them
up close a bit easier.

That's the theory.

So we've positioned this
camera here to try and get

a good perspective on the chick
on the nest.

It's taken quite a liking
to our camera.

Let's hope he doesn't break it.

Bull's-eye.

It's pooed right on the front
of the lens.

It's kind of a shot we need,
but, unfortunately,

my camera wasn't rolling
at the time it did it,

so now I've just got
a dirty lens.

After a thorough lens clean,

Oli eventually gets the shots

to reveal the extraordinary
relationship

between bird and plant.

But it's not just the bird
guano that influence

how the cardons grow.

They're way shorter,
they're dwarfed here.

Throughout the rest
of their range

they usually get upwards
of 50, 60 feet.

But here, on average,
they're 20, 24 feet in height.

They stop growing up
and they grow out.

Ben's research suggests
that they go wide here

as an adaptation
to the violent winds.

Too tall, and they'd blow over.

A gusting wind isn't helping
the drone crew, either.

We really need it
to calm down a bit,

otherwise it's going to
be impossible.

On the Sonoran mainland,
where the cardon is also found,

you have on average between
50 to 150 plants per hectare.

Here, on this island, you have
over 2,500 plants per hectare.

A lull in the wind, and the
team get a chance to reveal

the remarkably density
of the cacti -

almost 20 times greater
than anywhere else.

It appears that, here,
they're doing very well.

But even this island

isn't isolated from the effects
of a changing planet.

Every cactus you see there,

its body is filled with
nutrients from the sea.

Given that we know
that the cardons

are linked to the ocean,
what happens in the oceans

affects what happens
to the cardon.

So a concern we have right now

is that there's
a lot of overfishing,

and we know there are
less seabirds here

than there were 20 years ago,

and we have reason
to believe that

that will ripple and affect

the nutrients that fuel
the cardons as well.

This finely balanced
relationship is at risk,

and knowing that
makes leaving the island

particularly thought-provoking
for the crew.

The cardons look beautiful.
I've never seen

so many cactus in my life.
It's absolutely amazing.

I'm just hoping that
when we leave this place,

it stays as it is,

and things don't affect it
that are negative.

It's an absolutely wonderful
thing, and...

Yeah, and I don't want to go.
I want to stay.

This remote cactus forest
is a reminder

of the adaptability of plants,

that enables them
to establish green worlds

almost anywhere on Earth.