[narrator] Just 50 years ago,
we finally ventured to the moon.
For the very first time, we looked back at our own planet.
Since then, the human population has more than doubled.
This series will celebrate the natural wonders that remain
and reveal what we must preserve
to ensure people and nature thrive.
Forests.
Over half of all the world's trees, evergreen and deciduous,
stand in these great assemblies.
[birds chirping]
[narrator] For many of us, they are places of mystery and darkness.
They are key to our climate, and home to countless unique species.
In the past, we have destroyed them without hesitation.
Yet, forests do have an astonishing ability to recover.
This is the southern edge of the boreal forest,
the forest that dominates the far north.
It stretches eastwards across Russia for thousands of kilometers,
and now, in the middle of winter, it's largely silent,
seemingly empty of animals of any kind.
But this is the home of an animal so rare it's almost mythical.
A Siberian tiger.
There are less than 600 of them.
[caws]
[tiger growls]
[narrator] These are the most intimate pictures of them in the wild yet taken.
A male Siberian tiger patrols a territory of almost 2,000 square kilometers,
and it has to do so if it is to find enough prey
to keep itself alive during the long winter.
This is an impoverished land where food of any kind is scarce.
A pine cone.
Pine nuts provide vital energy during the winter months.
Wild boar depend on these nuts.
For them, it has to be grab and go,
for they themselves are food for a tiger.
[squeals]
[narrator] This game of hide-and-seek is played out over vast areas of forest,
as all the animals search for the life-giving stands of pine.
Poaching has taken the Siberian tiger to the brink of extinction,
but, since the 1980s, their numbers have slowly increased.
These rare glimpses reveal
that their future still depends on having vast areas of forest in which to hunt.
The boreal forest extends from Russia in the east,
across Europe, to North America.
It contains 750 billion trees,
and it stores over 40 percent of the world's carbon,
making it a vital element in the fight against climate change.
During the winter, the days are so short and the temperature so low,
that growth is at a standstill.
This far north, the forest can support very few animals
compared to the rain forests of the tropics.
Many are dependent on the supplement to be found in its rivers.
[birds caw]
[narrator] In western Alaska, both in spring and, as now, in autumn,
salmon, having left the ocean,
swim up rivers to reach their ancestral spawning grounds.
Their journey from the sea into the forest represents
the greatest transfer of nutrients from one habitat to another
anywhere on Earth.
The fish are crucial seasonal food
for all the predators that live in this forest.
Bald eagles live here the year round and nest close to the river.
[piercing chirp]
[narrator] Young eagles, still without white heads,
spend their first years searching for food in the forest.
But, like this four-year-old female,
they're now big enough to try and claim a place on the river.
At first, all she can get are the scraps left by others.
And she can't get even these without a fight.
[eagles chittering]
[narrator] She will have to look elsewhere.
The boreal forest may be vast,
but the places where the salmon spawn are known to all the predators.
As the rivers begin to freeze over, competition becomes even more intense.
This youngster is lucky, but her success is noticed immediately.
[chittering]
[narrator] She does have one advantage.
Females, even when young, are larger than the males.
And here, size matters.
[cawing]
[narrator] As winter advances,
young and old have to meet the challenge of the intense cold.
If she can survive, she will have gained a place
in one of the greatest and harshest forests on Earth.
A little further south
stand the last of the great redwood forests.
Not so long ago, these great trees grew throughout the Pacific Northwest.
Now, only five percent of them remain.
Here, conditions are less harsh.
Winds bring in warm, humid air from the Pacific Ocean,
so the trees are able to grow the year round.
Hidden in the vegetation of the moist forest floor
is a richly populated underworld.
A male rough-skinned newt.
Every spring, he is driven by a mysterious urge
to return to the pool where he hatched as a tadpole.
And he needs to get there quickly.
Because there are lots of others like him...
with exactly the same idea.
They're all searching for a female,
but trekking across hundreds of meters of old-growth forest is not easy.
There is strong competition.
And the female is anxious to get going.
Once paired, he hangs on,
for she may take several hours to discharge all her eggs.
Other males are only too eager to displace him if they can.
Competition is so vigorous
that the females in the center of these writhing balls
have been known to drown for lack of air.
But her first partner maintains his grip.
Within weeks, their tadpoles will hatch.
And none too soon, for the forest is about to change dramatically.
By the end of the summer, the sun has baked the forest so intensely
that they are as dry as tinder.
Strong winds drive the flames,
and temperatures rise to 700 degrees Celsius.
Its aftermath is seemingly total destruction.
The wind, scouring the newly exposed forest floor,
kicks up dust devils of ash.
The ground appears to be devoid of life.
But the forest is far from dead.
Within only a few months,
flowers and tree seedlings will rise from the soil.
Many, in fact, would not have germinated had they not received a baptism of fire.
[birds chirping]
[narrator] Light streaming down through the newly opened canopy
provides the energy for a surge of new growth.
The older, well-established redwoods have survived,
protected by their thick, fire-resistant bark.
This natural resilience is essential to the continued health of these forests.
Most forests, however, cannot recover on their own.
Many are helped to recover by animals.
The trees and their inhabitants are interdependent.
And nowhere is this dependence more apparent
than in India's Western Ghats.
This globally important habitat
contains a third of all animal species found in India.
[animals whoop and chirp]
[narrator] Lion-tailed macaques.
They feed on the fruits of many kinds of tree,
and, in doing so, they distribute the seeds,
which will emerge unscathed with their droppings.
But few monkeys travel very far.
If plants are to distribute their seeds across great distances,
they need another kind of transport.
Wings.
Great hornbills have wings that are almost two meters across,
and they enable the birds to travel long distances in search of food.
Hornbills feed on the fruit of 40 or so different kinds of trees,
and transport the indigestible seeds they contain
all over the Western Ghats.
So, it's to the trees' advantage to attract the hornbill's attention.
The figs themselves, although they taste nice,
are not, in fact, very nutritious,
so the hornbills have to eat great quantities of them.
It can be tiring work.
But it's not a free-for-all.
A single fig tree in fruit attracts great numbers of hornbills.
Competition between them is intense.
This aerial jousting between males has never been filmed before
and its purpose is not really understood.
It may be that the birds are simply squabbling over food,
but it seems rather more than that.
[squawking]
[narrator] The winner is able to demonstrate his strength and skill
to visiting females.
The males certainly seem keen to ingratiate themselves.
It's particularly important for hornbills to get the best pairing
because, once established, the bond between male and female
will last a lifetime.
The forest also benefits from these squabbles,
because even a defeated hornbill
will spread seeds over wide areas as he searches for his next meal.
The relationship between trees and animals in a forest
is not always so harmonious.
This is Africa's largest forest, the Miombo,
named after one of its common trees.
It stretches for over a thousand miles,
from Angola in the west to Mozambique in the east.
At the height of the dry season,
the Miombo attracts animals from all across southern Africa.
[trumpeting]
[narrator] Elephants prefer grass if they can get it. It's very nutritious.
In its absence,
they browse on the abundant leaves and branches of the Miombo.
[elephants huffing]
[narrator] But they're not the only hungry ones here.
These mopane worms
are not worms, of course, but caterpillars.
They hatch simultaneously in huge numbers.
And just as the forest is putting out new leaves,
they begin their attack.
They feed so voraciously
that in just six weeks they increase their size 40 times.
By the time they're fully developed, this million-strong army
will have stripped the entire forest of its foliage.
But the Miombo bounces back.
With the caterpillars gone,
the trees produce a second growth of leaves.
This fresh feast then attracts elephants.
They are less fussy than the caterpillars.
They will eat every part of the tree.
And a hungry elephant can munch through 200 kilos of vegetation in a day.
Yet, even this destruction has its benefits.
It shapes the forest in a way that helps one of Africa's most endangered animals.
Hunting dogs.
They're seen most frequently, and most easily, on grasslands.
But, in fact, these open forests are their preferred habitat.
[grunts]
[narrator] Browsing elephants open up a forest,
and that attracts the animals on which the dogs prey.
[barks]
[dogs yipping]
[narrator] For the dogs, the Miombo forest is perfect hunting country.
And it's also an excellent place in which to bring up pups.
The pups greet the adults returning from a hunt
with great excitement.
[squealing]
[narrator] Food.
The first three months of the pups' lives are spent sheltering underground.
[soft growling]
[narrator] Now, they are confident enough
to stay out in the open for much of the time.
And then, like all puppies, they have fun.
Playing is important for the youngsters,
for as they do so, they establish the social bonds
that they will need when they start to hunt together as a team.
-[bird squawks] -[squealing]
[narrator] The Miombo has always been important for hunting dogs,
both as a place to find prey and as a refuge.
Never has it been more crucial
for the survival of this endangered species than now.
But they will only survive if other creatures are here
to create the kind of habitat they need.
[elephant lows]
[narrator] Madagascar has a forest
dominated uniquely by one of the oddest of trees.
Baobabs.
The island has been isolated for over 80 million years.
During that immensity of time, its animals and plants
have evolved into forms quite different from any elsewhere.
This makes them one of the most precious forests on our planet.
This is not a monkey, but a distant relative, a lemur,
and there are at least 40 different kinds of lemurs,
all unique to Madagascar and all endangered.
[lemur hoots]
[narrator] Lemurs are crucial to the forest.
Without them, some species of tree cannot survive.
The forest even has its own specialized lemur hunter.
It's Madagascar's top predator,
and its presence is cause for alarm.
It can grow to a length of one and a half meters,
and it's very seldom seen in the wild.
It's a fossa.
For most of the year, fossas are solitary,
but in the breeding season, they assemble in a way that is all their own.
Each mature female takes up residence in a special mating tree.
Half a dozen or so male fossas have gathered in the forest below it,
but she is clearly occupied.
So, one of the males leaves his scent.
A visiting card, just to show that he called.
He will just have to wait around and see whether she takes any notice.
Her present engagement can last all night.
With its top predators distracted, the rest of the forest animals
can go about their normal nightly business undisturbed.
These are immature leaf bugs, a species found only here in Madagascar.
Why they have this extraordinary shape, no one knows.
They feed on tree sap,
absorbing the part they need and excreting the rest as a sweet liquid
sometimes known, perhaps flatteringly, as honeydew.
And honeydew, in turn, provides food for a particular species of small lemur.
The gray mouse lemur is only 15 centimeters long,
one of the smallest primates in the world.
It's very active and needs an energy-packed food.
And while the sugar drops are clearly delicious,
they're not very sustaining.
So, she's not going to let a single drop go to waste.
The male fossas below are still awaiting their turn.
[animal screeches]
[narrator] So, having eaten as much as she can,
she retreats to the safety of her nest hole
to sleep during the daylight hours.
Things are not looking so satisfactory on the ground
around the fossas' mating tree.
[sniffs]
[narrator] The pair above are clearly still engaged.
He will either have to find another mating tree or be very patient.
But he may well fail altogether.
A third of Madagascar's fossas have disappeared in the last 20 years,
a result of the continued destruction of their forests by people.
Since these pictures were recorded,
this forest, and the unique life it once contained,
have disappeared altogether.
Only three percent of Madagascar's dry forest remains.
Worldwide, we have now destroyed
over half of the forests that once flourished on our planet.
Not only are we losing the animals that once lived in them,
we are also changing the climate of the entire globe.
But our planet's forests, if given the chance,
are almost unbelievably resilient.
Perhaps the best proof we have of their ability to recover
can be seen on the site of one of our greatest disasters.
Chernobyl.
In 1986, one of the four reactors at the Chernobyl nuclear plant exploded.
It turned this utopian vision of the future into a ghost town.
Over 100,000 people were immediately evacuated,
never to return.
The fallout zone was declared uninhabitable for the next 20,000 years.
Yet despite the radiation, there has been a remarkable recovery.
Within only a decade,
vegetation began to germinate in the ruined city.
And as the forest reestablished itself, animals began to appear.
At first it was thought that these were rare visitors,
but it soon became clear that the former city
was occupied by an established and thriving wild community.
[chirping]
[narrator] Within only 20 years,
science has recorded populations of animals
similar to that in the wilder parts of Europe.
Roe deer are now a common sight, wandering through the suburbs.
Herds of the endangered Przewalski's horse
now roam freely through the once busy city.
Most surprising of all perhaps,
the top predator of these forests has reappeared.
Wolves.
Hunters like these would only return
if their prey and the surrounding forest is also thriving.
Now, studies have shown
that there are seven times more wolves inside the exclusion zone than outside it.
No unprotected human being
can stay here for long without lethal risk.
But in driving us out,
the radiation has created space for wildlife to return.
The dramatic recolonization of Chernobyl in the space of only 30 years
is proof of forests' extraordinary resilience.
If we choose to give forests time and space,
they could reclothe the earth
with much of the rich and varied communities of animals and plants
of which we have, so recently, robbed it.
A future with more forests is key to the resilience of our planet.
Please visit ourplanet.com
to discover what we need to do now to restore our forests.
♪ I can hear the whole world Singing together ♪
♪ I can hear the whole world Say it's now or never ♪
♪ 'Cause it's not too late If we change our ways ♪
♪ And connect the dots to our problems ♪
♪ I can hear the whole world Say we're in this together ♪
♪ We're in this together ♪