Our planet is a place of constant change.
Each year, the seasons shift and life is transformed.
But there are places where the changes are so epic in scale
they can be seen from space.
In this series,
we reveal three of the most miraculous transformations.
The islands of Svalbard - within a few weeks,
frozen wastelands burst into life.
The African Okavango -
a desert transforms into a magical waterworld.
And the mysterious forests of New England -
erupting in a blaze of seasonal colour.
Life finds the most ingenious and surprising ways to thrive...
..in the world's fastest-changing landscapes.
New England - home to the most colourful forest in America.
Stretching across six states...
..from Maine in the north to Connecticut in the south.
Every year, millions of people flock here to witness
one of the planet's greatest spectacles,
known here as the fall...
..when billions of trees explode into a riot of red, orange and gold.
There's nowhere else on Earth quite like it.
But despite this beauty, there's a battle raging.
One that holds the secret to this magical forest's most
flamboyant display.
The story of the fall begins
while winter still has a grip on the forest.
17 billion trees, rich with maples and oaks,
wait in suspended animation.
Amongst them,
many of New England's animals are hibernating from the cold.
But America's tallest mammal remains at large.
Moose survive by chewing on twigs.
Their calves will be born in just two months...
..and their survival will depend on the same
chain of events that will fuel the forest's climax of colour.
As the weather warms, water courses through every tree...
..and it picks up sugar stored in the wood.
This liquid energy is the life force of the entire forest.
It's so rich with sugar that maple syrup is made from it.
The spring sunshine warms the land...
..and the sugar surges faster...
..fuelling the growth of nutrient-rich buds.
These tiny packages contain everything needed to build a leaf.
But from this point on, each tree faces a battle.
All across New England, twigs are coming to life.
These creatures spend the winter disguised as twigs.
Looper caterpillars.
They awake with the warmth and immediately begin to seek out
the freshest buds, on a hunt for sugar.
Nearby, hundreds of baby tent caterpillars
hatch from their winter eggs.
Each smaller than a grain of rice. They join the feast.
Swarming along the branches, a torrent of bud destruction.
This is just the first wave in a battle that will escalate
through the year.
The buds race to open before they can be attacked.
Gradually, the first flush of green spreads across the forest.
But it will be a few weeks before the leaves are fully expanded...
..and they will need a constant supply of sugary
sap from under the bark.
In some trees, that sap is also at risk.
The warming spring weather attracts an animal with a serious
sugar addiction.
TAPPING
All the way from Mexico,
he's one of the first to come back after the trees wake.
The yellow-bellied sapsucker.
His beak hammers six times a second...
..wounding the tree deeply...
..and chiselling into the vessels carrying the precious sugar.
His feathery tongue quickly laps up the weeping liquid.
On this tree last year, he dug hundreds of holes,
but now, all the wells are dry.
It's not enough to deter a determined sapsucker.
He can dig as many as 1,000 holes in a season.
And on another tree, he's excavating a nest.
If he finishes it and keeps his wells running sweetly,
he could attract the attention of a female.
But there's another bird that could scupper his plans.
A ruby-throated hummingbird.
He's followed the sapsucker all the way from Mexico.
His wings beat 80 times a second,
putting him on a calorific knife edge.
The weeping sap is the best source of sugar currently available,
and feeding at 15 sips a second, he can quickly drain a well dry.
He's too fast for the sapsucker to chase off...
..so the sapsucker opens more and more wells.
Eventually, despite the interruption,
he finishes off his nest, creating a deep hollow in the tree.
Now, everything is prepared.
Despite relentless attack from birds and insects,
the warming weather keeps the trees pumping sap,
and, as the day length increases, the leaves continue to inflate.
As the leaves grow, they start to shade the forest floor.
In anticipation, the plants down below wake from their stupor.
The flowers must attract a pollinator before all
the light is stolen.
Now, hummingbirds can feed on their favourite source of sugar.
Nectar.
In turn helping to pollinate the flowers.
A looper caterpillar feeds amongst the flowers, too.
He's no longer hiding amongst the twigs.
This master of disguise has a different trick up his sleeve.
Swaying back and forth, he mimics a flower moving in the breeze.
He sticks petals to his back so that he can feed unnoticed by predators.
And there's a whole army of flower arrangers sporting the latest
spring fashion!
As the sun strengthens,
the building sap finally forces the leaves to fully unfurl.
As many as 200,000 leaves on every tree.
Together, they grow enough foliage to blanket an area six times
the size of New England.
As the leaves expand,
they produce one of nature's most powerful chemicals.
Chlorophyll.
This green pigment catches the sun's energy to power
a reaction crucial to all life.
Photosynthesis - creating sugar from sunshine.
This sugar is essential for the tree to grow,
but it's now in easy reach of New England's hungriest animals.
A moose.
Named by the Native Americans as moosu, "he who strips off",
they are leaf-eating machines...
..and can strip a branch clean in seconds...
..but the trees can defend themselves.
In response, they flood their leaves with a repulsive chemical
called tannin.
So moose must constantly roam to seek out fresh ones.
But this female doesn't want to travel far.
She has twins and they're just two weeks old.
Until now, they've remained hidden in the shade of the forest.
With the leaves now loaded with unpleasant tannins,
she needs to find an alternative food source.
She leads the twins away from the cover of the trees
for the very first time.
Out here, it's a big, new world.
The mother must stay close.
Another cow and her calf are already enjoying the coolness of the lake.
Moose have the longest legs in North America,
which allows her to reach something that other animals can't get to.
It's what makes this lake irresistible.
Water plants.
Just what this mother needs to enrich her milk...
..because they're packed with nutrients
washed out of the leaf litter.
The twins will increase in weight tenfold over the next few months.
It's not just the females who need the nutrients.
Big bulls are here to feed for a different reason.
To grow their antlers, one of the fastest-growing animal organs.
They keep a safe distance.
Neither wants to damage his prized possessions.
Because their racks are not just for fighting.
Male moose concentrate on looking good...
and attracting females.
With females watching on, it's a chance to show off.
A good try, but at this time of the year,
this female's attention is still fully on her calves.
It won't be until the fall that she will be
back on the market for a mate.
Late spring, the busiest time
for the forest's most notorious tree-eater.
Signs of his appetites surround almost every lake.
The beaver, New England's most industrious animal.
His lodge is his castle, built of sticks and hardened by mud.
But his masterpiece is his dam.
Over 50 metres long and built of thousands of logs and branches.
For 20 years it has held back the water to create a moat -
a defence against predators.
But this security comes at a price.
The dam needs constant maintenance.
A leak.
He's going to need supplies.
To avoid being spotted by predators,
beavers work under the cover of darkness.
There iron-infused teeth make powerful tools with which they can
fell a tree ten inches wide in just a couple of hours.
SNAPPING
Fixing a leak can take all night
and into the morning.
He stirs up mud, using this mortar to seal the cracks.
But fix one leak... and another is sure to spread.
A beaver's work is never done.
All this work isn't just for his own security.
MEWING
In spring, a beaver's lodge is busy with the activity of baby
beavers and their sounds as they call for milk.
MEWING AND PURRING
This is a crucial time to practise using their teeth before
they too are unleashed onto the forest.
PURRING
The beavers of New England fell millions of trees every year.
But surprisingly, it's this that makes them heroes of the forest.
By removing softer trees,
they create large open spaces where red maple saplings can take root.
And they leave bigger hardwoods standing, like maples
and oaks, with space to spread their branches.
With more leaves to create sugar, trees can grow ten times faster,
and their colours in the fall will be much brighter.
Beavers have helped to create a forest rich with maples and oaks.
But 400 years ago, something happened that was to rapidly
speed up what the beavers had started.
Clues to this event can be seen threading through the forest.
Stone walls.
240,000 miles of them.
Enough to reach the moon.
In 1620, British settlers landed on these shores.
Attracted by tales of green and pleasant lands...
..they had hoped to create a prosperous life.
What they encountered was an ancient dark forest,
creaking with giant trees.
And haunting sounds they had never heard before.
BIRDS SQUAWK
The trees towered above them,
far higher than any they had seen in Britain.
The biggest of them all was the white pine,
said to have reached as high as 200 feet.
By royal decree, the King of England claimed every one with
a diameter greater than 24 inches.
They were shipped across the Atlantic for use as the masts
of the Royal Navy.
The rest were left for settlers.
They felled trees to build homes, churches and mills.
Many animals, like mountain lions
and wolves, were wiped out as the wilderness was tamed.
By 1850, almost all of New England's
forest had been chopped down,
and much of this was turned to farmland,
surrounded by stone walls.
But then everything changed
as richer farmland and gold was discovered in the west...
..and many of the settlers chased their fortunes elsewhere.
Towns like Livermore disappeared as quickly as they had been formed.
Slowly, the trees of New England grew around the ruins
and reclaimed the land.
This new forest was very different.
By chopping down the old-growth trees,
people had given fast-growing maples and oaks a chance to claim the land.
They grew back in greater numbers than ever before,
and today they dominate this forest.
From now on, there would be nowhere else more colourful in the fall.
Today those stone walls are highways
for one of New England's busiest animals.
The chipmunk.
There can be as many as 15 living in every acre...
because New England is a chipmunk paradise.
The stone walls help them to get around the forest
and keep an eye out for predators.
And the new forest provides all the acorns and maple seeds
a chipmunk can eat.
Today the forest is treasured,
and 80% of New England is covered in trees,
ensuring the fall remains rich and colourful.
Because vast areas are uninhabited,
in many places the sky is dark with little light pollution.
New England is further south than the UK.
But it's dark enough that on special nights
the distant northern lights can be seen shining.
The growth of the new forest paved the way
for wildlife to move back in,
and animals that were once persecuted now thrive here.
DISTANT ANIMAL CALL
It's the beginning of summer.
And with daytime temperatures now in the mid-20s,
it's warm enough to draw out New England's most misunderstood animal.
RATTLING
A timber rattlesnake.
A creature at home hiding amongst the trees.
It was once so feared, a bounty was placed on its head.
But the timber rattlesnake is making a comeback,
with a few hundred now living in these forests.
Using his tongue, a large male seeks the scent of a potential meal.
He's detected a log heavy with the scent of rodents.
Coiled like a spring, he waits.
FAI NT RUSTLI NG
FAI NT PATTERI NG
Even one of the fastest hunters on the planet
can sometimes be off target.
But he's patient.
15 hours later, he's still in position.
FAINT RUSTLING
PATTERING
MOUSE SQUEAKS
He instantly withdraws his fangs,
eager not to damage them.
It won't take long for the venom to kill.
He follows the mouse's scent to claim his prize.
This should satisfy his hunger for a few weeks.
It's the height of summer,
and the trees' leaves are working at maximum capacity
to turn sunlight into sugar.
This is when they face their greatest battle.
CHOMPING
Billions of bugs are on the attack.
The trees do everything they can to resist the onslaught.
They increase the concentration of repulsive tannins
in the surface of their leaves.
But even this isn't enough to stop one hungry insect.
Only a few millimetres long,
this leaf miner is tunnelling under the skin,
where he can avoid the bitter tannins
and get to the juicy, sweet bits.
Under the safety of the leaf itself,
he devours so much green chlorophyll
that the leaf can no longer produce the sugar it needs to stay alive.
In just two days, he leaves a trail of destruction,
and his appetite shows no signs of slowing.
Most insects are too big to squeeze inside a leaf,
so they must be more selective in how they attack.
Many eat carefully between the veins,
avoiding areas with higher concentrations of tannins...
..Ieaving the leaf skeletonised in their wake.
The bigger caterpillars get,
the more they can process the leaves' unpleasant chemicals.
And working en masse, caterpillars can devour a leaf in minutes.
But they themselves could easily fall prey to birds.
So disguise is the key to their success.
Some mimic dangerous New England animals to deter their predators.
Swallowtails have eye spots to look like snakes.
The hag moth caterpillar resembles a big spider.
And the fur of this one makes it tricky
for a predator to get to the soft bits.
But the most cunning disguise of all
is to mimic the parts of the leaf that they've already eaten.
Many New England caterpillars look like nothing more than leaf damage.
Filling in the gaps with their bodies
makes them less visible to birds.
New England is swarming with undercover caterpillars.
But there's one predator that caterpillars can't hide from.
Because here the trees have an ally.
An army is being mobilised.
These are the Allegheny mound ants,
and the trees are their hunting grounds.
Like lions in the leaf litter, they hunt in a pack...
..efficiently trimming the hairs
so they can get to the sugary juices...
..draining the caterpillar dry.
But this isn't food for THEM to eat.
In the warm interiors of their mounds,
the summer heat is incubating the next generation.
Caterpillar juice is the perfect nourishment for a growing soldier,
supercharged with sugar that the caterpillars stole from the leaves.
Soon they will be ready to help the colony expand.
Every year ants dig miles of tunnels
and excavate as much as 12 tonnes in every acre.
This aerates and breaks down the leaf litter,
which fertilises the soil.
Trees with rich soil and ant protection
produce more sugar,
they're brighter,
and they will hang on to their leaves for longer during the fall.
Despite the battles raging through the forest,
billions of leaves continue to produce sugar.
This is transported down the trunk,
where it's stored to replace the tree's reserves.
Each will gain as much as 100kg in weight before the end of the year.
FAI NT TAPPING
BIRD CALLS
The yellow-bellied sapsucker has attracted a female,
and in their nest they have four young chicks just a few days old.
CHICKS CHEEP
Their parents bring back food 20 times every hour.
BIRD CALLS
It's exhausting, keeping up with the demand.
CHICK CHEEPS
The summer sap is sweeter,
and it attracts a swarm of insects.
This is why the father has been obsessively digging wells -
because the sap leaking from them is now bait.
And not even the trees' allies, the ants,
can resist a nibble of the free-flowing sugar.
CHICK CHEEPS
For the chicks to grow, they need protein.
Sugar-coated bugs make up two-thirds of their summer diet.
Because of the constant supply of insects,
the chicks increase in weight by 16 times
in just four weeks.
CHICKS CHEEP
And they're already learning the art of tapping for themselves.
CHICKS CHEEP
In three months' time,
they will depart the cooling forest for warmer climates in the south.
This will give the trees a chance
to repair the damage before the summer ends.
This female rattlesnake has spent three months basking in the sun,
but daytime temperatures
are now dropping as low as 14 degrees Celsius.
Being cold-blooded, she is the first in the forest
to feel a chill in the air as the days draw in.
She's getting too big for her skin,
but yawning widely helps to loosen it.
And snags in the leaf litter help her to undress,
peeling away the scaly layer.
This lethal hunter is now ready.
In a safe and secure place, specially adapted for filming,
she waits.
Through the night, months of preparation comes to an end.
She's given birth to seven tiny rattlesnakes.
Only 20 centimetres long,
and already their sharp fangs
are fully loaded with potent venom.
Unlike most other snakes,
timber rattlesnakes
carry their babies inside their bodies to keep them warm.
And there's one more on the way.
The mother's work doesn't end there. Her maternal bond is strong.
Having the fiercest mother in the forest,
there's very little that could threaten these baby snakes.
One by one, they snuggle into the safety of her coils.
It won't be long until the cooling fall weather
forces New England's rattlesnakes to lead their babies
to underground dens,
where they will hibernate as families until the spring.
The shortening days and cooling weather
trigger a change in the behaviour of New England's biggest animal.
Male moose have been growing their antlers all year,
and now they're dressed to impress.
And finally, the females are open to their advances.
FAINT BELLOW
But some moose have more luck than others.
SPLASHING
This younger male has been following a female for weeks
in the hope of getting her attention.
It's tiring work,
and to make matters worse,
she's still caring for a calf.
But with antlers like this, how could she possibly resist?
He decides to make a bolder move before a bigger bull shows up.
MOOSE SMACKS LI PS
Lip-smacking makes his intentions clear.
Her scent is irresistible.
Not the response he was hoping for.
Urination gives him a sign that she's still not in the mood.
Even after weeks of trying to court her,
persistence doesn't always pay off.
THUNDER RUMBLES
Fortunately, every year, thanks to the nutrition from the forest,
a moose grows a bigger rack.
THUNDER RUMBLES
And next time,
maybe his antlers will be big enough to impress the choosy female.
With the temperature now constantly below ten degrees,
the leaves can no longer work efficiently.
And with less than 12 hours of sunshine a day,
they have less time to create sugar for the trees.
There comes a point when they are no longer earning their keep,
and the tree must start to close down for the winter.
At first, the effects are subtle.
Individual leaves start to turn yellow.
Like tiny factories closing down,
the green pigment inside each cell is dismantled.
The tree salvages all that it can,
carrying it down in the sap to be stored in the tree's trunk.
The cooling weather quickens the process,
until the Midas touch of fall turns entire forests golden.
But this is only just the beginning
of the most magical transformation of all.
The fall in New England.
While most trees are already preparing for the winter...
..some also take this opportunity to secure a future for their offspring.
They drop millions of winged maple seeds and acorns.
Many will soon be safely hidden beneath leaf fall
to await the nourishing warmth of spring.
But they've been spotted.
Despite the cover, there's one animal
who is able to sniff out a fresh nut amongst the leaf litter.
A chipmunk.
His small size means that he's unable to pile on enough body fat
to survive hibernation through the winter.
And just when reserves are looking a little thin...
..a new air drop is delivered by the trees.
Perfect timing...
..if he can stockpile enough in his secret caches.
He can squeeze four acorns into his cheek pouches,
allowing him to collect up to 160 a day.
It takes a lot of work to amass a big stash.
But there's always one who's less prepared to put in the hours.
A lazy chipmunk.
He's spotted his neighbour's acorn and where it's being hidden.
It's too tempting.
But it's not an easy steal.
SQUEAKING
This is one chipmunk determined to protect his stash.
The chipmunk is a hero of the forest -
because even after all that work,
he will forget where he's buried some of his hard-earned treasure.
And protected underground, the seeds have a better chance of germinating.
Whether they are a tree's enemy or an ally,
the animals of New England have conspired
to make the fall a season of beauty.
And one thing is for sure -
in the end, it's the entire forest that wins.
And as the trees make their final preparations for winter,
the best is yet to come.
As the temperature drops towards freezing,
the trees increase the speed
at which they drain the leaves of their goodness.
A magical new chemical is conjured up
from within the leaves of the maple and oak trees.
Red anthocyanin.
It keeps the sap flowing for longer as the temperature plummets,
so the trees can hold on to their leaves
and extract every last drop of sugar.
The reds and oranges join the golds,
and together they set the forest ablaze.
From an ocean of green, every tree becomes an individual.
Red maples and oaks burn in shades of red.
Sugar maples glimmer in orange.
And for just a few weeks every year...
..New England is a wonderland of colour.
These colours can be seen from space,
spreading across this corner of America like wildfire.
The spectacle is intense, but brief.
As the last of the nutrients and sugars are extracted by the trees,
billions of leaves hang on tenterhooks.
All it takes...is a breeze.
It's the last chance for their most persistent enemy to feast.
CHOMPI NG
Caterpillars... in a hungry race against time.
Leaf miners are still feeding as the leaf changes around them.
They eat all that they can before a quick getaway.
Some caterpillars chase the colour through the fall.
The spicebush swallowtail swaps the green costume of summer
for a golden coat.
And, having had her fill,
she sheds this new skin to form an overwintering pupa that,
Iike a leaf, fades to brown.
Many other caterpillars turn red and orange in the fall.
And as the leaves lose the last of their sugar,
they climb to the edge of a leaf...
and take a leap of faith.
Amongst the leaf litter they seek out a refuge from the winter.
In the spring, they will emerge as moths
and unleash a new generation of caterpillars onto the forest.
It's the end of October,
and the planet's most colourful forest fades
as the last leaves fall.
They have given the trees all that they need to survive...
..until the battles begin again next year.