Original subtitles

Across the globe,

there is no place more changeable

than the seasonal forest,

going through constant new phases throughout the year.

Adapting to the seasons makes our majestic

woodlands of the world dynamic and varied.

It can be hard to see the wood for the trees.

But stop and look, and it's the trees themselves

that tell the story

in their never ending battle with the elements.

(rain pounding)

And around their feet, beneath their roots,

in their cavities and branches,

plants

and animals

find a generous

(fire crackling)

yet sometimes challenging homes.

Spend a year in nature

to watch the energetic and vibrant changes

through the "Seasons of the Forest."

(enchanting music)

From tiny, humble beginnings,

great things can come.

(dramatic music)

The tiny shoots breaking their way into the world

have the potential for long and glorious life.

Oak,

beech,

and pine.

All the giants of this landscape start out small.

But with lofty ambition,

(birds chirping)

each kind of tree faces different challenges

and will navigate in their own way

through the obstacles that lie ahead.

(dramatic music)

When trees produce these little babies,

they do so in volume,

and for good reason.

Perhaps only one in 10,000

will get the chance to realize its potential.

(dramatic music)

Nuts and seeds are food for just about

everything in the forest.

For the few that escape hungry mouths,

they also begin a lifelong battle with each other.

Trees, like all plants, need sunlight.

The green in their leaves harvest it,

converting it to sugars that fuel its growth.

In the woods, the canopy can be dense.

Each young tree needs to get tall

as quickly as it can.

Outcompeting its neighbors to get close to the light.

(birds chirping)

It's a race, but not one we can see.

The speedy growth can take decades.

For most of the creatures living in their shadows,

things move a lot faster,

especially in spring when their own race begins,

to breed.

(playful music)

Newts and salamander live in the damp

leaf litter of the forest floor.

But a feature that defines amphibians

is that their eggs are blobs of jelly

that can dry out,

so they must be laid in the water.

From all over the forest to the America's Sierra Mountains,

Sierra newts begin a march.

Bold-colored and boldly confident,

both because their skin is laced with a potent toxin

to keep predators at bay.

Who says romance is bad?

(playful music)

For the slimy-skinned newts,

the strategy is somewhat like a rugby scrum.

Males outnumber the females.

But in this amphibian orgy, anything goes.

During successful pairings,

the females will carefully place

sacks of fertilized eggs on the plants

before they can crawl their way back into the forest.

All around them, across forest all over the world,

reproduction is bringing about some major changes.

The plants of the forest explode with life.

Many have laid dormant in the soil

as seeds or bulbs over winter.

But now warmed by the lengthening hours of sunlight,

they have races of their own.

They need to breed and so quickly unfurl their beauty.

(dramatic music)

They are alluring, and that is their purpose.

Most plants can't fertilize themselves.

They need a third party, a matchmaker

to bring the male and female parts of the plants together.

The flowers are a lure for insects.

Like the flowers, bugs either died off for winter,

leaving eggs or grubs in the ground,

or lay dormant themselves,

but they merge on mass to coincide with the floral chorus.

(insects buzzing)

Insects' compound eyes

can see a much wider color spectrum than we can.

We think the flowers look stunning.

But to them, it must be an overwhelming sea of color.

(insects buzzing)

Each flower shouting, "Pick me, pick me."

(insects buzzing) (birds chirping)

It's not just color, but scent too.

A sweet smell promising a tasty reward

for the winged workers.

Flowers track the sun across the sky,

letting its rays gently warm their petals,

so that the insects can even enjoy a heated landing pad.

The warmth helps carry their fragrant pheromones.

(enchanting music)

Some plants go a step further.

Flowering in spring,

in the cold damp, corners of the forest,

warmth can't be guaranteed.

So the arum lily creates its own.

Its discreet flowers are shielded from sight

in a leaf cloak known as the spadix.

Like mammals, it uses cell metabolism to generate heat.

Though how it controls the temperature remains a mystery.

While most flowers offer sweet perfumes,

the arum emits an odor reminiscent of rotting meat.

Its heated body lifts the scent into the air,

an advertisement to insects, midges in particular.

That can't resist the suggestion food and the warm hideaway.

(insects buzzing)

The plants set a trap,

planning to put the insects to work.

The series of fine hairs temporarily trap the bugs.

And while they fight their way free,

they are doused with the plants pollen

by the male part of the flower,

the proud erection in the center.

Then the flies are free to be tricked again.

Harnessed as a free courier service,

they carry the pollen to other lilies

where it's dropped on the smaller female parts

at the base of the flower.

It's not just the flowers that are focused on reproducing.

It's spring in the forest and love is in the air.

One of the biggest birds in the forest of Europe,

a capercaillie has to work hard

before he'll get the chance to mate.

(capercaillie snorting)

He prances to show off his finery,

gurgling his distinctive call.

The difference between his plumage and hers

is a clue about what happens next.

The showy male will play no fatherly role.

The female has cryptic camo feathers,

ready for sitting on the nest.

(playful music)

Chaos reigns in the trees over head.

The squirrel play a game of kiss chase

as the females assess the stamina of each potential suitor.

(playful music)

The trees they are treating like climbing frames

are in the midst of breeding themselves.

Many of them produce catkins,

long chains of tiny flowers.

(enchanting music)

The bigger ones are male

and gently release their minute pollen into the air.

(enchanting music)

Drifting on the wind,

some will settle on the smaller female flowers

of neighboring trees.

(enchanting music)

(birds chirping)

Pine trees do the same.

The males contribution delivered by the wind.

(gentle music)

After a successful pollination,

the trees can get to work on seeds

that they will release later in the year.

Meanwhile, the deciduous trees put a lot of energy

into growing new leaves to make the most of the sunshine.

(enchanting music)

In the spring, everything has a light, bright,

lush green hue.

The young leaves wanting to soak up all the light they can

to fuel further growth.

(enchanting music)

It's an all you can eat salad bar for local vegetarians,

and so a perfect time for them

to be raising their young.

Deer mated last year

and were pregnant through winter,

but now they have their fawns.

(playful music)

(wild boars growling)

There's a lot of activity on the ground.

(gentle music)

As the spring flowers finish their performance,

they wither and drop their fertilized seeds to the ground.

After a long, cold winter,

ants rush to gather the spring's bounty,

ferrying the nutrient-rich seeds back to there nest.

They are taking the seeds as food,

but stored away underground, some will sprout,

unintentionally distributed and planted by the ants.

In some forests,

one in three seeds is planted this way.

(thunder rumbling)

Across the temperate zone,

spring is the time of those classic April showers.

(thunder rumbling) (rain pattering)

Regular downpours that help fuel the plant growth.

(rain pattering)

(birds chirping)

Animals can get a bit soggy,

but the trade off is plenty of food.

(rain pattering)

The plant life helps the insect population to swell,

and birds start their families

to coincide with the rich pickings.

The smallest bird of the forest lives in North America

and makes it thimble-sized nest

from hairs and bits of lichen,

woven together with spider silk.

It's like an elasticated waist band

that can grow the brood.

While this smallest of birds

can raise its family on the thinnest of twigs,

The huge black storks of Europe

need the whole crown of the tree.

Secretive in nature,

the canopy gives them the privacy they crave.

They can return to old nests,

piling branches higher to strengthen the platform.

For several months, both parents will dash back and forth,

collecting food for the hungry brood.

(birds chirping)

(gentle music)

The huge oak tree is a fortress to this family,

but other birds take a chance nesting on the ground.

Here they are much more at risk

from predator attack.

But in North America, the whip-poor-will,

a type of nightjar, is almost invisible,

thanks to its cryptic camouflage.

(gentle music)

As some progresses,

the forest of the world are alive with baby animals,

growing

and exploring their new home.

(gentle music)

European fox cubs spend their first weeks in a den,

but now practice their hunting techniques

one each other as they play.

Many of the animals take advantage of the dappled shade

provided by the canopy over head.

There are hundreds of species

that live up with the leaves themselves.

And the bigger, older, and more craggier tree,

the greater the number and variety

of species living on it,

including mammals,

birds,

insects,

and fungi.

An ancient oak tree like this giant

can support 2,300 other species.

In summer, the trees are a hive of activity, literally.

Insects competing for sunning spots.

(suspenseful music)

Upsetting hornets

that are nesting in the crag in the bark.

(suspenseful music)

And despite this rush hour traffic,

giant stag beetles race through the middle,

bulldozing their way into an arena,

closer to the canopy, a bigger colony, honeybees.

They don't welcome the intruders.

Despite the aggressive defense,

the beetles soldier on.

They are on a mission.

It's the breeding season.

The beetle sumo wrestlers lock their embrace

and try to throw each off balance.

(suspenseful music)

The less well-endowed females look on

and will select a mate from the winners.

(suspenseful music) (birds chirping)

The many bugs attract bird life,

(birds chirping)

some, like woodpeckers,

even digging into the trees themselves

to make their nesting chambers.

(gentle music)

Other birds don't dig the hole.

Just take advantage of natural cavities.

Nooks and holes can occur

on any part of the giant trees.

Gaps around the huge network of roots

shelter a family of wood mice.

(gentle music)

(birds chirping)

Now the sun is at its hottest.

The leaves of the trees have become much darker.

They have become thicker and waxier

and are producing more pigment cells for photosynthesis.

We mostly see greens,

but the leaves are also producing reds and blues

to harvest different parts of the light spectrum.

These darken the overall tone of the green leaves.

(gentle music)

Animals seek shade

(horse neighing)

(gentle music)

and a cool bath to beat the heat.

(gentle music)

But for the trees, this is a time of plenty,

long hours of sunlight that they can capture

and turn to food.

But the high temperatures can have drawbacks.

(thunder rumbling)

(thunder crashing)

Vegetation dries out.

And with high pressure, storm clouds build.

Just one lightning strike can start an inferno.

(suspenseful music)

A scene of devastation quickly sweeps across the forest.

Birds and large animals flee.

But for many, there's no way out.

(squirrel squeaking)

(fire crackling)

Nothing appears to escape the devastation.

But not all is as it seems.

Many forests around the world, like this in California,

actually need fire to keep them healthy.

Among the trees, the flames will weed out the weak.

Most of the species here have flame-resistant bark

to protect their bodies.

Even if they lose replaceable limbs,

the flames will kill of parasites.

And the wood that does burn

will enrich the poor quality soil with ash.

As seen of desolation follows,

but it is short-lived.

Like a phoenix rising from the ashes,

a shoot breaks the surface.

The heat from the fire actually cracks

the tree seeds' hard shells,

helping them to germinate.

Some trees, like the sequoias,

the biggest trees on the planet,

are dependent on fire

to unleash the potential of their seeds.

From the mineral-rich ashes of the fallen,

new lives begin.

There are many threats to young trees

trying to make it to the top.

Fire is just one of the natural disasters that can strike.

(winds howling)

Winds and wreak havoc.

And in late summer,

building storms can bring heavy rain.

(rain pounding) (thunder rumbling)

Water-laden branches

can be too heavy for their roots

to support in wet ground.

(dramatic music)

Swept by flood waters, they can form log jams,

the end of the road for some.

(gentle music)

But the carcass of a tree

is one of the greatest gifts the forest receives.

(enchanting music)

For decades, sometimes centuries,

these giants have been taking in,

making, and storing nutrients.

And now in their final act,

they are returning it to the forest.

Moses and fungi quickly colonize the use carcasses,

breaking down the bodies as they feed,

(birds chirping)

and in turn feeding a host of other species.

(animals squawking)

Insects too hone in on the rotting wood.

Many beetles are only beetles for the last weeks

or months of their lives.

Most have previously spent a few years

living in dead trees,

chomping at the rotting wood.

Gradually, the tree rots down into the ground,

enriching the soil that nourishes the roots of others.

It's ensuring food for its offspring,

the next generation of trees and their battle through life.

Some even get a headstart.

Their seeds landing on the dead giants,

giving a bed of compost

where they can lay down well-fed roots.

The plants work hard every day

to absorb food and water through their roots

and producing food in their leaves,

because each year is a race

to thrive and grow while the going is good,

knowing that some big changes lie ahead.

Gradually, the evenings begin to draw in.

(suspenseful music)

The window to soak up sunlight shortens every day

and temperature start to drop.

These are the signals that trigger

the biggest annual transformation of the forest.

First things first.

The trees have been ripening their fruits,

an assortment of seed pods

which are now ready to sent out to fend for themselves.

Witch hazel in North America flowers later than most,

just as autumn takes hold.

As the flowers fade,

the plants make sure each seed goes out with a bang.

Building pressure at its base,

ejects the seeds,

sending them flying forth,

scattering its legacy as far as it can,

something much appreciated by those below.

Soon goodies are raining down

from the trees and forest across the world.

Little parcels carrying the genes to grow a new tree,

bundled with a good food store to nurture its growth.

(graceful music)

Many of the plants' offspring

have had spiny protective coverings.

It's an attempt to stop anything nibbling at them

while they're still ripening on the tree.

As the prickly, sweet chestnuts fall,

the armor splits, spilling the nuts.

Squirrels never seem to sit still.

As if driven by an insatiable greed,

they gather as many nuts as they can.

Some will be eaten on sight,

but most are carted off and buried,

a handy snack pack for later.

But actually, many trees count on squirrels

and other food stashes

to export their seeds around the forest and bury them.

(playful music)

Squirrels stash so many

that they never get around to collecting them all.

In fact, up to 75% get left,

conveniently buried, planted, and ready to grow.

Not all animals are useful.

Boars just chomp through the treasure.

Some of the woodland animals

don't need to wait for the trees to drop their seeds.

Nutcrackers aim for the top.

They live up for their name,

with in-built tools for forceful extractions,

nipping out the pine seeds before the cones are ripe.

Bears try and get in on the act too.

(gentle music)

(leaves rustling)

But most animals will just wait for the cones

to ripen and fall, letting the food come to them.

As they ripen, many pine cones dry and open up,

releasing hundreds of small seeds into the air.

They have sails to help them drift further

from the parent tree.

All gifts from above are welcomed by those below.

(playful music)

In Siberian forests,

chipmunks are in hyperdrive,

gathering the seeds from fallen pine cones.

Their teeth never stop growing,

and self-sharpen as they rub together.

(playful music)

They fill their cheek pouches and go stash the food,

a winter ladder in case they wake up from hibernation

and need a night time snack.

(gentle music)

With winter approaching,

competition is fierce.

With rodent so deeply engrossed in foraging,

predators seize the opportunity for surprise attacks.

The American bobcat has camouflage,

patience, stealth, and speed.

(animals squawking)

One less nut thief for the trees to worry about.

Everyone needs to eat while the going is good.

(gentle music) (animals squawking)

In the temperate zone, winters can be harsh,

with many days of frost or even heavy snow.

Winter hits the extreme north first,

the land of the pine.

(animals squeaking)

Pine trees are well-equipped.

Their leaves are tiny, spiky needles.

A small surface areas, so less is exposed to the cold.

They have a waxy surface to reduce loss of water,

helping to protect them from the elements.

And the classic Christmas tree shape

prevents too much snow from building on their limbs.

When the snow burden gets heavy, it simply slides off.

They also use proteins their manufacture

as an antifreeze to protect their cells.

With these preventative measures in place,

the trees don't need to change for winter.

They can keep hold of their needles year round.

But the strategies of desiduous trees

couldn't be more dramatically different.

(playful music)

The big, thin, flat leaves have a large surface area,

prefect for catching the sun's rays,

but also very exposed and vulnerable to damage from frost.

So as the trees sense the shortening days

and dropping temperatures,

they start to pull the goodies from their leaves

back into their trunks.

Woody cells start to build at the base of the leave stems.

They are getting ready to shut up shop,

so no longer need to chlorophyll to photosynthesize.

But as the greens fade,

they reveal other pigments in the leaves

that had been hidden until now.

(playful music)

The leaves may be dying,

but they are going out with a bang.

(gentle music)

Putting on the greatest show nature has to offer.

(animals squawking)

Reds,

oranges,

and yellows flooded the forest.

(gentle music)

Despite the beauty,

animals don't seem to stop to enjoy it.

They are busier than ever,

making the most of the last food.

(moose bellows)

The changes are not only impacting the trees,

the personalities of some animals below

are altered by a surge in hormones.

(moose bellowing)

Horned and antlered animals prepare to go head to head.

Dear strut and bellow,

challenging rivals to a brawl.

Their antlers are grown anew for each annual tournament.

But the horns of sheep

keep growing throughout their lives.

These are mouflon.

The wild forest dwelling ancestors of domestic sheep.

To persuade perspective females to mate with them,

the rams must prove their worth.

It's a short-lived show.

(gentle music) (birds chirping)

The animals need to shift their focus to survival

as the temperatures drop.

(gentle music)

As birds begin their journey south,

it's time for now very plumped bears

to find sheltered dens where they sleep out the winter.

As the first snow falls, they vanish.

Some birds will migrate.

Many of the smaller animals

will join the bears in slumber,

but others will have others will have to stick it out.

Late offering from the trees

will be a lifeline to little birds.

They in turn passing the benefits of the food chain.

Each species has its own tactics,

a niche to help it through.

Siberian musk deer, in the absence of green leaves,

nibble lichens from the bear branches.

Ravens manage by monitoring the forest predators.

Scavenging from wolf kills, they'll find plenty to eat.

For predators that cope with the conditions,

there's plenty of prey,

weakened by the cold and lack of food.

But while the daily battles play out around them,

the trees are following a similar strategy to the bears.

They stand in torpor.

Bare branches furnished only with icicles and snow.

The blanket of snow protects the forest.

It's actually warmer underneath,

helping to prevent frost damage,

until finally the icy queen loosens her grip.

(gentle music)

The sounds of dripping through the trees

are the first hint that winter is coming to an end.

What now feels like a ghost town

is poised and ready to embrace a new look.

(playful music)

And weak sunlight slowly breaths life

back into the landscape.

As the temperatures slowly climb.

The trees get to work.

Fresh buds and shoots bulge at the tips of branches,

soon unfurling to reveal once again

the beauty of spring.

And thanks to the mulch of leaf litter from their parents,

the seeds that have laid dormant over winter

perform their greatest trick,

building a tree,

a tiny sapling ready to take part in the endless,

beautiful, fascinating performance

of the seasons of the forest.

(graceful music)