Original subtitles

Our planet is the greatest living puzzle in the universe.

A collection of worlds within worlds.

Each one a self-contained ecosystem, bursting with life.

But how do they work?

The intricate web of relationships

and the influence of natural forces

makes each microworld

complex and unique.

So, to discover their secrets,

we need to explore them one by one,

untangle their interlocking pieces

and ultimately reveal the vital piece -

the key to life itself, hidden deep within

each of Nature's Microworlds.

In the remote temperate region of the Pacific Northwest,

there's a remarkable ecosystem.

Canada's coastal forest has some of the largest trees on Earth,

and they reach right down to the shoreline.

But that's not all.

This place is also jam-packed with wildlife.

This coastline is an extraordinary merging of land and sea

which showcases some of nature's greatest living spectacles.

The forest is home to iconic species like bears...

..eagles

and wolves.

In fact, these coastal areas

are such great habitat for these top predators

that they're here in some of the highest densities on the continent.

Winters here can be harsh

with blanketing snow and very little sunlight.

Yet this forest is one of the most productive in the world.

The sheer volume of plant material this forest accumulates

outweighs even some of the world's tropical rainforests.

So, where do all the nutrients come from

that allow the trees of this forest to get so big?

This coastal forest stretches for thousands of kilometres

along the North American coast -

from Northern California right up to Canada and southern Alaska.

It's a landscape forged by glaciers

and bordered by a mountain range stretching right along the coast.

And to its west sits the Pacific Ocean.

Thousands of kilometres of water

that floods in to fill sheltered inlet and bays.

This microworld is more than just a forest.

And to see just what it is that makes this place tick,

we'll need to explore all of these parts.

In the North American Coastal Forest, there's one thing -

or rather a few million things - that dominate the landscape.

Spruce, cedar,

fir trees and redwoods tower above the forest floor.

These trees are huge.

Many are 70 metres tall

and some are over 1,000 years old.

But the great coniferous forests of North America

are more than just trees.

They're homes for squirrels...

..rich hunting grounds for pine martens...

..and nest sites for Great Grey Owls to raise a family.

There are top predators here too,

and the generally solitary brown bear

can live here in surprising numbers.

These brown bears managed to put on so much weight

that they've become the largest in the world.

Another top predator thrives here too - the grey wolf.

This population has become particularly adapted

to living in this unique forest environment.

Each in their own way, these animals depend on the giant trees

that stretch for thousands of kilometres along this coast.

These trees are actually some of the largest living things

on the planet, and they're still growing.

But how do they get so big?

Trees need nutrients in the form of phosphates and nitrates to grow.

These are essential building blocks that fuel growth -

and WHAT growth!

Each tree can weigh over 150,000 kilograms.

And to get to this size, more than a million kilograms of nutrients

are drawn up by the trees in this forest every year.

But with so many trees, the available nitrates and phosphates

are soon locked up in the forest's living tissue.

So where do these building blocks come from to make giant trees?

It's too wet for forest fires that might release nutrients in ash,

so the only way trees get recycled here

is when strong winds and old age put an end to a giant's life.

CREAKING

CRASHING

The nourishing chemicals locked up in its tissues provide a feast

for decomposing lichens and fungi, which gradually break it down

and return the life-giving elements into the soil.

Thanks to the nutrients provided by these decomposers,

these small seedlings might still be standing in 500 years' time.

This slow process of death, decay and recycling feeds the new life

that colonises gaps on the forest floor.

But the death of one or two trees

cannot justify this microworld's prolific growth.

The nutrients that feed these trees must be coming from somewhere else.

To find it, we need to go beneath the canopy

and get to know some of the animals in this forest.

Our journey begins in November

when the ice-cold grip of winter is setting in.

The cold can make this one of the toughest times of year

for the animals in this forest.

But there's still life here.

SQUAWKING

Bald eagles weather out the winter months in this coastal forest.

The eagle is another of the forest's top predators.

And in winter, these eagles group together around

the open waterways on the lookout for carrion and live prey.

These are the largest congregations of bald eagle

found anywhere on Earth.

The flowing rivers full of fish provide food year-round,

allowing the eagle to prosper in the freezing conditions.

But few other animals are so lucky.

Amongst the trees, bears are nowhere to be found.

They've escaped the brunt of the weather and have retreated

to dens in the mountains.

But this freeze doesn't last forever.

With the arrival of spring,

the North American days begin to lengthen.

Up in the mountains on the eastern flank of the forest,

the bears are now emerging with their newly born cubs.

BEARS BARK

The cubs were born in the heart of winter,

and this is their first journey outside the den.

They're still finding their feet on the slippery slopes

that descend down to the forest.

The adult bears might not have eaten for over half the year,

yet in the next few months, they can pack on

an impressive 100 kilograms, and in this forest, they thrive.

Bears are capable predators, but they're also opportunists,

able to eat a massive range of food.

And they even eat grass.

But for the bears, perhaps the best thing about these forests

is that they're right on the coast.

Bears that are after any protein they can find

are able to walk right down to the sea to find food.

BEAR SNUFFLES

Here, bears can find valuable protein from clams

that they dig up on the sandy shore.

And there's plenty more food available on the shoreline.

As the tide goes out,

other forest creatures take advantage of the shallows.

With forest cover just metres away,

racoon families catch crabs in the draining pools.

These morsels of food gathered along the shoreline by forest creatures

are a hint to the potential nutrients that the Pacific Ocean

can offer this forest.

For now, bears and raccoons must resign themselves

to foraging at low tide.

But the ocean has an important part to play in this forest's story.

And its great productivity may just hold the key

to the nutrients that feed this forest.

To understand this,

we need to take a look at just how spectacular this ocean is.

And this will help us see

just how the ocean nutrients might be getting onto land.

It's now early spring, and the warming waters attract herring

from the open Pacific Ocean to the bays and inlets along the coast.

And they gather in their millions.

It's an event that doesn't escape the attention of predators.

Sea lions head towards the commotion...

..and dolphins move into position.

The herring attempt to confuse their assailants

by schooling together in great shoals.

But attack comes from all angles.

Herring are considered a keystone species along this coast,

a species so important that the whole system could collapse

if they were removed.

SEA BIRDS CRY

One massive creature has travelled over 4,000 kilometres to be here.

The humpback whale.

Although thousands of humpbacks migrate here in the spring,

only a few have developed a neat predatory trick.

WHALES SING TO EACH OTHER

Working together, these humpbacks use circular streams of bubbles

and loud calls to corral the fish into tighter and tighter balls.

WHALES CALL OUT TO EACH OTHER

Lunging up from beneath, their huge mouths engulf their prey.

Humpbacks have to eat 1,500 tonnes of food a day.

And these herring provide about 20% of the food they eat

along this coast over the spring and summer.

The whales don't feed over winter,

and the herring provide essential energy

before they begin their long migration back to the tropics.

With such a swathe of predators,

it seems madness that the herring come to this coast at all.

But they need this coastline for the future of their species.

The coastal winds pull nutrient-rich water from the ocean depths

into the inlets and bays...

..and these fertile waters turn green with the plankton bloom.

These vast quantities of microscopic plants and animals

are potential food for thousands of tiny mouths.

This is why the herring are here.

But the adult herring haven't come here

so that they can eat the plankton, but so that their offspring can.

They're here to breed.

In a spawning frenzy, females coat the leaves and rocks

along this coast with eggs

and the males follow with a fertilising liquid called milt.

The small eggs are just over a millimetre across

and with each fish producing up to 130,000 of them,

they can coat rocks and vegetation more than 20 layers thick.

Coastal birds are quick to respond.

Gulls pluck eggs from the shallows.

And huge flocks of migrating birds feast as they journey northwards.

The herring and their eggs provide huge amounts of food

for animals along this coast,

allowing the nutrients in the open ocean and the plankton bloom

to reach the land.

But the fish and eggs are just a thin layer of potential nutrients

that sit right on the shoreline.

Their influence doesn't travel far into the forest.

Forest animals like bears and wolves unable to join in the herring feast

can only wait patiently on the beaches.

For hungry forest animals, life can become a bit of a waiting game.

As the summer arrives, the surviving herring move off into deeper waters.

But the key to this microworld is still out at sea

waiting for the rains.

As the sea warms, the Pacific winds carry water drawn up into clouds

towards the North American coast.

WIND BLOWS, THUNDER RUMBLES

The gathering clouds hit the coastal mountains

and release their moisture as rain.

And lots of it.

The forest is showered with three to five metres of rain every year...

..filling the rivers into torrents.

WATER ROARS

Their tributaries spread like arteries

winding deep into the forest.

The flowing rivers carry the nutrients that trees need to grow

out of the mountains, out of the forest and into the ocean.

So there must be one last piece to the puzzle.

The key that allows the nutrients to flow

from the highly-productive ocean into the forest.

It's a fish that's building up in numbers

along the North American coast.

Salmon.

These five species of Pacific salmon may have travelled

more than a thousand kilometres from the open ocean

and are reaching the end of their journey.

These mature salmon have spent their adult lives in the ocean,

building up their muscles and fat reserves

for this one final reproductive moment.

Mature salmon come to this coast every year to breed,

but unlike the herring, which spawn along the coast,

these salmon adopt a bizarre reproductive strategy.

A strategy which underpins the productivity of this entire forest.

They switch their biology, moving out of the ocean

into the freshwater streams along the North American coast.

These fish will travel sometimes hundreds of kilometres in land

to the rivers of their birth and only there will they lay their eggs.

But the rivers running through these forests can be treacherous.

Such huge parcels of protein from the ocean don't go unnoticed.

Bears line the rivers.

These normally solitary predators congregate in huge numbers.

You can find 25 individuals on a single waterfall.

But space at these busy falls is at a premium.

Mothers with cubs are often relegated

to the quieter sections of the river,

where young bears can learn the art of catching a salmon.

Catching salmon in deep water can be a challenge,

even for the experienced.

Most of the salmon arrive in autumn when the bears are preparing

to retire to the mountains for another year.

This is the bears' big chance

to put on body fat before the winter sets in.

The fish feast is the key reason

why these bears do so well in this forest.

There's no coincidence that there are so many bears here.

Without the salmon, nine out of every ten bears in this forest

would probably not be here at all.

Bears are messy eaters,

and their scraps become food for other forest creatures.

Grey wolves which normally hunt animal like deer

join the bears feeding along the riverbanks.

They're more than capable of catching salmon themselves,

but often let the bears do the hard work and turn to scavenging.

The wolves of this forest have developed such a strong relationship

with the coast that they barely venture beyond its limits.

This isolation could start them on the slow path

towards becoming a new wolf species -

the coastal wolf.

These wolves are not isolated on an island or in a valley,

but instead isolated by their unique behaviour.

It's a life that's centred around the coast

and the habits are passed on from mother to young.

It's just another reminder about the importance

of the marine ecosystem to the thriving of life here.

But it isn't just the bears and wolves that rely

so heavily on the salmon.

Larger life forces in this forest depend on the salmon too.

But the bustling rivers full of fish are no use to them yet.

The forest's waiting game continues.

The surviving salmon move on...

..driven by raging hormones which have now turned many of them red.

They travel far into the forest,

some for over 1,000 kilometres, into the tiniest streams.

Their incredible sense of smell carries them to the stream

where they themselves were born and where now,

they'll mate and lay their eggs.

This is their ultimate sacrifice.

With their eggs safely tucked away on the riverbed,

their one-way journey is at an end.

They've exhausted themselves to get here

and invested all their energy reserves.

Their wasted bodies can swim no more.

Salmon carcasses sprawl across the river,

but this seemingly useless death is not wasted.

These carcasses represent the massive injection of nutrients

that the forest ecosystem has been waiting for -

the nutrients that are the elements of life.

Even in death, the salmon feed the animals of the forest.

Carried onto land by scavengers, salmon become soil.

Their nutrients seep into the water table

and it's now the trees' turn to feast on the salmon.

These are the nutrients that drive the coastal forest

and the super-sized trees grow fast, tall and strong.

But the death of the salmon is not a completely selfless act.

The nutrients in their bodies feed the streams,

they feed algae and insects...

..that will be a miniature feast for the tiny baby salmon

that will emerge the following year.

The next generation of nutrient messengers that will live out

their adult lives in the ocean

and will one day return to this same spot in the riverbed

to make the ultimate sacrifice of their own.

Life on every level, from mosses to lichens, trees to animals,

flourish in this coastal rainforest.

The trees close to salmon streams grow taller and faster.

The forest animals have more food

and live in higher densities in these forests.

Some have even become so tied to the ocean

that they are truly becoming coastal specialists.

The secret of this forest's success doesn't come from the land at all,

but from the riches of the Pacific Ocean sitting just offshore.

This is a forest fuelled by the ocean.