Trees, surely among the most magnificent of all living things.
Some of the largest organisms on Earth, dwarfing all others
and these are the tallest of them all.
The deciduous and coniferous woodlands that grow in the seasonal parts of our planet
are the most extensive forests on Earth.
Their sheer extent stuns the imagination.
The barren snows of the Arctic.
A thousand miles from the North Pole and heading south.
This is the very first place that trees can grow.
To begin with, the conifers are sparse but soon they dominate the land.
This is the taiga forest.
There are as many trees here as in all the world's rainforests combined.
The taiga circles the globe and contains a third of all the trees on Earth.
It produces so much oxygen that it refreshes the atmosphere
of the entire planet.
At the taiga's northern extent,
the growing season can last for just one month a year.
It can take 50 years for a tree to get bigger than a seedling.
It's a silent world where little stirs.
But there are occasional signs of life, stories written in the snow.
The prints of an Arctic fox and the hare it might have been stalking.
A female polar bear and her two cubs.
Some animals are so difficult to glimpse that they're like spirits.
One could live a lifetime in these woods and never see a lynx.
The cat must roam hundreds of miles in search of prey
and may never visit the same patch of forest twice.
It's the very essence of wilderness.
With so few prey animals here, life for a hunter is particularly hard.
Creatures are scarce because few can eat conifer needles.
The moose is an exception.
Growth is so difficult
that conifers protect their precious leaves by filling them with resin.
That reduces water loss, but it also make them very distasteful.
At least the conifer's seeds are edible.
But they're protected within armour-plated cones
and it takes a specialist to reach them.
The crossbill's extraordinary beak can prise apart the scales
so that its tongue can extract the seeds.
Birds are fortunate.
When the seasonal crop is gathered, they can fly south.
But one animal is so expert at survival in this frozen forest
that it stays here and is active all year long.
In local folklore, the wolverine is a link to the spirit world
and a cross between a bear and a wolf.
In reality, it's a huge weasel.
Its bulk helps to conserve body heat and also broadens its menu.
It's so big and powerful, it can even bring down an adult caribou.
For its size, it's said that the animal can eat more in one sitting than any other.
Which is why it's also known as the glutton.
Being gluttonous here is a very effective strategy.
It's wise to eat all you can when you can.
And when even a glutton can't eat more,
it stores what's left for later in the surrounding deep freeze.
Spring in the ice forest.
The capercaillie can also digest conifer needles.
But feeding is not its priority at the moment.
Like gladiators, the males square up for a battle.
Each may have just a single chance to impress a female.
Neither can afford a lapse in concentration.
The injured loser may not survive.
The inhabitants of this great wilderness
may live and die without ever having contact with humanity.
Long may it be that way.
The northern forests may be the largest on Earth,
but to see coniferous trees that have reached their full potential
you must travel 1,000 miles south of here.
The Pacific coast of North America.
The land of hemlock, Douglas fir and giant redwood.
Here water is never locked up in ice.
And even if rains fail,
the needles can extract moisture from the fogs that roll in from the sea.
The sun's energy powers these forests, not for one month as it does in the taiga,
but for half the year.
These conifers grow at ten times the rate of those near the Arctic
and they live for thousands of years.
One grove of redwoods in California contains three of the tallest trees on Earth.
This one is over 100 metres high, the size of a 30-storey building.
These forests were growing here long before humans walked the Earth.
They were in their prime 20 million years ago
and existed before the Swiss Alps or the Rocky Mountains were even raised.
There is more living matter in a forest of giant conifers
than in any tropical rainforest.
But it's all contained within the trees.
These are as inedible as those in the taiga.
So animals are still scarce, but they are present.
A pine marten.
It's spring, the best time of year for a marten to find food.
Birds' eggs are a seasonal snack and for a short time there's plenty of them.
Sometimes perhaps too many.
But to live here permanently, the marten needs a more reliable food source.
Squirrels fit the bill.