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Trees, surely among
the most magnificent of all living things.

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Some of the largest organisms on Earth,
dwarfing all others

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and these are the tallest of them all.

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The deciduous and coniferous woodlands
that grow in the seasonal parts of our planet

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are the most extensive forests on Earth.

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Their sheer extent stuns the imagination.

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The barren snows of the Arctic.

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A thousand miles from the North Pole
and heading south.

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This is the very first place that trees can grow.

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To begin with, the conifers are sparse
but soon they dominate the land.

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This is the taiga forest.

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There are as many trees here
as in all the world's rainforests combined.

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The taiga circles the globe
and contains a third of all the trees on Earth.

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It produces so much oxygen that it refreshes
the atmosphere of the entire planet.

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At the taiga's northern extent,

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the growing season
can last for just one month a year.

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It can take 50 years for a tree
to get bigger than a seedling.

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It's a silent world where little stirs.

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But there are occasional signs of life,
stories written in the snow.

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The prints of an Arctic fox
and the hare it might have been stalking.

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A female polar bear and her two cubs.

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Some animals are so difficult to glimpse
that they're like spirits.

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One could live a lifetime in these woods
and never see a lynx.

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The cat must roam hundreds of miles
in search of prey

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and may never visit
the same patch of forest twice.

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It's the very essence of wilderness.

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With so few prey animals here,
life for a hunter is particularly hard.

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Creatures are scarce
because few can eat conifer needles.

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The moose is an exception.

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Growth is so difficult

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that conifers protect their precious leaves
by filling them with resin.

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That reduces water loss,
but it also make them very distasteful.

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At least the conifer's seeds are edible.

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But they're protected within armour-plated cones
and it takes a specialist to reach them.

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The crossbill's extraordinary beak
can prise apart the scales

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so that its tongue can extract the seeds.

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Birds are fortunate.

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When the seasonal crop is gathered,
they can fly south.

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But one animal is so expert at survival
in this frozen forest

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that it stays here and is active all year long.

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In local folklore,
the wolverine is a link to the spirit world

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and a cross between a bear and a wolf.

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In reality, it's a huge weasel.

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Its bulk helps to conserve body heat
and also broadens its menu.

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It's so big and powerful,
it can even bring down an adult caribou.

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For its size, it's said that the animal
can eat more in one sitting than any other.

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Which is why it's also known as the glutton.

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Being gluttonous here is a very effective strategy.

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It's wise to eat all you can when you can.

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And when even a glutton can't eat more,

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it stores what's left for later
in the surrounding deep freeze.

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Spring in the ice forest.

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The capercaillie can also digest conifer needles.

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But feeding is not its priority at the moment.

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Like gladiators, the males square up for a battle.

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Each may have just a single chance
to impress a female.

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Neither can afford a lapse in concentration.

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The injured loser may not survive.

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The inhabitants of this great wilderness

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may live and die
without ever having contact with humanity.

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Long may it be that way.

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The northern forests may be the largest on Earth,

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but to see coniferous trees
that have reached their full potential

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you must travel 1,000 miles south of here.

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The Pacific coast of North America.

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The land of hemlock, Douglas fir
and giant redwood.

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Here water is never locked up in ice.

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And even if rains fail,

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the needles can extract moisture from the fogs
that roll in from the sea.

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The sun's energy powers these forests,
not for one month as it does in the taiga,

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but for half the year.

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These conifers grow at ten times the rate
of those near the Arctic

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and they live for thousands of years.

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One grove of redwoods in California
contains three of the tallest trees on Earth.

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This one is over 100 metres high,
the size of a 30-storey building.

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These forests were growing here
long before humans walked the Earth.

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They were in their prime 20 million years ago

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and existed before the Swiss Alps
or the Rocky Mountains were even raised.

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There is more living matter
in a forest of giant conifers

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than in any tropical rainforest.

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But it's all contained within the trees.

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These are as inedible as those in the taiga.

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So animals are still scarce, but they are present.

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A pine marten.

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It's spring, the best time of year
for a marten to find food.

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Birds' eggs are a seasonal snack
and for a short time there's plenty of them.

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Sometimes perhaps too many.

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But to live here permanently,
the marten needs a more reliable food source.

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Squirrels fit the bill.

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They thrive here on the pine cones

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and although these are also seasonal,
they can be stored and eaten throughout the year.

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The squirrels are busy mating.

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Good news for the hunter.
A distracted squirrel is a vulnerable squirrel.

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But this time the amorous couple are safe.

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There is a loner stocking his larder
who will be the easier target.

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Early summer
and great grey owl chicks are fledging.

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Adults can only raise young here

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in years when the seasonal vole crop
is big enough to support them.

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The moment has arrived for their first flight.

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Leaping from the world's tallest trees
is not for the faint-hearted.

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If you're going to fall here,
it's quite a good idea to do it in stages.

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The ground is no place for an owl.

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If he's to climb to the top of his class,
he'll need to persevere.

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So now, let's have another go.

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The American conifer forests
may not be the richest in animal life

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but their trees are extraordinary.

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This giant sequoia, a relative of the redwood,
is the largest living thing on Earth.

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Known as General Sherman,
it's the weight of ten blue whales.

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Higher up in the nearby mountains,
bristlecone pines.

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The oldest organisms on the planet.

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Some have been here for 5, 000 years.

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They were alive before the pyramids were built

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and were already 3, 000 years old
when Christ was born.

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Across the equator in the southern hemisphere,
there are forests that mirror those of the north.

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Here in South America, araucaria trees, or
monkey puzzles, are like the conifers of the taiga.

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They have waterproof scales instead of needles
and their cones look a little different,

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but the principles are the same.

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Slender-billed parakeets rather than crossbills
extract their seeds.

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Where the growing season is longer,
there are alerce trees, the redwoods of the south.

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As in the frozen north,

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the Valdivian forests of Chile
support very few animals.

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But that is the end of the similarity.

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This is a bizarre world of miniature creatures.

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The pudu, the world's smallest deer,
feeds on the giant leaves of the gunnera plant.

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The female is just 30 centimetres high
at the shoulder

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and her infants are hardly bigger than kittens.

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The male must stay alert.

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There are hunters here
who would snatch his young.

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Another miniature, the kodkod cat.

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It's the smallest cat in all the Americas
and a young pudu would be a feast for it.

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But with the male on guard,
the kodkod must lower his sights.

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Moths are hatching.
They're the last of the summer.

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The tiny cat should be able to score with these.

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No one knows why the creatures here are so small,
but at least they can survive on meagre rations.

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You might call this a game of cat and moth.

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As winter approaches in Chile,
spring is arriving in the northern hemisphere.

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These are the deciduous forests of home.

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Dormant throughout the winter,

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they now undergo one of the most
magical transformations in the natural world.

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By late spring, the landscape is wrapped
in a vibrant fresh green.

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Here, instead of conifers,
there are broad-leaved trees

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and that makes the character of this forest
entirely different.

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Being broad, these leaves trap
much more light than needles.

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But they're also thin, soft and edible.

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And others can eat the leaf-eaters.

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It's spring in the great broad-leaved forests
of Eastern Europe and Asiatic Russia.

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The mandarin ducks are calling.

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The female mandarin nests in a tree hole.

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And when it's time for everyone to leave,
she leads the way.

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The ducklings are only 24 hours old.

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It's a long drop
and a few calls of encouragement are required.

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Two down, seven to go.

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There are still two missing.

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All present and correct.

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But they won't be safe until they reach water.

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And the forest pool is almost a mile away.

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By June, the days are at their longest

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and all across the northern hemisphere
the broadleaves are hard at work.

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On the east coast of North America,
it seems like any other summer's evening.

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But tonight is special.

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After 17 years underground, creatures are stirring.

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The nymphs of the periodical cicada
have been biding their time.

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Now they march like zombies
towards the nearest tree and start to climb.

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At first there are merely thousands.

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But soon more than a billion
swarm all over the forest.

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The biggest insect emergence on the planet
is underway.

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They invade the upper branches
where they climb out of their external skeletons

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and assume their adult winged form.

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At first, they're white and soft.

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But they have until dawn
to complete their transformation.

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After an absence of 17 years,
the forest is now overrun by cicadas.

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The adults are clumsy and very edible.

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For turtles and other inhabitants of the forest,

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this is a feast they're lucky to see
once in their lifetime

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and they gorge themselves while they can.

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Times have never been so good.

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The cicadas have no defences
and virtually offer themselves to their attackers.

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The stream of insects is so relentless

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that soon all the predators
are full to the point of bursting.

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And still the cicadas come.

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With the predators overwhelmed,
the survivors can achieve their purpose.

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After mating, the adults lay their eggs
and then their job is done.

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In just a few days they will all die
and the forest will fall silent.

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The cicadas here will not be heard again
for another 17 years.

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Having fed the predators, the cicadas leave
one final gift for the forest itself.

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The nutrients in a generation of cicadas
are returned to the soil all at once.

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And the trees enjoy a marked spurt in growth.

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This may be the single largest dose of fertiliser
in the natural world.

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In the great broadleaf forests of Eastern Europe,

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the days are beginning to shorten

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and a primeval sound
heralds the onset of autumn.

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Male red deer are starting their rut.

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The air is heavy with the scent of females.

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The rules are simple, winner takes all.

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Across the northern hemisphere,
the deciduous forests are changing.

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Leaves that have provided food and shelter
since the spring, are now shed.

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In the broadleaf forests of Russia,
winter is particularly severe.

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But there will always be some
who benefit from hardship.

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Black vultures scavenge
from the carcass of a seka deer

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that has died of cold or starvation.

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These endangered birds are visitors,

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they've come down from the north
to escape the even colder conditions in Siberia.

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An Amur leopard, the rarest cat on Earth.

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Winter is a difficult time for this hunter.

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There are no leaves for cover
and no young prey animals.

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This female has the added pressure
of having to provide for her one-year-old cub.

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It will be another 12 months
before he'll be able to fend for himself.

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The bickering vultures
have abandoned the carcass.

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It's a valuable discovery for the leopards.

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But the cub
doesn't share its mother's sense of urgency.

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The vultures have left behind plenty of good meat,
but it's stiff with frost.

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The mother works to open the hide
and make feeding a little easier for her cub.

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00:34:55,360 --> 00:34:59,030
There are only 40 Amur leopards left in the wild

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and that number is still falling.

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The harshness of the winter here,
hinders their increase in numbers.

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00:35:10,240 --> 00:35:14,390
It takes one of these females longer
to raise her young to independence

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than it does a leopard in Africa.

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If the mother can sustain her cub
for a few more weeks,

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spring will bring an increase in prey
and her task will lighten.

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For all the inhabitants of this seasonal forest,

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the long, cold wait is nearly over.

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Spring in a deciduous woodland is special.

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With no leaves overhead,
the rays of the sun strike the forest floor directly

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and their warmth rouses plants
from their winter sleep.

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The ground-living plants are in a hurry.

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Before long, the trees above will come into leaf
and steal their light.

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Their flowers decorate the forest floor

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as they advertise their sweet nectar
to the newly emerged insects.

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The spring blooms of the deciduous woodlands
have no equivalent

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in either the great conifer forests
or the tropicaljungles.

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Within a matter of weeks, the canopy has closed

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and only a few wheeling shafts of light
penetrate the woodland.

233
00:37:33,240 --> 00:37:38,070
In the tree tops,
the broad leaves rapidly expand to their full size

234
00:37:38,160 --> 00:37:41,190
to make the most of summer while it lasts.

235
00:37:47,600 --> 00:37:52,190
Then, after a few months,
the days begin to shorten again

236
00:37:52,280 --> 00:37:55,230
and the trees must shut down
and shed their leaves

237
00:37:55,320 --> 00:37:58,870
in preparation for the cold, dark time ahead.

238
00:38:03,880 --> 00:38:09,070
Great tracts of North America flush red
as the season progresses.

239
00:38:10,720 --> 00:38:17,030
The effect is so spectacular and so extensive
that it can be seen from space.

240
00:38:32,240 --> 00:38:37,710
The threat of winter frost
is not the only reason for trees to shed leaves.

241
00:38:42,480 --> 00:38:45,390
These forests stand in the tropics.

242
00:38:45,480 --> 00:38:48,190
Here, day length never changes.

243
00:38:48,280 --> 00:38:50,590
But the dry season is so severe

244
00:38:50,680 --> 00:38:53,670
that the trees can't afford to lose
the amount of water

245
00:38:53,760 --> 00:38:56,510
that would evaporate from their broad leaves,

246
00:38:56,600 --> 00:38:58,790
so the leaves must be shed.

247
00:39:16,280 --> 00:39:20,990
The forest resembles
a European woodland in midwinter

248
00:39:21,080 --> 00:39:25,670
but the heat is overpowering
and its inhabitants unfamiliar.

249
00:39:30,080 --> 00:39:35,270
For the creatures of India's teak forests
these are desperate times.

250
00:39:37,000 --> 00:39:39,270
But salvation is at hand.

251
00:39:39,360 --> 00:39:41,630
The mahua tree is about to bloom.

252
00:39:46,560 --> 00:39:50,270
Its flowers are full of liquid,
making them irresistible.

253
00:39:57,640 --> 00:40:01,830
The mahua is an oasis in a hot, dry desert.

254
00:40:12,280 --> 00:40:17,110
Those that fly or climb
are not the only ones to get a share.

255
00:40:20,920 --> 00:40:26,470
Chital deer follow the Langur monkeys,
collecting the flowers that fall.

256
00:40:32,560 --> 00:40:38,030
The monkeys welcome the deer,
for deer are unrivalled at spotting predators.

257
00:40:39,960 --> 00:40:43,950
If they are relaxed,
it must be safe to come down to the ground

258
00:40:44,040 --> 00:40:46,550
and gather the food that lies there.

259
00:40:56,880 --> 00:41:00,830
But it's not wise to travel far from the sentinels.

260
00:41:52,960 --> 00:41:56,670
Tropical Madagascar, the wet season.

261
00:42:03,680 --> 00:42:07,310
It's now that the baobab trees re-grow their leaves

262
00:42:07,440 --> 00:42:12,870
and collect water to store in their huge trunks
ready for the dry season ahead.

263
00:42:34,000 --> 00:42:37,470
The prehistoric shape of these trees
is rightly famous

264
00:42:37,560 --> 00:42:40,950
but few have ever witnessed
the baobab's real magic.

265
00:42:41,120 --> 00:42:45,030
For that happens at night
and high in the tree tops.

266
00:42:50,840 --> 00:42:57,030
Flush with water, the baobab prepares itself
for an unforgettable display.

267
00:43:13,920 --> 00:43:19,350
Once started, the foot-long flowers
can open fully in less than a minute.

268
00:44:02,480 --> 00:44:06,950
As the flowers open,
the creatures of the forest wake.

269
00:44:18,680 --> 00:44:23,030
The mouse lemurs have been hibernating
throughout the dry season.

270
00:44:23,120 --> 00:44:26,590
With the return of rains, it's time to get busy.

271
00:44:31,880 --> 00:44:36,070
A dozen share this tree-hole,
but there's plenty of room.

272
00:44:36,160 --> 00:44:40,350
The world's smallest primate
is no bigger than your hand.

273
00:44:45,960 --> 00:44:50,670
High in the branches above,
the baobab's nectar is starting to flow.

274
00:45:05,080 --> 00:45:12,030
A drink of this sugary, energy-packed liquid
is an ideal way for the lemurs to start their day.

275
00:45:16,240 --> 00:45:21,270
Liquid oozes from the flower's centre
and trickles down the petals.

276
00:45:37,200 --> 00:45:40,350
But the nectar is not intended for lemurs.

277
00:45:44,440 --> 00:45:50,230
These giant hawk moths are the drinkers
the tree needs to attract.

278
00:45:59,400 --> 00:46:02,550
As they sip, moving from tree to tree,

279
00:46:02,640 --> 00:46:06,510
so they transfer pollen and fertilise the flowers.

280
00:46:20,520 --> 00:46:24,670
Nectar was an excellent first course for lemurs,

281
00:46:24,760 --> 00:46:27,390
but moths are the main dish.

282
00:46:29,040 --> 00:46:34,350
The moths are very important to the lemurs
for they will replenish the fat reserves

283
00:46:34,440 --> 00:46:37,870
that the lemurs need
to survive the barren dry season.

284
00:46:46,160 --> 00:46:49,590
The lemurs might seem to be a pest
for the baobab,

285
00:46:49,720 --> 00:46:55,430
they kill its pollinators and rob it of its nectar
but they do give something in return.

286
00:46:55,800 --> 00:47:01,230
For as they wrestle with the moths,
their fur inevitably becomes dusted with pollen.

287
00:47:01,320 --> 00:47:04,310
So they too become pollinators.

288
00:47:26,240 --> 00:47:32,550
As the alternation of wet and dry seasons
brings change to some tropical forests,

289
00:47:32,920 --> 00:47:38,910
so the progression of summer to winter
dictates life in more temperate regions.

290
00:47:47,680 --> 00:47:51,150
Whether trees have needles or broad leaves,

291
00:47:51,240 --> 00:47:55,150
it is their ability to survive annual change

292
00:47:55,240 --> 00:47:59,590
that has enabled them to cover
such vast areas of the Earth

293
00:47:59,680 --> 00:48:04,310
and made the seasonal forests
the greatest forests of all.