The Magical Forest Secrets of our Living Planet


The Magical Forest

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Ten million species live on planet earth.

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Each one is remarkable.

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But none can survive on its own.

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All life depends upon connections.

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Unexpected, invariably complex, beautiful relationships between millions of plants and animals.

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This time, in our seasonal forests,

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why does this lynx need a caterpillar?

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Why does the tree need the fish?

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And why does this truffle fungus need one of these?!

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Flying squirrel!

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Connections like these form the planet's great ecosystems.

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They're vital for all life.

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I want to show you our world as you've never seen it before.

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JAUNTY MUSIC

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New England in autumn.

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There really can't be a more magical place anywhere on earth,

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to appreciate that dramatic transition between summer and winter.

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But we mustn't get blinded by this natural fiesta,

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because such an extreme transformation is a huge challenge for life.

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And autumn is just one of many transformations the forest must face.

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From summer to winter, this land of plenty will appear to collapse,

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before attempting to rebuild itself all over again in the spring.

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To see how, I'm going to, what is for me, the greatest seasonal forest on the planet.

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The wooded wilderness that stretches right across North America.

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From the land of the Canadian lynx,

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to the land of the grizzly bear.

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Our story begins in autumn.

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As the days are drawing shorter, less light is feeding the forests.

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Deciduous trees are shedding their leaves.

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Many creatures are burrowing away to escape the cold.

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Others are simply leaving.

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But there's one animal with a crucial job to do.

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Now, before the winter sets in.

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It's a job the entire forest depends upon.

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The best time to see them is in the first couple of hours after dark.

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And what I'm hoping is, if I stand here and stay really quiet, I'll be in for a real treat.

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It's a creature I've waited all my life to see.

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But they move so fast!

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Oh! Did you see that?!

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That was amazing, it went right past my face!

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Flying squirrel!

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They really are expert gliders.

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They can glide for up to 200 metres!

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When I was a kid, I was obsessed with things that were, you know, not meant to fly.

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Flying fish, flying frogs, flying lizards, flying squirrels.

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This is the first time I've ever seen them.

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It was worth a 45-year wait. Honestly!

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Did you... Did you see that?!

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I felt it. It went right through my hair. Seriously!

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Centre parting!

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It was like a sheet of A4 coming right over my face

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and as soon as they hit the tree they're running and up they go.

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They're just criss-crossing all the trees.

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They immediately scamper up to the top, then take off and glide again,

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and sometimes, I've noticed, they can even change direction in flight.

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Arghh!

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One hit me in the chest!

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It doesn't come better than that, does it?

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It doesn't get more exciting.

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But what on earth have they got to do with our story?

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Well, at the moment, these flying squirrels are in the woods

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trying to find as much food as possible before the weather turns nasty and the winter kicks in.

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But what are they after? Well, they're after these.

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Truffles.

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They're the fruiting bodies of fungi and they appear in the damp cool of autumn.

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In preparation for winter,

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the hungry squirrel needs to hoard food such as truffles.

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But the truffles also need the squirrel to eat them.

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As the squirrel moves through the forest, the spores are dispersed.

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And that's crucial, not just for the truffle, but for the trees.

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What's so special about these truffles?

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They certainly don't look much, and the smell can be said to be an acquired taste.

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And they're not just here as another organism to be eaten by hordes of hungry squirrels either,

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because without these truffles, and all the other fungi here in the wood,

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this woodland simply couldn't function. It couldn't exist.

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Why?

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Well, take a look beneath the soil down here.

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Each truffle has thread-like roots extending from it.

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The threads extract nutrients in the soil, from rotting material like leaves.

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And, cunningly, they also tap into the roots of the trees to siphon off sugars.

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But this is not a one-way relationship,

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because the tree can now tap into the nutrients extracted by the fungal threads.

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This symbiotic relationship between the trees and the fungus,

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where each is dependent on the other,

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clearly helps the tree grow, but it's not only that.

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It greatly extends the reach of its roots

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because, in effect, they become as extensive as the fungal network that they're connected to.

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In autumn, throughout the northern hemisphere, trees use fungi to extend their roots

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and absorb sufficient nutrients for the big freeze ahead.

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I love this web of relationships - the squirrels, the fungi, the trees.

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It ensures that they're all ready to face the winter.

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But for me, one of the most magical relationships of all is seen on the far west coast of Canada,

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as one of the world's most ancient forests

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prepares for the oncoming challenge.

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Here, I can stand at the foot of 1,000-year-old cedars

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and 90-metre-tall Sitka spruce trees.

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The combination of large mountains

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and ocean winds generates unusually heavy rainfall -

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earning this place the title The Raincoast.

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There's so much rain in autumn that the rivers are swollen.

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And that is vital to the forest's survival.

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There's a significant event happening here,

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which allows the whole forest not only to survive the winter,

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but also to flourish throughout the course of the year.

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But you know, the really incredible thing is this key to life

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is not here in the forest at all at the moment, but it will be soon.

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After years at sea, salmon are returning to spawn

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in the same forest streams in which they were hatched.

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The swollen rivers make it easy for them to swim deep into the forest.

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But the scent of home also draws them irresistibly towards danger.

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Predators make the most of this banquet of seafood.

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But none of them compare to the most formidable fish eater of all.

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Grizzly bears. Just look at this - there's a female here,

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about 40 metres in front of me, in the shallows, fishing for salmon.

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Behind her, on the bar over there, she's got three cubs.

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They're not struggling to catch the fish here.

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There's such a tremendous surfeit of tired salmon out there.

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All she really has to do is wander into those shallows

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until one comes close.

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And then she can grab it, much to the delight of her cubs.

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For these cubs, it's the first salmon run.

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They've got to learn how to catch fish by watching their mother.

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Look at this! Look!

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This is the adult grizzly,

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that's just leapt off the island there,

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and caught a salmon. Look at that! Right in its mouth.

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Over just six weeks in autumn,

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tens of millions of salmon are going to return to these rivers.

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And during the course of a day

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one adult bear like this can eat 40kg of salmon,

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and during the course of a salmon run 1400kg -

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that's just one bear's intake.

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But every salmon caught by these bears

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increases their chances of survival.

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They are incredibly important to these bears,

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particularly at this time of year,

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when it's essential that they bulk up as quickly as possible

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before they slip into hibernation with the winter coming.

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This cub hasn't quite got the hang of it yet,

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but he hasn't got long -

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the salmon run has only got a couple of weeks to go.

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Until they learn, Mum has to work even harder.

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Every salmon caught makes a real difference.

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These bears, those that are close to a huge amount of salmon,

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grow 80% larger than those in other areas.

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They have 25% more cubs,

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and occur at densities 50 times greater.

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So salmon, frankly, are great news for bears.

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Exciting as it is to watch,

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there's a lot more going on here

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than simply bears catching fish.

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And the reason is thanks to what happens next.

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And the only way to see it is with remote cameras,

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positioned deep in the forest.

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These younger bears have carried fish 30m from the river.

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Because here they are less likely to be challenged by hungry adults.

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So they can eat in peace.

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There's so much fish available, they just eat the richest bits

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to lay down enough fat for hibernation.

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The rest appears to be wasted, abandoned on the forest floor!

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Along with our camera.

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The aftermath of this feast is unbelievable.

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Up to four tonnes of carcasses are left in an area the size

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of a football pitch.

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But what have dead fish

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got to do with the forest preparing for winter?

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Well, this is where it starts to get really intriguing,

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because the catching of the salmon is just the start of it.

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Bears aren't the only creatures

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attracted by such a feast.

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A banana slug.

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At 25cm long, it's one of the largest slugs in the world.

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And masses of insects.

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These flies won't survive the winter,

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but if they plant their eggs in the salmon's flesh,

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their offspring might.

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This flurry of activity

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eventually breaks the flesh down into simple nutrients

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that are absorbed into the soil.

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The significance of all of this decaying fish

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goes far beyond it being just a feast for scavengers.

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Without all of these rotting salmon accumulating here every autumn,

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this forest would be a very different place.

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The salmon nutrients in the soil are taken up by the fungi.

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So this ancient forest is better equipped to face

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the almighty change that's fast approaching.

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For forests in the Northern Hemisphere, time has run out.

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Every day the sun sinks lower in the sky.

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Winter.

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And on the face of it,

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all of the life here seems to have just gone away.

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Those truffles and the seeds,

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they're locked away underneath all of this snow.

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The salmon run is over.

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The vegetation... look at it. It appears to have shut down.

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Even the water is in short supply - it's all frozen.

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All of those connections appear to be broken.

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The fungi have reduced their recycling to a bare minimum.

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And the trees they're connected to are producing little in return.

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The deciduous trees pre-empted the winter by shedding their leaves.

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The conifers are slowing down, too.

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The waxy coating on the needles protects their leaves from the cold.

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But not everything here can

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exist in a state of suspended animation.

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Some of the animals have to remain active,

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and surviving in conditions like this isn't easy.

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The icy cold is the cue for the bears

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to leave the forest altogether.

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With the salmon run over,

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they are retreating to their winter dens, up in the mountains.

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They must spend the entire winter living off their fat reserves

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gained by feeding on all of those salmon.

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The squirrels,

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and other small mammals, must keep activity to a minimum,

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only occasionally venturing out to retrieve their autumn caches.

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The lower the temperature falls,

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the more vulnerable creatures become.

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Winter has been too brutal for this young white-tailed deer,

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but at least it's an opportunity for some nocturnal scavengers.

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A racoon.

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Out of the forest, a fisher - a relative of martens and weasels.

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And it's smart enough to keep this meal to itself!

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But there is more to this lifeless-looking forest

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than just the scavengers.

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For most creatures, winter is a brutal and unforgiving time.

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But others actually thrive in these conditions.

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You see, for animals that are adapted to live in winter,

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this stripped-down forest ecosystem,

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well, it's a wonderland.

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In winter, here, there are beautiful connections,

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between some of the forest's most enchanting characters.

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There is one predator here,

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an incredibly important animal

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that has no intention of avoiding the snow,

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because, unlike me, it's perfectly adapted to it.

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But it's an enigma, a really, really shy animal,

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one that's difficult to study.

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Having said that,

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scientists have been tracking them through the forest here

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for more than a decade.

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Scientists from the Maine Department of Fisheries and Wildlife

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have set a trap to catch one alive.

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With those distinctly pointed ears, it can only be a Canadian lynx.

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Lynx are the world's most northerly-dwelling cats.

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And this particular lynx is well-known

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to chief scientist Jen Vashon.

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The ear tags are blue with white.

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That indicates it's L1-11.

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He's called L1-11 and was born in May 2004.

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They've discovered that he is just one of hundreds of lynx living here.

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It's too intimidated with everybody right there.

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In fact, there are more lynx living in these Eastern forests

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than anywhere else in North America.

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Now, the fact that L1-11 has lived all of his life

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in this frozen forest

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has to mean that this is a perfect place for a lynx to live.

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But how can a top predator like this

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survive in such a stripped-down environment,

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when there appears to be so little else here?

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The tracks of their prey are everywhere,

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but actually finding one is a real challenge

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because its winter camouflage is perfect.

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It's taken some finding, but it's there - the snowshoe hare!

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You can just make out its beady little black eye,

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and the black tips to its ears.

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And these things form 80% of a lynx's diet.

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But, as you can see, they don't make it easy for that lynx.

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Their camouflage is astonishing.

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In the summertime they're brown,

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but in the winter they moult through to a white coat.

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But they also use this thick brush.

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It provides them with excellent cover

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to hide from the lynx, also hide from the elements,

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but it's also crucial in keeping them alive,

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because they climb on top of the snow and nibble at

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all of the shoots and the bark growing from all of this brush.

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Look at that! Beautiful, and with those big snowshoe feet,

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it just sort of floats across the surface of the snow.

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But what the snowshoe hare needs most to survive the winter

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is a specific type of vegetation.

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It must be the right height to eat,

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and provide enough cover to hide from all those lynx.

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So, the vegetation, here, must be perfect.

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And the reason that it does grow into this perfect environment,

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well, you could never guess.

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The most beautiful thing about this story

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is that the lynx, the hare,

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patches of cover like this amongst the forest, didn't happen by chance.

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They're all controlled by the most unlikely of creatures,

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a tiny thing, less than the size of one of my fingernails.

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And at the moment it's hiding,

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having burrowed into the bark of one of these trees,

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or perhaps in a crack in a log lying on the forest floor,

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covered with frozen snow.

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But it's there, and it's waiting.

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It's waiting for springtime.

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As the hours of daylight increase and the ground thaws,

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as if by magic, the northern forests change again.

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As new leaves appear, trees start producing sugars,

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and that's good for the fungus in the soil.

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Entwined with the trees' roots, they can siphon off some of these sugars.

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But not everything appears so harmonious.

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In the land of the lynx,

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something extraordinary is happening to the forest.

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These trees may have endured the winter,

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but now it's spring, they're under attack.

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Some are even dying.

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But what's happening here now is vital

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for how this ecosystem functions over the year.

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This defoliation is entirely natural.

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And I might be able to find one of the culprits down here,

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although they're quite tricky to spot.

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They live in these fresh, green shoots.

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Yes, here we are.

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Now, wrapped delicately in these leaves

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is a species that is single-handedly

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influencing the ecology of this entire forest.

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Inside this nest is the caterpillar of the spruce moth. The budworm.

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And it hasn't only wrapped itself up in those leaves

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to hide from predators,

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because it's eating them as well.

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And it doesn't just eat the leaves,

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it also eats the buds, the flowers, and the cones on the tree here.

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Up in the canopy, a tiny budworm caterpillar

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has just emerged from hibernation.

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It's racing to fatten itself up.

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When it's finished on one branch, it releases a strand of silk,

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and abseils down to the next.

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It's a risky business being a juicy, fat caterpillar -

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you're in danger of being spied by all of those birds,

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just back from migration.

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But the caterpillar has a plan -

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it uses its silk

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to weave the needles together and hide in a dense web.

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Now, the springtime assault by these caterpillars

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is bad news for the trees.

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But for other inhabitants of these forests,

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these caterpillars are heroes.

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It's thanks to the behaviour of this species

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that one of North America's most elusive and charismatic predators -

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the Canadian lynx - is enjoying a bit of a renaissance

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in forests like this one.

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But the caterpillar lives all the way up there, in the canopy.

0:35:120:35:18

Whilst the cat with the pointed ears is prowling around down here.

0:35:180:35:22

So, how can a humble insect like this have any impact

0:35:220:35:27

on a formidable thing like that?

0:35:270:35:30

I bet the lynx never even sees the caterpillar

0:35:300:35:33

throughout the course of its life.

0:35:330:35:35

Why does the lynx need the caterpillar?

0:35:350:35:38

The clue is how they affect the lynx's prey on the forest floor.

0:35:410:35:46

For decades, scientists have studied budworm caterpillars,

0:35:480:35:53

and a remarkable pattern has emerged.

0:35:530:35:55

They've discovered

0:35:550:35:57

that the population of caterpillars fluctuates dramatically.

0:35:570:36:01

And at the peak of a cycle

0:36:030:36:05

there can be tens of thousands of budworms in a single tree.

0:36:050:36:09

And this has devastating consequences.

0:36:170:36:20

Whilst these dramatic natural events might be a catastrophe

0:36:240:36:28

for the established trees, for anything trying to grow

0:36:280:36:32

on the forest floor they are an absolute bonus.

0:36:320:36:35

In here, where it's dark, there's very little,

0:36:350:36:38

very poor diversity - just some mosses and a few ferns.

0:36:380:36:42

But as soon as there's a break in the canopy

0:36:420:36:44

and the sunlight can flood in, well, look at the difference.

0:36:440:36:49

Lots of wild flowers, there's a young maple coming through here,

0:36:490:36:53

mountain ash, and, most importantly of all, regenerating spruce and fir.

0:36:530:36:59

The hares essentially need these regenerating conifers as shelter.

0:37:010:37:07

And of course what's good for the hares is also good for the lynx.

0:37:080:37:13

It's such an elegant connection.

0:37:160:37:20

Without the spring emergence of the hungry caterpillars

0:37:200:37:23

to chew holes in a dense canopy,

0:37:230:37:25

there wouldn't be enough light flooding the forest floor.

0:37:250:37:30

And, with less light down here, there would be less growing

0:37:300:37:34

for our snowshoe hare to forage and to hide in,

0:37:340:37:38

and then there would be nothing for L1-11

0:37:380:37:41

and all of those hundreds of other lynx to eat.

0:37:410:37:45

And that's why the lynx needs the caterpillar.

0:37:450:37:50

And now it's spring,

0:37:500:37:51

there's no better time to see what the future holds

0:37:510:37:54

for the lynx population.

0:37:540:37:56

Wildlife biologist Jen is doing a count.

0:38:130:38:17

She has detected a signal from a radio-collared female.

0:38:190:38:24

There she is.

0:38:400:38:44

But there might be something else here.

0:38:440:38:47

Safe inside her den, a lynx cub.

0:38:500:38:56

He's just a few weeks old.

0:38:560:38:58

His eyes aren't even open.

0:39:110:39:13

Jen must work fast before Mum returns.

0:39:130:39:17

Thanks to the timing of the budworm opening the canopy this spring,

0:39:340:39:39

there's going to be enough prey for these lynx to hunt next winter.

0:39:390:39:43

Far away to the west, The Raincoast forest is coming back to life.

0:40:000:40:07

Thanks to the richness of the autumn salmon run,

0:40:200:40:23

the bears have survived the winter.

0:40:230:40:25

They've now returned to the forest, looking for something to eat.

0:40:320:40:36

They'll survive on vegetation until the next salmon run.

0:40:360:40:39

The emergence of the bears is a cue for scientists

0:40:440:40:48

to conduct a rather risky experiment.

0:40:480:40:51

They need a large, hungry, bear.

0:40:510:40:54

It's the only way to measure the impact of all those salmon

0:40:540:41:00

on this ecosystem

0:41:000:41:02

and to understand why this vast,

0:41:020:41:05

ancient forest has thrived for so long.

0:41:050:41:09

For such a big question,

0:41:150:41:17

the methods employed by senior researcher Chris Darimont

0:41:170:41:22

seem a bit curious.

0:41:220:41:23

He's equipped with a can full of old salmon guts,

0:41:260:41:30

effusing, probably, the most disgusting smell known to man.

0:41:300:41:36

This is wonderful stuff.

0:41:360:41:39

But he hopes the bears are going to love it.

0:41:420:41:46

He's made an aerial lure.

0:41:460:41:51

So, the wind will carry this distinctive perfume

0:41:510:41:53

deep into the forest.

0:41:530:41:55

Wind, extra boost.

0:41:550:41:56

Now they surround the area with barbed wire.

0:42:040:42:07

And it's this

0:42:080:42:10

that they hope will collect what they're so interested in -

0:42:100:42:13

a single hair from a visiting bear.

0:42:130:42:18

Now the site is prepared,

0:42:190:42:21

it's time to set some remote cameras,

0:42:210:42:24

and beat a hasty retreat.

0:42:240:42:26

Personally, I'm very happy to watch from a safe distance -

0:42:320:42:36

it's not the smell - some of those bears are huge!

0:42:360:42:40

Look at the size of this bear!

0:42:430:42:46

As a trap, this is the perfect bait, it's working brilliantly.

0:42:510:42:56

The bears have come in,

0:42:560:42:57

and they're snagging themselves on the wire there.

0:42:570:43:00

You can see it vibrating about. And that's just what we want.

0:43:000:43:04

Fresh out of hibernation,

0:43:040:43:06

it seems they can't resist this pile of stinking salmon.

0:43:060:43:11

This one's even rolling around in the stuff now.

0:43:110:43:14

No doubt it values the scent - I'm not sure we would.

0:43:140:43:17

The bear's coat has been growing for nearly a year.

0:43:210:43:24

But soon it will be moulted and lost.

0:43:240:43:27

The more bears we can attract, the better.

0:43:310:43:34

Now the coast is clear,

0:43:440:43:47

and it's time to retrieve any fur from the barbed wire.

0:43:470:43:51

So, what on earth can a hair tell us about this forest ecosystem?

0:43:560:44:04

Well, hair is made of protein,

0:44:090:44:11

sourced from whatever the bear has been eating over the last year.

0:44:110:44:16

And by analyzing this hair,

0:44:270:44:30

science can reveal an astonishing level of detail about a bear's life.

0:44:300:44:35

We can learn so much from a single bear's hair.

0:44:420:44:47

So I know, for instance, that this one has come from a female grizzly.

0:44:470:44:51

I know exactly what it's been eating even on a week-by-week basis,

0:44:510:44:54

where that food has come from

0:44:540:44:56

and even the impact on the quality of its life.

0:44:560:44:59

So this bear has been getting most of its protein,

0:44:590:45:03

not from the forest around here,

0:45:030:45:05

but actually from the deep ocean, via the salmon.

0:45:050:45:08

And we know that throughout the course of the year

0:45:080:45:12

80% of that bear's protein has come from these salmon.

0:45:120:45:16

And that's surprising because, remember,

0:45:160:45:18

they're only available to the bear for a few weeks during the autumn.

0:45:180:45:21

And yet the impact is clearly lasting all year.

0:45:210:45:25

So, how come the bears appear to be so full of salmon?

0:45:260:45:31

Well, back in autumn, we saw the bears scattering fish carcasses

0:45:420:45:46

all around the forest floor.

0:45:460:45:48

As the protein in those rotting salmon broke down,

0:45:560:46:00

nitrogen from it accumulated in the soil.

0:46:000:46:03

And this salmon nitrogen

0:46:030:46:05

is like fertiliser!

0:46:050:46:09

So, in spring,

0:46:110:46:13

nutrients all the way from the ocean gradually appear

0:46:130:46:17

in all the vegetation growing here.

0:46:170:46:20

Just in time for the hungry bears

0:46:210:46:23

to eat as they emerge from hibernation.

0:46:230:46:28

And hungry bears have huge appetites -

0:46:280:46:33

they'll eat a third of their body weight every day!

0:46:330:46:35

So that's why their bodies appear to contain so much salmon.

0:46:380:46:44

But the impact of this ocean-born nitrogen

0:46:520:46:56

extends far beyond bears and their food.

0:46:560:46:59

This particular form of nitrogen

0:47:020:47:04

can be found in almost all of the animals and plants

0:47:040:47:07

that appear here in the spring.

0:47:070:47:10

These Rufous Hummingbirds have migrated to the forest to breed.

0:47:200:47:25

They're drinking nectar from plants

0:47:250:47:27

that have been fertilised by rotted fish.

0:47:270:47:29

So, they'll carry the same salmon nutrients with them

0:47:290:47:33

as they fly through the forest.

0:47:330:47:35

Many of the insects pollinating the plants now

0:47:430:47:47

were incubated in that decaying flesh back in the autumn.

0:47:470:47:50

As they themselves are eaten,

0:47:530:47:56

the salmon nutrients are spread even further.

0:47:560:47:59

Thanks to the bears, the insects, and the birds,

0:48:020:48:06

this salmon fertiliser is spread deeper and deeper into the forest -

0:48:060:48:11

sometimes as much as 800m from the river,

0:48:110:48:14

and this pulse of nutrients then allows the organisms

0:48:140:48:19

which define the forest itself to prosper - its trees.

0:48:190:48:27

Doctor Tom Reimchen can measure exactly how much

0:48:410:48:45

these vast old trees need the fish.

0:48:450:48:49

The secret is to look inside the tree, by taking a core sample.

0:48:510:48:58

Written on it is the entire story of this 300-year-old tree.

0:49:050:49:09

The rings I see are two, three, even four millimetres,

0:49:160:49:20

which continues back

0:49:200:49:22

to even the early parts of the 1800s, late 1700s.

0:49:220:49:28

Tom has taken similar samples from thousands of trees.

0:49:280:49:34

An entire forest is lined up in his lab,

0:49:340:49:38

each tree waiting to tell its own story.

0:49:380:49:41

In this seasonal climate, annual rings are created as the tree grows.

0:50:010:50:06

From these rings, he can determine not just the age of the tree,

0:50:120:50:16

but also the amount of growth in each year.

0:50:160:50:19

Some of the rings are thicker than others,

0:50:190:50:22

showing that the tree has grown more.

0:50:220:50:26

Like the bear fur, each annual ring can be analyzed.

0:50:320:50:38

Tom can search for the same type of nitrogen

0:50:380:50:41

that's found in the bear's hairs.

0:50:410:50:44

It comes from the ocean

0:50:440:50:46

and it's called nitrogen-15.

0:50:460:50:50

And the data will tell us just how much nitrogen in those trees

0:50:540:51:00

comes from all those salmon.

0:51:000:51:03

I think this is really exciting.

0:51:080:51:12

You see, the annual growth rings here

0:51:120:51:15

show the presence of the stable isotope Nitrogen-15,

0:51:150:51:18

which significantly comes from the oceans.

0:51:180:51:21

It could only have been carried here by the salmon.

0:51:210:51:25

Now look, here is the present, the bark on the outside of the tree,

0:51:250:51:28

so these rings represent perhaps the last 15 years

0:51:280:51:31

and they're very closely packed together.

0:51:310:51:34

But here, back in the 1980s, the rings are twice as thick.

0:51:340:51:39

The trees have been growing twice as much during the course of a year.

0:51:390:51:43

So, perhaps the salmon runs then were even more productive

0:51:430:51:47

than they have been recently.

0:51:470:51:50

But that's not the best thing. Come and have a look at this.

0:51:500:51:53

By measuring the abundance of that nitrogen isotope in this material,

0:51:530:51:58

I can tell you that majestic old giants like this beauty here

0:51:580:52:04

are actually composed of up to 85% material

0:52:040:52:09

that's derived from salmon.

0:52:090:52:13

Now, when I was a teenager,

0:52:130:52:15

I remember learning that I was made of carbon,

0:52:150:52:19

and carbon could only be formed when stars died.

0:52:190:52:22

Effectively I was made of dead stars

0:52:220:52:24

and that struck me as terribly romantic.

0:52:240:52:28

But look at this.

0:52:280:52:30

This is a forest made of the ocean!

0:52:300:52:32

That's why the tree needs the fish.

0:52:350:52:39

Without this unlikely-sounding relationship,

0:52:390:52:44

this magnificent ancient forest just wouldn't be the place it is today.

0:52:440:52:48

But there is one more relationship,

0:52:510:52:56

crucial to seasonal forests all around the world,

0:52:560:53:00

when it comes to surviving constant change.

0:53:000:53:03

And it's one that reaches its greatest intensity now,

0:53:030:53:08

at the height of summer.

0:53:080:53:10

It's the driest time of year, and the trees need water.

0:53:120:53:16

Fortunately, united with their fungal partners,

0:53:200:53:23

the trees have massively extended their roots.

0:53:230:53:26

Fungal threads in the soil are absorbing water

0:53:260:53:29

and passing it to the tree.

0:53:290:53:31

But what has only recently been discovered

0:53:330:53:37

is the sheer scale of these fungal root networks.

0:53:370:53:42

A single cubic centimetre of the soil here

0:53:420:53:46

can have a mile of these white fungal threads running through it.

0:53:460:53:52

They're called mycorrhizae.

0:53:520:53:55

And, for me,

0:53:550:53:57

it's these organisms that are the real secret of the forest here.

0:53:570:54:01

In the lab, the genetic fingerprints

0:54:030:54:06

of individual mycorrhizae have been identified.

0:54:060:54:10

By mapping an area 30m across,

0:54:160:54:19

it's been discovered

0:54:190:54:21

that individual fungi connect to more than a single tree.

0:54:210:54:27

Just one fungus can be joined to 80% of all of the plants growing here.

0:54:270:54:33

And, amazingly, these physical links enable different species of plants

0:54:340:54:41

to exchange nutrients.

0:54:410:54:44

Older established plants are even nurturing

0:54:440:54:47

younger weaker ones.

0:54:470:54:49

It acts like an underground welfare system!

0:54:490:54:53

These giant webs

0:54:540:54:56

connect all of the trees in this forest,

0:54:560:55:01

and keep them, and all of the things that are dependent upon them, alive.

0:55:010:55:05

That's why scientists are calling this the Wood Wide Web.

0:55:050:55:11

It's thanks to this natural phenomenon, the Wood Wide Web,

0:55:220:55:27

that, together, the trees in the forest ecosystems are resilient -

0:55:270:55:32

resilient enough to cope with the dramatic changes

0:55:320:55:36

they encounter every year.

0:55:360:55:40

And what's really amazing is how the web is built.

0:55:480:55:52

It's thanks to hungry mammals like our flying squirrels

0:55:550:55:58

that this essential life support system is effectively maintained.

0:55:580:56:04

It's actually fair to say that these trees wouldn't be standing here,

0:56:050:56:11

wouldn't be thriving, unless a squirrel had eaten a truffle.

0:56:110:56:16

And that is fantastic!

0:56:160:56:19

It is fantastic.

0:56:220:56:23

It's fantastic to think that what animals do in one season

0:56:230:56:27

influences the forest ecosystem throughout the year.

0:56:270:56:33

It's almost as if all of these stories are choreographed.

0:56:350:56:42

The arrival of the salmon at exactly the right time

0:56:450:56:49

to fatten the bears for winter.

0:56:490:56:52

Then, the emergence of the lush green vegetation

0:56:520:56:56

fertilised by those salmon

0:56:560:56:58

to sustain the bears when they emerge from hibernation.

0:56:580:57:02

The squirrels - foraging for truffles in the autumn time,

0:57:020:57:06

and sowing their spores throughout the forest

0:57:060:57:09

to grow a fungal network

0:57:090:57:11

that joins all of the trees and all of the plants,

0:57:110:57:15

and provides them with nutrients.

0:57:150:57:17

The budworm - chewing a hole in springtime in the canopy,

0:57:170:57:23

so that in summer, sunlight floods down to the forest floor

0:57:230:57:28

and produces the perfect hunting habitat for lynx.

0:57:280:57:33

It's all in the timings.

0:57:330:57:36

And it's this that makes these temperate forests

0:57:360:57:40

such magical places.

0:57:400:57:42

Join me next time,

0:57:590:58:01

when I'll be travelling to some of the world's greatest water habitats.

0:58:010:58:05

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0:58:210:58:23

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