0:00:45 > 0:00:49This must be one of the strangest places I've ever taken a stroll.
0:00:49 > 0:00:51I've even had to bring my passport.
0:01:05 > 0:01:08Ah - this is what I've been looking for.
0:01:18 > 0:01:20RUMBLING
0:01:20 > 0:01:22Oh! Hear that?
0:01:22 > 0:01:24The 12:40 -
0:01:24 > 0:01:28bang on time, destination Paris.
0:01:28 > 0:01:29This is the Channel Tunnel.
0:01:29 > 0:01:31Back there, France...
0:01:31 > 0:01:34and straight ahead of me, good old Blighty.
0:01:34 > 0:01:39Today, this is the only way of walking between the two
0:01:39 > 0:01:42because up there is a 21-mile stretch of water.
0:01:46 > 0:01:51But just 8,000 years ago, none of this water was here.
0:01:51 > 0:01:56There would have been nothing to stop me from simply toddling off southwards to France.
0:01:56 > 0:02:01That's because sea levels were over 300 feet lower than they are today...
0:02:01 > 0:02:05leaving the floor of the Channel high and dry.
0:02:05 > 0:02:11This bridge of land and its eventual disappearance play a crucial role in our history.
0:02:11 > 0:02:15So what happened to separate us from them?
0:02:15 > 0:02:21The answer is the most dramatic thing to ever befall our country,
0:02:21 > 0:02:26and it led to the creation of Island Britain.
0:02:48 > 0:02:50We're lucky enough to live
0:02:50 > 0:02:54on some of the most glorious islands on Earth.
0:02:54 > 0:02:57BIRDSONG
0:03:02 > 0:03:08For me, our landscape, plants and animals, the ever-changing weather
0:03:08 > 0:03:13and the turn of the seasons make the British Isles a magical place.
0:03:16 > 0:03:20But all this richness that surrounds us today is the result
0:03:20 > 0:03:26of a chain of events that started at a time when Britain looked very different.
0:03:26 > 0:03:31It's hard to believe that not so long ago there was virtually nothing here.
0:03:34 > 0:03:37This is what Britain was once like -
0:03:37 > 0:03:40held in the grip of an Ice Age.
0:03:44 > 0:03:48As recently as 15,000 years ago,
0:03:48 > 0:03:52Northern Britain was still buried under a mile of ice.
0:03:54 > 0:03:58And to the south - bare rock and frozen tundra stretched away
0:03:58 > 0:04:03across the ancient land bridge and beyond into mainland Europe.
0:04:03 > 0:04:06And this is what it must have been like back then -
0:04:06 > 0:04:09absolutely perishing.
0:04:09 > 0:04:14The temperature here is -15 degrees Celsius,
0:04:14 > 0:04:17which would have been very mild for the Ice Age.
0:04:17 > 0:04:21But I can tell you this isn't mild, I've got layers of thermals on, quilted jacket, gloves
0:04:21 > 0:04:24and headgear to try and keep warm and already
0:04:24 > 0:04:26I can hardly feel the tips of my fingers.
0:04:26 > 0:04:30I am as they say up north - nithered.
0:04:30 > 0:04:34But the days of this deep freeze were numbered
0:04:34 > 0:04:37and we know that because of these -
0:04:37 > 0:04:39beetles.
0:04:39 > 0:04:45For thousands of years cold-loving beetles had eked out a living in Ice Age Britain.
0:04:45 > 0:04:48But then a new species suddenly appeared,
0:04:48 > 0:04:51and this one liked it hot...
0:04:53 > 0:04:56..which could only mean one thing - we were warming up,
0:04:56 > 0:05:03and warming up quickly - perhaps by as much as ten degrees in just 50 years.
0:05:03 > 0:05:08The great melt had begun.
0:05:14 > 0:05:20This rapid change in our fortunes was due to one of the periodic wobbles in the Earth's orbit -
0:05:20 > 0:05:25a wobble that took the northern hemisphere slightly nearer to the sun
0:05:25 > 0:05:28and kick-started the thaw.
0:05:32 > 0:05:37For a while, Britain must have been a very wet place indeed.
0:05:47 > 0:05:51The power of the meltwater was so great,
0:05:51 > 0:05:55it managed to change the courses of many of our rivers,
0:05:55 > 0:05:59leaving behind it a legacy of beautiful waterfalls,
0:05:59 > 0:06:04spectacular rapids, chutes and deep, deep plunge pools,
0:06:04 > 0:06:07which of course are ideal nowadays for...
0:06:07 > 0:06:09extreme water sports.
0:06:17 > 0:06:22I'm told that these rapids are Grade Three, but during the Ice Age melt
0:06:22 > 0:06:24there'd have been so much water
0:06:24 > 0:06:28that you'd probably have been paddling down a Grade 300!
0:06:34 > 0:06:35Oh!
0:06:57 > 0:06:59Oh, wow!
0:07:03 > 0:07:08The great melt has left its mark all over the British landscape -
0:07:08 > 0:07:11like here, in Yorkshire.
0:07:15 > 0:07:17The North York Moors railway
0:07:17 > 0:07:22winds its way through some of our most beautiful upland scenery,
0:07:22 > 0:07:26nowhere more so than Newtondale -
0:07:26 > 0:07:31an eight-mile long valley deeply incised into the hard gritstone.
0:07:35 > 0:07:39But once this valley would have echoed to a very different sound -
0:07:39 > 0:07:43billion of gallons of water on the move.
0:08:00 > 0:08:06At the height of the thaw, Newtondale was one of the main drains for the meltwater,
0:08:06 > 0:08:11and this valley was shaped by one of the most powerful rivers the British Isles has ever seen.
0:08:16 > 0:08:19To get some idea of what this would have been like,
0:08:19 > 0:08:24look what happened in Iceland, when a volcanic eruption melted a glacier,
0:08:24 > 0:08:28releasing a catastrophic flood that carried all before it.
0:08:34 > 0:08:39There are other signs of the scale of these floods just across the Pennines.
0:08:45 > 0:08:50The great horseshoe of cliffs at Mallam Cove in the Yorkshire Dales
0:08:50 > 0:08:53were once Britain's very own Niagara Falls.
0:08:57 > 0:09:00A huge meltwater cataract
0:09:00 > 0:09:03poured over the edge of this great arc of rock.
0:09:06 > 0:09:10Not all of this meltwater drained away to the sea.
0:09:10 > 0:09:14It also flooded the depressions gouged out by glaciers
0:09:14 > 0:09:19thousands of years before, creating huge lakes.
0:09:20 > 0:09:23Some of those glacial lakes are still around today,
0:09:23 > 0:09:26like here in the Lake District.
0:09:26 > 0:09:31Ullswater, Coniston Water, Wast Water, and Windermere
0:09:31 > 0:09:34were all created when water from the retreating ice sheets
0:09:34 > 0:09:37was trapped in these valleys.
0:09:47 > 0:09:50And water's not the only thing that's been trapped here.
0:09:50 > 0:09:55These glacial lakes also contain evidence of some of the first life
0:09:55 > 0:09:57to return to Britain as the ice melted.
0:09:57 > 0:10:01The ice sheets have long gone, and yet...
0:10:01 > 0:10:04it can be pretty cold out here at this time of year.
0:10:04 > 0:10:08But down there the Ice Age still exists.
0:10:13 > 0:10:17It's here in these dark depths that the evidence can still be found...
0:10:17 > 0:10:19a creature from the past.
0:10:19 > 0:10:23It's not Nessie, if that's what you're thinking, but these -
0:10:23 > 0:10:25Arctic char.
0:10:25 > 0:10:28They're a relative of the salmon and as their name suggests,
0:10:28 > 0:10:30they should be hundreds of miles away
0:10:30 > 0:10:32in the chilly waters of the Arctic Ocean.
0:10:32 > 0:10:36So just why are these fish still here in Britain?
0:10:38 > 0:10:41Every year, many of our rivers
0:10:41 > 0:10:44witness the return of Atlantic salmon.
0:10:44 > 0:10:46After spending years out at sea,
0:10:46 > 0:10:49they are impelled to fight their way up against the current
0:10:49 > 0:10:53to reach their spawning grounds in the headwaters upstream.
0:11:02 > 0:11:05Thousands of years ago, the Arctic char would have made
0:11:05 > 0:11:08similar journeys between salt and freshwater
0:11:08 > 0:11:13as they moved into Britain's newly-formed rivers and lakes.
0:11:17 > 0:11:21But as the meltwater floods subsided
0:11:21 > 0:11:23and the rivers began to shrink,
0:11:23 > 0:11:26some char became trapped by the falling water levels,
0:11:26 > 0:11:29and they've been here ever since.
0:11:31 > 0:11:34For fish, it would've been relatively easy
0:11:34 > 0:11:38to recolonise Britain as the Ice Age came to an end.
0:11:38 > 0:11:42But on land it was a much more difficult journey
0:11:42 > 0:11:46as life struggled to re-establish itself on the emerging ground.
0:11:47 > 0:11:49We'd been scoured by the ice,
0:11:49 > 0:11:53leaving behind a stark and barren landscape.
0:11:53 > 0:11:58This is The Burren in the West of Ireland.
0:11:58 > 0:12:02It looks more like the moon than a part of the Emerald Isle.
0:12:02 > 0:12:05This huge expanse of limestone
0:12:05 > 0:12:07is the perfect place to see
0:12:07 > 0:12:10how plants began to re-colonise the land.
0:12:10 > 0:12:13And the first in are the toughest of all -
0:12:13 > 0:12:16things like lichens.
0:12:16 > 0:12:20Lichens are made up of two distinct organisms -
0:12:20 > 0:12:24a fungus and an alga which depend upon each other for survival.
0:12:24 > 0:12:30The alga provides food for the fungus and the fungus provides shelter for the alga.
0:12:30 > 0:12:32That way, they don't need soil to grow.
0:12:32 > 0:12:35They are true wilderness pioneers,
0:12:35 > 0:12:39which means that even rocks can nurture life.
0:12:47 > 0:12:50And in more sheltered spots where there was just enough
0:12:50 > 0:12:54soil for them to cling to, more complex plants would take hold...
0:12:54 > 0:12:57but they'd have to be tough little beauties
0:12:57 > 0:12:59like the spiny Burnet rose
0:12:59 > 0:13:03and the hardy geranium - the Bloody Cranesbill.
0:13:03 > 0:13:07As these first plants died, they decayed
0:13:07 > 0:13:11and began to enrich what little soil there was in these crevices.
0:13:11 > 0:13:13More seeds would blow in
0:13:13 > 0:13:17and gradually, plant colonisation gained momentum.
0:13:20 > 0:13:24And because Britain and Ireland were still directly connected to Europe,
0:13:24 > 0:13:26new life began to spread northwards
0:13:26 > 0:13:28across these land bridges.
0:13:28 > 0:13:34For the first time in thousands of years, Britain turned green.
0:13:34 > 0:13:38Initially, tundra spread across this waterlogged landscape -
0:13:38 > 0:13:41with plants like dwarf willow and heather
0:13:41 > 0:13:45that could survive the winter freezes.
0:13:45 > 0:13:47Rannoch Moor in the Highlands
0:13:47 > 0:13:51probably looks much like it did 12,000 years ago,
0:13:51 > 0:13:54but with one or two significant differences.
0:13:54 > 0:13:59Great herds of caribou would have migrated across the open country,
0:13:59 > 0:14:02just as they do today in Scandinavia and Canada.
0:14:09 > 0:14:11Just imagine -
0:14:11 > 0:14:15this could have been Salisbury Plain a few thousand years ago.
0:14:19 > 0:14:22The caribou have long gone,
0:14:22 > 0:14:25but the white-coated Arctic hare has hung on.
0:14:25 > 0:14:28Today, the only place it can still find a home
0:14:28 > 0:14:32cold enough for its liking is on our highest mountains,
0:14:32 > 0:14:34like the Cairngorms.
0:14:40 > 0:14:44These snowy peaks are also the haunt of the ptarmigan,
0:14:44 > 0:14:46another relic of that first wave
0:14:46 > 0:14:50of cold-loving invaders that moved into Britain.
0:14:52 > 0:14:55And their predators would have followed.
0:15:01 > 0:15:05But as more new arrivals crossed the land bridge,
0:15:05 > 0:15:09our tundra landscape was about to be transformed.
0:15:09 > 0:15:12Trees started to spread northwards from southern Europe.
0:15:12 > 0:15:16Like an invading army marching across the land,
0:15:16 > 0:15:19at their peak, these trees were advancing at something like
0:15:19 > 0:15:22a quarter of a mile every year.
0:15:23 > 0:15:29Winters were still hard and these first colonisers had to be tough.
0:15:29 > 0:15:33It's no accident that today the remnants of this first forest
0:15:33 > 0:15:36can only be found in the more remote glens in the Highlands.
0:15:39 > 0:15:44These Caledonian forests are dominated by just three species.
0:15:46 > 0:15:49There's the scrubby juniper,
0:15:49 > 0:15:55the birch, that gives this forest its glorious autumn colour,
0:15:55 > 0:15:58and towering over both of them,
0:15:58 > 0:16:00the magnificent Scots Pine.
0:16:08 > 0:16:14These wonderful Caledonian forests have now fallen on hard times,
0:16:14 > 0:16:18and so too have some of the animals that depend on them.
0:16:19 > 0:16:22None more so than the capercaillie.
0:16:25 > 0:16:28Today it's one of our rarest birds,
0:16:28 > 0:16:31but when these pines and birches
0:16:31 > 0:16:35filled our forests, its calls would have echoed across Britain.
0:16:39 > 0:16:43Another early arrival in these woods was the red deer.
0:16:43 > 0:16:47Today, we think of them more as animals of open country,
0:16:47 > 0:16:51but they are really more at home in the cover of woodland.
0:16:53 > 0:16:5810,000 years ago, a walk in the woods would have been a very different experience...
0:16:58 > 0:17:01and rather more dangerous.
0:17:04 > 0:17:07Four times the size of a red deer stag,
0:17:07 > 0:17:09the elk - or moose -
0:17:09 > 0:17:12were common in our fledgling forests.
0:17:16 > 0:17:19Today, these huge beasts
0:17:19 > 0:17:23are largely confined to northern Scandinavia and Russia.
0:17:23 > 0:17:25BELLOW ECHOES
0:17:34 > 0:17:39Like the elk, brown bears once ranged all over Britain.
0:17:41 > 0:17:44Salmon returning to spawn each autumn
0:17:44 > 0:17:47would have been a welcome addition to their diet
0:17:47 > 0:17:50before they settled in for winter hibernation.
0:17:51 > 0:17:57This could well have been a scene played out on the ancient Thames or Shannon.
0:18:06 > 0:18:10The disappearance of the ice and the blossoming that followed
0:18:10 > 0:18:14was due to the tilting of the Earth taking us nearer the sun.
0:18:14 > 0:18:16But the warming process was helped
0:18:16 > 0:18:18by something a bit more down to earth.
0:18:20 > 0:18:21You can find evidence of it
0:18:21 > 0:18:24right the way down the west coast of Britain.
0:18:24 > 0:18:27All you need to do is a bit of beachcombing.
0:18:27 > 0:18:31And you'll find things like the sea bean...
0:18:33 > 0:18:36..the horse-eye bean...
0:18:36 > 0:18:39..and this, the delightfully named nickar nut -
0:18:39 > 0:18:41that's N-I-C-K-A-R -
0:18:41 > 0:18:47all of them seeds, but unlike anything I grow in my garden!
0:18:48 > 0:18:50For hundreds of years,
0:18:50 > 0:18:54people attached all sorts of folklore to these strange objects.
0:18:54 > 0:18:57They could be used for anything from curing the pain of childbirth
0:18:57 > 0:19:00to preventing baldness.
0:19:00 > 0:19:02The reason we're not familiar with these seeds
0:19:02 > 0:19:05is that they're not native to Britain.
0:19:05 > 0:19:07So where have they come from?
0:19:07 > 0:19:10The alternative name of the sea bean gives you a clue.
0:19:10 > 0:19:13Its other name is the monkey ladder vine.
0:19:13 > 0:19:17This little chap has come all the way from the Amazon.
0:19:19 > 0:19:22This plant grows along the banks of tropical rivers.
0:19:22 > 0:19:25Its seeds are dispersed by water
0:19:25 > 0:19:28and usually germinate further downstream.
0:19:32 > 0:19:35But if they don't drift ashore,
0:19:35 > 0:19:38they eventually find themselves in the sea
0:19:38 > 0:19:42where they are swept away by one of the world's great ocean currents -
0:19:42 > 0:19:44the Gulf Stream.
0:19:44 > 0:19:47Once in its powerful grip,
0:19:47 > 0:19:51these tropical seeds are carried across the North Atlantic
0:19:51 > 0:19:52to our western shores.
0:19:52 > 0:19:56But this current also brings with it something far more valuable
0:19:56 > 0:19:59to our islands - heat.
0:19:59 > 0:20:04Its waters wrap Britain in a warm, wet blanket,
0:20:04 > 0:20:08insulating us from the worst effects of our northerly position.
0:20:08 > 0:20:13At the far south-west corner of Britain lie the Isles of Scilly
0:20:13 > 0:20:17and here you can really see the impact of this warm current.
0:20:17 > 0:20:21In the summer, it looks and feels more like the Bahamas.
0:20:21 > 0:20:23Frosts are unheard of
0:20:23 > 0:20:27and palm trees can easily survive the northern winter.
0:20:28 > 0:20:31Gardening down here is a dream
0:20:31 > 0:20:35and our resident birds find themselves in a kaleidoscopic world
0:20:35 > 0:20:37of sub-tropical blooms.
0:20:46 > 0:20:50The mixing of the warm Gulf Stream with colder Atlantic waters
0:20:50 > 0:20:54makes our seas some of the richest in the world.
0:20:56 > 0:21:00In spring, the water blooms with plankton
0:21:00 > 0:21:03and this attracts something altogether more spectacular -
0:21:03 > 0:21:07our largest fish, the basking shark.
0:21:09 > 0:21:12These 30-foot giants appear
0:21:12 > 0:21:16off our southern shores each spring feasting on the plankton,
0:21:16 > 0:21:20and as summer progresses, they move gradually northwards.
0:21:20 > 0:21:23As they go, they filter the equivalent of
0:21:23 > 0:21:26an Olympic-sized swimming pool every hour.
0:21:29 > 0:21:33By late summer, they reach the west coast of Scotland.
0:21:38 > 0:21:43And the warmth of the Gulf Stream has a dramatic effect even here,
0:21:43 > 0:21:48keeping average temperatures something like ten degrees higher than they should be.
0:21:53 > 0:21:56So palm trees also thrive in places
0:21:56 > 0:21:58like Plockton near the Isle of Skye.
0:22:06 > 0:22:11Without the Gulf Stream, Plockton would be a lot colder -
0:22:11 > 0:22:16more like Churchill in Canada. It's on the same latitude as Plockton,
0:22:16 > 0:22:19but here the locals have polar bears for company.
0:22:21 > 0:22:24As the Gulf Stream appeared around our shores,
0:22:24 > 0:22:28it had a profound effect on our landscape.
0:22:29 > 0:22:31And how do we know?
0:22:31 > 0:22:33Because of this -
0:22:33 > 0:22:35pollen.
0:22:35 > 0:22:38Different plants produce their own unique type,
0:22:38 > 0:22:40and pollen is extremely tough.
0:22:40 > 0:22:43It can resist decay for thousands of years.
0:22:43 > 0:22:46So plants leave behind a botanical fingerprint
0:22:46 > 0:22:49which can be used to track their history.
0:22:51 > 0:22:54The difficult thing is finding those fingerprints.
0:22:54 > 0:22:59And strangely enough, this is one of the best places.
0:22:59 > 0:23:03But you need to proceed very steadily.
0:23:09 > 0:23:13Now if you look closely at the surface of the water here
0:23:13 > 0:23:15it isn't clear, it's slightly opaque,
0:23:15 > 0:23:21because floating on it are grains of pollen from all these trees surrounding the pond.
0:23:21 > 0:23:24Now eventually, those grains will sink to the bottom.
0:23:24 > 0:23:28More and more sediment will build up and that means
0:23:28 > 0:23:30if you take a core of mud
0:23:30 > 0:23:34from the bottom of a pond and analyse it,
0:23:34 > 0:23:37you can tell what was growing around here
0:23:37 > 0:23:39through different periods of time.
0:23:44 > 0:23:48So what do these pollen fingerprints tell us about our history?
0:23:51 > 0:23:54They show that around 9,000 years ago,
0:23:54 > 0:23:58birches and pines start to disappear from much of southern Britain,
0:23:58 > 0:24:03and in their wake appear wave upon wave of new arrivals.
0:24:06 > 0:24:11Hazel was one of the first to establish itself.
0:24:11 > 0:24:15One of the next to arrive was the oak.
0:24:15 > 0:24:20Then came elms and limes.
0:24:20 > 0:24:23And then ash...
0:24:23 > 0:24:25then holly...
0:24:25 > 0:24:28hornbeam...
0:24:28 > 0:24:31And one of the last to arrive was the beech.
0:24:34 > 0:24:37The rich woodlands these new invaders created
0:24:37 > 0:24:41became home to animals and other plants that in turn
0:24:41 > 0:24:43had filtered north from Europe
0:24:43 > 0:24:46to fill this new forest.
0:24:46 > 0:24:47At the same time,
0:24:47 > 0:24:51the cycle of the seasons had become firmly established,
0:24:51 > 0:24:57and life in these woods took on a character we'd recognise today.
0:25:43 > 0:25:45With every passing year,
0:25:45 > 0:25:50these new arrivals spread further and further afield,
0:25:50 > 0:25:54their seeds were carried by the wind, on water,
0:25:54 > 0:25:57and some, like the oak, spread far and wide by animals.
0:26:04 > 0:26:08Jays are one of the most prolific of seed collectors
0:26:08 > 0:26:10and acorns are a favourite food.
0:26:10 > 0:26:13They find them almost irresistible
0:26:13 > 0:26:16and will travel miles to find abundant supplies.
0:26:18 > 0:26:20Carried back to their home territory,
0:26:20 > 0:26:22the jays then bury the acorns
0:26:22 > 0:26:25to help them through the lean months of winter.
0:26:25 > 0:26:29A single jay can hoard as many as 3,000 acorns
0:26:29 > 0:26:32in a month of frenetic activity.
0:26:32 > 0:26:35But in spite of having phenomenal memories,
0:26:35 > 0:26:37it seems even jays have "senior moments"
0:26:37 > 0:26:40and forget where they've buried some of their booty.
0:26:40 > 0:26:42And we all know what grows from tiny acorns -
0:26:42 > 0:26:45mighty oaks!
0:26:59 > 0:27:01This oak is over 400 years old
0:27:01 > 0:27:04and has to be at least 100 feet tall.
0:27:07 > 0:27:11It's only by climbing up here that you can start to appreciate
0:27:11 > 0:27:17just how glorious these big old trees really are.
0:27:17 > 0:27:20As you come up here into the canopy,
0:27:20 > 0:27:26it feels very much a private, secret world all of its own.
0:27:26 > 0:27:29I fully expect some kind of rare bird to look at you and say,
0:27:29 > 0:27:31"What are you doing up here?"
0:27:31 > 0:27:34As you negotiate the branches
0:27:34 > 0:27:37with not quite the same amount of skill as they have.
0:27:39 > 0:27:43Oh! But I'm not the only one up here.
0:27:45 > 0:27:49Oak trees teem with life.
0:27:51 > 0:27:54They support over 500 species of insects alone.
0:27:56 > 0:27:59And most of them seem to be doing their level best
0:27:59 > 0:28:01to eat themselves out of house and home!
0:28:07 > 0:28:09Almost there.
0:28:15 > 0:28:18Made it!
0:28:18 > 0:28:20Yeah. Phew!
0:28:23 > 0:28:27Maybe it's just because I have a natural affinity with plants,
0:28:27 > 0:28:30but I can't tell you how special it feels to be up here,
0:28:30 > 0:28:32looking at all these old gnarled branches
0:28:32 > 0:28:35and realising this tree was growing
0:28:35 > 0:28:37when Elizabeth I was on the throne.
0:28:37 > 0:28:40Think what it's seen since then -
0:28:40 > 0:28:42an amazing number of things!
0:28:42 > 0:28:45But if I could have clambered to the top of an established oak tree
0:28:45 > 0:28:47like this 8,000 years ago,
0:28:47 > 0:28:50the view would have been spectacularly different -
0:28:50 > 0:28:55an almost unbroken canopy of trees as far as the eye could see.
0:28:57 > 0:28:59This was the great wildwood -
0:28:59 > 0:29:01north, south, east and west -
0:29:01 > 0:29:04nothing but trees.
0:29:04 > 0:29:08A good climber could probably have crossed Britain
0:29:08 > 0:29:10without ever touching the ground.
0:29:12 > 0:29:17But I for one prefer to have my feet planted on terra firma.
0:29:24 > 0:29:28Today, it's hard to find any trace of that ancient wildwood.
0:29:28 > 0:29:34We do still have some magnificent woodlands, but these have been intensively managed for centuries -
0:29:34 > 0:29:38places like Epping Forest and the Wye Valley...
0:29:39 > 0:29:43And Sussex, one of our most densely-wooded counties.
0:29:43 > 0:29:47And it's still possible to find individual trees
0:29:47 > 0:29:50that are incredibly old.
0:29:50 > 0:29:54In fact, Britain has the oldest trees in Europe -
0:29:54 > 0:29:58ancient oaks over 1,000 years old.
0:29:58 > 0:30:02And in many churchyards, there are yew trees certainly twice that age
0:30:02 > 0:30:06and maybe as much as five or six thousand years old.
0:30:07 > 0:30:10But these are rare exceptions
0:30:10 > 0:30:13and stand in stark contrast to the wildwood
0:30:13 > 0:30:17which would have been filled with ancient trees of all kinds.
0:30:20 > 0:30:23And it's not just the number of really old trees
0:30:23 > 0:30:27that distinguishes the wildwood from modern forests.
0:30:30 > 0:30:34We tend to be very tidy-minded today, even in our woodland.
0:30:34 > 0:30:37Fallen trees are cleared to allow access,
0:30:37 > 0:30:40some are sawn up and taken away for firewood.
0:30:40 > 0:30:42But in the wildwood,
0:30:42 > 0:30:45the trees would have laid where they fell and allowed to rot.
0:30:48 > 0:30:52This place is unusual for a modern British forest,
0:30:52 > 0:30:56but it gives a flavour of how the wildwood might have been -
0:30:56 > 0:30:59a right old mess!
0:30:59 > 0:31:03But the amount of deadwood lying around
0:31:03 > 0:31:05can have a dramatic effect on any forest.
0:31:05 > 0:31:09More than half the wildlife in a woodland lives on rotting timber.
0:31:09 > 0:31:14This is absolutely teeming with organisms.
0:31:14 > 0:31:18Ironically, a woodland which is full of death
0:31:18 > 0:31:20is simply teeming with life.
0:31:43 > 0:31:48With so much deadwood at its heart, the wildwood
0:31:48 > 0:31:50must have been bursting with life,
0:31:50 > 0:31:54and not all of it familiar... Our fairy-tale forests
0:31:54 > 0:31:58also had their fair share of fairy-tale animals.
0:32:22 > 0:32:25But perhaps what's most amazing of all
0:32:25 > 0:32:28is that all this life arrived in Britain
0:32:28 > 0:32:31as recently as 8,000 years ago.
0:32:38 > 0:32:41But there were more changes yet to come,
0:32:41 > 0:32:45changes that would finally create the islands we all recognise today.
0:32:47 > 0:32:50So much meltwater had been released into the oceans
0:32:50 > 0:32:53that sea levels had been steadily rising
0:32:53 > 0:32:54for several thousand years.
0:32:59 > 0:33:02Slowly but surely, that land bridge connecting us to Europe
0:33:02 > 0:33:06began to disappear beneath the waves.
0:33:06 > 0:33:10And around 8,000 years ago, it was finally submerged,
0:33:10 > 0:33:14casting Britain adrift from the rest of Europe once and for all.
0:33:17 > 0:33:22And what did it create? Well, I'll show you, courtesy of the RAF.
0:33:22 > 0:33:27The seas had risen by something like 300 feet,
0:33:27 > 0:33:29and the best place to see this new coastline
0:33:29 > 0:33:32is to take to the air for a birds-eye view.
0:33:38 > 0:33:42You only get this sort of attention when you're flying club class.
0:33:55 > 0:33:56As the seas rose,
0:33:56 > 0:34:00our coastline expanded to more than 10,000 miles,
0:34:00 > 0:34:03an incredible amount for such a small group of islands.
0:34:09 > 0:34:12The power of the sea around here is relentless.
0:34:19 > 0:34:25Its incessant pounding began to eat away at our rocky foundations,
0:34:25 > 0:34:29shaping the distinctive outline that's so familiar today.
0:34:29 > 0:34:31All around our coasts,
0:34:31 > 0:34:35some of our most celebrated scenery was being created.
0:34:37 > 0:34:40Nowhere is this more obvious
0:34:40 > 0:34:42than along our Channel coast.
0:34:42 > 0:34:48This has to be one of the most famous lumps of rock in the world.
0:34:51 > 0:34:57At Beachy Head, the cliffs rise to over 300 feet.
0:34:57 > 0:35:00They were initially carved as the seas flooded into the Channel,
0:35:00 > 0:35:03and they're still under attack today,
0:35:03 > 0:35:07retreating by about a foot each year.
0:35:07 > 0:35:12In some places, the sea breached the tougher coastal rocks
0:35:12 > 0:35:15then cut deeply into the softer ones behind,
0:35:15 > 0:35:18like here at Lulworth Cove.
0:35:21 > 0:35:24And there's Chesil Beach.
0:35:24 > 0:35:28This great arc of pebbles is made from rocks cut as the seas first rose
0:35:28 > 0:35:32and then dumped here by currents and storms.
0:35:36 > 0:35:38What an amazing sight!
0:35:38 > 0:35:41At 18 miles, it's the longest shingle beach in Britain.
0:35:57 > 0:36:00And it wasn't just our rocky coastlines
0:36:00 > 0:36:03that were shaped by the rising seas.
0:36:03 > 0:36:06Further west still, in Devon and Cornwall,
0:36:06 > 0:36:09sea water flooded up into coastal river valleys,
0:36:09 > 0:36:12creating these complex branched inlets
0:36:12 > 0:36:17at places like Falmouth, Salcombe and Kingsbridge.
0:36:17 > 0:36:21From up here, it's obvious how these flooded valleys
0:36:21 > 0:36:25track the shape of the rivers and tributaries that first cut them.
0:36:26 > 0:36:31Today, places like Fowey make perfect harbours.
0:36:45 > 0:36:51The rising seas also flooded up into broader valleys like the Thames,
0:36:51 > 0:36:53the Solway Firth and Morecambe Bay
0:36:53 > 0:36:56to create huge tidal estuaries.
0:36:58 > 0:37:01At low tide here at Snettersham
0:37:01 > 0:37:05on the Wash in East Anglia, the mud stretches for miles.
0:37:07 > 0:37:10But it's not the barren desert it first appears.
0:37:10 > 0:37:16Believe it or not, this is chock full of life, and for wading birds,
0:37:16 > 0:37:18this mud is a gastronomic treat.
0:37:18 > 0:37:21But you need the right equipment!
0:37:21 > 0:37:25Here, knot, redshank and oystercatchers
0:37:25 > 0:37:27can eat to their heart's content.
0:37:27 > 0:37:31But this paradise has one major drawback.
0:37:38 > 0:37:42Dining here is always a race against time and tide.
0:37:42 > 0:37:46This larder is only open for part of every day.
0:38:24 > 0:38:28The birds are pushed along in front of the rising waters,
0:38:28 > 0:38:30gathering into ever-larger flocks
0:38:30 > 0:38:35until eventually they are forced onto the wing.
0:38:40 > 0:38:45For me, this was an unforgettable sight...
0:38:50 > 0:38:53..doubly so when a peregrine
0:38:53 > 0:38:58flashed into the swirling flocks in search of a meal.
0:39:40 > 0:39:41For thousands of years,
0:39:41 > 0:39:45the richness of these tidal flats has attracted hungry animals,
0:39:45 > 0:39:47and not just birds.
0:39:54 > 0:39:58Bears too have a particular taste for shellfish,
0:39:58 > 0:40:02and these new estuaries must have proved irresistible.
0:40:18 > 0:40:20They are surprisingly adept
0:40:20 > 0:40:24at finding and dealing with these buried delicacies.
0:40:24 > 0:40:26Their presence would certainly
0:40:26 > 0:40:29have added to the views across Morecambe Bay!
0:40:29 > 0:40:32Bears were just one of many animals to colonise Britain
0:40:32 > 0:40:35before the sea-levels rose.
0:40:35 > 0:40:38But this stocking of our landscape with wildlife and plants
0:40:38 > 0:40:40was something of a lottery.
0:40:42 > 0:40:45Until the English Channel filled,
0:40:45 > 0:40:49animals moved freely between Britain and continental Europe.
0:40:49 > 0:40:53But as the waters flooded the land bridge, all that changed.
0:40:53 > 0:40:56The wildlife that surrounds us today
0:40:56 > 0:40:59was stranded here when the waters rose -
0:40:59 > 0:41:02stuck on an island
0:41:02 > 0:41:04with no return ticket.
0:41:04 > 0:41:09Today, we can zip back and forth across the Channel with ease,
0:41:09 > 0:41:12but 8,000 years ago, this narrow stretch of murky water
0:41:12 > 0:41:17created an insurmountable barrier for many plants and animals.
0:41:17 > 0:41:22Many failed to get to Britain before the door closed for ever.
0:41:22 > 0:41:25France is only 21 miles away,
0:41:25 > 0:41:29but is home to far more mammal species than southern England -
0:41:29 > 0:41:3252 natives compared with our 31.
0:41:33 > 0:41:36But even mainland Britain is doing pretty well
0:41:36 > 0:41:38compared with some parts of the British Isles,
0:41:38 > 0:41:41like here in Ireland.
0:41:42 > 0:41:45The land bridge between Ireland and the rest of Britain
0:41:45 > 0:41:47disappeared beneath the waves
0:41:47 > 0:41:51even earlier that the link between Britain and mainland Europe.
0:41:51 > 0:41:54Which meant it was much more difficult for plants and animals
0:41:54 > 0:41:57to reach this far-flung outpost.
0:41:57 > 0:42:01Even today there are only 20 mammals in Ireland
0:42:01 > 0:42:04as opposed to the 31 on mainland Britain.
0:42:05 > 0:42:08And it's surprising who did make it and who didn't.
0:42:08 > 0:42:12Before the sea levels rose, the stoat had colonised Ireland,
0:42:12 > 0:42:15but its close relative the weasel had missed the boat.
0:42:17 > 0:42:20There are red deer in Ireland, but no roe deer,
0:42:20 > 0:42:23and all Irish gardeners must thank their lucky stars
0:42:23 > 0:42:25that the mole was far too slow to get here.
0:42:27 > 0:42:30While the number of mammal species in Ireland is reduced,
0:42:30 > 0:42:33there are no snakes at all.
0:42:33 > 0:42:36Depending on your turn of mind,
0:42:36 > 0:42:39there are two possible explanations for this.
0:42:39 > 0:42:42The first is that St Patrick banished them all
0:42:42 > 0:42:44as being evil serpents.
0:42:44 > 0:42:47The second is that while some of them can swim,
0:42:47 > 0:42:50they're not exactly of Olympic standard!
0:42:55 > 0:42:58While the rising sea severely curtailed the movements
0:42:58 > 0:43:00of many plants and land animals,
0:43:00 > 0:43:03it wasn't all bad news.
0:43:03 > 0:43:06It created over 6,000 islands -
0:43:06 > 0:43:09some large, some mere specks of rock.
0:43:09 > 0:43:11But taken together,
0:43:11 > 0:43:14they create a magnificent natural treasure.
0:43:16 > 0:43:20The rich waters that swirled around our coast
0:43:20 > 0:43:22made the newly-formed British Isles
0:43:22 > 0:43:25the perfect home for more maritime creatures.
0:43:25 > 0:43:29Our greatest numbers of otters live along the west coast of Scotland.
0:43:32 > 0:43:35And the British Isles is home to two-thirds
0:43:35 > 0:43:38of the world population of the grey seal.
0:43:44 > 0:43:47Sculpted by time and tide,
0:43:47 > 0:43:51our coastline shelters all kinds of wonders.
0:43:57 > 0:43:59And the jewels in its crown
0:43:59 > 0:44:01are our sea birds.
0:44:18 > 0:44:23Since the ice retreated and the British Isles were formed,
0:44:23 > 0:44:26we've become one of the great sea bird centres of the world.
0:44:28 > 0:44:31Our coastal cliffs and islands are havens where millions of them
0:44:31 > 0:44:35have found a safe and secluded place to breed.
0:44:36 > 0:44:40But it's not just the safety of the cliffs that attracts them.
0:45:02 > 0:45:04What a sight. These are gannets,
0:45:04 > 0:45:08Britain's largest sea bird, entering the water like white torpedoes
0:45:08 > 0:45:11at around 60mph.
0:45:15 > 0:45:17The fish that shoal in these waters
0:45:17 > 0:45:20stand little chance from this surprise attack
0:45:20 > 0:45:23and the gannets are able to pick them off one at a time.
0:45:23 > 0:45:26Now their name has become synonymous with greed,
0:45:26 > 0:45:28but they're not just gorging themselves -
0:45:28 > 0:45:31they've got other mouths to feed back home at the roost,
0:45:31 > 0:45:32here on Bass Rock.
0:45:35 > 0:45:38An ancient volcano just one mile out
0:45:38 > 0:45:39into the Firth of Forth
0:45:39 > 0:45:42on Scotland's east coast,
0:45:42 > 0:45:44this isolated rock is now home
0:45:44 > 0:45:46to a spectacular breeding colony.
0:45:49 > 0:45:53Today, nearly three-quarters of the world population
0:45:53 > 0:45:56of gannets breed around our coasts.
0:45:56 > 0:45:59From March through to September,
0:45:59 > 0:46:03this lonely spot is packed.
0:46:03 > 0:46:07It seems as though every square inch of land has a nesting bird on it.
0:46:12 > 0:46:13Gannets pair for life
0:46:13 > 0:46:18and they come back here to exactly the same nesting spot every year.
0:46:18 > 0:46:21On a small island like this,
0:46:21 > 0:46:23with around 100,000 birds,
0:46:23 > 0:46:25that's no mean achievement.
0:46:29 > 0:46:32And they must have been finding their way back here
0:46:32 > 0:46:34ever since the rising seas
0:46:34 > 0:46:39first separated this lump of rock from the surrounding mainland,
0:46:39 > 0:46:44creating a home safe from predators and surrounded by food.
0:46:46 > 0:46:49The changes that have affected the Bass Rock
0:46:49 > 0:46:51since the Ice Age mirror those
0:46:51 > 0:46:54that have overtaken the British Isles as a whole.
0:46:54 > 0:46:58At times, these changes seem miraculous.
0:46:58 > 0:47:01We've emerged from beneath the ice.
0:47:04 > 0:47:08The land has been colonised by new life.
0:47:08 > 0:47:13And we became isolated from Europe by rising seas.
0:47:13 > 0:47:17It's easy to forget just how quickly and how recently
0:47:17 > 0:47:20these monumental changes took place.
0:47:20 > 0:47:24And surely the most important legacy of all
0:47:24 > 0:47:28is that severing of our links with mainland Europe.
0:47:28 > 0:47:31From being on the fringes of a great continent,
0:47:31 > 0:47:35we were now a collection of green and fertile islands
0:47:35 > 0:47:38surrounded by a fruitful sea.
0:47:38 > 0:47:41Around 8,000 years ago,
0:47:41 > 0:47:44we finally became the British Isles!