Islands Apart British Isles: A Natural History

This must be one of the strangest places I've ever taken a stroll.

I've even had to bring my passport.

Ah - this is what I've been looking for.

RUMBLING

Oh! Hear that?

The 12:40 -

bang on time, destination Paris.

This is the Channel Tunnel.

Back there, France...

and straight ahead of me, good old Blighty.

Today, this is the only way of walking between the two

because up there is a 21-mile stretch of water.

But just 8,000 years ago, none of this water was here.

There would have been nothing to stop me from simply toddling off southwards to France.

That's because sea levels were over 300 feet lower than they are today...

leaving the floor of the Channel high and dry.

This bridge of land and its eventual disappearance play a crucial role in our history.

So what happened to separate us from them?

The answer is the most dramatic thing to ever befall our country,

and it led to the creation of Island Britain.

We're lucky enough to live

on some of the most glorious islands on Earth.

BIRDSONG

For me, our landscape, plants and animals, the ever-changing weather

and the turn of the seasons make the British Isles a magical place.

But all this richness that surrounds us today is the result

of a chain of events that started at a time when Britain looked very different.

It's hard to believe that not so long ago there was virtually nothing here.

This is what Britain was once like -

held in the grip of an Ice Age.

As recently as 15,000 years ago,

Northern Britain was still buried under a mile of ice.

And to the south - bare rock and frozen tundra stretched away

across the ancient land bridge and beyond into mainland Europe.

And this is what it must have been like back then -

absolutely perishing.

The temperature here is -15 degrees Celsius,

which would have been very mild for the Ice Age.

But I can tell you this isn't mild, I've got layers of thermals on, quilted jacket, gloves

and headgear to try and keep warm and already

I can hardly feel the tips of my fingers.

I am as they say up north - nithered.

But the days of this deep freeze were numbered

and we know that because of these -

beetles.

For thousands of years cold-loving beetles had eked out a living in Ice Age Britain.

But then a new species suddenly appeared,

and this one liked it hot...

..which could only mean one thing - we were warming up,

and warming up quickly - perhaps by as much as ten degrees in just 50 years.

The great melt had begun.

This rapid change in our fortunes was due to one of the periodic wobbles in the Earth's orbit -

a wobble that took the northern hemisphere slightly nearer to the sun

and kick-started the thaw.

For a while, Britain must have been a very wet place indeed.

The power of the meltwater was so great,

it managed to change the courses of many of our rivers,

leaving behind it a legacy of beautiful waterfalls,

spectacular rapids, chutes and deep, deep plunge pools,

which of course are ideal nowadays for...

extreme water sports.

I'm told that these rapids are Grade Three, but during the Ice Age melt

there'd have been so much water

that you'd probably have been paddling down a Grade 300!

Oh!

Oh, wow!

The great melt has left its mark all over the British landscape -

like here, in Yorkshire.

The North York Moors railway

winds its way through some of our most beautiful upland scenery,

nowhere more so than Newtondale -

an eight-mile long valley deeply incised into the hard gritstone.

But once this valley would have echoed to a very different sound -

billion of gallons of water on the move.

At the height of the thaw, Newtondale was one of the main drains for the meltwater,

and this valley was shaped by one of the most powerful rivers the British Isles has ever seen.

To get some idea of what this would have been like,

look what happened in Iceland, when a volcanic eruption melted a glacier,

releasing a catastrophic flood that carried all before it.

There are other signs of the scale of these floods just across the Pennines.

The great horseshoe of cliffs at Mallam Cove in the Yorkshire Dales

were once Britain's very own Niagara Falls.

A huge meltwater cataract

poured over the edge of this great arc of rock.

Not all of this meltwater drained away to the sea.

It also flooded the depressions gouged out by glaciers

thousands of years before, creating huge lakes.

Some of those glacial lakes are still around today,

like here in the Lake District.

Ullswater, Coniston Water, Wast Water, and Windermere

were all created when water from the retreating ice sheets

was trapped in these valleys.

And water's not the only thing that's been trapped here.

These glacial lakes also contain evidence of some of the first life

to return to Britain as the ice melted.

The ice sheets have long gone, and yet...

it can be pretty cold out here at this time of year.

But down there the Ice Age still exists.

It's here in these dark depths that the evidence can still be found...

a creature from the past.

It's not Nessie, if that's what you're thinking, but these -

Arctic char.

They're a relative of the salmon and as their name suggests,

they should be hundreds of miles away

in the chilly waters of the Arctic Ocean.

So just why are these fish still here in Britain?

Every year, many of our rivers

witness the return of Atlantic salmon.

After spending years out at sea,

they are impelled to fight their way up against the current

to reach their spawning grounds in the headwaters upstream.

Thousands of years ago, the Arctic char would have made

similar journeys between salt and freshwater

as they moved into Britain's newly-formed rivers and lakes.

But as the meltwater floods subsided

and the rivers began to shrink,

some char became trapped by the falling water levels,

and they've been here ever since.

For fish, it would've been relatively easy

to recolonise Britain as the Ice Age came to an end.

But on land it was a much more difficult journey

as life struggled to re-establish itself on the emerging ground.

We'd been scoured by the ice,

leaving behind a stark and barren landscape.

This is The Burren in the West of Ireland.

It looks more like the moon than a part of the Emerald Isle.

This huge expanse of limestone

is the perfect place to see

how plants began to re-colonise the land.

And the first in are the toughest of all -

things like lichens.

Lichens are made up of two distinct organisms -

a fungus and an alga which depend upon each other for survival.

The alga provides food for the fungus and the fungus provides shelter for the alga.

That way, they don't need soil to grow.

They are true wilderness pioneers,

which means that even rocks can nurture life.

And in more sheltered spots where there was just enough

soil for them to cling to, more complex plants would take hold...

but they'd have to be tough little beauties

like the spiny Burnet rose

and the hardy geranium - the Bloody Cranesbill.

As these first plants died, they decayed

and began to enrich what little soil there was in these crevices.

More seeds would blow in

and gradually, plant colonisation gained momentum.

And because Britain and Ireland were still directly connected to Europe,

new life began to spread northwards

across these land bridges.

For the first time in thousands of years, Britain turned green.

Initially, tundra spread across this waterlogged landscape -

with plants like dwarf willow and heather

that could survive the winter freezes.

Rannoch Moor in the Highlands

probably looks much like it did 12,000 years ago,

but with one or two significant differences.

Great herds of caribou would have migrated across the open country,

just as they do today in Scandinavia and Canada.

Just imagine -

this could have been Salisbury Plain a few thousand years ago.

The caribou have long gone,

but the white-coated Arctic hare has hung on.

Today, the only place it can still find a home

cold enough for its liking is on our highest mountains,

like the Cairngorms.

These snowy peaks are also the haunt of the ptarmigan,

another relic of that first wave

of cold-loving invaders that moved into Britain.

And their predators would have followed.

But as more new arrivals crossed the land bridge,

our tundra landscape was about to be transformed.

Trees started to spread northwards from southern Europe.

Like an invading army marching across the land,

at their peak, these trees were advancing at something like

a quarter of a mile every year.

Winters were still hard and these first colonisers had to be tough.

It's no accident that today the remnants of this first forest

can only be found in the more remote glens in the Highlands.

These Caledonian forests are dominated by just three species.

There's the scrubby juniper,

the birch, that gives this forest its glorious autumn colour,

and towering over both of them,

the magnificent Scots Pine.

These wonderful Caledonian forests have now fallen on hard times,

and so too have some of the animals that depend on them.

None more so than the capercaillie.

Today it's one of our rarest birds,

but when these pines and birches

filled our forests, its calls would have echoed across Britain.

Another early arrival in these woods was the red deer.

Today, we think of them more as animals of open country,

but they are really more at home in the cover of woodland.

10,000 years ago, a walk in the woods would have been a very different experience...

and rather more dangerous.

Four times the size of a red deer stag,

the elk - or moose -

were common in our fledgling forests.

Today, these huge beasts

are largely confined to northern Scandinavia and Russia.

BELLOW ECHOES

Like the elk, brown bears once ranged all over Britain.

Salmon returning to spawn each autumn

would have been a welcome addition to their diet

before they settled in for winter hibernation.

This could well have been a scene played out on the ancient Thames or Shannon.

The disappearance of the ice and the blossoming that followed

was due to the tilting of the Earth taking us nearer the sun.

But the warming process was helped

by something a bit more down to earth.

You can find evidence of it

right the way down the west coast of Britain.

All you need to do is a bit of beachcombing.

And you'll find things like the sea bean...

..the horse-eye bean...

..and this, the delightfully named nickar nut -

that's N-I-C-K-A-R -

all of them seeds, but unlike anything I grow in my garden!

For hundreds of years,

people attached all sorts of folklore to these strange objects.

They could be used for anything from curing the pain of childbirth

to preventing baldness.

The reason we're not familiar with these seeds

is that they're not native to Britain.

So where have they come from?

The alternative name of the sea bean gives you a clue.

Its other name is the monkey ladder vine.

This little chap has come all the way from the Amazon.

This plant grows along the banks of tropical rivers.

Its seeds are dispersed by water

and usually germinate further downstream.

But if they don't drift ashore,

they eventually find themselves in the sea

where they are swept away by one of the world's great ocean currents -

the Gulf Stream.

Once in its powerful grip,

these tropical seeds are carried across the North Atlantic

to our western shores.

But this current also brings with it something far more valuable

to our islands - heat.

Its waters wrap Britain in a warm, wet blanket,

insulating us from the worst effects of our northerly position.

At the far south-west corner of Britain lie the Isles of Scilly

and here you can really see the impact of this warm current.

In the summer, it looks and feels more like the Bahamas.

Frosts are unheard of

and palm trees can easily survive the northern winter.

Gardening down here is a dream

and our resident birds find themselves in a kaleidoscopic world

of sub-tropical blooms.

The mixing of the warm Gulf Stream with colder Atlantic waters

makes our seas some of the richest in the world.

In spring, the water blooms with plankton

and this attracts something altogether more spectacular -

our largest fish, the basking shark.

These 30-foot giants appear

off our southern shores each spring feasting on the plankton,

and as summer progresses, they move gradually northwards.

As they go, they filter the equivalent of

an Olympic-sized swimming pool every hour.

By late summer, they reach the west coast of Scotland.

And the warmth of the Gulf Stream has a dramatic effect even here,

keeping average temperatures something like ten degrees higher than they should be.

So palm trees also thrive in places

like Plockton near the Isle of Skye.

Without the Gulf Stream, Plockton would be a lot colder -

more like Churchill in Canada. It's on the same latitude as Plockton,

but here the locals have polar bears for company.

As the Gulf Stream appeared around our shores,

it had a profound effect on our landscape.

And how do we know?

Because of this -

pollen.

Different plants produce their own unique type,

and pollen is extremely tough.

It can resist decay for thousands of years.

So plants leave behind a botanical fingerprint

which can be used to track their history.

The difficult thing is finding those fingerprints.

And strangely enough, this is one of the best places.

But you need to proceed very steadily.

Now if you look closely at the surface of the water here

it isn't clear, it's slightly opaque,

because floating on it are grains of pollen from all these trees surrounding the pond.

Now eventually, those grains will sink to the bottom.

More and more sediment will build up and that means

if you take a core of mud

from the bottom of a pond and analyse it,

you can tell what was growing around here

through different periods of time.

So what do these pollen fingerprints tell us about our history?

They show that around 9,000 years ago,

birches and pines start to disappear from much of southern Britain,

and in their wake appear wave upon wave of new arrivals.

Hazel was one of the first to establish itself.

One of the next to arrive was the oak.

Then came elms and limes.

And then ash...

then holly...

hornbeam...

And one of the last to arrive was the beech.

The rich woodlands these new invaders created

became home to animals and other plants that in turn

had filtered north from Europe

to fill this new forest.

At the same time,

the cycle of the seasons had become firmly established,

and life in these woods took on a character we'd recognise today.

With every passing year,

these new arrivals spread further and further afield,

their seeds were carried by the wind, on water,

and some, like the oak, spread far and wide by animals.

Jays are one of the most prolific of seed collectors

and acorns are a favourite food.

They find them almost irresistible

and will travel miles to find abundant supplies.

Carried back to their home territory,

the jays then bury the acorns

to help them through the lean months of winter.

A single jay can hoard as many as 3,000 acorns

in a month of frenetic activity.

But in spite of having phenomenal memories,

it seems even jays have "senior moments"

and forget where they've buried some of their booty.

And we all know what grows from tiny acorns -

mighty oaks!

This oak is over 400 years old

and has to be at least 100 feet tall.

It's only by climbing up here that you can start to appreciate

just how glorious these big old trees really are.

As you come up here into the canopy,

it feels very much a private, secret world all of its own.

I fully expect some kind of rare bird to look at you and say,

"What are you doing up here?"

As you negotiate the branches

with not quite the same amount of skill as they have.

Oh! But I'm not the only one up here.

Oak trees teem with life.

They support over 500 species of insects alone.

And most of them seem to be doing their level best

to eat themselves out of house and home!

Almost there.

Made it!

Yeah. Phew!

Maybe it's just because I have a natural affinity with plants,

but I can't tell you how special it feels to be up here,

looking at all these old gnarled branches

and realising this tree was growing

when Elizabeth I was on the throne.

Think what it's seen since then -

an amazing number of things!

But if I could have clambered to the top of an established oak tree

like this 8,000 years ago,

the view would have been spectacularly different -

an almost unbroken canopy of trees as far as the eye could see.

This was the great wildwood -

north, south, east and west -

nothing but trees.

A good climber could probably have crossed Britain

without ever touching the ground.

But I for one prefer to have my feet planted on terra firma.

Today, it's hard to find any trace of that ancient wildwood.

We do still have some magnificent woodlands, but these have been intensively managed for centuries -

places like Epping Forest and the Wye Valley...

And Sussex, one of our most densely-wooded counties.

And it's still possible to find individual trees

that are incredibly old.

In fact, Britain has the oldest trees in Europe -

ancient oaks over 1,000 years old.

And in many churchyards, there are yew trees certainly twice that age

and maybe as much as five or six thousand years old.

But these are rare exceptions

and stand in stark contrast to the wildwood

which would have been filled with ancient trees of all kinds.

And it's not just the number of really old trees

that distinguishes the wildwood from modern forests.

We tend to be very tidy-minded today, even in our woodland.

Fallen trees are cleared to allow access,

some are sawn up and taken away for firewood.

But in the wildwood,

the trees would have laid where they fell and allowed to rot.

This place is unusual for a modern British forest,

but it gives a flavour of how the wildwood might have been -

a right old mess!

But the amount of deadwood lying around

can have a dramatic effect on any forest.

More than half the wildlife in a woodland lives on rotting timber.

This is absolutely teeming with organisms.

Ironically, a woodland which is full of death

is simply teeming with life.

With so much deadwood at its heart, the wildwood

must have been bursting with life,

and not all of it familiar... Our fairy-tale forests

also had their fair share of fairy-tale animals.

But perhaps what's most amazing of all

is that all this life arrived in Britain

as recently as 8,000 years ago.

But there were more changes yet to come,

changes that would finally create the islands we all recognise today.

So much meltwater had been released into the oceans

that sea levels had been steadily rising

for several thousand years.

Slowly but surely, that land bridge connecting us to Europe

began to disappear beneath the waves.

And around 8,000 years ago, it was finally submerged,

casting Britain adrift from the rest of Europe once and for all.

And what did it create? Well, I'll show you, courtesy of the RAF.

The seas had risen by something like 300 feet,

and the best place to see this new coastline

is to take to the air for a birds-eye view.

You only get this sort of attention when you're flying club class.

As the seas rose,

our coastline expanded to more than 10,000 miles,

an incredible amount for such a small group of islands.

The power of the sea around here is relentless.

Its incessant pounding began to eat away at our rocky foundations,

shaping the distinctive outline that's so familiar today.

All around our coasts,

some of our most celebrated scenery was being created.

Nowhere is this more obvious

than along our Channel coast.

This has to be one of the most famous lumps of rock in the world.

At Beachy Head, the cliffs rise to over 300 feet.

They were initially carved as the seas flooded into the Channel,

and they're still under attack today,

retreating by about a foot each year.

In some places, the sea breached the tougher coastal rocks

then cut deeply into the softer ones behind,

like here at Lulworth Cove.

And there's Chesil Beach.

This great arc of pebbles is made from rocks cut as the seas first rose

and then dumped here by currents and storms.

What an amazing sight!

At 18 miles, it's the longest shingle beach in Britain.

And it wasn't just our rocky coastlines

that were shaped by the rising seas.

Further west still, in Devon and Cornwall,

sea water flooded up into coastal river valleys,

creating these complex branched inlets

at places like Falmouth, Salcombe and Kingsbridge.

From up here, it's obvious how these flooded valleys

track the shape of the rivers and tributaries that first cut them.

Today, places like Fowey make perfect harbours.

The rising seas also flooded up into broader valleys like the Thames,

the Solway Firth and Morecambe Bay

to create huge tidal estuaries.

At low tide here at Snettersham

on the Wash in East Anglia, the mud stretches for miles.

But it's not the barren desert it first appears.

Believe it or not, this is chock full of life, and for wading birds,

this mud is a gastronomic treat.

But you need the right equipment!

Here, knot, redshank and oystercatchers

can eat to their heart's content.

But this paradise has one major drawback.

Dining here is always a race against time and tide.

This larder is only open for part of every day.

The birds are pushed along in front of the rising waters,

gathering into ever-larger flocks

until eventually they are forced onto the wing.

For me, this was an unforgettable sight...

..doubly so when a peregrine

flashed into the swirling flocks in search of a meal.

For thousands of years,

the richness of these tidal flats has attracted hungry animals,

and not just birds.

Bears too have a particular taste for shellfish,

and these new estuaries must have proved irresistible.

They are surprisingly adept

at finding and dealing with these buried delicacies.

Their presence would certainly

have added to the views across Morecambe Bay!

Bears were just one of many animals to colonise Britain

before the sea-levels rose.

But this stocking of our landscape with wildlife and plants

was something of a lottery.

Until the English Channel filled,

animals moved freely between Britain and continental Europe.

But as the waters flooded the land bridge, all that changed.

The wildlife that surrounds us today

was stranded here when the waters rose -

stuck on an island

with no return ticket.

Today, we can zip back and forth across the Channel with ease,

but 8,000 years ago, this narrow stretch of murky water

created an insurmountable barrier for many plants and animals.

Many failed to get to Britain before the door closed for ever.

France is only 21 miles away,

but is home to far more mammal species than southern England -

52 natives compared with our 31.

But even mainland Britain is doing pretty well

compared with some parts of the British Isles,

like here in Ireland.

The land bridge between Ireland and the rest of Britain

disappeared beneath the waves

even earlier that the link between Britain and mainland Europe.

Which meant it was much more difficult for plants and animals

to reach this far-flung outpost.

Even today there are only 20 mammals in Ireland

as opposed to the 31 on mainland Britain.

And it's surprising who did make it and who didn't.

Before the sea levels rose, the stoat had colonised Ireland,

but its close relative the weasel had missed the boat.

There are red deer in Ireland, but no roe deer,

and all Irish gardeners must thank their lucky stars

that the mole was far too slow to get here.

While the number of mammal species in Ireland is reduced,

there are no snakes at all.

Depending on your turn of mind,

there are two possible explanations for this.

The first is that St Patrick banished them all

as being evil serpents.

The second is that while some of them can swim,

they're not exactly of Olympic standard!

While the rising sea severely curtailed the movements

of many plants and land animals,

it wasn't all bad news.

It created over 6,000 islands -

some large, some mere specks of rock.

But taken together,

they create a magnificent natural treasure.

The rich waters that swirled around our coast

made the newly-formed British Isles

the perfect home for more maritime creatures.

Our greatest numbers of otters live along the west coast of Scotland.

And the British Isles is home to two-thirds

of the world population of the grey seal.

Sculpted by time and tide,

our coastline shelters all kinds of wonders.

And the jewels in its crown

are our sea birds.

Since the ice retreated and the British Isles were formed,

we've become one of the great sea bird centres of the world.

Our coastal cliffs and islands are havens where millions of them

have found a safe and secluded place to breed.

But it's not just the safety of the cliffs that attracts them.

What a sight. These are gannets,

Britain's largest sea bird, entering the water like white torpedoes

at around 60mph.

The fish that shoal in these waters

stand little chance from this surprise attack

and the gannets are able to pick them off one at a time.

Now their name has become synonymous with greed,

but they're not just gorging themselves -

they've got other mouths to feed back home at the roost,

here on Bass Rock.

An ancient volcano just one mile out

into the Firth of Forth

on Scotland's east coast,

this isolated rock is now home

to a spectacular breeding colony.

Today, nearly three-quarters of the world population

of gannets breed around our coasts.

From March through to September,

this lonely spot is packed.

It seems as though every square inch of land has a nesting bird on it.

Gannets pair for life

and they come back here to exactly the same nesting spot every year.

On a small island like this,

with around 100,000 birds,

that's no mean achievement.

And they must have been finding their way back here

ever since the rising seas

first separated this lump of rock from the surrounding mainland,

creating a home safe from predators and surrounded by food.

The changes that have affected the Bass Rock

since the Ice Age mirror those

that have overtaken the British Isles as a whole.

At times, these changes seem miraculous.

We've emerged from beneath the ice.

The land has been colonised by new life.

And we became isolated from Europe by rising seas.

It's easy to forget just how quickly and how recently

these monumental changes took place.

And surely the most important legacy of all

is that severing of our links with mainland Europe.

From being on the fringes of a great continent,

we were now a collection of green and fertile islands

surrounded by a fruitful sea.

Around 8,000 years ago,

we finally became the British Isles!