Gum Tree Country Wild Down Under

In this driest of continents there's a vast green landscape

that stretches for thousands of kilometres round Australia's edge.

This is the Australian bush - its most characteristic landscape.

The first European settlers, pushing through it 200 years ago,

didn't like the bush.

It was daunting and alien, and so big you could get lost and die.

In these hot, endless forests, the very trees seemed to droop.

These, they said, were "forests in rags".

And from one end of the country to another,

they all looked strangely alike...

..because these thousands of kilometres of green

are dominated by just one kind of tree - the eucalypt, or gumtree.

And around these trees

live Australia's oddest and most charismatic animals.

The eucalypt has transformed itself

into 700 different species - some growing monstrously tall.

Some thrive in the baking north,

some in the chilly south, and some even grow in the snow.

Wherever they find a foothold,

gumtrees attract a vast assortment of wildlife.

Australia is the eucalypt's native home - it was born here.

But how has this peculiar tree

managed to spread itself over the entire continent?

And why is it that so much lives around it?

Fifty million years ago, when the climate was wetter,

much of Australia was covered in rainforest.

In this lush land eucalypts barely existed.

But the continent was gradually drying out

and the eucalypts seized their chance.

Far better able to cope with the harsh new conditions,

they rushed out and thrived.

Now eucalypt bushland encircles Australia

in an almost unbroken line.

But in this vast land, every gumtree landscape is different.

The tropical north is Crocodile Dundee country,

where the year swings between months of dryness and weeks of rain.

It's a hot and sultry place.

But eucalypts thrive here.

And up in these trees live big and watchful lizards.

A frilled lizard can spot its prey from three metres up a tree.

All it has to do then is jump down and catch it.

For their size and big teeth,

frilled lizards have moderate tastes.

They eat almost nothing but insects.

A good feeding area like this is worth hanging onto.

A frilled lizard won't tolerate a rival in its territory.

Competing males hiss and lash their tails, raising their frills

to make themselves look bigger than they really are.

But it's dangerous on the ground.

Whistling kites eat frilled lizards round here.

All that frill-waving and hissing forgotten,

the lizards make a two-legged dash back to the safety of their trees.

The eucalypt's rough bark helps them get a grip as they climb.

Once safely back up there,

they make themselves look as small and inconspicuous as possible.

And for 90% of their lives, this is where they stay,

using the gumtrees as lookout posts and bolt holes.

In these tropical northern woodlands,

the temperature most days can top 30 degrees Celsius.

But Australia is a land of enormous contrasts.

Move from the far north to the far south,

at the same time of year, and the change couldn't be more extreme.

Here it's mountainous and metres deep in snow.

Australia is so big, it can have baking heat in one place

and winter in another. And eucalypts can cope with both.

On the ancient mountains of Australia's southern Alps

grow woodlands of snow gums.

They can tolerate temperatures as low as minus 20,

twisted and dwarfed by the wind and the cold.

And in these snowy uplands, among these hardy trees,

there are parrots.

Gang-gang cockatoos feast on the eucalypt's hard seed capsules,

cracking them open with their strong beaks.

Many birds move to lower ground in winter,

but gang-gangs brave the cold to take advantage of this valuable food.

Up here, the weather can quickly turn nasty.

The mountains are snowbound for months of the year.

This is no place for wimps.

But wombats, with their thick fur,

trudge out to dig for grass buried under the snow.

And up in the trees, the gang-gangs keep on feeding,

even with their jaunty feathers all caked in ice.

The red-headed males, grey-headed females and blushing juveniles

pick away together at the gumtree feast.

Australia's south-eastern mountains

trap the cold and soaking air that blows in from the southern seas.

Moisture falls as snow and rain.

Australia may be the driest inhabited continent on Earth,

but here there's plenty of water.

And on the lower slopes of these misty mountains,

the trees grow monumentally tall.

With wetter weather and slightly better soil,

they reach a height of over 100m.

Towering above the rest of the forest greenery,

these trees can grow over a metre a year.

These are the tallest hardwood trees in the world -

and they're eucalypts.

The first British settlers called them mountain ash,

because they were homesick for the old country.

And they do have the feeling of lush European forests -

until the inhabitants turn up.

VARIOUS CALLS

From the dense, damp undergrowth comes a strange recital.

Not a flock of different birds, but just one.

The superb lyrebird is striking up.

Male lyrebirds mimic the other birds around them,

pulling their songs together into an impressive repertoire.

Wattlebirds, honeyeaters, whip birds, kookaburras -

he does them all!

CROAKS AND WHISTLES

WHIRRING CALL

CACKLES

WHISTLES

His powerful voice can carry up to a kilometre through the forest.

Clearing a stage for himself on a mound of earth,

he belts out his performance.

All this effort is to attract as many females as possible.

He'll carry on like this for hours.

When darkness falls and the lyrebirds are asleep in the trees,

a different set of wildlife emerges.

Mountain ash can live to be 300 years old. Many are full of holes.

At night, these holes produce some curious animals.

Australia has no monkeys - instead it has these.

They're possums, and just after dark,

they come out of their gumtree nests to feed.

Tiny Leadbeater's possums zip through the lower trees

looking for insects and sap.

They're sociable animals, and eight or more may share a single hollow.

Hollow eucalypts are desirable homes,

but to live in these big trees, you have to be agile.

Mountain brush-tailed possums are far bigger and slower,

but they're competent climbers. They're tree-dwellers,

but they spend a fair bit of time on the forest floor,

coming down in the darkness to eat fungi and fallen seeds.

It's tricky having to negotiate these dense trees by yourself,

but imagine what it's like having to haul a baby around with you.

This female has carried her baby in her pouch for six months,

and it will ride on her back for another two.

But alongside her, and safe from attack by owls,

it learns all the skills it will need for a life on its own.

For now it can feast on fallen seeds,

and it might even have a quick suckle while Mum's grooming herself

with her huge tree-climber's feet.

And before daylight comes,

mother and baby will vanish into the safety of their gumtree den.

These giant eucalypts thrive here because there's more water

and fractionally better soil than in other parts of Australia.

But though eucalypts do well in the wetter fringes of the land,

they don't just stop there.

The further you move inland, the more arid the scenery becomes.

The typical Australian landscape is hot, dry and sandy -

not an easy place to put down roots.

But gumtrees pop up almost everywhere.

They grow alongside trickles of inland rivers,

where there's barely any water flowing, putting down deep roots

to suck what moisture there is.

They grow in the outback,

where conditions couldn't be more different from the misty highlands.

There's a 10th of the rainfall,

and the soil is thin, worn down by sheer age.

A white trunk reflects the glare of the sun,

and leaves hang down to avoid overheating.

But when daytime temperatures climb to 40 plus,

red kangaroos are grateful for even this thin shade.

Once parked, a big red will spend its day under the trees,

until the sun goes down and the land cools again.

Even here, among the red rocks of the centre,

gumtrees have a toehold.

This most ethereal tree is a ghost gum,

and it grows in Australia's heart.

It clings to crumbling gorges, where water is scarce

and only the hardiest survive.

This is one tough tree.

But even the scrawniest of eucalypts

in the most desiccated places have a surprise.

They produce the most beautiful nectar-filled flowers.

The colours and shapes are as diverse as the trees themselves,

each attractive to different animal visitors.

Many flowers are cup-shaped,

allowing insects inside to gather pollen and nectar.

Blossoms appear on different trees at different times of year,

providing an ever-moving feast.

Lorikeets and honeyeaters are energetic nectar specialists -

always on the lookout for new flowers to drink at.

Eucalypts are such a draw

that flying foxes in the tropics will fly 50 kilometres every night,

moving from flowering tree to flowering tree to feed.

In return for this feast of nectar,

the trees use these big bats as couriers, covering them in pollen,

which they'll leave at the flowers of the next tree they visit.

Even if you can't fly, eucalypt flowers are worth the climb.

The tiny western pygmy possum in southern Australia

emerges at nightfall.

It eats plenty of insects, but it's also very partial to nectar.

Weighing little more than a boiled sweet,

and not much bigger than the flowers themselves,

it laps up the nectar with a tongue shaped like a brush.

This possum is a strictly nocturnal animal.

At dawn, it goes to its tree-hollow nest - made of gum leaves.

Nectar is cheap for these trees to produce,

and they give it away freely.

But their leaves are another story.

They're precious in a land where nutrients are in short supply,

and the eucalypts do their best to hang on to them.

They're hard and full of toxic chemicals, including the oils -

which give them their distinctive smell.

It's enough to stop most animals eating them, but not all.

And this is the classic gum eater.

In fact, it doesn't eat much else.

Koalas evolved with the eucalypts,

and they can just about cope with their leaves,

thanks to a large and complicated digestive system.

But it has to be careful -

before it eats, it has a sniff to check the chemical strength.

And those leaves are so hard,

it has to chew more than 16,000 times a day to break them down.

An old koala will eventually wear out its teeth completely.

It's all such hard work for so little nutrients,

that koalas have to sleep for 20 hours a day, just to save energy.

This is a highly specialised way of life.

A tiny baby koala, barely out of the pouch,

won't be able to cope with eating gum leaves straightaway.

First, it must have a snack of its mother's special droppings.

Disgusting as it may seem, the baby koala wouldn't survive otherwise.

By eating "pap", it's taking in vital bacteria

passed from its mother's gut,

which will later help it digest those leaves.

It's a bit like eating live yoghurt.

When you're this tiny,

it's sometimes hard to work out which way is up,

which is especially hazardous when you're ten metres above the ground.

And koala mums are pretty laid-back when it comes to childcare.

But at six months, this baby has to get used to a life in the trees.

If it's lucky, it will live to be 15 years old.

Young koalas stay dependent on their mothers for a whole year,

but as they grow, they start to become more adventurous.

In spite of the hazards, most koalas survive their childhood,

and the bond with their mothers is usually broken

only when she gives birth to her next baby.

Koalas don't make dens,

so a mother has nowhere that she can leave her offspring in safety.

She has to carry it round with her as she moves from tree to tree.

Most mothers carry their children on their back,

but others have slightly more unconventional ways.

And when your baby can be a quarter of your weight,

that's a lot to heave around.

It's all very hard work.

Gumtrees tend to grow widely spaced apart,

but other woodland dwellers have cracked the problem of travelling.

They glide.

A yellow-bellied glider can sail as far as 120 metres

from tree to tree, making strange noises in the night.

It spends its days inside hollow trees,

only emerging when darkness falls.

A cape of skin stretches from wrists to ankles,

and this is what gives it lift.

As it comes in to land, it swings its limbs forward, touching down

with all four feet together.

Gripping toes and big claws help it to hang on.

It's out and about to feed.

Yellow-bellied gliders are fond of insects and eucalypt nectar.

But they also bite notches in the bark of trees

and eat the oozing sap - often in the company of a few relatives.

On such a meagre diet, gliding is a low-energy way to travel.

This is an economical place.

Eucalypts are almost all evergreen,

and evergreen leaves are expensive to produce when nutrients are low.

But they do last for a good long time.

Eucalypts stand dusty and ragged, with leaves several years old.

And even when they do fall,

something is sure to want to put them to good use.

In the arid gumtree shrublands of southern Australia,

the mallee fowl is busy.

The female has laid her eggs in a huge mound of soil and dead leaves

that she and her mate have carefully scraped into shape.

As this pile rots down, the heat generated incubates the eggs.

Too much or too little heat and the eggs will die,

so the birds keep on adjusting the mound to keep it at 34 degrees.

Both birds have temperature sensors in their mouths -

a quick taste keeps things monitored.

Two months after they're laid, the eggs begin to hatch.

The chick bursts out and starts its journey upwards.

When you're buried a metre down, this is no picnic.

It can take two days to get to the surface,

and it gets no help at all from its parents.

This is one tough little chick!

When it finally gets out,

it's able to walk immediately and it toddles off into the bush.

It can even feed itself and it'll be able to fly within a day.

It's just as well it's so self-sufficient,

because from now on, it's on its own.

And with all those dry, dead leaves around,

the bush is a dangerous place to be.

Of all that gumtrees have to endure,

this surely seems the most devastating.

Australia's landscape has been dramatically shaped by fires.

They happen right across the country -

and in some areas very frequently.

Whether started by lightning or careless matches,

bushfires are a fact of life.

In dry conditions, the fires quickly take hold.

Strips of bark peel away in flames,

carried off in the wind to start new fires as much as 30km away.

In eucalypt woodlands, the litter that collects round the trees

is highly flammable, and can create a fire as hot as 1,000 degrees C.

It may look like a disaster for the trees, but the bizarre truth is,

eucalypts seem to encourage their surroundings to burst into flames.

Many have thick and insulating bark,

able to withstand all but the most ferocious fires.

Some gums actually NEED a really good blaze to release their seeds,

and provide a fertile bed of ash on which they'll later sprout.

This dry old country has been burning like this for millennia.

Although it may not look like it,

the gumtrees have the situation well under control.

And this devastation is a prelude to something quite remarkable.

Within weeks of a fire that seems to have killed them,

many gumtrees start popping out fresh green shoots.

They grow from buds under the bark,

where they'd been protected from the intense heat.

Bare and blackened branches are green again,

and the trees carry on as normal. It's almost like a magic trick.

In this volatile country, eucalypts seem able to cope with anything.

To add to the damage begun by fire and rain,

they are chewed away by millions of termites.

Australia's gumtrees are among the most termite-ridden in the world.

Some are completely hollowed out by the activities of these insects.

But with so many termites around,

there are other animals ready to eat them.

Including these. They're numbats...

and they live in the woodlands of Australia's south-west.

Numbats have tiny mouths and their teeth are not very effective.

But as they only eat termites, all they need is a good sense of smell

and the right tongue - sticky, manoeuvrable and very, very long.

It can flick termites into its mouth and swallow them whole.

Most of Australia's small mammals are nocturnal,

but numbats don't get out of bed until the sun's warmed the ground,

and the termites are active just below the surface.

Numbats are solitary animals,

but these are young ones - out and about together.

When they're old enough, they'll feed alone, like their parents,

eating 20,000 termites a day.

These youngsters will stay together for a few months,

learning to fend for themselves.

Until then, the slightest danger - real or imaginary -

will make them flee to the den in the safety of a gumtree hollow.

Hollow trees are a real feature of the bush.

There was once a man who lived inside a giant gumtree -

and raised a family of four there.

Tall trees, strange tales.

There is a particular type of gum

that thrives on the banks of the Murray River of southern Australia.

The river red gum grows here in enormous forests,

and some of the trees may be 500 years old.

The oldest are full of holes and are very popular with parrots.

Regent parrots make their homes here.

In the breeding season, the male brings food to the female,

who's never far away from the nest.

And that nest may be more than five metres down inside the tree.

It may seem like hard work to have to climb so far,

but it's sensible - it protects the eggs and young from the elements,

and from other hazards.

There are thieves around.

Given the chance,

a lace monitor would easily make a meal of an egg or a chick.

In the nesting season, they're a major part of its diet.

And it knows where they live.

The danger passes,

and the lace monitor turns its attentions elsewhere.

These gumtree forests flank the river for hundreds of kilometres,

and they're full of wildlife.

Some of it has the oddest behaviour.

When night falls,

a strange, savage little marsupial makes its appearance.

It's a yellow-footed antechinus.

The size of a mouse, it's a voracious, feisty little carnivore.

Thus fortified, this male has a busy time ahead of him.

It's a bizarre life cycle.

These animals have just one short, sharp mating season,

and competition for females during that time is so strong

that the males even give up food.

Each mating can last 12 hours, and it's a bit of a free-for-all,

with the females having a pretty rough time of it.

The stress is all so much

that after two weeks of frantic activity, all the males drop dead.

The pregnant females are left to carry on alone.

But with the males out of the way,

it does mean there will be more food left for mother and the kids.

It's a perilous environment, this gumtree bushland -

in more ways than one.

These giant old red gums have been nicknamed "widow-makers".

-And this is why.

-CREAKING

They have an alarming tendency to drop their branches,

without warning, on the calmest of days.

The wood is so heavy that if it falls into the river,

it sinks like a stone.

And so the river is full of snags -

a tangle of fallen branches and collapsed trees.

But even these drowned limbs have their uses.

Water birds use them as lookout posts.

These underwater woodlands are also the perfect hideout

for Australia's biggest freshwater fish.

The Murray cod can reach more than a metre long - even bigger,

if fishermen's tales are true - and weigh more than a man.

Under these snags it can hide from predators,

rest from the flow of the river and shelter from the sun,

while it lives to be 100 years old.

In the Australian bush, even the fish live in trees.

The Murray river is shallow and the banks are low.

Once every few years, when spring rains are especially heavy,

and snow melts fast in the mountains upstream,

the big river breaks its banks

and it moves into the surrounding forest.

It looks like a beautiful disaster.

But the bushland inhabitants are surprisingly adaptable.

When put to it, a kangaroo can swim.

And the gumtrees themselves are perfectly at home.

In this dry place, where rainfall is generally so low,

these big trees would die of thirst without floods from time to time.

For now, they can drink deep and put on a spurt of green growth.

For a while, the forest is transformed into a wetland -

a maze of swamps and billabongs.

Where, a few days ago, kangaroos browsed in grassy clearings,

now there are spoonbills and egrets fishing among the trees.

Floods like these are less frequent than they once were.

The Murray's flow has been altered by people

because the water was needed elsewhere.

But when they do happen, the results are spectacular.

The wildlife is tuned to events like these.

Fish begin to breed, and thousands of water birds start nesting

around the flooded trees.

This is the driest inhabited continent in the world,

and yet here are kangaroos up to their knees in water!

The Australian bush is nothing if not contradictory.

The first European settlers had dismissed these vast green swathes

as just "forests in rags".

But as they got to grips with the curious land, the bush, with its resilience and strange wildlife,

became the essence of Australia.

It's a land of pioneers,

where adaptability and tenacity are the keys to survival.

And gumtrees seem to suit it very well.

Next week, Wild Down Under explores the exotic islands

that surround Australia,

from tropical New Guinea to icy New Zealand.

Each of these islands has its own cargo

of unique and extraordinary wildlife.

This breathtaking journey reveals bizarre creatures

in spectacular landscapes - island-hopping on an epic scale.

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