Original subtitles

This is the Congo... Africa's mightiest forest...

a place explorers once called the green hell.

Join me for an epic adventure beneath the jungle canopy...

...a journey into heart of darkness...

l'm on a quest to find a garden of Eden hidden deep in the forest.

On the way, l'll meet some of the jungle's most elusive animals...

and l'll need their help to get on the right trail.

This adventure could take me to hell and back...

the Congo is home to some of the most deadly plants and animals on Earth,

armed with stings, bites and poisons.

And they're all out to eat me alive.

lf l survive all that,

l'll unearth some of the best-kept secrets of the Underworld....

So how does anything manage to survive in such a tough inhospitable place?

Well the key to discovering the secrets of survival

may be to look at some of our closest relatives.

These baby gorillas were orphaned when their mothers were shot by poachers.

lt's hoped eventually they'll be returned to the jungle,

but its no easy task, the underworld is a complex place.

ln the wild it takes gorillas about 1 0 years to learn all the skills

that they need to survive.

They need to know what food to eat and where to find it.

lt may look like a salad bowl here but eat the wrong thing and you're dead.

Putting one of these infants back into the jungle at this stage

would be a bit like abandoning a toddler in the middle of a busy city.

But if it takes them a decade to get to grips with this place,

how am l going to cope?

Dense jungle cloaks over a million sq kms of central Africa...

and l'm about to travel deep into its heart...

to one of the remotest places on earth.

For years, the Congo was known as the white man's grave...

Many European explorers who entered this forest were never seen again.

Fortunately l'm in good hands.

Even today this place feels like the ends of the earth...

many animals that live here have never seen people.

A ride in a dug out canoe is a gentle start to my journey,

but things are going to get tougher.

Waterways can take me so far... but not far enough...

if l want to get deeper into the jungle, l'll have to go on foot.

Here at the gateway of the underworld

it really is a case of not being able to see the wood for the trees.

Everywhere you turn is just a barrier of dense green vegetation.

lt's absolutely amazing to think

that early explorers like Stanley and Livingston managed to cover

about a thousand kilometres of this on foot.

This is certainly not an easy place to get around...

lt's not just exhausting...

you've also got to watch exactly where you put your hands and feet...

But why should this place be a walk in the park?

lt's not here to suit us, or even the animals....

lt's a world made by the trees for the trees

and they dominate every aspect of life here in the Underworld.

They black out the sun with their crowns,

coat the floor with their cast-offs... and loom over everything.

These giants got where they are today by taking almost all the light and water,

leaving the jungle low-life to struggle at their feet.

lt feels like a strange and alien place full of death and decay.

The sunny canopy is only 40 metres above my head, but it's a world away.

While the masters of the forest have their heads in the sky,

down here it's a bewildering monotonous maze.

lt's like being a stranger in a new city,

all l have to do is wonder off alone to realise how easy it is to get lost here.

l am not sure where l am or how far l've come.

lts just a tangle of green, one tree starts to look much like another.

l can't even see the position of the sun or try to orientate myself.

You can easily imagine how early explorers never found their way out...

it's just an endless sea of green... mile after mile.

l'm just going round in circles to get to that special place l'm looking for.

l need to find some kind of a path.

Luckily this jungle does have a network of trails...

but they weren't made by humans.

These piles of dung show there's plenty of traffic passing through.

Though they were left by an animal l don't want to surprise...

These parasitic ticks often live on its back...

And here's the real clue... deep cuts in the earth...

l'm on the trail of an elephant.

There are lots of elephants around here, about 200,000 in the Congo basin,

and for such large animals they can be amazingly quiet.

Chances are they'll try and avoid me.

But l can find them another way.

Forest elephants do communicate...

it's just that we can't always hear them...

But with this kit l can tap into their conversations.

With a computer and a microphone, l can see the sounds that l can't hear...

Even from elephants several kilometres away.

There you go, a real rumble in the jungle.

Most of the sound is too low for human ears to pick up.

So why do elephants have such deep voices?

ln a place like this sound is easily smothered by the vegetation

and the only thing that gets through are low frequency sounds...

these elephant rumbles slice through the forest like a hot knife through butter.

These long distance trunk calls carry information several kilometres

through the densest rainforest.

And forest elephants couldn't manage without them.

They're forced to scatter far and wide to find enough food.

So these rumbles in the jungle are the main way

they can socialise and keep in touch.

So what is it they're talking about?

lt may be news about a tree coming into fruit,

locating members of your family or even a female calling a mate.

Because low frequency sounds travel through the ground much faster

then they travel through the air,

it's likely that elephants sense the message with their feet

before they pick it up with their ears.

They may even compute the time difference and so judge the distance of the caller.

But what do other animals do that live in this dense underworld?

Our closest relatives have the same problems

as we do they can't hear low frequency sounds,

so how do they manage to keep in touch here?

Chimps can communicate over quite long distances by drumming on buttresses roots.

And they often have a favourite tree which every time they pass

they'll drum on which allows other chimps

in the vicinity to pin-point their precise location.

But all this racket isn't as chaotic as it sounds.

Chimps eat fruits, nuts and meat -

foods that are scattered over a wide area and hard to find...

So their best strategy is to split up into small gangs,

each covering a different patch of jungle.

Like this, chimps can comb up to 1 0 sq kms in just a few hours.

As soon as one gang finds a decent meal, they summon the others to share it.

These calls can't be heard as far away as buttress drumming,

but they probably carry more information...

such as what trees are in fruit and where to find them.

ln this way they can find enough food to survive.

So the calls are an important part of the chimps' jungle survival kit.

There's another of our close relatives living here,

and l'm going to venture further into the forest to find them.

But it's not going to be easy...

They're much less noisy and boisterous than chimps.

lnstead they live quietly in close family groups

and are becoming increasingly rare.

But l've come across signs of them so l know they're around here somewhere.

lt's a western lowland gorilla...

in the wild they're much more timid than the orphans l met earlier...

You can just see them, like,

intensely deep black shadows in the gloom just moving about...

You can also smell them... at this range it's quite intense.

Their senses are actually quite comparable to ours,

and if l'm having difficulty seeing them,

they must have some of the same problems

seeing each other in the dense undergrowth.

Gorillas don't move very far or very fast

but even so they often give these deep contact calls, belch grunts,

that allow them to keep tabs on each other.

The Silverback there -

see his big grey back and the reddish top of his head

which is so distinctive of Western lowland gorillas.

He's huge!

The young one... got some sort of termite clay which he's breaking open and eating.

The silverback is boss... he dictates when the group eats and sleeps...

and guides them around the jungle in search of food.

Gorillas spend most of their time on the ground and eat fruits and leaves.

They have to be choosy... some of these plants aren't edible -

they're full of poisons like strychnine and cyanide.

These forests can seem very inhospitable...

so what's really surprising is that people live here too.

Although they are few and far between, their voices fill the forest.

The BaAka pygmies have a unique understanding of the forest

and can teach me a great deal about jungle survival tactics...

Over time they've learnt how to use

a huge variety of animals and plants in different ways.

These are Ngungu leaves...

which the BaAka collect when they make temporary hunting camps

and with a few alterations they can be turned into something very useful.

Compared to them l feel like a complete beginner!

lt's actually harder than it looks,

but with their expertise it takes less than an hour

to make a weatherproof Ngungu tent.

There's no point building anything more permanent...

traditionally, the BaAka have to move on every few weeks to get enough to eat.

These forests can only support a small, sparse population...

Even with a wealth of ingenuity and knowledge,

this is one place that people will never truly master...

There's always something out to get you...

This is one sight that sends everyone running for their lives...

a swarm of driver ants.

Drivers form colonies up to 22 million strong.

And when they mobilise, they turn into a living, marching weapon of destruction.

These fiendish looking soldiers are guarding the flanks of the column

while the main body of ants are rushing over each other

in their frenzy to reach the front.

Like other army ants, the drivers are completely blind.

They find their way by following the scent trails of their frontline scouts,

as they fan out in search of prey.

And once the gang has found a victim, they eat it - alive...

The swarm consumes anything in its path...

and even those that flee the carnage are picked off ahead by birds...

Meanwhile the drivers chop their victims into portable chunks.

There are particularly horrifying stories of people actually been eaten alive

when they've fallen over drunk in the forest.

ln a single day it can strip a patch of forest the size of a football pitch.

A 1 00,000 victims maybe flushed out, exterminated,

processed and transported back to the underground headquarters.

Even this nest is a mass of moving ants...

soldiers grapple together to create a living wall...

But soon they'll all be gone.

Once the driver gang has trashed one neighbourhood,

it has to move on to fresh hunting grounds.

And their impact is temporary too.

Animals soon return to fill the ravaged area...

and in less than a week it can be as if the massacre never took place.

At least with ants you can see them coming and get out of their way.

But there's another creature living in the water here

that really makes my skin crawl.

lt lurks in jungle streams and pools and waits until his victim passes by.

As soon as it picks up the smell or any movement in the water, it homes in.

You can't feel it even one is already sucking your blood.

A leech.

lt's got two suckers, one at either end.

And once it is on, it sticks like glue.

Leech can pass on infection.

But it is nothing compared to the other things if you catch around here.

These forest are full of horrible diseases like river blindness,

sleeping sickness, and the dreaded ebola.

But the Underworld can save life too... and the people here learned that long ago.

As well has plants to cure stomach upsets, there's antibiotics, anti-diuretics,

there's even a plant that helps impotence.

Most of these plants are actually poisonous

but in small quantities it's a case of cure rather than kill.

Chimps also use the forest pharmacy.

They chew the pith of this plant to settle an upset stomach,

and use others to get rid of parasites.

Like the BaAka they hand this knowledge down through the generations.

The rainforest is just full of precious resources

that science has yet to discover.

lf we don't know what the underworld might hide by day,

it's even more mysterious at night...

Many animals like chimps move away from the forest floor

as the light begins to fade.

They make a bed in the safety of the tree tops...

ready to snuggle up before darkness descends.

Even the people here stick close together once the sun goes down...

Huddled around their camp fires,

the BaAka have their own ways of warding off the dangers of the night.

They're singing about forest spirits, one of which is called Jengi,

a malevolent spirit, covered in leaves, comes in at night,

steals people away into the forest and kills them.

Like many legends it may well have its basis in fact.

After all who knows what's really out there....

This really is the heart of darkness... no moonlight reaches the forest floor.

But many forest animals only come out at night...

so we'll just have to brave it...

Walking through the forest at night makes you

makes you confront your most basic instinctive fears.

You can't really see anything at night...

all your other senses become incredibly highly tuned...

l feel completely useless in this darkness, l can't see a thing.

But there's certainly plenty going on...

One of the things that strikes you at night is just the,

the amount of noise, it's as if someone's turned up the volume of the forest.

lt's not surprising that the BaAka has stories and legends of fierce creatures

that come out at night.

ln this blackness,

animals use their own personal sound track to broadcast who and where they're.

Those are hammerhead bats...

it's an extraordinary volume for a relatively small animal.

lt's just the male that calls this way... he's trying to attract a mate...

He's got a huge voice box that fills most of his chest,

and his peculiar head seems specially designed to blow his own trumpet...

And there's another thing about the forest at night... it's full of powerful smells.

But then, smell is also a good way to say you're here.

The male bush baby urinates on his own hands...

and marks his territory by leaving stinky paw prints everywhere he goes.

Whatever kind of animal you are, you need your wits about you...

you never know what lies ahead...

One spider's creepy enough...

But these communal spiders live in groups of up to 1 500, in a single giant web.

They move together in a sinister synchronised dance,

it's like something out of a nightmare.

Just the faintest vibration and they all rush to see what's there...

The victim doesn't stand a chance...

lt's very unusual to see spiders working together like this,

but it makes sense here in the underworld as webs are often destroyed by rain

and falling debris or animals charging through.

The spiders do most of their web repairs at night...

and l can't see me getting much rest either.

l've got to admit, l'll be glad when it's dawn...

As the sun rises the canopy is bathed in light,

but very little of that light ends up down here...

Just over one per cent will make it to the forest floor...

which means that for plants here life can be a desperate struggle.

The only way you can tell

where the sun is overhead is by the movement of these sun flecks -

tiny scraps of light that make it through the trees.

Some plants have to survive on just a few minutes of dappled light a day...

And even these precious rays can suddenly disappear.

Like all rainforests, the Congo gets more than its share of water...

almost 2m of rain each year.

Around me the forest is plunged into even deeper gloom.

These downpours are short but intense...

ln the canopy the animals can sit it out...

...but for the creatures of the underworld

this deluge can be a catastrophe pounding the forest floor

and causing life threatening floods.

Storms can also change the balance of power in the jungle...

High winds whip the canopy and water loosens the soil below...

a combination that can spell disaster for the trees.

When a giant like this dies its big news...

suddenly a massive hole is punctured in the canopy

and all the plants on the forest floor get the chance they've been waiting for.

As soon as light begins to stream in through the gap,

it triggers an explosion of plant life.

First specialised sprinters race into action...

Some like the yam can shoot up half a metre in a day.

But this is just the start of redeveloping the site.

Although the sprinters are first off the mark,

they only have a short time in the sun.

ln just a few months, shrubs and bushes take their place to dominate the clearing.

Next, skinny pioneer trees overtake them...

and so it goes on...

each new wave of redevelopment is the foundation for the next...

But it's no easy ride -

as soon as a new shoot appears it's under attack from hungry animals.

With all their energy used up on growth, the plants can't make their poisons.

So how do they protect themselves?

This barteria tree has a very special form of defence

as soon as anything comes close to it let alone touches it

they're in for a nasty surprise.

Out comes a private army of body guards... these are tetrapanera ants

and they're vicious enough to put off any potential attacker.

ln exchange, the ants get a home and food - a perfect friendship.

But like the plants that came before it, the barteria is on borrowed time.

Growing in its shadow, protected from direct sunlight, is a tiny sapling.

lt's like the story of the tortoise and the hare.

This young mahogany is last to leave the starting line,

and slow to grow... but a century from now,

it will emerge the winner... and finally plug the canopy gap.

From above, the jungle may look fixed and timeless,

but it's just that we can't see behind the scenes.

At any moment, one third of the forest is being demolished and rebuilt.

And this dynamic green metropolis is all powered by sunlight.

But light alone can't build a forest.

Giants like mahogany need tonnes of fertiliser.

You'd think the soil here would be every gardener's dream; rich, thick and fertile.

All there is, is a few millimetres of soil and beneath that it's a sandy desert.

So how could the plants get enough food to survive?

ln this case the answer to life is death...

Nearly all the nutrients in the rainforest aren't in the soil at all,

they're trapped in the trees.

So when one dies, a giant food parcel comes crashing down into the underworld.

Where an army of recyclers are ready for it.

Recyclers like termites,

they live in colonies some 2 million strong in these fortress-like mounds.

And deep beneath the surface, termites build these dark,

damp galleries to house a great recycling centre.

These termites can't break down wood on their own,

so they farm a special fungus that can do it for them.

The fungus absorbs all the goodness from the wood

and then the termites eat the fungus.

The termites are so keen to protect their fungus gardens

that they'll repair any damage to the mound.

Rebuilding a strong city is vital to keep them safe from attack,

but some animals have found a sneaky way in.

Termites pack a huge amount of protein -

almost twice as many calories gram for gram as steak -

and chimps have worked out how to fish for them with slender stems.

Outings to the termite mound are like a picnic.

But snacking chimps hardly tend the termite population.

On any fallen tree there'll be millions of termites at work.

But termites are only the first link in the recycling machine.

Within the soil, another army continues the process.

These are the hidden hordes that staff the underworld...

none larger than a grain of sand.

Miniature carnivores... preying on herds of microscopic grazers...

...millions of nematode worms in between the particles of soil...

and smallest of them all, countless bacteria.

Each member of this micro-world

helps decompose the jungle's cast-offs into ever smaller pieces...

Helped by the tropical heat and humidity,

this high speed team recycles half the leaf litter every six weeks.

But the biggest rotters of them all -

and crucial last link in this process - are fungi.

Fungi deal with the stuff no other members of the compost crew can cope with.

But fungi don't just help make fertiliser, they distribute it too...

Under the ground tree roots span out to gather nutrients,

but they can't manage it alone...

they link up with another type of fungi - mycorrhizae.

Mycorrhizae link the tree roots like an underground mat...

They work like a super-efficient sponge,

soaking up all the goodness from the ground

and posting it back through the roots into the trees.

This trade-off is the hub of a recycling system we can only dream of!

Amazingly, without a fungus thinner than a cotton thread -

none of these huge trees would exist.

The more time l spend here, the more l realize

that everything is connected in an intricate web of relationships.

Plants rely on animals... and animals rely on plants...

from the smallest to the largest.

And there's one relationship that can get me back on the track

of the biggest movers and shakers of the jungle.

This tree is a partner in one

of the underworld's most fascinating relationships.

lt produces this huge omphalocarpum or belly button fruit.

Only one forest animal can eat this fruit...

and some say when it hears the thud it comes to collect.

Forest elephants love fruit, and when they find a good tree they never forget.

Over generations they've built up their trails

to link the richest fruit trees in the forest.

The omphalocarpum isn't easy to get into,

but these elephants have got what it takes.

They're the only ones with downward pointing tusks...

perfect for splitting belly button fruit.

But the elephants simply act as couriers for the trees.

As they head back out on the trail they scatter the belly button seeds.

They even provide the seeds with fertilizer.

On average elephants drop 45 kilos of dung every day

and 9 out of 1 0 piles contain seedlings

and because they drop it right on the path

there's even a decent amount of light to help them grow.

Since more than thirty different trees rely on elephants to spread their seeds,

these trails end up like avenues of fruit trees...

each one like a jungle high street with a wealth of goods

to tempt anyone passing by.

Carving trails and planting fruit trees,

elephants are like the city planners of the underworld...

this trail should lead me to the special place l've been looking for...

More and more trails are joining the main path.

lt's a real highway now with lots of traffic.

There's light up ahead... l'm nearly there.

At last, this is what l've come to find...

lt's called a bai, and after the endless oppressive darkness of the underworld

it's just a euphoric feeling to come out again into the sunlight.

And to see all the animals gathered here

it really feels like stepping out into the garden of Eden.

And it seems to have the same pull for the elephants...

They meet at bais like this one all over the Congo...

lt's like a park, where they can gather and enjoy the freedom of an open space.

Members of the herd are reunited after being scattered in the forest...

now, instead of using distant rumbles to communicate,

they can catch up properly and relax.

There really is a kind of party atmosphere...

But there's something more serious on the agenda here...

beneath the water the earth is rich in mineral salts;

sodium, potassium, magnesium, calcium

it's like some sort of mineral supplement from a health food shop.

A regular dose of minerals is vital for these animals.

And the clay neutralizes the toxic chemicals of jungle plants,

and can help settle even the largest stomach...

The elephants use their trunks to blow down into the stream bed,

releasing fresh supplies of salts.

These dissolve in the water and the elephants suck them up.

All this activity helps keep the trees at bay.

No one's sure how long the elephants have come here...

these clearings could be the result of generations prospecting for minerals...

There are hundreds of bais all across the Congo basin...

hubs of a network of elephant trails.

The bai draws other animals into the open too...

including our elusive lowland gorillas.

One of the great attractions about this place for gorillas

is just the array of wonderful plants growing here,

there's wild ginger, water lilies, aquatic herbs,

it's like one gigantic luxurious salad bowl.

These bais are unique windows on the forest.

But it isn't just the creatures of the underworld

that like a day out at the park...

this place is important to canopy dwellers too...

Colobus monkeys make a rare trip down to the ground...

to eat the same mineral rich plants as the gorillas.

And otters fill the bai's rich waterways searching for worms and crabs.

l could sit here for hours and it seems the animals

just love hanging out here too.

There's time for friends and family... and just to have fun in the sun.

But the forests are these animals' true home...

and sooner or later they return to the trees.

Without the forest, nothing we've seen could exist.

Trees are the creators and protectors of this huge hothouse of life...

the most varied and complex living system on the planet.

But it is also one of the most fragile.

Everything here relies on everything else to survive.

The rainforest is home to more than half of all the animals on earth...

including some of our closest relatives.

We're only just beginning to discover the secrets of these amazing places,

and their significance to us.

lf we lose our jungles, we loose them for ever.