Tropical Worlds

♪ [Birds chirping] ♪ The biggest living thing that exists on this planet is a plant, like this giant Sequoia tree in California.

[Chirping continues] Plants, whether they are enormous like this one, or microscopic, are the basis of all life, including ourselves.

We depend upon them for every mouthful of food that we eat and every lungful of air that we breathe.

♪ Plants flourish in remarkable ways, yet, for the most part, the secrets of their world have been hidden from us until now.

♪ Now, we have new, ground-breaking technology that enables us to enter their extraordinary world and see their lives from their perspective.

♪ This series will reveal the extraordinary and dramatic ways in which plants behave... ♪ and we will explore the challenges demanded by the very different landscapes in which they live.

♪ The tropics, the richest and most competitive place in which to survive.

♪ The bizarre water world... ♪ where giants fight ferocious battles and plants eat animals alive.

Deserts.

Ah!

The world of extremes.

♪ Seasonal lands... where survival depends on precision timing.

♪ And everywhere, we will explore the critical and intimate relationships between plants and animals, including ourselves.

♪ Join me in a world that takes you by surprise.

♪ [Laughs] ♪ See our planet as never before... ♪ from the plants' perspective.

This is "The Green Planet."

♪ ♪ ♪ ♪ [Insects and animals chirping] I'm in Costa Rica, in the heart of a rainforest, the richest and most dynamic environment on earth.

Rainforests only cover a very small proportion of the earth's surface, yet they contain over half of all known species of animals and plants.

[Chirping continues] Up here, the forest's canopy is bathed by life-giving sunlight.

♪ The branches of the great trees carry rich, flourishing sky-gardens... ♪ home to countless different kinds of beautiful plants.

♪ Each species has evolved its own exquisite solution to the challenges of survival.

♪ This forest-world may look peaceful, timeless, and unchanging, but that is far from the truth.

This is a battlefield.

Throughout this forest, plants are competing ferociously with one another to claim the light.

[Trees creaking] The battle is at its fiercest on the forest floor... [Creaking continues] where only 2% of the sunlight filters through.

Plants here have to bide their time.

♪ Their opportunity comes when an old tree dies.

♪ When that happens, sunlight floods the forest floor for the first time in, perhaps, a hundred years.

♪ ♪ A seedling's wait is over.

♪ It must now race skywards and claim a place in the canopy, but it's not alone.

♪ Rivals are everywhere, each with its own survival strategy.

♪ ♪ Some plants, like this Monstera, stretch out divided leaves to collect what light they can.

♪ This vine is groping blindly around with its tendrils.

♪ It attempts to reach the light by hitching a ride.

Its tendrils are highly sensitive to touch... ♪ and a suitable target is in range.

♪ Got it!

♪ ♪ The vine tightens its grip and begins to haul itself upwards.

♪ But it's now overtaken by the forest's fastest-growing tree... ♪ a young balsa.

♪ Its giant leaves are already 40 centimeters across and are stealing the light from its rivals below.

♪ But the balsa's battle is not yet won.

Other, different vines are lying in wait.

♪ ♪ Each is armed with dozens of claw-like hooks.

♪ If just one hook gets a grip... the vine will be able to smother its victim.

♪ ♪ ♪ ♪ But the balsa is defended by a shield of slippery hairs.

♪ The vine's hooks just can't get a hold.

♪ The balsa brushes them aside and continues to rush skywards... ♪ leaving the losers in its shadow to fight among themselves.

♪ This balsa has won its battle for the light... ♪ and it's done so in a little over a year.

♪ Most trees would have grown an inch or so in that time, but this one is already 30 feet, 10 meters tall.

[Insects and birds chirping] Balsas owe their success to the special character of their wood.

If this section of tree trunk came from a hardwood tree, it would be really quite heavy.

But as it is, it's from balsa, and it's really very light, and that's because of its internal structure.

♪ Under the microscope, balsawood looks like a honeycomb.

It contains more air than wood, so not only can it grow very fast, but it gets the maximum height for minimum weight.

But fast growth needs something else-- fuel, and lots of it.

♪ That fuel is created in a plant's leaves as they soak up the sun.

♪ It's a process called photosynthesis... ♪ a chemical reaction that is the basis of all life on earth.

♪ Leaves are covered by thousands of microscopic pores called stomata.

When open, they extract carbon dioxide from the air and, using energy from the sun, combine it with nutrients to build the plant's tissues.

♪ And, critically for us, the process releases the oxygen that we-- and all animals--need in order to breathe.

♪ [Distant bird squawking] ♪ But for plants, there is a downside.

These precious, energy-packed leaves attract predators... ♪ in every shape, size, and agility.

♪ ♪ A sloth can only move slowly, but you don't need speed to gather leaves, and it eats nothing else.

♪ ♪ The plants here are under constant attack from all kinds of leaf eaters, but the most voracious by far is hardly ever seen.

It consumes 50,000 leaves every day.

It's created this great clearing in the forest, and it lives just beneath my feet.

♪ It's called Leucoagaricus.

It's neither animal nor plant.

It's a fungus.

It lives 16 feet underground, far from the leaves that it devours.

♪ To get them, it employs the best leaf-gatherers in the tropics.

♪ Leafcutter ants.

♪ Millions of them provide the fungus with its food, and in return, the fungus cultivates tiny mushrooms as food for the ants.

♪ The fungus releases chemical signals that tell the worker ants what type of leaf it wants to eat.

Scouts are sent out with the latest orders.

♪ Worker ants will travel many hundreds of feet to find the right kind.

♪ Today's crop is being taken from a young Bixa tree.

♪ Just a few years old and still battling to reach the canopy, it can ill afford to lose any of its leaves.

♪ [Crunching] ♪ ♪ Between them, the ants can demolish a large leaf in a matter of minutes.

♪ The sound of cutting attracts more ants.

[Overlapping crunching] [Distant birds chirping] Now the pieces are carried back to the underground fungus.

[Chirping continues] The ants can run at speeds of six feet a minute... and each can carry a load ten times its own weight.

♪ ♪ It's a river of leaves across the jungle floor... part of a vast network that extends for miles through the forest.

♪ To avoid congestion, worker ants dig trenches around obstacles.

♪ ♪ ♪ Thousands of pieces are delivered every hour to the waiting fungus.

♪ ♪ Fed by such a continuous supply, the fungus grows rapidly, filling the chambers in which it lives... so the ants excavate more space.

It seems that the fungus has the upper hand... and the Bixa tree will not survive.

♪ But it fights back... using chemical warfare.

♪ The Bixa tree floods its leaves with toxins that could kill the distant fungus.

As the ants carry the fragments back, they are themselves poisoning the fungus on the tree's behalf.

♪ It's a long-distance attack.

♪ As the poison takes effect, the ants sense that their fungus is weakening... ♪ and they respond to its signals by changing to another source of leaves.

♪ So the plant's chemical response forces the ants to constantly switch from tree...to tree.

♪ Strike and counterstrike... ♪ and that ensures that enough leaves remain uneaten for each tree to recover.

♪ [Snorting] [Birds chirping] ♪ Once a plant becomes adult, it can switch its energies from growth to reproduction.

♪ The tropical forests of the Americas stretch from Mexico to the southern reaches of the Amazon.

They contain more than 100,000 different species of plant... each with its own particular survival strategy.

One species that has adopted a grow-fast lifestyle flourishes throughout this vast region... ♪ the balsa, but it has to pay a high price for doing so.

The lightweight wood that enables it to grow at such speed is not strong and is easily broken.

Few balsas live longer than 20 years.

♪ This one is approaching the end of its brief life, so the time has come for it to reproduce.

♪ It has used a huge amount of energy to produce some of the most extravagant flowers in the forest in immense numbers.

♪ Each is the size of a human hand.

♪ [Insects chirping] As night falls, the tree prepares an enticing treat.

♪ This is a kinkajou, a kind of fruit-eating raccoon.

[Chirping continues] ♪ Each flower is filled with huge quantities of exceptionally rich nectar, supercharged with sugar.

♪ Irresistible.

♪ The kinkajous drink so greedily that they get pollen all over their faces... ♪ so, as they move from tree to tree, they carry pollen with them.

♪ But the balsa leaves little to chance.

The nectar might appear to have run out, but this is just the first round.

Now the balsa refills its flowers, enticing the kinkajous back to repeat the process seven times a night.

Pollination is complete.

♪ And the kinkajous?

They also get well-served with over a hundred pints of nectar in just a few weeks.

♪ Both plant and animal do well out of this arrangement... [Insects and birds chirping] but in the tropical world, that isn't always so.

[Chirping continues] Borneo.

♪ Here, on the slopes of Mount Kinabalu, live plants that eat animals using pitcher-shaped leaves full of water.

♪ Insects are attracted by the expectation of nectar, but tumble into the pitcher, where they're drowned and absorbed.

♪ On the lower slopes of the mountain, a plant grows that has no leaves at all, or even a stem.

All that can be seen is this--a bud.

♪ It is a parasite.

♪ The rest of its body lies within the tissues of a liana, on which it feeds.

♪ After about five years, the bud finally opens into a monstrous flower.

♪ It now has only a day or so in which to be pollinated before it starts to wither.

Its petals are the color of blood.

Their surface is tough and warty.

♪ It appears to have fur... ♪ even whiskers and teeth.

♪ At first sight, it might be mistaken for a dead animal.

This is Rafflesia, the corpse flower.

♪ More than three feet across, it's the world's biggest flower... ♪ and this one is a male.

[Fly buzzes] From its center comes the pungent odor of death.

♪ It's a scent that might not appeal to every animal... ♪ but it's very attractive to carrion flies.

[Flies buzzing] They lay their eggs on rotting flesh.

♪ ♪ The scent lures the fly deep into the flower, in search of meat.

♪ The fly finds nothing.

The Rafflesia, however, has the fly exactly where it wants it.

♪ It's stuck pollen to the fly's back.

♪ ♪ If this male Rafflesia's strategy is to work, the fly carrying its pollen must now visit a female corpse flower... ♪ such as this one.

♪ [Fly buzzes] Success.

[Buzzing echoes] ♪ [Birds chirping] [Tree creaking] [Leaves rustling] Once pollinated, plants are able to produce seeds-- the next generation-- but once again, there are animals all over the forest that are eager to make a meal of them.

♪ The Malay archipelago, a vast tropical world of a thousand islands.

♪ It's home to giants, the tallest trees in the tropics, many of which live for centuries.

♪ They produce seeds in enormous numbers, but only do so when the time is right.

♪ This individual hasn't produced a single seed for nearly a decade, but in the last weeks, it has become festooned with more than 10,000 of them.

♪ Each seed has the potential to produce a giant like its parent.

♪ But success will depend... on timing.

♪ ♪ [Oinking] Seed-hunters are gathering.

♪ Bearded pigs.

♪ But these seeds have been produced by a dipterocarp... trees that create the tropical world's largest seed nursery.

♪ After years of waiting, thousands upon thousands of individual dipterocarps have synchronized to produce the next generation, all at exactly the same time.

♪ ♪ [Birds chirping] ♪ And now these seeds will face the dangers below together.

♪ ♪ ♪ ♪ ♪ [Oinking] By releasing billions of seeds all at the same time, they swamp the pigs and any other animals with more than they could possibly eat.

♪ [Birds chirping] ♪ And that buys time for some of the seeds to take root and sprout.

♪ ♪ ♪ The tree's strategy has worked.

But a seedling will have to overcome many more dangers over the years if it too is to become a giant.

And there are many ways in a tropical forest by which a tree's life can be ended before it reaches its prime.

The northernmost tip of Australia.

[Distant animals chirping] This is the world's most ancient rainforest.

[Animal chortling] Battles between animals and plants have raged here for 180 million years... [Tree creaking] so the plants have had time to develop effective defenses.

This is a poison-arrow tree, one of the tropical world's most heavily defended plants.

[Creaking continues] Its trunk is tall and slippery and exudes a poisonous sap.

It appears to be almost invulnerable.

But even so, just as this individual reaches maturity, its life has become endangered.

[Birds chirping] ♪ Each monsoon season, it is invaded from above.

♪ It attracts hundreds of shining starlings.

♪ Its immense, smooth trunk makes its high branches above a safe place to nest, but over the years, this has created a major problem for the tree.

After feeding, the starlings return to the nest to digest their food, with inevitable consequences.

♪ Every year, they produce almost a quarter of a ton of droppings.

♪ The toxic chemicals they contain create a dead zone that completely surrounds the tree.

♪ The toxins are absorbed by its roots and travel up through the trunk and into every leaf.

[Loud snap] ♪ ♪ Branch by branch, the tree is slowly dying.

♪ It has become a victim of its own success.

It has been poisoned.

♪ And now, a new battle begins, one to claim the tree's dead body and the vast amount of nutrients that it contains.

It's a battle that is fought throughout the natural world, involving a group of organisms that we rarely notice.

Here, on the floor of a tropical rainforest, it's dark, it's humid, and it's hot-- ideal conditions for fungi.

We normally think of fungi as things like this-- mushrooms of one kind or another-- but these are just the fruiting bodies.

They exist for most of the time hidden in the leaf litter and the earth as a network of fine, white threads.

The threads of competing fungi envelop their victim's body, releasing enzymes which digest the tree's tissues and unlock the nutrients within.

♪ There are a million or so different species of fungi in the tropics.

Some feed on dead plants, others eat them alive, and some reveal their existence in an eerily beautiful way.

♪ In Africa, in the Congo, this is known as Chimpanzee Fire.

♪ The mysterious, bioluminescent glow becomes brighter as the fungus digests the tree.

♪ When fungi have fed sufficiently, they develop their reproductive organs.

♪ ♪ ♪ Each can produce literally billions of spores, the tiny particles that carry the species' genetic blueprint.

Each spore like this has the potential to kill a tree.

♪ ♪ ♪ The spores are so light, they can be carried by the slightest air currents.

♪ At least a billion float above every ten square feet of rainforest.

♪ Recently, it has been discovered that these spores do far more than just bring death and decay.

They are, in fact, at the very center of the rainforest's life-support system.

High in the humid air, the spores combine with molecules of water.

[Wind whooshing] Gradually, they collect into droplets, which, when they are heavy enough, fall... [Thunderclap] as rain.

♪ ♪ ♪ ♪ Over a hundred inches of rain falls every year in a rainforest.

♪ And in the center of almost every raindrop, there is a fungal spore.

♪ The ancient battle never ends.

After a rainstorm, plants have a chance to steal nutrients back, and they do this on an astronomical scale.

Twenty years ago, I climbed this particular tree using ropes, and I remember only too clearly what a huge effort it cost me.

But this tree can shift much more than my weight.

It can shift two tons of water up into its canopy every day.

♪ Water containing dissolved nutrients is extracted by the roots.

♪ It then flows to the trunk.

♪ Here, thousands of miniscule cubes carry it rapidly up the tree.

♪ Much like the veins and arteries in our own bodies, they deliver nutrients to where they're needed for the tree to grow, and as it does, they are locked away within the growing wood.

♪ The vessels run all the way from the roots right up to the leaves, where the water is eventually released back into the air, completing the cycle.

♪ It's the complex connections and relationships between plants, fungi, and animals that make the rainforest the richest and most dynamic environment on earth.

[Distant bird calling] [Thunder rumbling] [Thunderclap] When Charles Darwin was exploring the tropical world nearly 200 years ago, he wrote this in his diary: "Among the scenes which are deeply impressed on my mind, "none exceed in sublimity "the primeval forests undefaced by the hand of man."

He would struggle to find such a place today.

♪ ♪ Today, 70% of all the world's rainforest plants grow within a mile of a road or a clearing that we have cut into the forest.

♪ And this is creating new battlefields in the tropical world.

Alien armies of identical cultivated plants now stand where thousands of different species once grew.

We have planted vast regiments of crops in order to provide ourselves with food and other commodities, and the ancient forest has been reduced to ever fewer isolated fragments.

♪ All, however, is not lost.

The fragments can still be sanctuaries, keeping alive the intimate relationships within them.

Their size is nonetheless critical.

♪ This is the seven-hour flower.

♪ This plant produces its flowers at night.

They open about 6:00, and each blossom only lasts that night.

It opens for about seven hours, and then it dies.

But during that time, it provides food for one particular animal-- a bat, and here it is.

♪ ♪ [Chuckles] ♪ During the seven-hour flower's flowering season, Underwood's bat feeds almost exclusively on its nectar.

It is the plant's primary pollinator.

♪ It might seem that this is a fairly evenly balanced relationship, but not so.

The bat likes this nectar because it's sweet, but it's not very nourishing, so the bat must visit hundreds of flowers a night... and it pollinates them as it feeds.

♪ But if a patch of forest becomes too small, with too few flowers, the bats will disappear, and without the bats, the flowers can't reproduce and will soon die out.

The partnership is broken.

♪ Life in the forest depends on countless close relationships, but they are increasingly under threat as forests become more fragmented.

The solution, of course, is to join these remaining fragments together again.

Thirty years ago, I came to this exact spot.

This land belonged to a scientific research establishment, and it was covered with grass being grazed by cattle.

The scientists got rid of the cattle and allowed nature to take its course.

Just look at it now.

♪ This new forest has become a bridge that connects several fragments, allowing plants and animals to both renew old connections and create fresh ones.

♪ ♪ Of course, we urgently need to protect what healthy forests still remain.

♪ But looking forward, we must take what may well be our last chance to reestablish the lost rainforest... ♪ and help the tropical world to heal itself.

It will take the cooperation of nations around the world, but it is the only way in which we will be able to preserve the treasures of the tropical rainforest for future generations, and with it, ultimately protect all life on this... our green planet.

♪ (pensive music) (birds singing) (inspirational music) - [David] The aim of "The Green Planet" team was to take the viewer into the world of plants so that it could be seen from the plant's perspective in a way that had not been possible 'til now.

That meant developing an entirely new camera system.

(inspirational music) (plants rustling) (grinding sounds) And it started life in the garage of American ex-military engineer Chris Field.

- I've seen quite a few of these "Planet Earth" style documentaries.

They always absolutely blew my mind, especially the botanic time lapse really spoke to me.

(camera whirring) - [David] In his spare time, Chris spent a decade building elaborate motion-controlled time lapse camera rigs and teaching himself how to film plants.

- [Chris] Plants often behave like animals in so many ways.

And being able to see it through time lapse is one thing but using the motion control brings you into that time scale.

(plant growing) (lively music) - [David] It was a chance internet encounter with a "Green Planet" producer that first brought Chris to the attention of the team.

- And apparently, he had stumbled on my website and he saw this robot that I had built in my basement.

He was really interested in how it worked and what I was doing with it because it just looked a little bit more advanced than what a lot of other people were playing with.

(camera whirring) - [Paul] I was absolutely blown away by the level of detail and the kind of intricate movements that Chris was doing.

And we could really see the potential in how we could use this sort of movement to bring plants alive and film them in the same way that we film animals.

- [David] Soon, Chris joins the team in a quiet corner of the British countryside and their robot army begins to take shape.

(camera whirring) Six months later, a new robotic camera system is born that the team affectionately call the Triffid.

It's time for the Triffid to face the challenges of the Costa Rican rainforest.

While the Triffid seems to be handling the pressure well, for the crew, trying to take a tree's eye view of ants, is turning into a bit of a nightmare.

- Wake up, film ants, go to sleep, dream of ants, wake up, film ants, sleep, dream of ants, wake up, film ants, go to sleep, dream of ants.

(tranquil music) (insects humming) - [David] After two weeks in the jungle, ambition and ability finally come together, for the Triffid at least.

Thousands of individual images creating a single extraordinary time lapse, (leaves rustling) one that follows a river of leaves across the jungle floor from a unique perspective.

(inspirational music) (leaves rustling) For the Triffid, this was just the beginning.

(inspirational music) Take a bow, Triffid.

(Triffid whirring)