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AnimalsTranscript
00:00Thank you for listening.
00:30The Tatlamakan Desert in northern China, a constantly shifting landscape of sand, temperatures that swing from minus 20 to more
00:48than 40 degrees centigrade, and most critically, almost entirely, without rain.
01:04Yet, here on the dunes, a Euphrates poplar tree.
01:47And if one strikes water, others can share it.
01:53In every desert, across the planet, plants have found ways to not only survive, but flourish.
02:17This is the Grand Desierto of Mexico and the United States.
02:34These dunes may appear to be totally barren.
02:40In fact, they are full of life.
02:43In the sand beneath my feet, there are seeds of many different kinds.
02:50In fact, you could say that the dune itself is one great seed bank.
02:53And when it rains, it bursts into life.
03:04But rain may come only once a decade.
03:08And even then, the long-awaited storm may be very brief.
03:16So seeds must respond immediately.
03:33This is sand verbena.
03:35It can grow from a seed to a sweetly-scented flowering plant in just a few weeks.
03:49Primroses and many other plants soon join the race to flower before the sand dries.
04:00Desert blooms like this, however, are rare.
04:07This is the first year for 20 years.
04:15The combination of vibrant color and powerful scent attracts migrating pollinators, such as these Painted Lady Butterflies,
04:25which fly into the middle of what were, only recently, barren dunes.
04:32Everything is rushing to complete their lives before the moisture has gone.
04:46Such spectacular blooms transform deserts all around the world.
05:01From the Atacama in South America to the dusty plains of Southern Africa.
05:10From the Atacama in South America to the dusty plains of Southern Africa.
05:28The rain in deserts, however, never lasts long, and all too soon the flowers wither and die.
05:42But not before they've produced the next generation.
05:51The seeds that will now wait in the sand for the next rains.
06:01In the Sonoran Desert of North America, the huge Saguaro Cacti have a different strategy.
06:08They store water in quantity and can live to a great age.
06:15But in their early years, they are extremely vulnerable.
06:24This little Saguaro Cactus is about ten years old.
06:29When they're really small and growing out in the open, there's a real chance that they may shrivel up and
06:36die.
06:36But this one has been lucky.
06:39It's been growing in the shade of this mesquite tree.
06:44And it's got a very good chance of surviving to maturity.
06:49The young Saguaro is protected by the mesquite's branches.
06:54They halve the amount of scorching sunlight reaching the cactus.
07:00And so keep it cool.
07:04And the mesquite's extremely long roots draw up water, bringing it within reach of the young Saguaro.
07:16So the mesquite is known as a nurse plant.
07:20And a very effective one it is too.
07:24In fact, this particular mesquite has already nurtured seven young Saguaros over the past 30 years.
07:36As a young cactus grows, it needs the protection of its nurse plant not only from the heat,
07:43but from the other hazards of desert life.
07:50Temperatures can drop to minus 10 degrees overnight.
07:56And very occasionally, it even snows.
08:07If the water stored inside a young cactus should freeze, the cactus will die.
08:16But the nurse plant traps a blanket of slightly warmer air around it, just enough to keep it alive.
08:27Eventually, Saguaros outgrow their nurses.
08:30But by that time, they are robust enough to face the elements by themselves.
08:39No matter how old a desert plant is, water is always precious.
08:45Whether gathered from melting snow...
08:52...or a shower of rain.
08:59So Kankai have developed extraordinary adaptations that enable them to not only collect water...
09:07...but to retain it.
09:12Instead of leaves, which would lose precious moisture through evaporation,
09:18...they have spines.
09:21The spine has a tiny pad at its base, where the water is absorbed...
09:28...and then stored in the great swollen trunk.
09:35A large Saguaro can hold 5,000 liters of water...
09:40...and is able to do so because it has another special adaptation.
09:54The ridges on its surface are like the pleats on an accordion.
09:59They allow the Saguaro to change its shape.
10:04After rain has fallen, the pleats expand...
10:07...and the Saguaro fills up its water tank.
10:15In the dry times, it uses its water to grow, produce flowers...
10:21...and eventually, siemens.
10:27Fully loaded with thousands of liters of water...
10:30...this Saguaro won't need to drink a single drop for another year.
10:36But such valuable stores of water attract thieves.
10:42Now the spine's function changes from collecting...
10:47...to guarding.
10:51The spines of some species are a quarter of a meter long.
11:02Others are needle-like barbs that grow in clusters...
11:06...and easily break off in the skin of any animal that touches them.
11:12But perhaps the most vicious cacti...
11:14...belong to a group called the Choyas.
11:18This is called a Teddy Bear Choyas because of the thick coating of spines on it.
11:26But don't be deceived by the name.
11:29There is nothing cuddly about this particular teddy bear.
11:33In fact, it's the most dangerous plant in the desert.
11:37And I wouldn't dream of putting my hand anywhere near it...
11:41...without proper protection.
11:45Brush against it.
11:48This can happen...
11:49Ow!
11:50This can happen even with this glove on.
11:52One of them has just gone through, I can feel it.
11:54It's quite painful.
11:57Look closely at the spine...
11:59...and you can see very clearly why they're so dangerous.
12:03Each is like a splinter of glass...
12:06...sharp enough to pierce flesh.
12:09And they're covered with backward-pointing barbs.
12:14So getting them out, even with a pair of pliers...
12:17...is quite hard.
12:18This is not pleasant at all.
12:22It won't come off or without.
12:25Oh, look at that.
12:29It's hard to imagine a more aggressive defence than this.
12:34And it makes both the plant and its buds virtually invulnerable.
12:50Most animals know to keep clear.
12:56Cholla buds grow like tiny barrels from the top of the adult plant...
13:01...and then drop off.
13:04Yip!
13:12If the young Cholla put down roots here...
13:15...it would compete with its parent for water.
13:22Night falls.
13:25And this one is on the move.
13:37The pack rat...
13:39...she knows how to deal with the Cholla.
13:47She avoids the spines by gripping it at the place where it broke off from its parent.
13:58And she works fast.
14:03There are pack rat hunters here.
14:14She uses the Cholla to build a spiny wall around her nest.
14:36The flesh of the Cholla supplies her with water...
14:41...and the severed spines further reinforce the defences.
14:57This Cholla bud...
15:00...might be next.
15:05But one accidental nudge...
15:12...and it escapes.
15:15And it escapes.
15:42The bud starts to put down roots.
15:53So the Cholla, thanks to the pack rats, finds new territory...
15:59...and sets about claiming it.
16:09Few plants deal with the problems of desert living better than cacti.
16:16There are almost 2,000 different species of them.
16:21They're spread across the deserts of the American West...
16:24...from Arizona all the way to Mexico and beyond.
16:33In South America, the ice-covered peaks of the Andes act as a rain barrier...
16:41...beyond which lies the world's driest desert...
16:45...the Atacama.
16:56In the desert world, water thieves can come in many forms...
17:01...to exploit even the smallest chink in a plant's defence.
17:11One of the strangest travels within the gut of a fruit-eating mockingbird.
17:22These are the seeds...
17:25...of trysterix.
17:27They're kind of mistletoe.
17:33Their goal is the water inside this hedgehog cactus.
17:40Using the spines as anchors...
17:42...the seeds start to germinate.
17:48Each produces a long probe...
17:51...with which to try and locate the cactus's skin.
17:57For most, that's a stretch too far...
18:01...and they perish.
18:04But for this one...
18:06...the cactus's surface is within reach.
18:18It clamps onto it with a special sucker...
18:25...and then waits for darkness.
18:29At night, the cactus opens its pores in order to respire.
18:37Oxygen goes out...
18:40...carbon dioxide goes in...
18:43...and so does trysterix.
18:51Once within, its tissues spread throughout the body of the cactus...
18:56...sustained by the precious store of water that they find there.
19:05Then, a year later, it breaks through the cactus's skin...
19:17...and bursts into flower.
19:37Hummingbirds come to drink their nectar...
19:39...and pollinate them as they do so.
19:52And then, to complete the cycle...
19:55...Trysterix produces hundreds of white, eye-catching seeds...
20:00...ready to be carried away by a bird...
20:03...to invade another cactus.
20:16The Karoo Desert in Southern Africa.
20:21And although it may look bare...
20:24...its rocky ground contains an unrivaled variety of plants...
20:28...that, one way or another, store water in their tissues.
20:34They belong to many different families, but as a group...
20:38...they're known as succulents.
20:59Some are small and low...
21:01...and barely distinguishable from their surroundings.
21:06These look like little pebbles.
21:11They resemble them so closely...
21:14...that animals, which might be only too glad to steal their water...
21:18...just pass them by.
21:23When rain does fall, they absorb it...
21:26...and quickly expand.
21:30But even this doesn't spoil their disguise.
21:33They just look like larger pebbles.
21:37Nor are they green.
21:39The cells on their top surface are transparent...
21:43...and allow sunlight to pass through.
21:47Deep within and out of sight are the green cells...
21:51...where photosynthesis occurs.
21:53The process which uses this light to make food for the plant.
22:04When the time comes to reproduce, however...
22:07...the stone plant abandons its disguise.
22:31And now, it blooms.
22:42The flowers open and close...
22:45...every 24 hours.
22:56So, for a few dangerous days...
22:58...the plant advertises for pollinators...
23:01...before returning to life as a pebble.
23:18Some desert plants have developed a very different way...
23:22...of attracting pollinators.
23:26This is stapelia.
23:29It produces what is perhaps the desert's strangest disguise.
23:34It uses water stored in its stems...
23:37...to grow buds the size of tennis balls.
24:00The flower, once opened, is called a desert starfish.
24:08The flower, once opened, is called a desert starfish.
24:10When it comes to the desert starfish...
24:10...packs of loose pollen grains, as most flowers do...
24:13...the desert starfish produces them...
24:16...packed in five tiny sacks.
24:21But if its strategy is successful...
24:24...just one of them will produce hundreds of seeds.
24:31And this depends on deception.
24:36The flower appears to have hair...
24:42...wrinkly skin...
24:46...and it produces a stench...
24:48...like the carcass of a dead animal.
25:04And when a carrion fly investigates...
25:10...the flower clamps a tiny sack of pollen to its proboscis.
25:22It's not easy to feed...
25:24...with such encumbered mouth parts.
25:28But try as it might, the fly can't get rid of it.
25:34And it's still there when the fly leaves...
25:37...to try and feed from another bogus carcass.
25:45This time, however...
25:47...when its clamped-up proboscis slots into the flower...
25:50...the pollen sack is released.
25:59With pollination complete, the fly is no longer needed.
26:08And just as well.
26:15Some deserts can be so dry...
26:17...that plants must find techniques of surviving for long periods...
26:21...without any water whatsoever.
26:24One of them is to grow extremely slowly.
26:29And few plants grow more slowly...
26:32...than this one, the creosote bush.
26:36It is inactive for most of its life...
26:39...and only wakes up and grows for a brief period...
26:43...if and when there is a fall of rain.
26:49I've seen evidence of this grow slow strategy for myself.
26:55Forty years ago, I came here to California's Mojave Desert...
26:59...to visit one particular plant.
27:03An individual creosote bush tends to spread...
27:07...not by setting seeds and producing a new generation...
27:11...but by sending out new stems around its base.
27:15This plant started growing between 10 and 12,000 years ago.
27:23That was in 1982.
27:28Since then, careful measurement has shown...
27:32...that it has increased its size...
27:35...by less than one inch.
27:39Its ability to endure is truly extraordinary.
27:48So efficient is creosote collecting what little rain falls here...
27:53...that few other plants can compete with it.
27:56As a result, over the last 12,000 years...
28:00...it has come to completely dominate this landscape.
28:20The Chihuahuan Desert in North Mexico.
28:25Here, one particular plant...
28:27...plays the waiting game so well...
28:29...that it spends much of its life looking dead.
28:33...and certainly not worth eating.
28:38And it can survive like this...
28:40...for a decade.
28:49This is the resurrection plant.
28:55It's a kind of moss.
28:57It barely has roots and it certainly can't store much water.
29:01...but it can travel.
29:10After a particularly long drought...
29:14...it breaks away from its roots...
29:19...and becomes...
29:21...a tumbleweed.
29:26...brewing across the desert...
29:28...it can travel a mile in a week.
29:34With luck...
29:35...it may find water.
29:44Just a shower of rain can bring it back to life.
29:52As its fronds soak up the water...
29:55...they unfurl.
30:10In its protected center...
30:13...it still has green cells...
30:15...which absorb both the water and sunlight...
30:17...and rapidly produce the food it needs...
30:20...to resume its growth.
30:27It will grow for just as long as there is moisture.
30:35But when that disappears...
30:37...it closes up once more...
30:41...and resumes its travels.
30:54Here in the canyon lands of Utah...
30:56...lives a plant that has developed...
30:59...a finely balanced relationship...
31:01...with the animals with which it shares...
31:03...this dramatic desert.
31:09Rain does occasionally fall here...
31:13...and turns dust...
31:15...into mud.
31:20But that...
31:22...doesn't last long.
31:24A brief window of opportunity opens.
31:38Seeds that have been buried for years...
31:41...may now be exposed to light...
31:44...and come to life.
32:02This is coyote tobacco.
32:18In just a few weeks...
32:20...it grows a meter tall...
32:22...and produces dozens of flowers.
32:31The night air becomes heavy...
32:33...with their fragrance.
32:37Soon they attract hawk moths...
32:39...which sip their nectar...
32:41...and in doing so...
32:43...pollinate them.
32:46But the moths also...
32:48...lay their eggs on them.
33:05Soon their caterpillars have hatched...
33:08...and are munching the leaves.
33:13Their nipples expose the plant's sap...
33:16...to the drying air.
33:20But the tobacco plant has a defense.
33:26The leaves under attack...
33:29...produce nicotine.
33:35This chemical sedates the caterpillars...
33:37...and slows them down.
33:45And what is more...
33:46...it makes them give off a particular scent.
33:52One that summons others...
33:54...to come to the plant's aid.
33:58Big-eyed bugs...
34:01...miniature assassins...
34:02...only two millimeters long.
34:06...and whip-tailed lizards.
34:09Big or small...
34:11...they make a meal of the caterpillars.
34:23It's certainly effective.
34:28But there's more to this strategy...
34:31...than meets the eye.
34:34When the leaf of a tobacco plant...
34:37...is attacked by a caterpillar...
34:39...all the rest of the leaves...
34:41...prepare to defend themselves.
34:44But how does this leaf...
34:46...know that that leaf there...
34:48...is under attack?
34:51Well, scientists here...
34:53...in the United States...
34:54...have specially genetically modified...
34:56...these tobacco plants...
34:58...so that under special lighting conditions...
35:00...this microscope...
35:02...can show us exactly...
35:03...what is going on.
35:07I'm going to attack...
35:09...one of the leaves of this plant...
35:11...with these tweezers.
35:13So the plant...
35:14...will seem as if it's being nibbled...
35:16...by a caterpillar.
35:32Signals are being transmitted...
35:34...along the veins...
35:34...that link the leaf...
35:36...to the rest of the plant.
35:38It's rather like...
35:39...a very simple nervous system.
35:46From that initial injury...
35:48...the whole of this little plant...
35:49...is aware...
35:50...that something has happened.
35:56This signal...
35:58...warns each leaf...
35:59...of the danger...
36:01...so that it is ready...
36:03...to produce nicotine...
36:04...the moment it's attacked.
36:09With this defence at the ready...
36:11...the tobacco plant...
36:12...can continue to grow...
36:14...until eventually...
36:15...it produces seeds.
36:30It's particularly important in desert...
36:33...for seeds to be distributed...
36:35...as widely as possible...
36:37...so that some...
36:39...will have a chance...
36:40...of reaching moisture.
36:43And deserts...
36:45...have an excellent agent...
36:46...to help them do that.
36:49The wind.
36:54Many seeds have adaptations...
36:56...to help them exploit it.
36:58They have shells...
37:00...to protect the seeds within...
37:01...from abrasion.
37:04Or wings...
37:05...to help them catch the air.
37:11As the temperature rises...
37:13...throughout the day...
37:13...desert winds increase in strength.
37:40Here in Arizona...
37:42...the land is regularly...
37:44...swept by...
37:44...what is known...
37:45...as...
37:45...a haboob.
37:47It's a giant sandstorm...
37:49...but also...
37:50...in effect...
37:51...a seed storm.
38:01Countless millions of them...
38:03...were swept up into the air.
38:11Some seeds can travel...
38:12...thousands of miles...
38:13...from the wind...
38:17...so that plants...
38:19...may eventually reach...
38:20...even the most isolated desert.
38:32Some have landed...
38:34...on an island...
38:35...in the middle...
38:35...of the world's largest...
38:37...salt flat...
38:38...in Bolivia.
38:44In the Galapagos...
38:46...they sprout...
38:47...on fields...
38:48...of recently erupted lava.
38:56They've even reached...
38:58...one of the most...
38:59...inhospitable...
39:00...of all sites...
39:02...the tiny island...
39:04...of San Pedro...
39:05...Matea...
39:06...the scorched...
39:07...only rock...
39:08...off the coast...
39:09...of Mexico.
39:14This is the home...
39:16...of the giant Cardón...
39:18...the species...
39:19...of huge cactus...
39:21...that can weigh...
39:22...up to 12 tons.
39:30They're able to thrive here...
39:33...because of an...
39:34...extraordinary partnership...
39:39...with brown...
39:41...and blue-footed boobies.
39:48The Cardones here...
39:50...can become so broad...
39:52...that they provide...
39:53...cooling shade...
39:54...for nesting birds.
40:07As the booby chicks get older...
40:09...they repay the Cardones.
40:17...with their droppings.
40:21Guano...
40:22...the digested remains...
40:25...of vast shells of fish.
40:28This guano...
40:29...is of such strength...
40:31...and quantity...
40:32...that most plants...
40:33...would be poisoned by it.
40:41These Cardones, however...
40:43...have evolved the ability...
40:45...to tolerate the toxins...
40:46...in the guano...
40:47...and digest the nutrients.
40:51As a result...
40:53...the cacti...
40:54...now grow in a dense forest...
40:55...over a million strong.
41:02But such relationships...
41:04...are very finely balanced...
41:06...and can only too easily...
41:08...tip into catastrophe.
41:12As is now happening...
41:14...in northern Zimbabwe.
41:19For six months of the year...
41:21...the savannah here...
41:22...is kept lush and green...
41:24...by daily rains.
41:34But when the rainy season...
41:36...is over...
41:37...it becomes as dry...
41:39...as any desert.
41:44So to survive here...
41:46...trees must be able...
41:48...to tolerate both conditions.
41:52And these giants...
41:54...are adapted...
41:55...to do just that.
41:57They are Baobabs.
42:07This one...
42:08...might be over...
42:09...a thousand years old.
42:11It survives here...
42:12...in part...
42:13...thanks to its ability...
42:15...to store thousands...
42:16...of litres of water...
42:17...within the spongy wood...
42:19...of its trunk.
42:23But its battered surface...
42:26...is evidence...
42:27...of a very finely...
42:28...balanced relationship.
42:31These huge trees...
42:34...are a focus...
42:35...for animals...
42:36...of all kinds.
42:40And they're particularly important...
42:43...for elephants.
42:49In the wet season...
42:51...they eat...
42:52...the Baobabs' fruit...
42:53...and disperse...
42:54...the seeds...
42:55...in their dung.
43:01Now...
43:02...as the dry season begins...
43:05...they migrate...
43:07...to distant watering holes.
43:12The Baobabs have damp inner wood...
43:17...and the elephants use it...
43:18...to quench their thirst...
43:20...on the journey.
43:40This relationship can only work...
43:43...because Baobabs have a remarkable ability...
43:47...to heal themselves.
44:06Between each damaging attack...
44:09...they expand their spongy wood...
44:12...and grow new skin.
44:18And they've done this...
44:19...time and time again...
44:21...over centuries.
44:27Today, however...
44:28...it's harder...
44:29...for the Baobabs...
44:30...to recover...
44:31...as dry seasons...
44:32...become longer...
44:33...and drier...
44:34...due to climate change.
44:38Not only that...
44:39...but the elephants...
44:40...are forced to take...
44:41...ever more wood...
44:42...from the trees...
44:43...in order to survive.
44:50In some parts of Africa...
44:52...many of the largest...
44:53...and oldest Baobabs...
44:55...have fallen...
44:56...in the last decade.
45:10The loss of a vital species...
45:13...like the Baobab...
45:14...strikes a blow...
45:15...at all life...
45:16...in the desert.
45:21In these hostile lands...
45:24...few living organisms...
45:26...can survive...
45:26...without help...
45:27...from others.
45:33You can find...
45:34...an extraordinary illustration...
45:36...of this...
45:37...in Arizona's...
45:38...saguaro country.
45:46If you wander off...
45:48...the beaten track here...
45:49...you may be lucky enough...
45:50...to find one of these.
45:52It might look like...
45:54...an old boot...
45:55...but in fact...
45:56...it's part...
45:57...of a...
45:58...saguaro cactus.
46:00Almost...
46:00...every...
46:01...saguaro...
46:01...has one.
46:03There's one up there.
46:08It has been produced...
46:10...indirectly...
46:11...by woodpeckers...
46:13...which regularly...
46:14...dig homes...
46:15...by themselves...
46:16...in the bloated trunks...
46:17...of the saguaros.
46:31In the next six months...
46:34...the cactus...
46:35...heals the wound...
46:36...and so creates...
46:38...a safe, cool...
46:39...and watertight...
46:40...nest hole.
46:43Its tough lining...
46:45...will persist for years...
46:46...even after the cactus...
46:48...itself has died...
46:49...and rotted away.
46:54A single...
46:55...saguaro may hold...
46:57...several of these...
46:57...extraordinary homes.
47:02So over its lifetime...
47:04...it may provide accommodation...
47:06...for some 3,000 chicks...
47:08...of several different species.
47:17But in the long term...
47:19...the saguaro benefits...
47:20...as their lodgers...
47:21...repay the cactus...
47:23...by pollinating its flowers...
47:27...and dispersing its seeds.
47:37It's relationships like these...
47:39...that enable life...
47:41...to flourish...
47:41...in some of the world's...
47:43...harshest landscapes.
47:57Over millions of years...
48:00...plants...
48:01...have become...
48:01...superbly adapted...
48:03...to hostile...
48:04...desert conditions.
48:05...but it's a very finely...
48:08...balanced existence...
48:09...and one...
48:10...that makes them uniquely vulnerable.
48:15However...
48:15...our growing understanding...
48:17...of the complex ways...
48:19...by which desert animals...
48:20...and plants rely on one another...
48:22...is now helping us...
48:23...to understand...
48:24...how best we can protect them.
48:31Ninety years ago...
48:32...a photograph was taken...
48:34...from this very spot...
48:35...that shows a population...
48:37...of saguaro cactus...
48:38...that was very different...
48:40...from what it is today.
48:44In the last 50 years...
48:46...the population of saguaros here...
48:48...has greatly diminished.
48:50Not because of a direct...
48:52...assault on the cactus...
48:53...but because many of the shade...
48:55...giving nurse trees...
48:57...were harvested for firewood...
48:59...leaving young saguaro...
49:00...to die in the sun.
49:07Now...
49:07...that this relationship...
49:09...is understood...
49:10...and the nurse trees...
49:11...are protected...
49:12...there are already signs...
49:14...that the saguaro...
49:15...are recovering.
49:20Wherever there's a desert...
49:22...plants have evolved...
49:23...to meet its challenge.
49:26But everywhere...
49:28...they need our help.
49:31As we understand...
49:32...more about them...
49:33...and their intimate...
49:34...and complex relationships...
49:37...we will be better able...
49:39...to protect them...
49:40...and all life...
49:42...in these beautiful...
49:44...but increasingly fragile...
49:46...worlds.
50:01The most remote shoot...
50:03...for the desert's team...
50:04...is to the island...
50:06...in San Pedro Martir...
50:07...in the Sea of Cortes...
50:09...Mexico.
50:13They're to film...
50:14...the giant cacti...
50:15...that have found...
50:16...a unique way...
50:17...to thrive here.
50:20It takes 48 hours...
50:22...to travel the 260 miles...
50:25...over...
50:27...unpleasantly...
50:28...choppy seas.
50:35It's not made some of us...
50:36...feel very well...
50:37...I think one of us...
50:38...is quite seasick.
50:41It's not in the...
50:42...big blue...
50:43...out there...
50:44...and...
50:44...the island is somewhere...
50:45...in that direction...
50:47...can't see it yet.
50:50...as they draw close...
50:51...to the island...
50:52...there's a spectacular...
50:54...reminder...
50:54...of how rich...
50:55...life in the sea...
50:56...is here.
50:57Oh, look in front of me!
50:58Look at that!
50:59For a pot!
51:02Oh, they're everywhere!
51:09Show us the way!
51:18Meeting them here...
51:19...is desert scientist...
51:20...Ben Wilder.
51:23It's through his research...
51:25...that the team first heard...
51:26...about the island's...
51:27...peculiar residents.
51:29I'll never forget...
51:30...the first time...
51:31...I came to actually...
51:33...exactly where we're...
51:34...standing right now.
51:35It was April of 2006...
51:37...and saw this view...
51:40...and...
51:40...it both settled in my heart...
51:43...and captivated my mind.
51:45...and so...
51:46...that started...
51:48...a process...
51:49...of trying to...
51:50...understand...
51:51...you know...
51:51...what can produce this?
51:55The secret...
51:56...is in the relationship...
51:58...between the cactus...
51:59...and a type of seabird...
52:01...called a booby.
52:05All the boobies...
52:06...that we need to film...
52:07...are right up there...
52:08...at the top of the island...
52:09...so...
52:10...it's gonna be...
52:11...a bit of a scramble.
52:14The crew soon...
52:15...discover...
52:15...how harsh...
52:16...the conditions are here.
52:19It's pretty tight.
52:20It's pretty hot.
52:21It's a great view.
52:29There's very few places...
52:31...on earth...
52:31...where you're gonna see...
52:32...this many cactus.
52:33I mean...
52:33...it's absolutely amazing.
52:36I would say...
52:36...this is the only place...
52:37...you're gonna see this.
52:38Well there you go then.
52:42Ben's research...
52:43...is uncovering...
52:44...the ingenious ways...
52:45...the cacti have adapted...
52:47...to the conditions here.
52:50The waters...
52:51...just off shore here...
52:52...are some of the most...
52:52...productive marine waters...
52:54...in the world.
52:54And so it's kind of...
52:55...an ideal habitat...
52:57...for seabirds to roost...
52:58...but when they do so...
52:59...they deposit...
53:01...tons of guano.
53:02And so...
53:02...those nutrients...
53:03...really high in nitrogen...
53:05...phosphorus...
53:05...actually are toxic...
53:07...to most plant species.
53:09The Cardones thrive...
53:11...because they're uniquely...
53:12...able to process the guano...
53:14...and extract what they need...
53:16...to fuel their growth.
53:19One of the first shots...
53:21...the crew need to get...
53:22...is of the boobies...
53:24...nesting under the cacti.
53:26The lack of predators...
53:28...means the birds...
53:29...aren't afraid of people.
53:31It should make filming them...
53:33...up close a bit easier.
53:35That's the theory.
53:36So we better position this camera here...
53:38...to try and get a good perspective...
53:39...on the cheek...
53:40...on the nest.
53:41It's taken quite a liking...
53:43...to our camera...
53:45...so she doesn't break it.
53:53Bullseye.
53:54It's pooed right...
53:55...on the front of the lens.
53:56It's kind of a shot we need...
53:58...but unfortunately...
53:59...my camera wasn't rolling...
54:00...at the time it did it...
54:01...so now I've just got a dirty lens.
54:06After a thorough lens clean...
54:08...Oli eventually gets the shots...
54:10...to reveal the extraordinary relationship...
54:12...between bird and plant.
54:18But it's not just the bird guano...
54:20...that influence how the Cardones grow.
54:24They're way shorter.
54:26They're dwarfed here.
54:27Throughout the rest of their range...
54:29...they usually get...
54:29...in upwards of 50, 60 feet.
54:31But here...
54:32...and on average they're...
54:34...20, 24 feet in height.
54:35They stop growing up...
54:38...and they grow out.
54:41Ben's research suggests...
54:43...that they grow wide here...
54:44...as an adaptation...
54:46...to the violent winds.
54:48Too tall...
54:49...and they'd blow over.
54:51A gusting wind isn't helping...
54:53...the drone crew either.
54:55We really need it to calm down a bit...
54:57...otherwise it's going to be impossible.
55:01We have to be quick.
55:03Come on, keep it on it.
55:05It's not safe.
55:06Yeah.
55:07Let's bring it out.
55:22On the Sonoran mainland...
55:24...where the Cardone is also found...
55:26...you have on average...
55:27...between 50 to 150 plants...
55:29...per hectare.
55:30Here on this island...
55:32...you have over...
55:33...2,500 plants...
55:35...per hectare.
55:36A lull in the wind...
55:38...and the team get a chance...
55:39...to reveal...
55:40...the remarkable density...
55:41...of the cacti.
55:43Almost 20 times greater...
55:45...than anywhere else.
55:47It appears that here...
55:48...they're doing very well.
55:51But even this island...
55:53...isn't isolated...
55:54...from the effects...
55:55...of a changing planet.
55:58Every cactus you see there...
56:00...its body is filled...
56:01...with nutrients from the sea.
56:04Given that we know...
56:05...that the Cardones...
56:07...are linked to the ocean...
56:08...what happens in the ocean...
56:10...affects what happens to the Cardone.
56:11So a concern we have right now...
56:13...is that there's a lot of overfishing.
56:15And we know...
56:17...there are less seabirds here...
56:18...than there were 20 years ago.
56:20And we have reason to believe...
56:22...then that will ripple...
56:23...and affect the nutrients...
56:25...that fuel the Cardones as well.
56:29This finely balanced relationship...
56:32...is at risk.
56:33And knowing that...
56:34...makes leaving the island...
56:35...particularly thought-provoking...
56:37...for the crew.
56:40The Cardones look beautiful.
56:42I've never seen so many cactus in my life.
56:44It's absolutely amazing.
56:46I'm just hoping that...
56:47...when we leave this place...
56:49...it stays as it is...
56:50...and things don't affect it...
56:52...they're negative.
56:53It's an absolutely wonderful thing...
56:55...and...
56:55...yeah, I don't wanna go.
56:56I wanna stay.
56:58This remote cactus forest...
57:01...is a reminder of the adaptability of plants...
57:05...that enables them to establish green worlds...
57:08...almost anywhere on Earth.
57:14Next time on The Green Planet...
57:17...our extraordinary relationship...
57:20...with plants.
57:23From those we eat...
57:28...to those we help...
57:33...are our greatest allies.
57:38The Open University has produced a poster...
57:42...that explores the vital role...
57:44...that plants have for our planet.
57:46To order your free copy...
57:48...call 0300 303 4200...
57:52...or go to bbc.co.uk forward slash green planet...
57:58...and follow the links to The Open University.
58:04Be taken on a journey to calm...
58:07...with beautiful music...
58:08...and Sir David's wonderful voice.
58:10The Green Planet, Mindful Mix...
58:11...listen now on sounds.
58:13An emotional odyssey...
58:14...The Caribbean with Andy and Makita...
58:16...continues with songs, swimming and surprises...
58:18...on BBC Two at nine.
58:20On BBC Four now...
58:22...a celebration of classic MGM music.
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