1 00:00:37,580 --> 00:00:43,100 The Taklamakan Desert in northern China, 2 00:00:43,100 --> 00:00:47,380 a constantly shifting landscape of sand. 3 00:00:47,380 --> 00:00:48,780 WIND WHISTLES 4 00:00:50,420 --> 00:00:53,580 Temperatures that swing from -20 5 00:00:53,580 --> 00:00:57,660 to more than 40 degrees centigrade... 6 00:00:59,100 --> 00:01:04,860 ..and, most critically, almost entirely without rain. 7 00:01:12,100 --> 00:01:15,580 Yet, here on the dunes... 8 00:01:21,940 --> 00:01:24,540 {\an8}..a Euphrates poplar tree. 9 00:01:31,860 --> 00:01:34,500 And it's not alone. 10 00:01:35,780 --> 00:01:40,140 Some of these trees have lived here for 1,000 years. 11 00:01:43,180 --> 00:01:48,300 They have exceptionally long roots with which to collect water, 12 00:01:48,300 --> 00:01:53,500 and what is more, those roots are connected to neighbouring trees, 13 00:01:53,500 --> 00:01:56,660 so that if one strikes water, 14 00:01:56,660 --> 00:01:58,260 others can share it. 15 00:02:00,780 --> 00:02:03,460 In every desert across the planet, 16 00:02:03,460 --> 00:02:08,020 plants have found ways to not only survive, 17 00:02:08,020 --> 00:02:09,900 but flourish. 18 00:02:25,100 --> 00:02:30,580 {\an8}This is the Gran Desierto of Mexico and the United States. 19 00:02:42,020 --> 00:02:46,700 These dunes may appear to be totally barren. 20 00:02:46,700 --> 00:02:50,100 In fact, they are full of life. 21 00:02:50,100 --> 00:02:53,100 In the sand beneath my feet 22 00:02:53,100 --> 00:02:56,260 there are seeds of many different kinds. 23 00:02:56,260 --> 00:03:00,740 In fact, you could say that the dune itself is one great seed bank, 24 00:03:00,740 --> 00:03:04,740 and when it rains, it bursts into life. 25 00:03:04,740 --> 00:03:06,420 WIND WHISTLES 26 00:03:06,420 --> 00:03:07,860 THUNDER CRACKLES 27 00:03:10,780 --> 00:03:15,700 But rain may come only once a decade, and even then, 28 00:03:15,700 --> 00:03:19,740 the long-awaited storm may be very brief. 29 00:03:23,300 --> 00:03:26,940 So seeds must respond immediately. 30 00:03:40,420 --> 00:03:42,300 This is sand verbena. 31 00:03:42,300 --> 00:03:46,740 It can grow from a seed to a sweetly-scented flowering plant 32 00:03:46,740 --> 00:03:48,580 in just a few weeks. 33 00:03:55,780 --> 00:04:00,140 Primroses and many other plants soon join the race 34 00:04:00,140 --> 00:04:02,860 to flower before the sand dries. 35 00:04:06,780 --> 00:04:10,780 Desert blooms like this, however, are rare. 36 00:04:14,180 --> 00:04:18,300 This is the first year for 20 years. 37 00:04:22,540 --> 00:04:25,100 The combination of vibrant colour 38 00:04:25,100 --> 00:04:29,180 and powerful scent attracts migrating pollinators, 39 00:04:29,180 --> 00:04:32,340 such as these Painted Lady butterflies, 40 00:04:32,340 --> 00:04:37,900 which fly into the middle of what were, only recently, barren dunes. 41 00:04:39,740 --> 00:04:42,660 Everything is rushing to complete their lives 42 00:04:42,660 --> 00:04:44,780 before the moisture has gone. 43 00:04:53,220 --> 00:04:58,660 Such spectacular blooms transform deserts all around the world. 44 00:05:08,780 --> 00:05:11,620 From the Atacama in South America... 45 00:05:13,340 --> 00:05:16,940 ..to the dusty plains of southern Africa. 46 00:05:35,980 --> 00:05:40,020 Rain in deserts, however, never lasts long, 47 00:05:40,020 --> 00:05:43,700 and all too soon, the flowers wither and die. 48 00:05:49,460 --> 00:05:52,980 But not before they've produced the next generation... 49 00:05:58,220 --> 00:06:02,820 ..the seeds that will now wait in the sand for the next rains. 50 00:06:08,380 --> 00:06:11,300 In the Sonoran Desert of North America, 51 00:06:11,300 --> 00:06:15,500 the huge saguaro cacti have a different strategy. 52 00:06:15,500 --> 00:06:18,660 They store water in quantity 53 00:06:18,660 --> 00:06:21,140 and can live to a great age. 54 00:06:22,460 --> 00:06:24,820 But in their early years, 55 00:06:24,820 --> 00:06:27,180 they are extremely vulnerable. 56 00:06:31,100 --> 00:06:35,380 This little saguaro cactus is about ten-years-old. 57 00:06:35,380 --> 00:06:40,100 When they're really small and growing out in the open, 58 00:06:40,100 --> 00:06:43,900 there's a real chance that they may shrivel up and die. 59 00:06:43,900 --> 00:06:46,220 But this one has been lucky. 60 00:06:46,220 --> 00:06:50,820 It's been growing in the shade of this mesquite tree, 61 00:06:50,820 --> 00:06:54,980 and it's got a very good chance of surviving to maturity. 62 00:06:56,260 --> 00:07:01,580 The young saguaro is protected by the mesquite's branches. 63 00:07:01,580 --> 00:07:05,460 They halve the amount of scorching sunlight reaching the cactus... 64 00:07:07,380 --> 00:07:09,220 ..and so, keep it cool. 65 00:07:11,580 --> 00:07:15,620 And the mesquite's extremely long roots draw up water, 66 00:07:15,620 --> 00:07:19,100 bringing it within reach of the young saguaro. 67 00:07:23,460 --> 00:07:27,140 So the mesquite is known as a 'nurse plant', 68 00:07:27,140 --> 00:07:29,540 and a very effective one it is, too. 69 00:07:31,300 --> 00:07:35,300 In fact, this particular mesquite has already nurtured 70 00:07:35,300 --> 00:07:38,980 seven young saguaros over the past 30 years. 71 00:07:43,420 --> 00:07:45,660 As a young cactus grows, 72 00:07:45,660 --> 00:07:50,700 it needs the protection of its nurse plant, not only from the heat, 73 00:07:50,700 --> 00:07:53,980 but from the other hazards of desert life. 74 00:07:56,860 --> 00:08:00,660 Temperatures can drop to -10 degrees overnight... 75 00:08:03,620 --> 00:08:06,820 ..and very occasionally... 76 00:08:06,820 --> 00:08:08,740 ..it even snows. 77 00:08:14,940 --> 00:08:19,340 If the water stored inside a young cactus should freeze, 78 00:08:19,340 --> 00:08:21,620 the cactus will die. 79 00:08:23,460 --> 00:08:27,940 But the nurse plant traps a blanket of slightly warmer air around it, 80 00:08:27,940 --> 00:08:30,980 just enough to keep it alive. 81 00:08:33,540 --> 00:08:37,420 Eventually, saguaros outgrow their nurses, 82 00:08:37,420 --> 00:08:39,020 but by that time, 83 00:08:39,020 --> 00:08:42,700 they are robust enough to face the elements by themselves. 84 00:08:46,380 --> 00:08:49,140 No matter how old a desert plant is, 85 00:08:49,140 --> 00:08:52,300 water is always precious, 86 00:08:52,300 --> 00:08:54,620 whether gathered from melting snow... 87 00:08:54,620 --> 00:08:56,780 THUNDER BOOMS 88 00:08:59,180 --> 00:09:01,260 ..or a shower of rain. 89 00:09:06,580 --> 00:09:10,260 So, cacti have developed extraordinary adaptations 90 00:09:10,260 --> 00:09:13,020 that enable them to not only collect water... 91 00:09:14,540 --> 00:09:16,660 ..but to retain it. 92 00:09:19,900 --> 00:09:21,380 Instead of leaves, 93 00:09:21,380 --> 00:09:24,900 which would lose precious moisture through evaporation, 94 00:09:24,900 --> 00:09:26,780 they have spines. 95 00:09:28,300 --> 00:09:31,260 Each spine has a tiny pad at its base 96 00:09:31,260 --> 00:09:33,540 where the water is absorbed... 97 00:09:35,020 --> 00:09:38,980 ..and then stored in the great swollen trunk. 98 00:09:41,900 --> 00:09:47,580 A large saguaro can hold 5,000 litres of water 99 00:09:47,580 --> 00:09:52,620 and is able to do so because it has another special adaptation. 100 00:10:01,580 --> 00:10:06,340 The ridges on its surface are like the pleats on an accordion. 101 00:10:06,340 --> 00:10:09,140 They allow the saguaro to change its shape. 102 00:10:10,900 --> 00:10:14,220 After rain has fallen, the pleats expand 103 00:10:14,220 --> 00:10:17,700 and the saguaro fills up its water tank. 104 00:10:22,300 --> 00:10:26,100 In the dry times, it uses its water to grow, 105 00:10:26,100 --> 00:10:30,900 produce flowers and, eventually, seeds. 106 00:10:33,740 --> 00:10:37,060 Fully-loaded with thousands of litres of water, 107 00:10:37,060 --> 00:10:41,380 this saguaro won't need to drink a single drop for another year. 108 00:10:43,860 --> 00:10:47,540 But such valuable stores of water attract thieves. 109 00:10:49,820 --> 00:10:52,980 Now the spine's function changes from collecting... 110 00:10:54,660 --> 00:10:56,020 ..to guarding. 111 00:10:58,380 --> 00:11:03,100 The spines of some species are a quarter of a metre long. 112 00:11:09,100 --> 00:11:11,420 Others are needle-like barbs 113 00:11:11,420 --> 00:11:15,900 that grow in clusters and easily break off in the skin of any animal 114 00:11:15,900 --> 00:11:17,700 that touches them. 115 00:11:19,100 --> 00:11:21,340 But perhaps the most vicious cacti 116 00:11:21,340 --> 00:11:24,660 belong to a group called the chollas. 117 00:11:25,780 --> 00:11:29,540 This is called a teddy-bear cholla 118 00:11:29,540 --> 00:11:33,340 because of the thick coating of spines on it. 119 00:11:33,340 --> 00:11:35,940 But don't be deceived by the name, 120 00:11:35,940 --> 00:11:39,780 there is nothing cuddly about THIS particular teddy bear. 121 00:11:39,780 --> 00:11:43,980 In fact, it's the most dangerous plant in the desert, 122 00:11:43,980 --> 00:11:47,460 and I wouldn't dream of putting my hand anywhere near it 123 00:11:47,460 --> 00:11:49,620 without proper protection. 124 00:11:51,700 --> 00:11:53,380 Brush against it... 125 00:11:54,380 --> 00:11:55,660 ..this can happen. 126 00:11:55,660 --> 00:11:56,980 Ow! 127 00:11:56,980 --> 00:11:58,900 This can happen, even with this glove on. 128 00:11:58,900 --> 00:12:01,180 One of them has just gone through, I can feel it. 129 00:12:01,180 --> 00:12:02,540 It's quite painful! 130 00:12:04,460 --> 00:12:07,940 Look closely at the spine and you can see very clearly 131 00:12:07,940 --> 00:12:09,460 why they're so dangerous. 132 00:12:10,660 --> 00:12:12,940 Each is like a splinter of glass, 133 00:12:12,940 --> 00:12:14,980 sharp enough to pierce flesh... 134 00:12:16,540 --> 00:12:19,540 ..and they're covered with backward-pointing barbs. 135 00:12:20,980 --> 00:12:25,140 So getting them out, even with a pair of pliers, is quite hard. 136 00:12:25,140 --> 00:12:28,900 This is not pleasant at all. 137 00:12:28,900 --> 00:12:31,100 It won't come off, or without. 138 00:12:32,460 --> 00:12:33,980 Oh, look at that! 139 00:12:36,700 --> 00:12:41,300 It's hard to imagine a more aggressive defence than this, 140 00:12:41,300 --> 00:12:45,500 and it makes both the plant and its buds virtually invulnerable. 141 00:12:56,980 --> 00:13:00,060 Most animals know to keep clear. 142 00:13:03,380 --> 00:13:08,060 Cholla buds grow like tiny barrels from the top of the adult plant 143 00:13:08,060 --> 00:13:10,780 and then drop off. 144 00:13:10,780 --> 00:13:12,020 BARKS 145 00:13:19,100 --> 00:13:22,500 If the young cholla put down roots here, 146 00:13:22,500 --> 00:13:25,900 it would compete with its parent for water. 147 00:13:28,380 --> 00:13:30,060 Night falls... 148 00:13:31,980 --> 00:13:34,260 ..and this one is on the move. 149 00:13:43,900 --> 00:13:48,380 A pack rat. She knows how to deal with a cholla. 150 00:13:54,260 --> 00:13:57,060 She avoids the spines by gripping it at the place 151 00:13:57,060 --> 00:13:59,420 where it broke off from its parent. 152 00:14:04,940 --> 00:14:06,940 And she works fast. 153 00:14:10,140 --> 00:14:12,660 There are pack rat hunters here. 154 00:14:21,300 --> 00:14:26,220 She uses the cholla to build a spiny wall around her nest. 155 00:14:43,180 --> 00:14:45,980 The flesh of the cholla supplies her with water... 156 00:14:47,620 --> 00:14:52,700 ..and the severed spines further reinforce the defences. 157 00:15:04,300 --> 00:15:06,260 This cholla bud... 158 00:15:07,860 --> 00:15:08,900 ..might be next. 159 00:15:12,780 --> 00:15:15,460 But one accidental nudge... 160 00:15:19,900 --> 00:15:22,020 ..and it escapes. 161 00:15:22,020 --> 00:15:24,460 DRAMATIC MUSIC PLAYS 162 00:15:48,780 --> 00:15:51,980 The bud starts to put down roots. 163 00:16:00,140 --> 00:16:03,380 So, the cholla, thanks to the pack rats, 164 00:16:03,380 --> 00:16:05,900 finds new territory 165 00:16:05,900 --> 00:16:08,100 and sets about claiming it. 166 00:16:16,540 --> 00:16:21,660 Few plants deal with the problems of desert living better than cacti. 167 00:16:23,580 --> 00:16:28,100 There are almost 2,000 different species of them. 168 00:16:28,100 --> 00:16:31,660 They're spread across the deserts of the American West, 169 00:16:31,660 --> 00:16:35,940 from Arizona, all the way to Mexico and beyond. 170 00:16:41,020 --> 00:16:44,940 In South America, the ice-covered peaks of the Andes 171 00:16:44,940 --> 00:16:46,740 act as a rain barrier... 172 00:16:48,500 --> 00:16:52,940 ..beyond which lies the world's driest desert - 173 00:16:52,940 --> 00:16:54,580 the Atacama. 174 00:17:03,340 --> 00:17:07,580 In the desert world, water thieves can come in many forms 175 00:17:07,580 --> 00:17:11,660 to exploit even the smallest chink in a plant's defence. 176 00:17:17,660 --> 00:17:20,820 One of the strangest travels within the gut 177 00:17:20,820 --> 00:17:23,220 of a fruit-eating mockingbird. 178 00:17:30,140 --> 00:17:34,140 {\an8}These are the seeds of Tristerix, 179 00:17:34,140 --> 00:17:36,460 a kind of mistletoe. 180 00:17:39,500 --> 00:17:44,900 Their goal is the water inside this hedgehog cactus. 181 00:17:47,140 --> 00:17:49,500 Using the spines as anchors, 182 00:17:49,500 --> 00:17:52,260 the seeds start to germinate. 183 00:17:55,740 --> 00:17:58,060 Each produces a long probe 184 00:17:58,060 --> 00:18:00,900 with which to try and locate the cactus' skin. 185 00:18:04,220 --> 00:18:07,020 For most, that's a stretch too far, 186 00:18:07,020 --> 00:18:09,220 and they perish. 187 00:18:11,460 --> 00:18:16,780 But for this one, the cactus' surface is within reach. 188 00:18:25,660 --> 00:18:28,500 It clamps onto it with a special sucker... 189 00:18:32,020 --> 00:18:34,740 ..and then waits for darkness. 190 00:18:37,140 --> 00:18:41,460 At night, the cactus opens its pores in order to respire. 191 00:18:44,180 --> 00:18:46,540 Oxygen goes out, 192 00:18:46,540 --> 00:18:50,300 carbon dioxide goes in, 193 00:18:50,300 --> 00:18:52,220 and so does Tristerix. 194 00:18:57,660 --> 00:19:03,020 Once within, its tissues spread throughout the body of the cactus, 195 00:19:03,020 --> 00:19:06,860 sustained by the precious store of water that they find there. 196 00:19:12,580 --> 00:19:14,620 Then, a year later, 197 00:19:14,620 --> 00:19:17,180 it breaks through the cactus' skin... 198 00:19:23,940 --> 00:19:26,140 ..and bursts into flower. 199 00:19:43,500 --> 00:19:46,540 Hummingbirds come to drink their nectar 200 00:19:46,540 --> 00:19:49,180 and pollinate them as they do so. 201 00:19:59,860 --> 00:20:02,420 And, then, to complete the cycle, 202 00:20:02,420 --> 00:20:07,140 Tristerix produces hundreds of white, eye-catching seeds, 203 00:20:07,140 --> 00:20:09,660 ready to be carried away by a bird 204 00:20:09,660 --> 00:20:12,420 to invade another cactus. 205 00:20:23,740 --> 00:20:26,540 The Karoo Desert in southern Africa. 206 00:20:28,780 --> 00:20:31,060 And although it may look bare, 207 00:20:31,060 --> 00:20:35,540 its rocky ground contains an unrivalled variety of plants that, 208 00:20:35,540 --> 00:20:39,060 one way or another, store water in their tissues. 209 00:20:41,860 --> 00:20:44,980 They belong to many different families, but as a group, 210 00:20:44,980 --> 00:20:47,500 they're known as succulents. 211 00:21:05,980 --> 00:21:09,580 Some are small and low and barely distinguishable 212 00:21:09,580 --> 00:21:11,340 from their surroundings. 213 00:21:13,260 --> 00:21:16,140 These look like little pebbles. 214 00:21:18,060 --> 00:21:20,740 They resemble them so closely 215 00:21:20,740 --> 00:21:24,980 that animals which might be only too glad to steal their water 216 00:21:24,980 --> 00:21:27,460 just pass them by. 217 00:21:30,500 --> 00:21:34,940 When rain does fall, they absorb it and quickly expand. 218 00:21:37,300 --> 00:21:40,500 But even this doesn't spoil their disguise. 219 00:21:40,500 --> 00:21:43,380 They just look like larger pebbles. 220 00:21:44,780 --> 00:21:46,900 Nor are they green. 221 00:21:46,900 --> 00:21:50,180 The cells on their top surface are transparent 222 00:21:50,180 --> 00:21:52,540 and allow sunlight to pass through. 223 00:21:54,380 --> 00:21:56,540 Deep within and out of sight 224 00:21:56,540 --> 00:22:00,580 are the green cells where photosynthesis occurs - 225 00:22:00,580 --> 00:22:04,900 the process which uses this light to make food for the plant. 226 00:22:11,380 --> 00:22:14,260 When the time comes to reproduce, however, 227 00:22:14,260 --> 00:22:18,620 the stone plant abandons its disguise. 228 00:22:38,900 --> 00:22:42,140 And now, it blooms. 229 00:22:49,740 --> 00:22:54,060 The flowers open and close every 24 hours. 230 00:23:02,900 --> 00:23:05,380 So for a few dangerous days, 231 00:23:05,380 --> 00:23:08,100 the plant advertises for pollinators 232 00:23:08,100 --> 00:23:10,940 before returning to life as a pebble. 233 00:23:25,780 --> 00:23:29,380 Some desert plants have developed a very different way 234 00:23:29,380 --> 00:23:31,260 of attracting pollinators. 235 00:23:33,060 --> 00:23:36,060 This is a Stapelia. 236 00:23:36,060 --> 00:23:41,540 It produces what is perhaps the desert's strangest disguise. 237 00:23:41,540 --> 00:23:44,180 It uses water stored in its stems 238 00:23:44,180 --> 00:23:48,140 to grow buds the size of tennis balls. 239 00:24:07,500 --> 00:24:12,020 The flower, once opened, is called a desert starfish. 240 00:24:15,060 --> 00:24:18,500 Instead of releasing millions of loose pollen grains 241 00:24:18,500 --> 00:24:20,460 as most flowers do, 242 00:24:20,460 --> 00:24:25,260 the desert starfish produces them packed in five tiny sacks. 243 00:24:27,660 --> 00:24:30,140 But if its strategy is successful, 244 00:24:30,140 --> 00:24:34,140 just one of them will produce hundreds of seeds... 245 00:24:37,940 --> 00:24:40,580 ..and this depends on deception. 246 00:24:43,900 --> 00:24:46,140 The flower appears to have hair... 247 00:24:48,060 --> 00:24:50,980 ..wrinkly skin... 248 00:24:53,100 --> 00:24:57,300 ..and it produces a stench like the carcass of a dead animal. 249 00:25:11,780 --> 00:25:14,580 And when a carrion fly investigates... 250 00:25:17,060 --> 00:25:21,340 ..the flower tempts a tiny sack of pollen to its proboscis. 251 00:25:28,660 --> 00:25:33,460 It isn't easy to feed with such encumbered mouthparts. 252 00:25:35,260 --> 00:25:38,380 But try as it might, the fly can't get rid of it. 253 00:25:41,700 --> 00:25:44,660 And it's still there when the fly leaves to try and feed 254 00:25:44,660 --> 00:25:47,260 from another bogus carcass. 255 00:25:52,740 --> 00:25:55,700 This time, however, when its clamped-up proboscis 256 00:25:55,700 --> 00:25:59,740 slots into the flower, the pollen sack is released. 257 00:26:06,020 --> 00:26:08,300 With pollination complete, 258 00:26:08,300 --> 00:26:10,660 the fly is no longer needed... 259 00:26:14,540 --> 00:26:16,700 ..and just as well. 260 00:26:21,820 --> 00:26:25,780 Some deserts can be so dry that plants must find techniques 261 00:26:25,780 --> 00:26:30,020 of surviving for long periods without any water whatsoever. 262 00:26:31,260 --> 00:26:36,100 One of them is to grow extremely slowly, 263 00:26:36,100 --> 00:26:40,500 and few plants grow more slowly than this one - 264 00:26:40,500 --> 00:26:42,700 the creosote bush. 265 00:26:43,780 --> 00:26:46,180 It is inactive for most of its life 266 00:26:46,180 --> 00:26:50,340 and only wakes up and grows for a brief period, 267 00:26:50,340 --> 00:26:53,300 if and when there is a fall of rain. 268 00:26:56,860 --> 00:27:01,140 I've seen evidence of this "grow slow" strategy for myself. 269 00:27:02,340 --> 00:27:06,340 40 years ago, I came here to California's Mojave Desert 270 00:27:06,340 --> 00:27:09,020 to visit one particular plant. 271 00:27:10,260 --> 00:27:12,700 ARCHIVE: An individual creosote bush 272 00:27:12,700 --> 00:27:15,740 tends to spread not by setting seeds 273 00:27:15,740 --> 00:27:17,980 and producing a new generation, 274 00:27:17,980 --> 00:27:22,220 but by sending out new stems around its base. 275 00:27:22,220 --> 00:27:27,980 This plant started growing between 10,000 and 12,000 years ago. 276 00:27:29,660 --> 00:27:31,940 NOW: That was in 1982. 277 00:27:35,100 --> 00:27:40,420 Since then, careful measurement has shown that it has increased 278 00:27:40,420 --> 00:27:43,980 its size by less than one inch. 279 00:27:46,500 --> 00:27:50,260 Its ability to endure is truly extraordinary. 280 00:27:54,780 --> 00:27:58,940 So efficient is creosote at collecting what little rain 281 00:27:58,940 --> 00:28:02,380 falls here, that few other plants can compete with it. 282 00:28:02,380 --> 00:28:06,820 As a result, over the last 12,000 years, 283 00:28:06,820 --> 00:28:10,900 it's come to completely dominate this landscape. 284 00:28:26,700 --> 00:28:31,220 The Chihuahuan Desert in north Mexico. 285 00:28:31,220 --> 00:28:36,140 Here, one particular plant plays the waiting game so well 286 00:28:36,140 --> 00:28:39,260 that it spends much of its life looking dead 287 00:28:39,260 --> 00:28:41,540 and certainly not worth eating. 288 00:28:44,820 --> 00:28:48,660 And it can survive like this for a decade. 289 00:28:56,300 --> 00:28:59,220 This is the resurrection plant. 290 00:29:02,300 --> 00:29:04,780 It's a kind of moss. 291 00:29:04,780 --> 00:29:09,220 It barely has roots, and it certainly can't store much water, 292 00:29:09,220 --> 00:29:11,460 but it can travel. 293 00:29:18,020 --> 00:29:20,220 After a particularly long drought... 294 00:29:21,660 --> 00:29:23,620 ..it breaks away from its roots... 295 00:29:26,180 --> 00:29:27,340 ..and becomes... 296 00:29:28,980 --> 00:29:30,460 ..a tumbleweed. 297 00:29:33,220 --> 00:29:35,220 {\an8}Blowing across the desert, 298 00:29:35,220 --> 00:29:38,300 {\an8}it can travel a mile in a week. 299 00:29:41,140 --> 00:29:43,780 With luck, it may find water. 300 00:29:47,020 --> 00:29:49,140 {\an8}THUNDER RUMBLES 301 00:29:51,140 --> 00:29:54,780 {\an8}Just a shower of rain can bring it back to life. 302 00:29:59,700 --> 00:30:03,620 As its fronds soak up the water, they unfurl. 303 00:30:17,740 --> 00:30:19,700 In its protected centre, 304 00:30:19,700 --> 00:30:21,700 it still has green cells 305 00:30:21,700 --> 00:30:24,460 which absorb both the water and sunlight 306 00:30:24,460 --> 00:30:29,700 and rapidly produce the food it needs to resume its growth. 307 00:30:34,620 --> 00:30:37,620 It will grow for just as long as there is moisture... 308 00:30:42,420 --> 00:30:44,380 ..but when that disappears... 309 00:30:45,980 --> 00:30:48,260 ..it closes up once more 310 00:30:48,260 --> 00:30:51,140 and resumes its travels. 311 00:31:00,780 --> 00:31:03,380 Here in the Canyonlands of Utah 312 00:31:03,380 --> 00:31:05,900 lives a plant that has developed 313 00:31:05,900 --> 00:31:08,060 a finely-balanced relationship 314 00:31:08,060 --> 00:31:11,820 with the animals with which it shares this dramatic desert. 315 00:31:16,780 --> 00:31:19,660 Rain does occasionally fall here 316 00:31:19,660 --> 00:31:23,460 and turns dust into mud. 317 00:31:27,940 --> 00:31:30,380 But that doesn't last long. 318 00:31:32,100 --> 00:31:35,460 A brief window of opportunity opens. 319 00:31:45,180 --> 00:31:47,460 Seeds that have been buried for years 320 00:31:47,460 --> 00:31:50,540 may now be exposed to light 321 00:31:50,540 --> 00:31:52,980 and come to life. 322 00:32:09,660 --> 00:32:13,020 This is coyote tobacco. 323 00:32:25,780 --> 00:32:29,180 In just a few weeks, it grows a metre tall 324 00:32:29,180 --> 00:32:31,980 and produces dozens of flowers. 325 00:32:38,460 --> 00:32:41,980 The night air becomes heavy with their fragrance. 326 00:32:44,060 --> 00:32:46,300 Soon, they attract hawk moths 327 00:32:46,300 --> 00:32:48,260 which sip their nectar, 328 00:32:48,260 --> 00:32:50,540 and in doing so, pollinate them. 329 00:32:52,900 --> 00:32:55,980 But the moths also lay their eggs on them. 330 00:33:12,340 --> 00:33:15,220 Soon, the caterpillars have hatched 331 00:33:15,220 --> 00:33:16,980 and are munching the leaves. 332 00:33:20,380 --> 00:33:24,900 Their nibbles expose the plant's sap to the drying air. 333 00:33:27,900 --> 00:33:31,540 But the tobacco plant has a defence. 334 00:33:33,900 --> 00:33:37,460 The leaves under attack produce nicotine. 335 00:33:41,820 --> 00:33:44,460 This chemical sedates the caterpillars 336 00:33:44,460 --> 00:33:46,780 and slows them down. 337 00:33:52,260 --> 00:33:55,780 And what is more, it makes them give off a particular scent... 338 00:33:58,980 --> 00:34:01,300 ..one that summons others 339 00:34:01,300 --> 00:34:03,940 to come to the plant's aid. 340 00:34:05,820 --> 00:34:07,580 Big-eyed bugs, 341 00:34:07,580 --> 00:34:10,900 miniature assassins, only two millimetres long... 342 00:34:12,780 --> 00:34:14,580 ..and whiptail lizards. 343 00:34:16,380 --> 00:34:19,860 Big or small, they make a meal of the caterpillars. 344 00:34:30,380 --> 00:34:32,540 It's certainly effective... 345 00:34:35,340 --> 00:34:38,860 ..but there's more to this strategy than meets the eye. 346 00:34:41,060 --> 00:34:45,980 When the leaf of a tobacco plant is attacked by a caterpillar, 347 00:34:45,980 --> 00:34:50,660 all the rest of the leaves prepare to defend themselves. 348 00:34:50,660 --> 00:34:53,740 But how does this leaf know 349 00:34:53,740 --> 00:34:56,980 that that leaf there is under attack? 350 00:34:56,980 --> 00:35:00,660 Well, scientists here in the United States 351 00:35:00,660 --> 00:35:04,300 have specially genetically modified these tobacco plants 352 00:35:04,300 --> 00:35:07,140 so that under special lighting conditions, 353 00:35:07,140 --> 00:35:11,580 this microscope can show us exactly what is going on. 354 00:35:14,180 --> 00:35:17,620 I'm going to attack one of the leaves of this plant 355 00:35:17,620 --> 00:35:21,100 with these tweezers which, to the plant, 356 00:35:21,100 --> 00:35:23,940 will seem as if it's being nibbled by a caterpillar. 357 00:35:38,580 --> 00:35:41,340 Signals are being transmitted along the veins 358 00:35:41,340 --> 00:35:45,180 that link the leaf to the rest of the plant. 359 00:35:45,180 --> 00:35:48,220 It's rather like a very simple nervous system. 360 00:35:52,980 --> 00:35:54,900 From that initial injury, 361 00:35:54,900 --> 00:35:58,820 the whole of this little plant is aware that something has happened. 362 00:36:03,420 --> 00:36:08,020 This signal warns each leaf of the danger, 363 00:36:08,020 --> 00:36:10,940 so that it is ready to produce nicotine 364 00:36:10,940 --> 00:36:13,100 the moment it's attacked. 365 00:36:15,860 --> 00:36:17,860 With this defence at the ready, 366 00:36:17,860 --> 00:36:20,540 the tobacco plant can continue to grow 367 00:36:20,540 --> 00:36:23,420 until eventually, it produces seeds. 368 00:36:36,980 --> 00:36:39,700 It's particularly important in deserts 369 00:36:39,700 --> 00:36:44,220 for seeds to be distributed as widely as possible 370 00:36:44,220 --> 00:36:48,300 so that some will have a chance of reaching moisture. 371 00:36:50,500 --> 00:36:54,540 And deserts have an excellent agent to help them do that - 372 00:36:56,580 --> 00:36:58,260 the wind. 373 00:37:00,540 --> 00:37:05,340 Many seeds have adaptations to help them exploit it. 374 00:37:05,340 --> 00:37:10,420 They have shell to protect the seeds within from abrasion 375 00:37:10,420 --> 00:37:13,620 or wings to help them catch the air. 376 00:37:18,060 --> 00:37:20,420 As the temperature rises throughout the day, 377 00:37:20,420 --> 00:37:22,660 desert winds increase in strength. 378 00:37:47,060 --> 00:37:48,980 Here in Arizona, 379 00:37:48,980 --> 00:37:54,180 the land is regularly swept by what is known as a haboob. 380 00:37:54,180 --> 00:37:56,380 It's a giant sandstorm, 381 00:37:56,380 --> 00:38:00,180 but also, in effect, a seed storm. 382 00:38:07,740 --> 00:38:11,780 Countless millions of them are swept up into the air. 383 00:38:17,700 --> 00:38:21,780 Some seeds can travel thousands of miles on the wind... 384 00:38:24,780 --> 00:38:29,780 ..so that plants may eventually reach even the most isolated desert. 385 00:38:39,060 --> 00:38:41,820 Some have landed on an island 386 00:38:41,820 --> 00:38:45,260 in the middle of the world's largest salt flat in Bolivia. 387 00:38:50,820 --> 00:38:56,060 In the Galapagos, they sprout on fields of recently-erupted lava. 388 00:39:03,420 --> 00:39:08,940 They've even reached one of the most inhospitable of all sites - 389 00:39:08,940 --> 00:39:12,660 the tiny island of San Pedro Martir, 390 00:39:12,660 --> 00:39:15,220 a scorched, lonely rock 391 00:39:15,220 --> 00:39:17,060 off the coast of Mexico. 392 00:39:21,300 --> 00:39:24,700 This is the home of the giant cardon, 393 00:39:24,700 --> 00:39:27,540 a species of huge cactus 394 00:39:27,540 --> 00:39:30,100 that can weigh up to 12 tonnes. 395 00:39:38,220 --> 00:39:43,100 They're able to thrive here because of an extraordinary partnership... 396 00:39:46,300 --> 00:39:50,340 ..with brown and blue-footed boobies. 397 00:39:55,260 --> 00:39:58,060 The cardones here can become so broad 398 00:39:58,060 --> 00:40:02,300 that they provide cooling shade for nesting birds. 399 00:40:13,820 --> 00:40:16,660 As the booby chicks get older, 400 00:40:16,660 --> 00:40:19,260 they repay the cardones... 401 00:40:25,060 --> 00:40:26,540 ..with their droppings... 402 00:40:28,100 --> 00:40:29,500 ..guano - 403 00:40:29,500 --> 00:40:33,740 the digestive remains of vast shoals of fish. 404 00:40:35,380 --> 00:40:38,900 This guano is of such strength and quantity 405 00:40:38,900 --> 00:40:42,060 that most plants would be poisoned by it. 406 00:40:48,460 --> 00:40:51,780 These cardones, however, have evolved the ability 407 00:40:51,780 --> 00:40:56,500 to tolerate the toxins in the guano and digest the nutrients. 408 00:40:58,620 --> 00:41:02,420 As a result, the cacti now grow in a dense forest 409 00:41:02,420 --> 00:41:04,020 over a million strong. 410 00:41:09,500 --> 00:41:12,860 But such relationships are very finely balanced 411 00:41:12,860 --> 00:41:15,980 and can only too easily tip into catastrophe... 412 00:41:19,420 --> 00:41:22,420 ..as is now happening in northern Zimbabwe. 413 00:41:26,620 --> 00:41:28,460 For six months of the year, 414 00:41:28,460 --> 00:41:32,700 the savannah here is kept lush and green by daily rains. 415 00:41:37,980 --> 00:41:39,460 {\an8}ELEPHANTS TRUMPET 416 00:41:41,180 --> 00:41:44,060 {\an8}But when the rainy season is over, 417 00:41:44,060 --> 00:41:46,780 {\an8}it becomes as dry as any desert. 418 00:41:52,180 --> 00:41:57,140 So to survive here, trees must be able to tolerate both conditions. 419 00:41:59,460 --> 00:42:04,380 And these giants are adapted to do just that. 420 00:42:04,380 --> 00:42:06,460 They are baobabs. 421 00:42:14,340 --> 00:42:17,900 This one might be over 1,000 years old. 422 00:42:17,900 --> 00:42:21,500 It survives here in part thanks to its ability 423 00:42:21,500 --> 00:42:24,500 to store thousands of litres of water 424 00:42:24,500 --> 00:42:27,100 within the spongy wood of its trunk. 425 00:42:30,780 --> 00:42:33,980 But its battered surface is evidence 426 00:42:33,980 --> 00:42:36,820 of a very finely-balanced relationship. 427 00:42:38,700 --> 00:42:40,620 These huge trees 428 00:42:40,620 --> 00:42:44,580 are a focus for animals of all kinds. 429 00:42:48,260 --> 00:42:51,900 And they're particularly important for elephants. 430 00:42:56,420 --> 00:43:00,180 In the wet season, they eat the baobab's fruit 431 00:43:00,180 --> 00:43:02,660 and disperse the seeds in their dung. 432 00:43:08,180 --> 00:43:10,580 Now as the dry season begins... 433 00:43:10,580 --> 00:43:12,180 ELEPHANT RUMBLES 434 00:43:12,180 --> 00:43:15,340 ..they migrate to distant watering holes. 435 00:43:19,660 --> 00:43:22,220 The baobabs have damp inner wood... 436 00:43:23,700 --> 00:43:29,380 ..and the elephants use it to quench their thirst on the journey. 437 00:43:29,380 --> 00:43:31,180 ELEPHANT ROARS 438 00:43:48,020 --> 00:43:51,780 This relationship can only work because baobabs 439 00:43:51,780 --> 00:43:55,020 have a remarkable ability to heal themselves. 440 00:44:13,900 --> 00:44:16,900 Between each damaging attack, 441 00:44:16,900 --> 00:44:20,620 they expand their spongy wood and grow new skin. 442 00:44:25,020 --> 00:44:29,140 And they've done this time and time again over centuries. 443 00:44:33,820 --> 00:44:38,020 Today, however, it's harder for the baobabs to recover 444 00:44:38,020 --> 00:44:42,980 as dry seasons become longer and drier due to climate change. 445 00:44:45,140 --> 00:44:48,980 Not only that, but the elephants are forced to take ever more wood 446 00:44:48,980 --> 00:44:51,820 from the trees in order to survive. 447 00:44:57,460 --> 00:44:59,220 In some parts of Africa, 448 00:44:59,220 --> 00:45:02,100 many of the largest and oldest baobabs 449 00:45:02,100 --> 00:45:04,540 have fallen in the last decade. 450 00:45:17,540 --> 00:45:20,740 The loss of a vital species like the baobab 451 00:45:20,740 --> 00:45:23,780 strikes a blow at all life in the desert. 452 00:45:28,780 --> 00:45:30,660 In these hostile lands, 453 00:45:30,660 --> 00:45:35,180 few living organisms can survive without help from others. 454 00:45:40,140 --> 00:45:43,580 You can find an extraordinary illustration of this 455 00:45:43,580 --> 00:45:46,100 in Arizona's saguaro country. 456 00:45:53,500 --> 00:45:55,860 If you wander off the beaten track here, 457 00:45:55,860 --> 00:45:59,340 you may be lucky enough to find one of these. 458 00:45:59,340 --> 00:46:02,100 It might look like an old boot, 459 00:46:02,100 --> 00:46:06,340 but in fact, it's part of a saguaro cactus. 460 00:46:06,340 --> 00:46:09,620 Almost every saguaro has one. 461 00:46:09,620 --> 00:46:11,220 There's one up there. 462 00:46:15,660 --> 00:46:19,620 It has been produced indirectly by woodpeckers, 463 00:46:19,620 --> 00:46:23,740 which regularly dig homes for themselves in the bloated trunks 464 00:46:23,740 --> 00:46:25,460 of the saguaros. 465 00:46:38,660 --> 00:46:40,580 In the next six months, 466 00:46:40,580 --> 00:46:43,460 the cactus heals the wound 467 00:46:43,460 --> 00:46:47,700 and so creates a safe, cool, and watertight nest hole. 468 00:46:50,500 --> 00:46:53,180 Its tough lining will persist for years, 469 00:46:53,180 --> 00:46:57,260 even after the cactus itself has died and rotted away. 470 00:47:01,380 --> 00:47:06,300 A single saguaro may hold several of these extraordinary homes. 471 00:47:09,140 --> 00:47:15,060 So over its lifetime, it may provide accommodation for some 3,000 chicks 472 00:47:15,060 --> 00:47:18,140 of several different species. 473 00:47:18,140 --> 00:47:20,140 BIRDS SCREECH 474 00:47:24,340 --> 00:47:26,980 But in the long term, the saguaro benefits, 475 00:47:26,980 --> 00:47:29,860 as their lodgers repay the cactus 476 00:47:29,860 --> 00:47:32,820 by pollinating its flowers... 477 00:47:34,260 --> 00:47:36,780 ..and dispersing its seeds. 478 00:47:44,260 --> 00:47:46,380 It's relationships like these 479 00:47:46,380 --> 00:47:48,380 that enable life to flourish 480 00:47:48,380 --> 00:47:51,460 in some of the world's harshest landscapes. 481 00:48:04,980 --> 00:48:06,980 Over millions of years, 482 00:48:06,980 --> 00:48:10,100 plants have become superbly adapted 483 00:48:10,100 --> 00:48:12,340 to hostile desert conditions. 484 00:48:12,340 --> 00:48:15,820 But it's a very finely-balanced existence 485 00:48:15,820 --> 00:48:18,940 and one that makes them uniquely vulnerable. 486 00:48:21,500 --> 00:48:25,220 However, our growing understanding of the complex ways 487 00:48:25,220 --> 00:48:28,860 by which desert animals and plants rely on one another 488 00:48:28,860 --> 00:48:33,100 is now helping us to understand how best we can protect them. 489 00:48:37,940 --> 00:48:42,340 90 years ago, a photograph was taken from this very spot 490 00:48:42,340 --> 00:48:45,660 that shows a population of saguaro cactus 491 00:48:45,660 --> 00:48:48,620 that was very different from what it is today. 492 00:48:51,380 --> 00:48:52,820 In the last 50 years, 493 00:48:52,820 --> 00:48:57,220 the population of saguaros here has greatly diminished, 494 00:48:57,220 --> 00:49:00,780 not because of a direct assault on the cactus, 495 00:49:00,780 --> 00:49:03,620 but because many of the shade-giving nurse trees 496 00:49:03,620 --> 00:49:08,460 were harvested for firewood, leaving young saguaro to die in the sun. 497 00:49:13,620 --> 00:49:16,580 Now that this relationship is understood 498 00:49:16,580 --> 00:49:18,700 and the nurse trees are protected, 499 00:49:18,700 --> 00:49:23,580 there are already signs that the saguaro are recovering. 500 00:49:27,020 --> 00:49:32,060 Wherever there's a desert, plants have evolved to meet its challenge. 501 00:49:33,780 --> 00:49:36,260 But everywhere, they need our help. 502 00:49:38,420 --> 00:49:40,140 As we understand more about them 503 00:49:40,140 --> 00:49:43,140 and their intimate and complex relationships... 504 00:49:44,660 --> 00:49:49,220 ..we will be better able to protect them and all life 505 00:49:49,220 --> 00:49:53,860 in these beautiful but increasingly fragile worlds. 506 00:50:08,180 --> 00:50:11,340 The most remote shoot for the deserts team 507 00:50:11,340 --> 00:50:13,980 is to the island of San Pedro Martir 508 00:50:13,980 --> 00:50:16,300 in the Sea of Cortez, Mexico. 509 00:50:19,700 --> 00:50:22,100 They are to film the giant cacti 510 00:50:22,100 --> 00:50:24,780 that have found a unique way to thrive here. 511 00:50:27,580 --> 00:50:31,580 It takes 48 hours to travel the 260 miles... 512 00:50:32,940 --> 00:50:35,500 ..over unpleasantly choppy seas. 513 00:50:41,820 --> 00:50:43,860 {\an8}It's not made some of us feel very well. 514 00:50:43,860 --> 00:50:46,980 {\an8}I think one of us is quite seasick. 515 00:50:48,460 --> 00:50:50,980 It's nothing but big blue out there, 516 00:50:50,980 --> 00:50:53,620 and the island is somewhere in that direction. 517 00:50:53,620 --> 00:50:55,100 Can't see it yet. 518 00:50:56,940 --> 00:50:59,100 As they draw close to the island, 519 00:50:59,100 --> 00:51:04,220 there's a spectacular reminder of how rich life in the sea is here. 520 00:51:04,220 --> 00:51:07,180 Oh, look in front of us! Look at that for a pod! 521 00:51:08,660 --> 00:51:10,460 Oh! They're everywhere! 522 00:51:16,460 --> 00:51:17,740 Show us the way. 523 00:51:17,740 --> 00:51:19,180 HE CHUCKLES 524 00:51:24,700 --> 00:51:28,620 Meeting them here is desert scientist Ben Wilder. 525 00:51:30,060 --> 00:51:33,100 It's through his research that the team first heard 526 00:51:33,100 --> 00:51:36,420 about the island's peculiar residents. 527 00:51:36,420 --> 00:51:39,020 {\an8}I'll never forget the first time I came 528 00:51:39,020 --> 00:51:41,660 {\an8}to, actually, exactly where we're standing right now. 529 00:51:41,660 --> 00:51:44,100 {\an8}It was April of 2006, 530 00:51:44,100 --> 00:51:46,660 and saw this view. 531 00:51:46,660 --> 00:51:52,460 And it both settled in my heart and captivated my mind. 532 00:51:52,460 --> 00:51:57,940 And so that started a process of trying to understand, 533 00:51:57,940 --> 00:52:00,460 you know, what can produce this? 534 00:52:02,500 --> 00:52:06,340 The secret is in the relationship between the cactus 535 00:52:06,340 --> 00:52:09,980 and a type of sea bird called a booby. 536 00:52:12,140 --> 00:52:14,780 {\an8}All the boobies that we need to film are right up there 537 00:52:14,780 --> 00:52:16,020 {\an8}at the top of the island. 538 00:52:16,020 --> 00:52:18,900 So, it's going to be a bit of a scramble. 539 00:52:20,540 --> 00:52:24,100 The crew soon discover how harsh the conditions are here. 540 00:52:25,780 --> 00:52:28,180 I'm pretty tired. It's pretty hot. 541 00:52:28,180 --> 00:52:29,500 It's a great view. 542 00:52:36,460 --> 00:52:37,940 There's very few places on Earth 543 00:52:37,940 --> 00:52:39,820 where you're going to see this many cactus. 544 00:52:39,820 --> 00:52:43,020 I mean, it's absolutely amazing. 545 00:52:43,020 --> 00:52:45,380 I would say this is the only place you're going to see this. 546 00:52:45,380 --> 00:52:47,100 Well, there you go, then. 547 00:52:48,940 --> 00:52:52,860 Ben's research is uncovering the ingenious ways the cacti 548 00:52:52,860 --> 00:52:55,460 have adapted to the conditions here. 549 00:52:56,940 --> 00:52:59,860 The waters just offshore here are some of the most productive 550 00:52:59,860 --> 00:53:01,420 marine waters in the world. 551 00:53:01,420 --> 00:53:04,420 And so it's kind of an ideal habitat for sea birds to roost. 552 00:53:04,420 --> 00:53:08,420 But when they do so, they deposit tonnes of guano. 553 00:53:08,420 --> 00:53:12,460 And so those nutrients, really high in nitrogen and phosphorus, 554 00:53:12,460 --> 00:53:16,300 actually are toxic to most plant species. 555 00:53:16,300 --> 00:53:19,500 The cardones thrive because they're uniquely able 556 00:53:19,500 --> 00:53:24,060 to process the guano and extract what they need to fuel their growth. 557 00:53:26,780 --> 00:53:29,340 One of the first shots the crew need to get 558 00:53:29,340 --> 00:53:32,180 is of the boobies nesting under the cacti. 559 00:53:33,780 --> 00:53:37,380 The lack of predators means the birds aren't afraid of people. 560 00:53:37,380 --> 00:53:41,860 It should make filming them up close a bit easier. 561 00:53:41,860 --> 00:53:43,500 That's the theory. 562 00:53:43,500 --> 00:53:46,380 So we've positioned this camera here to try and get a good perspective 563 00:53:46,380 --> 00:53:48,580 on the chick on the nest. 564 00:53:48,580 --> 00:53:51,460 It's taken quite a liking to our camera. 565 00:53:51,460 --> 00:53:53,980 Let's hope he doesn't break it. 566 00:53:59,660 --> 00:54:00,820 Bull's-eye. 567 00:54:00,820 --> 00:54:03,500 It's pooed right on the front of the lens! 568 00:54:03,500 --> 00:54:05,900 It's kind of a shot we need, but unfortunately, 569 00:54:05,900 --> 00:54:07,780 my camera wasn't rolling at the time it did it. 570 00:54:07,780 --> 00:54:09,820 So now, I've just got a dirty lens. 571 00:54:12,780 --> 00:54:16,900 After a thorough lens clean, Ollie eventually gets the shot 572 00:54:16,900 --> 00:54:21,340 to reveal the extraordinary relationship between bird and plant. 573 00:54:25,420 --> 00:54:27,940 But it's not just the bird guano that influence 574 00:54:27,940 --> 00:54:29,620 how the cardones grow. 575 00:54:30,700 --> 00:54:34,180 They're way shorter, they're dwarfed here, 576 00:54:34,180 --> 00:54:35,780 throughout the rest of their range, 577 00:54:35,780 --> 00:54:38,380 they usually get in upwards of 50-60 feet. 578 00:54:38,380 --> 00:54:42,460 But here, on average, they're 20-24 feet in height. 579 00:54:42,460 --> 00:54:46,100 They stop growing up, and they grow out. 580 00:54:47,780 --> 00:54:51,500 Ben's research suggests that they go wide here 581 00:54:51,500 --> 00:54:54,740 as an adaptation to the violent winds. 582 00:54:54,740 --> 00:54:57,860 Too tall, and they'd blow over. 583 00:54:57,860 --> 00:55:01,700 A gusting wind isn't helping the drone crew, either. 584 00:55:01,700 --> 00:55:03,340 {\an8}We really need it to calm down a bit, 585 00:55:03,340 --> 00:55:05,340 {\an8}otherwise it's going to be impossible. 586 00:55:11,580 --> 00:55:12,940 {\an8}WIND GUSTS 587 00:55:24,260 --> 00:55:26,060 BIRD CHIRPS 588 00:55:29,580 --> 00:55:32,980 On the Sonoran mainland, where the cardon is also found, 589 00:55:32,980 --> 00:55:37,060 you have on average between 50 to 150 plants per hectare. 590 00:55:37,060 --> 00:55:42,860 Here on this island, you have over 2,500 plants per hectare. 591 00:55:42,860 --> 00:55:46,780 A lull in the wind, and the team get the chance to reveal 592 00:55:46,780 --> 00:55:49,620 the remarkable density of the cacti, 593 00:55:49,620 --> 00:55:53,820 almost 20 times greater than anywhere else. 594 00:55:53,820 --> 00:55:56,940 It appears that here they're doing very well. 595 00:55:58,220 --> 00:56:01,220 But even this island isn't isolated 596 00:56:01,220 --> 00:56:03,660 from the effects of a changing planet. 597 00:56:04,940 --> 00:56:06,740 Every cactus you see there, 598 00:56:06,740 --> 00:56:10,900 its body is filled with nutrients from the sea. 599 00:56:10,900 --> 00:56:14,940 Given that we know that the cardones are linked to the ocean, 600 00:56:14,940 --> 00:56:18,380 what happens in the oceans affects what happens to the cardon. 601 00:56:18,380 --> 00:56:22,380 So a concern we have right now is that there's a lot of overfishing, 602 00:56:22,380 --> 00:56:27,100 and we know there are less sea birds here than there were 20 years ago. 603 00:56:27,100 --> 00:56:31,340 And we have reason to believe then that will ripple and affect 604 00:56:31,340 --> 00:56:34,660 the nutrients that fuel the cardones as well. 605 00:56:36,620 --> 00:56:40,220 This finely-balanced relationship is at risk, 606 00:56:40,220 --> 00:56:42,940 and knowing that makes leaving the island 607 00:56:42,940 --> 00:56:45,620 particularly thought provoking for the crew. 608 00:56:47,020 --> 00:56:49,180 The cardones look beautiful. 609 00:56:49,180 --> 00:56:51,380 I've never seen so many cactus in my life. 610 00:56:51,380 --> 00:56:53,300 It's absolutely amazing. 611 00:56:53,300 --> 00:56:55,940 I'm just hoping that when we leave this place, 612 00:56:55,940 --> 00:56:59,980 it stays as it is, and things don't affect it that are negative. 613 00:56:59,980 --> 00:57:03,260 It's an absolutely wonderful thing, and, yeah, I don't want to go. 614 00:57:03,260 --> 00:57:04,580 I want to stay. 615 00:57:05,900 --> 00:57:10,740 This remote cactus forest is a reminder of the adaptability 616 00:57:10,740 --> 00:57:15,020 of plants that enables them to establish green worlds 617 00:57:15,020 --> 00:57:17,300 almost anywhere on Earth. 618 00:57:21,940 --> 00:57:24,700 Next time on The Green Planet... 619 00:57:24,700 --> 00:57:28,060 ..our extraordinary relationship with plants. 620 00:57:30,380 --> 00:57:32,260 From those who eat... 621 00:57:35,620 --> 00:57:37,380 ..to those we help... 622 00:57:39,420 --> 00:57:42,180 ..plants are our greatest allies. 623 00:57:45,140 --> 00:57:48,620 The Open University has produced a poster 624 00:57:48,620 --> 00:57:53,140 that explores the vital role that plants have for our planet. 625 00:57:53,140 --> 00:57:55,460 {\an8}To order your free copy call... 626 00:57:59,500 --> 00:58:01,300 {\an8}Or go to... 627 00:58:05,460 --> 00:58:07,940 {\an8}..and follow the links to the Open University.