1 00:00:32,800 --> 00:00:34,920 David Attenborough: The taklamakan desert 2 00:00:35,040 --> 00:00:36,920 in northern China. 3 00:00:38,240 --> 00:00:41,240 A constantly shifting landscape of sand... 4 00:00:41,360 --> 00:00:43,960 (Wind whooshes) 5 00:00:45,560 --> 00:00:48,800 Temperatures that swing from minus 20... 6 00:00:48,920 --> 00:00:50,400 (Sand rustles) 7 00:00:50,520 --> 00:00:52,880 To more than 40 degrees centigrade... 8 00:00:54,360 --> 00:00:56,080 And most critically, 9 00:00:56,200 --> 00:01:00,240 almost entirely without rain. 10 00:01:07,480 --> 00:01:10,240 Yet, here on the dunes... 11 00:01:16,960 --> 00:01:19,480 A euphrates poplar tree. 12 00:01:26,720 --> 00:01:29,560 And it's not alone. 13 00:01:30,960 --> 00:01:35,440 Some of these trees have lived here for 1,000 years. 14 00:01:38,560 --> 00:01:40,920 They have exceptionally long roots 15 00:01:41,040 --> 00:01:43,440 with which to collect water. 16 00:01:43,560 --> 00:01:45,280 And what is more, 17 00:01:45,400 --> 00:01:48,400 those roots are connected to neighbouring trees 18 00:01:48,520 --> 00:01:50,600 so that if one strikes water... 19 00:01:51,920 --> 00:01:53,880 Others can share it. 20 00:01:55,800 --> 00:01:58,560 In every desert across the planet, 21 00:01:58,680 --> 00:02:03,160 plants have found ways to not only survive... 22 00:02:03,280 --> 00:02:04,600 But flourish. 23 00:02:20,760 --> 00:02:25,880 This is the gran desierto of Mexico and the United States. 24 00:02:37,080 --> 00:02:41,600 These dunes may appear to be totally barren. 25 00:02:41,720 --> 00:02:45,400 In fact, they are full of life. 26 00:02:45,520 --> 00:02:48,240 In the sands beneath my feet, 27 00:02:48,360 --> 00:02:51,400 there are seeds of many different kinds. 28 00:02:51,520 --> 00:02:54,120 In fact, you could say that the dune itself 29 00:02:54,240 --> 00:02:55,920 is one great seed bank, 30 00:02:56,040 --> 00:02:57,680 and when it rains, 31 00:02:57,800 --> 00:02:59,880 it bursts into life. 32 00:03:00,000 --> 00:03:03,120 (Thunder crashes and rolls) 33 00:03:05,960 --> 00:03:09,920 But rain may come only once a decade, 34 00:03:10,040 --> 00:03:14,920 and even then, the long-awaited storm may be very brief. 35 00:03:18,560 --> 00:03:22,160 So seeds must respond immediately. 36 00:03:36,160 --> 00:03:37,440 This is sand verbena. 37 00:03:37,560 --> 00:03:41,880 It can grow from a seed to a sweetly scented flowering plant 38 00:03:42,000 --> 00:03:44,640 in just a few weeks. 39 00:03:51,080 --> 00:03:53,280 Primroses and many other plants 40 00:03:53,400 --> 00:03:58,200 soon join the race to flower before the sand dries. 41 00:04:01,400 --> 00:04:06,000 Desert blooms like this, however, are rare. 42 00:04:08,920 --> 00:04:13,520 This is the first year for 20 years. 43 00:04:18,280 --> 00:04:21,720 The combination of vibrant colour and powerful scent 44 00:04:21,840 --> 00:04:24,560 attracts migrating pollinators, 45 00:04:24,680 --> 00:04:27,800 such as these painted lady butterflies, 46 00:04:27,920 --> 00:04:31,920 which fly into the middle of what were only recently 47 00:04:32,040 --> 00:04:33,440 barren dunes. 48 00:04:34,520 --> 00:04:37,800 Everything is rushing to complete their lives 49 00:04:37,920 --> 00:04:40,600 before the moisture has gone. 50 00:04:48,480 --> 00:04:50,720 Such spectacular blooms 51 00:04:50,840 --> 00:04:53,760 transform deserts all around the world... 52 00:05:03,840 --> 00:05:06,760 From the atacama in South America... 53 00:05:08,600 --> 00:05:12,120 To the dusty plains of Southern Africa. 54 00:05:30,760 --> 00:05:34,720 Rain in deserts, however, never lasts long, 55 00:05:34,840 --> 00:05:38,880 and all too soon, the flowers wither and die. 56 00:05:44,440 --> 00:05:48,200 But not before they've produced the next generation... 57 00:05:52,880 --> 00:05:57,960 The seeds that will now wait in the sand for the next rains. 58 00:05:58,080 --> 00:06:01,360 (Sand rustles) 59 00:06:03,480 --> 00:06:06,240 In the sonoran desert of North America, 60 00:06:06,360 --> 00:06:08,400 the huge saguaro cacti 61 00:06:08,520 --> 00:06:10,240 have a different strategy. 62 00:06:10,360 --> 00:06:13,040 They store water in quantity... 63 00:06:14,080 --> 00:06:16,320 And can live to a great age. 64 00:06:17,720 --> 00:06:19,800 But in their early years, 65 00:06:19,920 --> 00:06:22,240 they are extremely vulnerable. 66 00:06:26,160 --> 00:06:30,720 This little saguaro cactus is about ten years old. 67 00:06:30,840 --> 00:06:34,960 When they're really small and growing out in the open, 68 00:06:35,080 --> 00:06:38,760 there's a real chance that they may shrivel up and die. 69 00:06:38,880 --> 00:06:41,360 But this one has been lucky. 70 00:06:41,480 --> 00:06:45,720 It's been growing in the shade of this mesquite tree, 71 00:06:45,840 --> 00:06:50,240 and it's got a very good chance of surviving to maturity. 72 00:06:51,720 --> 00:06:55,800 The young saguaro is protected by the mesquite's branches. 73 00:06:56,880 --> 00:06:59,320 They halve the amount of scorching sunlight 74 00:06:59,440 --> 00:07:01,000 reaching the cactus... 75 00:07:02,240 --> 00:07:04,200 And so keep it cool. 76 00:07:06,520 --> 00:07:09,040 And the mesquite's extremely long roots 77 00:07:09,160 --> 00:07:10,680 draw up water, 78 00:07:10,800 --> 00:07:14,360 bringing it within reach of the young saguaro. 79 00:07:18,560 --> 00:07:22,400 So the mesquite is known as a "nurse plant", 80 00:07:22,520 --> 00:07:24,840 and a very effective one it is, too. 81 00:07:26,160 --> 00:07:28,520 In fact, this particular mesquite 82 00:07:28,640 --> 00:07:32,320 has already nurtured seven young saguaros 83 00:07:32,440 --> 00:07:34,120 over the past 30 years. 84 00:07:38,760 --> 00:07:40,440 As a young cactus grows, 85 00:07:40,560 --> 00:07:43,200 it needs the protection of its nurse plant 86 00:07:43,320 --> 00:07:45,640 not only from the heat, 87 00:07:45,760 --> 00:07:49,240 but from the other hazards of desert life. 88 00:07:51,480 --> 00:07:56,440 Temperatures can drop to minus 10 degrees overnight... 89 00:07:58,600 --> 00:08:01,160 And very occasionally, 90 00:08:01,280 --> 00:08:03,400 it even snows. 91 00:08:09,840 --> 00:08:14,400 If the water stored inside a young cactus should freeze, 92 00:08:14,520 --> 00:08:16,440 the cactus will die. 93 00:08:18,600 --> 00:08:20,760 But the nurse plant traps 94 00:08:20,880 --> 00:08:23,240 a blanket of slightly warmer air around it, 95 00:08:23,360 --> 00:08:26,240 just enough to keep it alive. 96 00:08:28,720 --> 00:08:32,240 Eventually, saguaros outgrow their nurses, 97 00:08:32,360 --> 00:08:35,320 but by that time, they are robust enough 98 00:08:35,440 --> 00:08:38,000 to face the elements by themselves. 99 00:08:41,680 --> 00:08:44,440 No matter how old a desert plant is, 100 00:08:44,560 --> 00:08:47,240 water is always precious, 101 00:08:47,360 --> 00:08:49,720 whether gathered from melting snow... 102 00:08:49,840 --> 00:08:51,760 (Thunder crashes and rolls) 103 00:08:54,480 --> 00:08:56,600 Or a shower of rain. 104 00:09:01,880 --> 00:09:05,320 So cacti have developed extraordinary adaptations 105 00:09:05,440 --> 00:09:08,120 that enable them to not only collect water... 106 00:09:09,320 --> 00:09:11,360 But to retain it. 107 00:09:15,400 --> 00:09:18,200 Instead of leaves, which would lose precious moisture 108 00:09:18,320 --> 00:09:20,040 through evaporation, 109 00:09:20,160 --> 00:09:21,920 they have spines. 110 00:09:23,360 --> 00:09:26,360 Each spine has a tiny pad at its base 111 00:09:26,480 --> 00:09:28,720 where the water is absorbed... 112 00:09:30,320 --> 00:09:34,440 And then stored in the great swollen trunk. 113 00:09:37,160 --> 00:09:41,920 A large saguaro can hold 5,000 litres of water... 114 00:09:43,160 --> 00:09:44,400 And is able to do so 115 00:09:44,520 --> 00:09:48,560 because it has another special adaptation. 116 00:09:50,360 --> 00:09:52,280 (Slow creaking) 117 00:09:56,840 --> 00:09:58,760 The ridges on its surface 118 00:09:58,880 --> 00:10:01,240 are like the pleats on an accordion. 119 00:10:01,360 --> 00:10:04,360 They allow the saguaro to change its shape. 120 00:10:06,360 --> 00:10:07,960 After rain has fallen, 121 00:10:08,080 --> 00:10:10,160 the pleats expand, 122 00:10:10,280 --> 00:10:12,920 and the saguaro fills up its water tank. 123 00:10:17,280 --> 00:10:20,760 In the dry times, it uses its water 124 00:10:20,880 --> 00:10:23,040 to grow, produce flowers, 125 00:10:23,160 --> 00:10:26,160 and, eventually, seeds. 126 00:10:28,800 --> 00:10:31,920 Fully loaded with thousands of litres of water, 127 00:10:32,040 --> 00:10:35,120 this saguaro won't need to drink a single drop 128 00:10:35,240 --> 00:10:37,120 for another year. 129 00:10:38,600 --> 00:10:43,520 But such valuable stores of water attract thieves. 130 00:10:45,000 --> 00:10:48,720 Now the spines' function changes from collecting... 131 00:10:49,840 --> 00:10:51,280 To guarding. 132 00:10:53,720 --> 00:10:57,920 The spines of some species are a quarter of a metre long. 133 00:11:03,720 --> 00:11:06,600 Others are needle-like barbs 134 00:11:06,720 --> 00:11:08,960 that grow in clusters, 135 00:11:09,080 --> 00:11:11,320 and easily break off in the skin of any animal 136 00:11:11,440 --> 00:11:12,920 that touches them. 137 00:11:14,280 --> 00:11:16,360 But perhaps the most vicious cacti 138 00:11:16,480 --> 00:11:19,640 belong to a group called the chollas. 139 00:11:20,880 --> 00:11:24,640 This is called a Teddy bear cholla 140 00:11:24,760 --> 00:11:28,280 because of the thick coating of spines on it. 141 00:11:28,400 --> 00:11:30,960 But don't be deceived by the name. 142 00:11:31,080 --> 00:11:35,000 There is nothing cuddly about this particular Teddy bear. 143 00:11:35,120 --> 00:11:39,080 In fact, it's the most dangerous plant in the desert, 144 00:11:39,200 --> 00:11:42,480 and I wouldn't dream of putting my hand anywhere near it 145 00:11:42,600 --> 00:11:44,840 without proper protection. 146 00:11:47,680 --> 00:11:49,160 Brush against it... 147 00:11:49,280 --> 00:11:51,480 This can happen. Ow! 148 00:11:51,600 --> 00:11:53,840 This can happen. Even with this glove on, 149 00:11:53,960 --> 00:11:56,360 one of them has just gone through, I can feel it. 150 00:11:56,480 --> 00:11:58,520 It's quite painful. 151 00:12:00,040 --> 00:12:01,480 Look closely at the spine 152 00:12:01,600 --> 00:12:04,880 and you can see very clearly why they're so dangerous. 153 00:12:05,000 --> 00:12:08,040 Each is like a splinter of glass, 154 00:12:08,160 --> 00:12:10,160 sharp enough to Pierce flesh. 155 00:12:11,680 --> 00:12:14,280 And they're covered with backward-pointing barbs. 156 00:12:15,800 --> 00:12:18,600 So getting them out, even with a pair of pliers, 157 00:12:18,720 --> 00:12:20,280 is quite hard. 158 00:12:20,400 --> 00:12:24,040 This is not pleasant at all. 159 00:12:24,160 --> 00:12:26,200 They won't come off without... 160 00:12:27,920 --> 00:12:29,840 Oh, look at that. 161 00:12:31,720 --> 00:12:35,240 It's hard to imagine a more aggressive defence than this. 162 00:12:35,360 --> 00:12:38,960 And it makes both the plant and its buds 163 00:12:39,080 --> 00:12:40,760 virtually in vulnerable. 164 00:12:52,000 --> 00:12:55,240 Most animals know to keep clear. 165 00:12:55,360 --> 00:12:57,080 (Sniffs) 166 00:12:58,720 --> 00:13:01,240 Cholla buds grow like tiny barrels 167 00:13:01,360 --> 00:13:04,560 from the top of the adult plant and then drop off. 168 00:13:06,120 --> 00:13:08,000 (Barks) 169 00:13:14,520 --> 00:13:18,120 If the young cholla put down roots here, 170 00:13:18,240 --> 00:13:21,160 it would compete with its parent for water. 171 00:13:23,280 --> 00:13:24,720 (Barking) 172 00:13:24,840 --> 00:13:26,200 Night falls... 173 00:13:27,440 --> 00:13:29,960 And this one is on the move. 174 00:13:39,760 --> 00:13:41,280 A pack rat. 175 00:13:41,400 --> 00:13:43,960 She knows how to deal with a cholla. 176 00:13:49,400 --> 00:13:52,080 She avoids the spines by gripping it 177 00:13:52,200 --> 00:13:54,800 at the place where it broke off from its parent. 178 00:14:00,200 --> 00:14:02,120 And she works fast. 179 00:14:05,040 --> 00:14:07,360 There are pack rat hunters here. 180 00:14:16,640 --> 00:14:21,120 She uses the cholla to build a spiny wall around her nest. 181 00:14:37,520 --> 00:14:41,360 The flesh of the cholla supplies her with water... 182 00:14:42,920 --> 00:14:46,920 And the severed spines further reinforce the defences. 183 00:14:59,800 --> 00:15:01,200 This cholla bud... 184 00:15:02,760 --> 00:15:04,120 Might be next. 185 00:15:08,080 --> 00:15:10,680 But one accidental nudge... 186 00:15:15,040 --> 00:15:17,200 And it escapes. 187 00:15:39,560 --> 00:15:41,560 (Spines crackle) 188 00:15:44,200 --> 00:15:46,800 The bud starts to put down roots... 189 00:15:54,960 --> 00:15:58,200 So the cholla, thanks to the pack rats, 190 00:15:58,320 --> 00:15:59,920 finds new territory... 191 00:16:01,360 --> 00:16:03,400 And sets about claiming it. 192 00:16:09,240 --> 00:16:11,160 - (Birdsong) - (Insects buzzing) 193 00:16:11,280 --> 00:16:15,120 Few plants deal with the problems of desert living 194 00:16:15,240 --> 00:16:16,880 better than cacti. 195 00:16:18,520 --> 00:16:22,400 There are almost 2,000 different species of them. 196 00:16:22,520 --> 00:16:26,960 They're spread across the deserts of the American west, 197 00:16:27,080 --> 00:16:30,760 from Arizona all the way to Mexico and beyond. 198 00:16:34,960 --> 00:16:36,480 In South America, 199 00:16:36,600 --> 00:16:40,080 the andes catch virtually all the rain-carrying clouds 200 00:16:40,200 --> 00:16:42,160 that blow in from the pacific... 201 00:16:44,520 --> 00:16:47,240 And that has created to the east of them 202 00:16:47,360 --> 00:16:49,720 the world's driest desert - 203 00:16:49,840 --> 00:16:51,440 the atacama. 204 00:16:58,240 --> 00:16:59,880 In the desert world, 205 00:17:00,000 --> 00:17:02,600 water thieves can come in many forms, 206 00:17:02,720 --> 00:17:06,720 to exploit even the smallest chink in a plant's defence. 207 00:17:12,960 --> 00:17:16,160 One of the strangest travels within the gut 208 00:17:16,280 --> 00:17:18,320 of a fruit-eating mockingbird. 209 00:17:20,240 --> 00:17:23,120 (Burbling call) 210 00:17:25,160 --> 00:17:26,680 These are the seeds... 211 00:17:28,240 --> 00:17:29,760 Of tristerix, 212 00:17:29,880 --> 00:17:31,680 a kind of mistletoe. 213 00:17:34,720 --> 00:17:40,160 Their goal is the water inside this hedgehog cactus. 214 00:17:41,760 --> 00:17:44,640 Using the spines as anchors, 215 00:17:44,760 --> 00:17:47,720 the seeds start to germinate. 216 00:17:51,000 --> 00:17:52,720 Each produces a long probe 217 00:17:52,840 --> 00:17:56,960 with which to try and locate the cactus's skin. 218 00:17:58,720 --> 00:18:02,160 For most, that's a stretch too far 219 00:18:02,280 --> 00:18:03,800 and they perish. 220 00:18:06,560 --> 00:18:08,040 But for this one, 221 00:18:08,160 --> 00:18:11,680 the cactus's surface is within reach. 222 00:18:20,560 --> 00:18:23,720 It clamps onto it with a special sucker... 223 00:18:27,120 --> 00:18:30,080 And then waits for darkness. 224 00:18:32,080 --> 00:18:35,600 At night, the cactus opens its pores 225 00:18:35,720 --> 00:18:36,760 in order to respire. 226 00:18:39,560 --> 00:18:41,800 Oxygen goes out, 227 00:18:41,920 --> 00:18:44,560 carbon dioxide goes in. 228 00:18:45,720 --> 00:18:47,520 And so does tristerix, 229 00:18:52,840 --> 00:18:54,120 Once within, 230 00:18:54,240 --> 00:18:58,720 its tissues spread throughout the body of the cactus, 231 00:18:58,840 --> 00:19:01,800 sustained by the precious store of water that they find there. 232 00:19:08,200 --> 00:19:09,720 Then, a year later, 233 00:19:09,840 --> 00:19:12,520 it breaks through the cactus's skin... 234 00:19:19,200 --> 00:19:22,120 And bursts into flower. 235 00:19:39,080 --> 00:19:41,160 Hummingbirds come to drink their nectar 236 00:19:41,280 --> 00:19:44,800 and pollinate them as they do so. 237 00:19:54,560 --> 00:19:57,200 And then, to complete the cycle, 238 00:19:57,320 --> 00:20:02,160 tristerix produces hundreds of white eye-catching seeds, 239 00:20:02,280 --> 00:20:04,440 ready to be carried away by a bird 240 00:20:04,560 --> 00:20:07,720 to invade another cactus. 241 00:20:18,640 --> 00:20:22,160 The karoo desert in Southern Africa. 242 00:20:23,880 --> 00:20:26,000 And although it may look bare, 243 00:20:26,120 --> 00:20:30,040 its rocky ground contains an unrivalled variety of plants 244 00:20:30,160 --> 00:20:34,360 that, one way or another, store water in their tissues. 245 00:20:35,920 --> 00:20:39,320 They belong to many different families, 246 00:20:39,440 --> 00:20:42,720 but as a group, they're known as succulents. 247 00:21:00,280 --> 00:21:03,640 Some are small and low 248 00:21:03,760 --> 00:21:06,600 and barely distinguishable from their surroundings. 249 00:21:08,720 --> 00:21:11,160 These look like little pebbles. 250 00:21:13,360 --> 00:21:15,760 They resemble them so closely 251 00:21:15,880 --> 00:21:18,840 that animals which might be only too glad 252 00:21:18,960 --> 00:21:21,840 to steal their water just pass them by. 253 00:21:26,000 --> 00:21:28,160 When rain does fall, they absorb it 254 00:21:28,280 --> 00:21:30,080 and quickly expand. 255 00:21:32,600 --> 00:21:35,400 But even this doesn't spoil their disguise. 256 00:21:35,520 --> 00:21:38,400 They just look like larger pebbles. 257 00:21:40,040 --> 00:21:42,080 Nor are they green. 258 00:21:42,200 --> 00:21:45,360 The cells on their top surface are transparent 259 00:21:45,480 --> 00:21:48,120 and allow sunlight to pass through. 260 00:21:49,840 --> 00:21:51,680 Deep within, and out of sight, 261 00:21:51,800 --> 00:21:55,640 are the green cells where photosynthesis occurs - 262 00:21:55,760 --> 00:21:58,000 the process which uses this light 263 00:21:58,120 --> 00:22:00,000 to make food for the plant. 264 00:22:06,680 --> 00:22:09,360 When the time comes to reproduce, however, 265 00:22:09,480 --> 00:22:12,640 the stone plant abandons its disguise. 266 00:22:33,560 --> 00:22:37,040 And now it blooms. 267 00:22:44,840 --> 00:22:49,120 The flowers open and close every 24 hours. 268 00:22:57,720 --> 00:23:00,880 So, for a few dangerous days, 269 00:23:01,000 --> 00:23:03,200 the plant advertises for pollinators, 270 00:23:03,320 --> 00:23:06,480 before returning to life as a pebble. 271 00:23:15,120 --> 00:23:16,560 (Antlers clatter) 272 00:23:20,680 --> 00:23:24,680 Some desert plants have developed a very different way 273 00:23:24,800 --> 00:23:27,080 of attracting pollinators. 274 00:23:28,240 --> 00:23:30,880 This is stapelia. 275 00:23:31,000 --> 00:23:35,120 It produces what is perhaps the desert's strangest disguise. 276 00:23:36,600 --> 00:23:40,040 It uses water stored in its stems 277 00:23:40,160 --> 00:23:42,360 to grow buds the size of tennis balls. 278 00:23:42,480 --> 00:23:44,000 (Creaking) 279 00:24:02,640 --> 00:24:04,480 The flower, once opened, 280 00:24:04,600 --> 00:24:07,160 is called a desert starfish. 281 00:24:10,160 --> 00:24:13,840 Instead of releasing millions of loose pollen grains, 282 00:24:13,960 --> 00:24:15,200 as most flowers do, 283 00:24:15,320 --> 00:24:20,360 the desert starfish produces them packed in five tiny sacs. 284 00:24:22,800 --> 00:24:25,440 But if its strategy is successful, 285 00:24:25,560 --> 00:24:29,440 just one of them will produce hundreds of seeds. 286 00:24:33,600 --> 00:24:36,000 And this depends on deception. 287 00:24:38,640 --> 00:24:41,440 The flower appears to have hair... 288 00:24:43,280 --> 00:24:46,200 Wrinkly skin... 289 00:24:48,080 --> 00:24:50,400 And it produces a stench 290 00:24:50,520 --> 00:24:52,840 like the carcass of a dead animal. 291 00:24:55,960 --> 00:24:57,480 (Sniffs) 292 00:24:58,560 --> 00:25:00,800 (Flies buzz) 293 00:25:07,080 --> 00:25:09,840 And when a carrion fly investigates... 294 00:25:12,200 --> 00:25:15,800 The flower clamps a tiny sac of pollen to its proboscis. 295 00:25:23,960 --> 00:25:29,040 It's not easy to feed with such encumbered mouth parts. 296 00:25:30,240 --> 00:25:33,720 But try as it might, the fly can't get rid of it. 297 00:25:35,480 --> 00:25:36,800 (Leaves creak) 298 00:25:36,920 --> 00:25:39,080 And it's still there when the fly leaves 299 00:25:39,200 --> 00:25:42,080 to try and feed from another bogus cactus. 300 00:25:45,960 --> 00:25:47,760 (Fly buzzes) 301 00:25:47,880 --> 00:25:50,360 This time, however, when its clamped-up proboscis 302 00:25:50,480 --> 00:25:54,920 slots into the flower, the pollen sac is released. 303 00:26:01,480 --> 00:26:03,480 With pollination complete, 304 00:26:03,600 --> 00:26:05,880 the fly is no longer needed. 305 00:26:09,840 --> 00:26:11,600 And just as well! 306 00:26:16,840 --> 00:26:19,360 Some deserts can be so dry 307 00:26:19,480 --> 00:26:22,160 that plants must find techniques of surviving 308 00:26:22,280 --> 00:26:25,920 for long periods without any water whatsoever. 309 00:26:26,040 --> 00:26:30,960 One of them is to grow extremely slowly, 310 00:26:31,080 --> 00:26:35,400 and few plants grow more slowly than this one - 311 00:26:35,520 --> 00:26:37,920 the creosote bush. 312 00:26:39,040 --> 00:26:41,720 It is inactive for most of its life 313 00:26:41,840 --> 00:26:44,560 and only wakes up and grows for a brief period... 314 00:26:45,720 --> 00:26:49,000 If and when there is a fall of rain. 315 00:26:52,560 --> 00:26:55,160 I've seen evidence of this grow-slow strategy 316 00:26:55,280 --> 00:26:56,400 for myself. 317 00:26:57,680 --> 00:26:59,000 40 years ago, 318 00:26:59,120 --> 00:27:01,480 I came here to California's mojave desert 319 00:27:01,600 --> 00:27:03,800 to visit one particular plant. 320 00:27:05,560 --> 00:27:07,720 An individual creosote bush 321 00:27:07,840 --> 00:27:11,320 tends to spread not by setting seeds 322 00:27:11,440 --> 00:27:13,120 and producing a new generation, 323 00:27:13,240 --> 00:27:17,360 but by sending out new stems around its base. 324 00:27:17,480 --> 00:27:19,920 This plant started growing 325 00:27:20,040 --> 00:27:23,200 between 10,000 and 12,000 years ago. 326 00:27:25,280 --> 00:27:27,560 That was in 1982. 327 00:27:30,520 --> 00:27:33,800 Since then, careful measurement has shown 328 00:27:33,920 --> 00:27:39,120 that it has increased its size by less than one inch. 329 00:27:42,080 --> 00:27:45,600 Its ability to endure is truly extraordinary. 330 00:27:47,000 --> 00:27:48,680 (Birdsong) 331 00:27:50,040 --> 00:27:52,400 So efficient is creosote 332 00:27:52,520 --> 00:27:55,040 at collecting what little rain falls here 333 00:27:55,160 --> 00:27:58,000 that few other plants can compete with it. 334 00:27:58,120 --> 00:28:02,080 As a result, over the last 12,000 years, 335 00:28:02,200 --> 00:28:05,080 it's come to completely dominate this landscape. 336 00:28:22,080 --> 00:28:25,320 The chihuahuan desert in north Mexico. 337 00:28:26,480 --> 00:28:29,320 Here, one particular plant 338 00:28:29,440 --> 00:28:31,400 plays the waiting game so well 339 00:28:31,520 --> 00:28:34,520 that it spends much of its life looking dead 340 00:28:34,640 --> 00:28:37,040 and certainly not worth eating. 341 00:28:39,920 --> 00:28:43,720 And it can survive like this for a decade. 342 00:28:51,920 --> 00:28:54,560 This is the resurrection plant. 343 00:28:56,840 --> 00:28:59,160 It's a kind of moss. 344 00:28:59,280 --> 00:29:01,560 It barely has roots 345 00:29:01,680 --> 00:29:04,160 and it certainly can't store much water. 346 00:29:05,440 --> 00:29:06,920 But it can travel. 347 00:29:08,200 --> 00:29:10,120 (Wind blows) 348 00:29:13,040 --> 00:29:15,400 After a particularly long drought... 349 00:29:16,600 --> 00:29:18,640 It breaks away from its roots... 350 00:29:21,240 --> 00:29:22,640 And becomes... 351 00:29:24,400 --> 00:29:26,600 A tumbleweed. 352 00:29:28,160 --> 00:29:33,520 Blowing across the desert, it can travel a mile in a week. 353 00:29:35,960 --> 00:29:38,600 With luck, it may find water. 354 00:29:42,320 --> 00:29:45,200 (Thunder rolls) 355 00:29:46,360 --> 00:29:49,880 Just a shower of rain can bring it back to life. 356 00:29:55,400 --> 00:29:59,200 As its fronds soak up the water, they unfurl. 357 00:30:12,240 --> 00:30:16,760 In its protected centre, it still has green cells, 358 00:30:16,880 --> 00:30:19,680 which absorb both the water and sunlight, 359 00:30:19,800 --> 00:30:24,480 and rapidly produce the food it needs to resume its growth. 360 00:30:29,680 --> 00:30:33,000 It will grow for just as long as there is moisture. 361 00:30:33,120 --> 00:30:34,720 (Leaves crackle) 362 00:30:37,480 --> 00:30:39,480 But when that disappears... 363 00:30:41,120 --> 00:30:43,400 It closes up once more 364 00:30:43,520 --> 00:30:46,080 and resumes its travels. 365 00:30:56,080 --> 00:30:58,040 Here in the canyon lands of Utah 366 00:30:58,160 --> 00:31:00,400 lives a plant that has developed 367 00:31:00,520 --> 00:31:03,360 a finely balanced relationship 368 00:31:03,480 --> 00:31:07,080 with the animals with which it shares this dramatic desert. 369 00:31:12,160 --> 00:31:15,080 Rain does occasionally fall here 370 00:31:15,200 --> 00:31:18,680 and turns dust into mud. 371 00:31:21,480 --> 00:31:23,280 (Cracking) 372 00:31:23,400 --> 00:31:25,480 But that doesn't last long. 373 00:31:27,200 --> 00:31:30,040 A brief window of opportunity opens. 374 00:31:39,760 --> 00:31:42,920 Seeds that have been buried for years 375 00:31:43,040 --> 00:31:44,920 may now be exposed to light... 376 00:31:46,320 --> 00:31:48,280 And come to life. 377 00:32:05,120 --> 00:32:07,360 This is coyote tobacco. 378 00:32:21,040 --> 00:32:24,360 In just a few weeks, it grows a metre tall 379 00:32:24,480 --> 00:32:27,360 and produces dozens of flowers. 380 00:32:33,480 --> 00:32:37,640 The night air becomes heavy with their fragrance. 381 00:32:39,680 --> 00:32:41,240 Soon, they attract hawk moths, 382 00:32:41,360 --> 00:32:43,400 which sip their nectar, 383 00:32:43,520 --> 00:32:45,800 and in doing so, pollinate them. 384 00:32:47,840 --> 00:32:51,800 But the moths also lay their eggs on them. 385 00:33:07,680 --> 00:33:10,440 Soon, their caterpillars have hatched 386 00:33:10,560 --> 00:33:13,160 and are munching the leaves. 387 00:33:16,000 --> 00:33:18,040 Their nibbles expose the plant's sap 388 00:33:18,160 --> 00:33:20,120 to the drying air. 389 00:33:23,280 --> 00:33:25,720 But the tobacco plant has a defence. 390 00:33:28,960 --> 00:33:32,800 The leaves under attack produce nicotine. 391 00:33:37,240 --> 00:33:39,600 This chemical sedates the caterpillars 392 00:33:39,720 --> 00:33:41,400 and slows them down. 393 00:33:47,480 --> 00:33:50,960 And what is more, it makes them give off a particular scent... 394 00:33:54,280 --> 00:33:59,320 One that summons others to come to the plant's aid. 395 00:34:00,960 --> 00:34:02,760 Big-eyed bugs - 396 00:34:02,880 --> 00:34:06,800 miniature assassins only 2mm long. 397 00:34:08,080 --> 00:34:09,800 And whiptail lizards. 398 00:34:11,360 --> 00:34:15,080 Big or small, they make a meal of the caterpillars. 399 00:34:25,960 --> 00:34:27,800 It's certainly effective. 400 00:34:30,320 --> 00:34:33,960 But there's more to this strategy than meets the eye. 401 00:34:36,040 --> 00:34:38,840 When the leaf of a tobacco plant 402 00:34:38,960 --> 00:34:41,000 is attacked by a caterpillar, 403 00:34:41,120 --> 00:34:45,080 all the rest of the leaves prepare to defend themselves. 404 00:34:46,240 --> 00:34:49,000 But how does this leaf know that 405 00:34:49,120 --> 00:34:52,120 that leaf there is under attack? 406 00:34:52,240 --> 00:34:56,040 Well, scientists here in the United States 407 00:34:56,160 --> 00:35:00,040 have specially genetically modified these tobacco plants 408 00:35:00,160 --> 00:35:02,480 so that under special lighting conditions, 409 00:35:02,600 --> 00:35:06,920 this microscope can show us exactly what is going on. 410 00:35:09,040 --> 00:35:12,800 I'm going to attack one of the leaves of this plant 411 00:35:12,920 --> 00:35:15,760 with these tweezers, which, to the plant, 412 00:35:15,880 --> 00:35:19,160 will seem as if it's being nibbled by a caterpillar. 413 00:35:33,680 --> 00:35:36,480 Signals are being transmitted along the veins 414 00:35:36,600 --> 00:35:39,240 that link the leaf to the rest of the plant. 415 00:35:40,440 --> 00:35:43,440 It's rather like a very simple nervous system. 416 00:35:48,400 --> 00:35:51,320 From that initial injury, the whole of this little plant 417 00:35:51,440 --> 00:35:54,040 is aware that something had happened. 418 00:35:58,760 --> 00:36:02,000 This signal warns each leaf of the danger... 419 00:36:03,440 --> 00:36:05,840 So that it is ready to produce nicotine 420 00:36:05,960 --> 00:36:08,200 the moment it's attacked. 421 00:36:11,160 --> 00:36:14,040 With this defence at the ready, the tobacco plant 422 00:36:14,160 --> 00:36:18,720 can continue to grow until, eventually, it produces seeds. 423 00:36:32,520 --> 00:36:34,880 It's particularly important in deserts 424 00:36:35,000 --> 00:36:39,200 for seeds to be distributed as widely as possible 425 00:36:39,320 --> 00:36:42,880 so that some will have a chance of reaching moisture. 426 00:36:46,080 --> 00:36:49,720 And deserts have an excellent agent to help them do that. 427 00:36:49,840 --> 00:36:52,080 (Wind blows) 428 00:36:52,200 --> 00:36:53,520 The wind. 429 00:36:55,840 --> 00:36:59,640 Many seeds have adaptations to help them exploit it. 430 00:37:00,880 --> 00:37:03,360 They have shells to protect the seeds within 431 00:37:03,480 --> 00:37:04,520 from abrasion... 432 00:37:05,880 --> 00:37:09,240 Or wings to help them catch the air. 433 00:37:12,480 --> 00:37:15,480 As the temperature rises throughout the day, 434 00:37:15,600 --> 00:37:17,760 desert winds increase in strength. 435 00:37:42,600 --> 00:37:46,560 Here in Arizona, the land is regularly swept by 436 00:37:46,680 --> 00:37:49,080 what is known as a haboob. 437 00:37:49,200 --> 00:37:51,640 It's a giant sandstorm, 438 00:37:51,760 --> 00:37:54,920 but also, in effect, a seed storm. 439 00:38:02,960 --> 00:38:07,080 Countless millions of them are swept up into the air. 440 00:38:13,280 --> 00:38:14,640 Some seeds can travel 441 00:38:14,760 --> 00:38:17,040 thousands of miles on the wind... 442 00:38:18,520 --> 00:38:20,040 (Thunder cracks) 443 00:38:20,160 --> 00:38:22,280 So that plants may eventually reach 444 00:38:22,400 --> 00:38:24,400 even the most isolated desert. 445 00:38:27,520 --> 00:38:29,360 (Thunder rolls) 446 00:38:34,240 --> 00:38:37,080 Some have landed on an island 447 00:38:37,200 --> 00:38:40,720 in the middle of the world's largest salt flat, in Bolivia. 448 00:38:40,840 --> 00:38:42,800 (Birds call) 449 00:38:46,040 --> 00:38:47,680 In the galapagos, 450 00:38:47,800 --> 00:38:51,560 they sprout on fields of recently erupted lava. 451 00:38:51,680 --> 00:38:54,160 (Fire crackles) 452 00:38:59,000 --> 00:39:00,280 They've even reached 453 00:39:00,400 --> 00:39:03,680 one of the most inhospitable of all sites - 454 00:39:03,800 --> 00:39:08,040 the tiny island of San Pedro martir, 455 00:39:08,160 --> 00:39:12,120 a scorched, lonely rock off the coast of Mexico. 456 00:39:16,440 --> 00:39:19,840 This is the home of the giant cardon, 457 00:39:19,960 --> 00:39:25,920 a species of huge cactus that can weigh up to 12 tonnes. 458 00:39:33,360 --> 00:39:35,160 They're able to thrive here 459 00:39:35,280 --> 00:39:38,480 because of an extraordinary partnership... 460 00:39:41,400 --> 00:39:45,520 With brown and blue-footed boobies. 461 00:39:50,560 --> 00:39:53,560 The cardons here can become so broad 462 00:39:53,680 --> 00:39:57,520 that they provide cooling shade for nesting birds. 463 00:40:09,120 --> 00:40:15,080 As the booby chicks get older, they repay the cardons... 464 00:40:20,440 --> 00:40:21,760 With their droppings. 465 00:40:23,200 --> 00:40:24,640 Guano. 466 00:40:24,760 --> 00:40:28,400 The digested remains of vast shoals of fish. 467 00:40:30,240 --> 00:40:33,840 This guano is of such strength and quantity 468 00:40:33,960 --> 00:40:37,440 that most plants would be poisoned by it. 469 00:40:43,760 --> 00:40:47,840 These cardons, however, have evolved the ability to tolerate 470 00:40:47,960 --> 00:40:52,760 the toxins in the guano and digest the nutrients. 471 00:40:53,960 --> 00:40:57,320 As a result, the cacti now grow in a dense forest 472 00:40:57,440 --> 00:40:59,480 over a million strong. 473 00:41:04,640 --> 00:41:08,120 But such relationships are very finely balanced 474 00:41:08,240 --> 00:41:11,200 and can only too easily tip into catastrophe... 475 00:41:14,720 --> 00:41:17,520 As is now happening in northern Zimbabwe. 476 00:41:21,920 --> 00:41:23,440 For six months of the year, 477 00:41:23,560 --> 00:41:27,760 the Savannah here is kept lush and green by daily rains. 478 00:41:31,800 --> 00:41:34,480 (Animals call) 479 00:41:36,600 --> 00:41:38,560 But when the rainy season is over, 480 00:41:38,680 --> 00:41:42,000 it becomes as dry as any desert. 481 00:41:46,440 --> 00:41:50,840 So to survive here, trees must be able to tolerate 482 00:41:50,960 --> 00:41:52,440 both conditions. 483 00:41:54,120 --> 00:41:58,520 And these giants are adapted to do just that. 484 00:41:59,760 --> 00:42:01,760 They are baobabs. 485 00:42:09,760 --> 00:42:13,160 This one might be over a thousand years old. 486 00:42:13,280 --> 00:42:16,040 It's survived here in part thanks to 487 00:42:16,160 --> 00:42:19,360 its ability to store thousands of litres of water 488 00:42:19,480 --> 00:42:22,080 within the spongy wood of its trunk. 489 00:42:26,080 --> 00:42:27,760 But its battered surface 490 00:42:27,880 --> 00:42:31,640 is evidence of a very finely balanced relationship. 491 00:42:33,680 --> 00:42:38,680 These huge trees are a focus for animals of all kinds. 492 00:42:40,840 --> 00:42:43,120 (Rumbling and snorting) 493 00:42:43,240 --> 00:42:46,000 And they're particularly important for elephants. 494 00:42:51,320 --> 00:42:55,160 In the wet season, they eat the baobabs' fruit 495 00:42:55,280 --> 00:42:57,680 and disperse the seeds in their dung. 496 00:43:03,640 --> 00:43:05,160 Now, as the dry season begins... 497 00:43:05,280 --> 00:43:07,360 (Snorts) 498 00:43:07,480 --> 00:43:10,520 They migrate to distant watering holes. 499 00:43:14,880 --> 00:43:17,440 The baobabs have damp inner wood... 500 00:43:19,240 --> 00:43:21,080 And the elephants use it 501 00:43:21,200 --> 00:43:23,360 to quench their thirst on the journey. 502 00:43:24,800 --> 00:43:28,240 (Elephant trumpets) 503 00:43:37,680 --> 00:43:39,760 (Low rumbling) 504 00:43:43,200 --> 00:43:47,040 This relationship can only work because baobabs 505 00:43:47,160 --> 00:43:50,960 have a remarkable ability to heal themselves. 506 00:44:09,040 --> 00:44:11,040 Between each damaging attack, 507 00:44:11,160 --> 00:44:15,800 they expand their spongy wood and grow new skin. 508 00:44:20,280 --> 00:44:22,760 And they've done this time and time again, 509 00:44:22,880 --> 00:44:24,240 over centuries. 510 00:44:28,600 --> 00:44:33,040 Today, however, it's harder for the baobabs to recover, 511 00:44:33,160 --> 00:44:36,280 as dry seasons become longer and drier 512 00:44:36,400 --> 00:44:38,200 due to climate change. 513 00:44:39,640 --> 00:44:42,720 Not only that, but the elephants are forced 514 00:44:42,840 --> 00:44:46,840 to take ever more wood from the trees in order to survive. 515 00:44:52,560 --> 00:44:55,760 In some parts of Africa, many of the largest 516 00:44:55,880 --> 00:44:59,800 and oldest baobabs have fallen in the last decade. 517 00:45:13,040 --> 00:45:15,640 The loss of a vital species like the baobab 518 00:45:15,760 --> 00:45:18,640 strikes a blow at all life in the desert. 519 00:45:23,840 --> 00:45:28,400 In these hostile lands, few living organisms can survive 520 00:45:28,520 --> 00:45:31,160 without help from others. 521 00:45:35,600 --> 00:45:38,720 You can find an extraordinary illustration of this 522 00:45:38,840 --> 00:45:41,480 in Arizona's saguaro country. 523 00:45:48,800 --> 00:45:51,080 If you wander off the beaten track here, 524 00:45:51,200 --> 00:45:54,040 you may be lucky enough to find one of these. 525 00:45:54,160 --> 00:45:56,920 It might look like an old boot, 526 00:45:57,040 --> 00:46:01,520 but in fact, it's part of a saguaro cactus. 527 00:46:01,640 --> 00:46:03,960 Almost every saguaro has one. 528 00:46:04,080 --> 00:46:05,440 There's one up there. 529 00:46:05,560 --> 00:46:07,560 (Birds call) 530 00:46:10,840 --> 00:46:14,480 It has been produced, indirectly, by woodpeckers, 531 00:46:14,600 --> 00:46:17,720 which regularly dig homes for themselves 532 00:46:17,840 --> 00:46:20,480 in the bloated trunks of the saguaros. 533 00:46:33,240 --> 00:46:35,640 In the next six months, 534 00:46:35,760 --> 00:46:38,240 the cactus heals the wound, 535 00:46:38,360 --> 00:46:43,560 and so creates a safe, cool and watertight nest hole. 536 00:46:45,320 --> 00:46:48,200 It's tough lining will persist for years, 537 00:46:48,320 --> 00:46:52,360 even after the cactus itself has died and rotted away. 538 00:46:57,000 --> 00:46:58,640 A single saguaro may hold 539 00:46:58,760 --> 00:47:01,480 several of these extraordinary homes. 540 00:47:03,680 --> 00:47:06,040 So over its lifetime, 541 00:47:06,160 --> 00:47:08,560 it may provide accommodation 542 00:47:08,680 --> 00:47:11,840 for some 3,000 chicks of several different species. 543 00:47:11,960 --> 00:47:14,800 (Bird squawks) 544 00:47:19,240 --> 00:47:22,240 But in the long term, the saguaro benefits, 545 00:47:22,360 --> 00:47:25,040 as their lodgers repay the cactus 546 00:47:25,160 --> 00:47:28,040 by pollinating its flowers... 547 00:47:29,160 --> 00:47:32,000 And dispersing its seeds. 548 00:47:38,800 --> 00:47:44,000 It's relationships like these that enable life to flourish 549 00:47:44,120 --> 00:47:47,560 in some of the world's harshest landscapes. 550 00:48:00,160 --> 00:48:02,080 Over millions of years, 551 00:48:02,200 --> 00:48:05,200 plants have become superbly adapted 552 00:48:05,320 --> 00:48:07,520 to hostile desert conditions. 553 00:48:07,640 --> 00:48:11,280 But it's a very finely balanced existence, 554 00:48:11,400 --> 00:48:14,160 and one that makes them uniquely vulnerable. 555 00:48:16,920 --> 00:48:19,880 However, our growing understanding 556 00:48:20,000 --> 00:48:22,920 of the complex ways by which desert animals and plants 557 00:48:23,040 --> 00:48:26,000 rely on one another is now helping us to understand 558 00:48:26,120 --> 00:48:28,280 how best we can protect them. 559 00:48:33,240 --> 00:48:37,400 90 years ago, a photograph was taken from this very spot 560 00:48:37,520 --> 00:48:40,520 that shows a population of saguaro cactus 561 00:48:40,640 --> 00:48:43,680 that was very different from what it is today. 562 00:48:45,800 --> 00:48:48,120 In the last 50 years, 563 00:48:48,240 --> 00:48:52,360 the population of saguaros here has greatly diminished - 564 00:48:52,480 --> 00:48:55,360 not because of a direct assault on the cactus, 565 00:48:55,480 --> 00:48:58,920 but because many of the shade-giving nurse trees 566 00:48:59,040 --> 00:49:00,880 were harvested for firewood, 567 00:49:01,000 --> 00:49:03,600 leaving young saguaro to die in the sun. 568 00:49:09,240 --> 00:49:11,680 Now that this relationship is understood 569 00:49:11,800 --> 00:49:13,840 and the nurse trees are protected, 570 00:49:13,960 --> 00:49:16,160 there are already signs 571 00:49:16,280 --> 00:49:19,520 that the saguaro are recovering. 572 00:49:21,840 --> 00:49:23,400 Wherever there's a desert, 573 00:49:23,520 --> 00:49:26,320 plants have evolved to meet its challenge. 574 00:49:29,040 --> 00:49:31,360 But everywhere, they need our help. 575 00:49:33,440 --> 00:49:35,240 As we understand more about them 576 00:49:35,360 --> 00:49:38,360 and their intimate and complex relationships... 577 00:49:40,360 --> 00:49:42,800 We will be better able to protect them, 578 00:49:42,920 --> 00:49:45,720 and all life, in these beautiful 579 00:49:45,840 --> 00:49:49,240 but increasingly fragile worlds. 580 00:50:03,480 --> 00:50:06,360 The most remote shoot for the deserts team 581 00:50:06,480 --> 00:50:09,120 is to the island of San Pedro martir 582 00:50:09,240 --> 00:50:11,520 in the sea of Cortez, Mexico. 583 00:50:14,560 --> 00:50:17,240 They are to film the giant cacti 584 00:50:17,360 --> 00:50:19,760 that have found a unique way to thrive here. 585 00:50:22,920 --> 00:50:26,760 It takes 48 hours to travel the 260 miles... 586 00:50:27,880 --> 00:50:30,800 Over unpleasantly choppy seas. 587 00:50:37,120 --> 00:50:39,240 It's not made some of us feel very well. 588 00:50:39,360 --> 00:50:41,280 I think one of us is quite seasick. 589 00:50:43,600 --> 00:50:46,120 There is nothing but big blue out there, 590 00:50:46,240 --> 00:50:48,480 and the island is somewhere in that direction. 591 00:50:48,600 --> 00:50:49,880 Can't see it yet. 592 00:50:52,240 --> 00:50:53,960 As they draw close to the island, 593 00:50:54,080 --> 00:50:55,520 there's a spectacular reminder 594 00:50:55,640 --> 00:50:58,760 of how rich life in the sea is here. 595 00:50:58,880 --> 00:51:01,920 Oh, look in front of us, look at that for a pod! 596 00:51:03,960 --> 00:51:06,640 Oh, they're everywhere. 597 00:51:11,160 --> 00:51:12,840 Show us the way! 598 00:51:12,960 --> 00:51:14,280 (Laughs) 599 00:51:19,720 --> 00:51:24,240 Meeting them here is desert scientist Ben Wilder. 600 00:51:25,320 --> 00:51:29,280 It's through his research that the team first heard about 601 00:51:29,400 --> 00:51:31,640 the island's peculiar residents. 602 00:51:31,760 --> 00:51:34,400 I'll never forget the first time I came to 603 00:51:34,520 --> 00:51:37,160 actually exactly where we're standing right now. 604 00:51:37,280 --> 00:51:41,400 It was April of 2006, and saw this view, 605 00:51:41,520 --> 00:51:47,520 and it both settled in my heart and captivated my mind. 606 00:51:47,640 --> 00:51:53,240 And so that started a process of trying to understand, 607 00:51:53,360 --> 00:51:55,800 you know, what can produce this? 608 00:51:57,840 --> 00:52:01,240 The secret is in the relationship between the cactus 609 00:52:01,360 --> 00:52:05,400 and a type of seabird called a booby. 610 00:52:06,760 --> 00:52:09,120 All the boobies that we need to film 611 00:52:09,240 --> 00:52:11,840 are right up there at the top of the island, 612 00:52:11,960 --> 00:52:14,120 so it's going to be a bit of a scramble. 613 00:52:15,920 --> 00:52:19,920 The crew soon discover how harsh the conditions are here. 614 00:52:20,040 --> 00:52:23,400 I'm pretty tired. It's pretty hot. 615 00:52:23,520 --> 00:52:24,920 But it's a great view. 616 00:52:31,760 --> 00:52:34,840 There's very few places on earth where you're going to see 617 00:52:34,960 --> 00:52:37,520 this many cactus. I mean, it's absolutely amazing. 618 00:52:37,640 --> 00:52:39,400 I would say this is the only place 619 00:52:39,520 --> 00:52:41,720 - you're going to see this. - Well, there you go, then. 620 00:52:44,000 --> 00:52:47,400 Ben's research is uncovering the ingenious ways 621 00:52:47,520 --> 00:52:50,680 the cacti have adapted to the conditions here. 622 00:52:51,800 --> 00:52:54,320 The waters just offshore here are some of the most productive 623 00:52:54,440 --> 00:52:56,520 marine waters in the world, 624 00:52:56,640 --> 00:52:59,960 and so it's kind of an ideal habitat for seabirds to roost. 625 00:53:00,080 --> 00:53:03,400 But when they do so, they deposit tonnes of guano, 626 00:53:03,520 --> 00:53:05,400 and so those nutrients, 627 00:53:05,520 --> 00:53:08,120 really high in nitrogen and phosphorus, 628 00:53:08,240 --> 00:53:11,080 actually are toxic to most plant species. 629 00:53:11,200 --> 00:53:14,640 The cardons thrive because they're uniquely able 630 00:53:14,760 --> 00:53:16,000 to process the guano 631 00:53:16,120 --> 00:53:19,280 and extract what they need to fuel their growth. 632 00:53:21,680 --> 00:53:24,440 One of the first shots the crew need to get 633 00:53:24,560 --> 00:53:27,840 is of the boobies nesting under the cacti. 634 00:53:27,960 --> 00:53:29,200 The lack of predators 635 00:53:29,320 --> 00:53:32,440 means the birds aren't afraid of people. 636 00:53:32,560 --> 00:53:36,440 It should make filming them up close a bit easier. 637 00:53:36,560 --> 00:53:38,600 That's the theory. 638 00:53:38,720 --> 00:53:41,280 Oli: So we've positioned this camera here to try and get 639 00:53:41,400 --> 00:53:43,880 a good perspective on the chick on the nest. 640 00:53:44,000 --> 00:53:46,600 It's taken quite a liking to our camera. 641 00:53:46,720 --> 00:53:48,720 Let's hope he doesn't break it. 642 00:53:54,160 --> 00:53:55,880 Bull's-eye. 643 00:53:56,000 --> 00:53:57,840 It's pooed right on the front of the lens. 644 00:53:57,960 --> 00:54:01,000 It's kind of a shot we need, but, unfortunately, 645 00:54:01,120 --> 00:54:02,960 my camera wasn't rolling at the time it did it, 646 00:54:03,080 --> 00:54:05,040 so now I've just got a dirty lens. 647 00:54:08,080 --> 00:54:10,640 After a thorough lens clean, 648 00:54:10,760 --> 00:54:12,040 oli eventually gets the shots 649 00:54:12,160 --> 00:54:14,880 to reveal the extraordinary relationship 650 00:54:15,000 --> 00:54:16,600 between bird and plant. 651 00:54:19,680 --> 00:54:23,400 But it's not just the bird guano that influence 652 00:54:23,520 --> 00:54:25,520 how the cardons grow. 653 00:54:25,640 --> 00:54:29,320 They're way shorter, they're dwarfed here. 654 00:54:29,440 --> 00:54:30,840 Throughout the rest of their range 655 00:54:30,960 --> 00:54:33,240 they usually get upwards of 50, 60 feet. 656 00:54:33,360 --> 00:54:37,640 But here, on average, they're 20, 24 feet in height. 657 00:54:37,760 --> 00:54:41,320 They stop growing up and they grow out. 658 00:54:43,080 --> 00:54:46,600 Ben's research suggests that they go wide here 659 00:54:46,720 --> 00:54:50,000 as an adaptation to the violent winds. 660 00:54:50,120 --> 00:54:52,520 Too tall, and they'd blow over. 661 00:54:52,640 --> 00:54:56,840 A gusting wind isn't helping the drone crew, either. 662 00:54:56,960 --> 00:54:58,336 We really need it to calm down a bit, 663 00:54:58,360 --> 00:55:00,000 otherwise it's going to be impossible. 664 00:55:01,760 --> 00:55:03,080 (Drone whirs) 665 00:55:24,680 --> 00:55:28,560 On the sonoran mainland, where the cardon is also found, 666 00:55:28,680 --> 00:55:32,200 you have on average between 50 to 150 plants per hectare. 667 00:55:32,320 --> 00:55:38,000 Here, on this island, you have over 2,500 plants per hectare. 668 00:55:38,120 --> 00:55:41,360 A lull in the wind, and the team get a chance to reveal 669 00:55:41,480 --> 00:55:44,760 the remarkably density of the cacti - 670 00:55:44,880 --> 00:55:48,960 almost 20 times greater than anywhere else. 671 00:55:49,080 --> 00:55:52,880 It appears that, here, they're doing very well. 672 00:55:53,000 --> 00:55:54,600 But even this island 673 00:55:54,720 --> 00:55:58,440 isn't isolated from the effects of a changing planet. 674 00:55:59,720 --> 00:56:02,280 Every cactus you see there, 675 00:56:02,400 --> 00:56:05,000 its body is filled with nutrients from the sea. 676 00:56:06,240 --> 00:56:08,680 Given that we know that the cardons 677 00:56:08,800 --> 00:56:11,960 are linked to the ocean, what happens in the oceans 678 00:56:12,080 --> 00:56:14,200 affects what happens to the cardon. 679 00:56:14,320 --> 00:56:15,600 So a concern we have right now 680 00:56:15,720 --> 00:56:17,480 is that there's a lot of overfishing, 681 00:56:17,600 --> 00:56:20,480 and we know there are less seabirds here 682 00:56:20,600 --> 00:56:22,240 than there were 20 years ago, 683 00:56:22,360 --> 00:56:24,720 and we have reason to believe that 684 00:56:24,840 --> 00:56:26,800 that will ripple and affect 685 00:56:26,920 --> 00:56:29,080 the nutrients that fuel the cardons as well. 686 00:56:31,320 --> 00:56:34,760 This finely balanced relationship is at risk, 687 00:56:34,880 --> 00:56:38,040 and knowing that makes leaving the island 688 00:56:38,160 --> 00:56:40,480 particularly thought-provoking for the crew. 689 00:56:42,320 --> 00:56:44,960 The cardons look beautiful. I've never seen 690 00:56:45,080 --> 00:56:48,280 so many cactus in my life. It's absolutely amazing. 691 00:56:48,400 --> 00:56:50,560 I'm just hoping that when we leave this place, 692 00:56:50,680 --> 00:56:51,840 it stays as it is, 693 00:56:51,960 --> 00:56:54,400 and things don't affect it that are negative. 694 00:56:54,520 --> 00:56:57,480 It's an absolutely wonderful thing, and... 695 00:56:57,600 --> 00:57:00,360 Yeah, and I don't want to go. I want to stay. 696 00:57:00,480 --> 00:57:04,640 This remote cactus forest is a reminder 697 00:57:04,760 --> 00:57:06,640 of the adaptability of plants, 698 00:57:06,760 --> 00:57:09,760 that enables them to establish green worlds 699 00:57:09,880 --> 00:57:12,680 almost anywhere on earth.