1 00:00:52,000 --> 00:00:55,000 David Attenborough: This is the boreal forest. 2 00:01:00,240 --> 00:01:02,640 The largest forest on earth. 3 00:01:04,360 --> 00:01:08,160 750 billion trees. 4 00:01:10,520 --> 00:01:14,120 Smothered by snow throughout the winter... 5 00:01:19,080 --> 00:01:21,720 This is the northernmost boundary 6 00:01:21,840 --> 00:01:23,920 of an extraordinary world. 7 00:01:27,880 --> 00:01:32,200 I'm standing at the edge of the arctic circle. 8 00:01:32,320 --> 00:01:33,920 To the north of me 9 00:01:34,040 --> 00:01:36,880 lies a land dominated for most of the year 10 00:01:37,000 --> 00:01:39,200 by snow and ice. 11 00:01:39,320 --> 00:01:42,760 3,000 miles to the south, the tropics, 12 00:01:42,880 --> 00:01:46,200 bathed the year round in warm sunshine. 13 00:01:46,320 --> 00:01:50,760 And in between, a very different world, 14 00:01:50,880 --> 00:01:54,040 dominated by relentless change. 15 00:01:59,480 --> 00:02:03,760 An endless cycle of four distinct seasons, 16 00:02:03,880 --> 00:02:07,000 each with its own challenges. 17 00:02:07,120 --> 00:02:10,440 The short, freezing days of winter 18 00:02:10,560 --> 00:02:14,320 give way to the urgent awakening of spring. 19 00:02:17,280 --> 00:02:20,800 And the long, hot days of summer 20 00:02:20,920 --> 00:02:24,200 yield to the cooling of Autumn. 21 00:02:28,720 --> 00:02:31,520 Opportunities will be brief. 22 00:02:39,080 --> 00:02:41,720 To survive these extremes, 23 00:02:41,840 --> 00:02:44,920 plants have not only got to be Hardy and resilient, 24 00:02:45,040 --> 00:02:49,000 but many of them have developed special strategies 25 00:02:49,120 --> 00:02:53,160 in order to meet the demands of this seasonal world. 26 00:02:55,160 --> 00:02:59,640 To succeed, they must get their timing just right. 27 00:03:02,600 --> 00:03:06,720 For months now, this world has been asleep. 28 00:03:06,840 --> 00:03:09,920 But change is coming. 29 00:03:25,080 --> 00:03:27,960 Spring is on its way. 30 00:03:46,320 --> 00:03:48,640 (Tick/ng) 31 00:03:50,680 --> 00:03:55,280 In Canada, the forests are starting to stir. 32 00:03:57,600 --> 00:04:00,480 Throughout the winter, the sugar maples here 33 00:04:00,600 --> 00:04:05,720 have kept stores of nutrients ready for this moment. 34 00:04:05,840 --> 00:04:08,200 (Creaking) 35 00:04:08,320 --> 00:04:10,480 Now, as temperatures start to rise, 36 00:04:10,600 --> 00:04:14,880 those nutrients must be brought up from the roots. 37 00:04:15,000 --> 00:04:17,120 (Gurgung) 38 00:04:22,640 --> 00:04:25,560 Sap is on the rise. 39 00:04:30,440 --> 00:04:33,440 Fuel for new green growth. 40 00:04:44,640 --> 00:04:47,200 But just as growth reaches full speed... 41 00:04:48,400 --> 00:04:50,280 Robbers arrive. 42 00:04:50,400 --> 00:04:53,240 (Hammering) 43 00:04:57,920 --> 00:05:00,720 (Tapping) 44 00:05:10,280 --> 00:05:11,960 A sapsucker. 45 00:05:13,720 --> 00:05:17,560 A thief in search of maple syrup. 46 00:05:35,080 --> 00:05:38,440 The tree can tolerate hundreds of wounds. 47 00:05:45,320 --> 00:05:48,840 But if they completely encircle the trunk, 48 00:05:48,960 --> 00:05:52,640 the tree will eventually die. 49 00:05:59,480 --> 00:06:03,480 The sapsucker's break-in hasn't gone unnoticed. 50 00:06:05,200 --> 00:06:07,360 (Wings vibrate) 51 00:06:12,720 --> 00:06:14,760 Hummingbirds, 52 00:06:14,880 --> 00:06:16,480 squirrels 53 00:06:16,600 --> 00:06:18,920 and insects 54 00:06:19,040 --> 00:06:22,200 all invade the sapsucker's territory, 55 00:06:22,320 --> 00:06:24,480 trying to steal a meal. 56 00:06:28,880 --> 00:06:31,680 But unwittingly, they help the tree. 57 00:06:34,000 --> 00:06:35,800 (Sapsucker calls) 58 00:06:37,240 --> 00:06:40,000 Time spent chasing the competition... 59 00:06:41,960 --> 00:06:44,880 Means less time to drill new holes. 60 00:06:53,360 --> 00:06:55,600 (Squawking) 61 00:06:59,200 --> 00:07:01,320 (Squeaking) 62 00:07:15,080 --> 00:07:19,160 The tree gets a chance to repair its wounds... 63 00:07:20,360 --> 00:07:24,120 And the sap can rise freely again. 64 00:07:30,800 --> 00:07:33,080 So this year at least, 65 00:07:33,200 --> 00:07:36,480 the tree will once more produce its leaves. 66 00:07:41,000 --> 00:07:43,400 Hundreds of miniature solar panels 67 00:07:43,520 --> 00:07:46,800 that collect energy from the sunlight. 68 00:07:49,520 --> 00:07:54,480 Each leaf is covered by millions of microscopic pores - 69 00:07:54,600 --> 00:07:57,320 stomata. 70 00:07:59,480 --> 00:08:02,840 They take in carbon dioxide... 71 00:08:04,200 --> 00:08:07,120 And release oxygen and water vapour 72 00:08:07,240 --> 00:08:11,000 in a process that produces high-energy fuel. 73 00:08:23,320 --> 00:08:27,000 All the trees here can now use that fuel to grow 74 00:08:27,120 --> 00:08:28,560 over the coming months. 75 00:08:48,040 --> 00:08:53,200 As spring proceeds, the power of the sun increases. 76 00:08:56,680 --> 00:08:58,960 On river banks across Europe, 77 00:08:59,080 --> 00:09:02,840 many plants have been lying dormant underground... 78 00:09:04,360 --> 00:09:07,200 Waiting for the earth to warm. 79 00:09:13,600 --> 00:09:17,120 And now a race begins. 80 00:09:23,400 --> 00:09:26,760 Among the first to start are nettles. 81 00:09:26,880 --> 00:09:28,320 The sprinters. 82 00:09:34,240 --> 00:09:38,200 Then, only just behind, come the brambles. 83 00:09:38,320 --> 00:09:43,160 They're much more aggressive, and have backward-pointed hooks 84 00:09:43,280 --> 00:09:46,560 with which to scramble over their rivals. 85 00:09:48,320 --> 00:09:51,680 Last to come, the climbers. 86 00:09:54,800 --> 00:09:58,360 Hops and bryony. 87 00:10:02,360 --> 00:10:05,800 They lasso their way towards the light. 88 00:10:34,480 --> 00:10:38,520 Soon, every inch of space and every patch of light 89 00:10:38,640 --> 00:10:40,840 has been claimed. 90 00:10:43,240 --> 00:10:45,200 But hidden in the shadows, 91 00:10:45,320 --> 00:10:49,040 another plant has been waiting to make its move. 92 00:10:58,760 --> 00:11:00,080 This... 93 00:11:02,000 --> 00:11:03,600 Is dodder. 94 00:11:09,920 --> 00:11:11,440 A hunter... 95 00:11:13,280 --> 00:11:16,040 With an exceptional sense of smell. 96 00:11:22,880 --> 00:11:26,800 Moving swiftly, it searches for its prey. 97 00:11:30,120 --> 00:11:33,080 It detects the scent of a young nettle. 98 00:11:52,400 --> 00:11:54,680 The dodder punctures the nettle's stem 99 00:11:54,800 --> 00:11:57,880 and sucks out the nutritious sap. 100 00:12:02,040 --> 00:12:05,120 And it doesn't stop at just one victim. 101 00:12:08,040 --> 00:12:12,160 With its energy supply assured, it multiplies. 102 00:12:21,840 --> 00:12:23,400 It's a parasite 103 00:12:23,520 --> 00:12:26,320 with an insatiable appetite. 104 00:13:18,360 --> 00:13:20,280 (Birdsong) 105 00:13:27,520 --> 00:13:33,280 But remarkably, its victims can now exploit the dodder... 106 00:13:34,560 --> 00:13:38,080 When other springtime enemies appear. 107 00:13:41,840 --> 00:13:44,040 Caterpillars. 108 00:13:55,400 --> 00:13:58,880 When under attack, a leaf sends out a signal 109 00:13:59,000 --> 00:14:02,720 telling the rest of the plant to start building defences... 110 00:14:06,080 --> 00:14:09,960 Foul-tasting toxins that deter the caterpillars. 111 00:14:12,400 --> 00:14:15,000 In an extraordinary twist, 112 00:14:15,120 --> 00:14:18,440 the stems of the dodder interconnecting the plants 113 00:14:18,560 --> 00:14:21,520 are now being used as lines of communication 114 00:14:21,640 --> 00:14:26,800 to relay these warning signals from plant to plant. 115 00:14:33,280 --> 00:14:37,040 They respond by producing their own protective chemicals. 116 00:14:41,280 --> 00:14:43,360 Eventually, the whole river bank 117 00:14:43,480 --> 00:14:47,160 becomes one huge defensive network, 118 00:14:47,280 --> 00:14:52,240 and the one-time rivals are now better off together. 119 00:14:57,520 --> 00:14:59,360 (Water ripples) 120 00:15:13,560 --> 00:15:18,640 The first warm days of spring encourage some plants to flower 121 00:15:18,760 --> 00:15:21,520 and get ahead of the competition... 122 00:15:23,240 --> 00:15:25,080 Creating beautiful displays 123 00:15:25,200 --> 00:15:27,560 throughout the seasonal world... 124 00:15:30,160 --> 00:15:33,400 From the spectacular cherry blossoms of Japan... 125 00:15:37,160 --> 00:15:40,680 To the Goldfield flowers of California. 126 00:15:45,160 --> 00:15:47,360 But spring flowering is risky. 127 00:15:47,480 --> 00:15:50,520 If they flower too early, it may not be warm enough 128 00:15:50,640 --> 00:15:53,320 for pollinating insects to be active. 129 00:15:54,880 --> 00:15:59,040 But the common Daisy gives them every opportunity. 130 00:16:02,880 --> 00:16:06,560 The warmer the flowers are, the more attractive they are, 131 00:16:06,680 --> 00:16:09,280 and they have a remarkable strategy 132 00:16:09,400 --> 00:16:11,760 in order to maximise this. 133 00:16:13,040 --> 00:16:16,800 They were closed up tightly throughout the night 134 00:16:16,920 --> 00:16:18,920 as a protection against the elements. 135 00:16:19,040 --> 00:16:22,600 But once they feel the warmth and the light of the sun, 136 00:16:22,720 --> 00:16:24,960 they spring into action. 137 00:16:38,840 --> 00:16:42,920 It's a behaviour called heliotropism. 138 00:16:44,400 --> 00:16:48,040 They turn to keep facing the sun, 139 00:16:48,160 --> 00:16:50,760 absorbing as much heat as they can. 140 00:17:07,440 --> 00:17:10,600 This is a thermal camera, 141 00:17:10,720 --> 00:17:13,360 and it will tell me the difference between 142 00:17:13,480 --> 00:17:16,240 the surrounding temperature 143 00:17:16,360 --> 00:17:20,160 and the temperature in the centre of a Daisy flower. 144 00:17:20,280 --> 00:17:24,640 The surroundings - 12 degrees. 145 00:17:24,760 --> 00:17:27,680 In the centre of a flower... 146 00:17:28,840 --> 00:17:31,080 21. 147 00:17:31,200 --> 00:17:32,600 (Buzzing) 148 00:17:32,720 --> 00:17:36,040 Pollinators such as bees and wasps 149 00:17:36,160 --> 00:17:39,080 prefer the warmed-up flowers 150 00:17:39,200 --> 00:17:42,200 because they can get a share of the heat for themselves. 151 00:17:43,720 --> 00:17:46,320 As a consequence, they can collect more nectar 152 00:17:46,440 --> 00:17:49,560 from more flowers, pollinating as they go. 153 00:17:53,200 --> 00:17:56,320 And the daisies, with the help of their pollinators, 154 00:17:56,440 --> 00:17:59,680 are able to have a particularly long flowering season. 155 00:18:03,000 --> 00:18:05,600 But when the window of opportunity is brief, 156 00:18:05,720 --> 00:18:08,680 even more ingenious tactics are necessary. 157 00:18:10,120 --> 00:18:11,600 (Birdsong) 158 00:18:21,480 --> 00:18:24,760 Here in south-west Australia, 159 00:18:24,880 --> 00:18:28,440 summer temperatures can soar to up to 40 degrees celsius. 160 00:18:39,520 --> 00:18:42,520 Now, for a brief moment in the cooler spring, 161 00:18:42,640 --> 00:18:45,640 flowering plants must get busy. 162 00:18:50,400 --> 00:18:53,560 And this hammer orchid, with its strange flower, 163 00:18:53,680 --> 00:18:56,080 is doing exactly that. 164 00:18:59,280 --> 00:19:01,000 It needs to attract a pollinator, 165 00:19:01,120 --> 00:19:02,520 but has no nectar, 166 00:19:02,640 --> 00:19:05,680 and doesn't even look like a flower... 167 00:19:09,080 --> 00:19:12,480 Unlike these neighbouring huge grass trees. 168 00:19:14,440 --> 00:19:16,640 (Buzzing) 169 00:19:16,760 --> 00:19:21,360 These produce thousands of tiny white flowers, 170 00:19:21,480 --> 00:19:23,760 all dripping with nectar. 171 00:19:29,320 --> 00:19:33,000 But the orchid has a different strategy. 172 00:19:34,760 --> 00:19:37,240 It synchronises its emergence 173 00:19:37,360 --> 00:19:41,880 with the brief mating season of the thynnid wasp. 174 00:19:48,360 --> 00:19:52,000 The flightless female wasp produces pheromones 175 00:19:52,120 --> 00:19:54,360 to attract males. 176 00:20:01,960 --> 00:20:06,520 This male detects a scent that seems to be hers... 177 00:20:14,680 --> 00:20:17,280 Yet flies right on by. 178 00:20:23,440 --> 00:20:26,600 The orchid not only has the same shape and colour 179 00:20:26,720 --> 00:20:28,000 as a female wasp, 180 00:20:28,120 --> 00:20:31,040 but it sits at the same height as she does. 181 00:20:33,560 --> 00:20:35,760 It even mimics her smell. 182 00:20:37,800 --> 00:20:42,760 And the beguiled male attempts to mate with it. 183 00:20:56,960 --> 00:21:01,080 It hammers against the orchid's pollen sacs. 184 00:21:07,120 --> 00:21:10,560 And the wasp leaves, doubtless a little shaken... 185 00:21:12,800 --> 00:21:15,280 Only to be duped once again. 186 00:21:26,040 --> 00:21:27,160 The pollen on his back 187 00:21:27,280 --> 00:21:29,640 now sticks to this different orchid... 188 00:21:31,000 --> 00:21:33,600 And the deception has worked. 189 00:21:37,000 --> 00:21:40,520 The orchid's imitation is even more intoxicating, 190 00:21:40,640 --> 00:21:42,200 it seems, 191 00:21:42,320 --> 00:21:43,960 than the real thing. 192 00:22:04,120 --> 00:22:10,160 Eventually, the male wasps tire of the orchid's enticements. 193 00:22:13,560 --> 00:22:17,000 Now the wasps, both male and female, 194 00:22:17,120 --> 00:22:20,200 find the flowers of the grass trees to feed. 195 00:22:22,240 --> 00:22:24,320 And there, at long last... 196 00:22:26,240 --> 00:22:27,640 They mate. 197 00:22:34,440 --> 00:22:36,680 And as for the hammer orchid... 198 00:22:38,680 --> 00:22:40,800 Pollination is complete. 199 00:22:53,840 --> 00:22:55,760 As summer approaches, 200 00:22:55,880 --> 00:22:59,400 the need to flower becomes more urgent. 201 00:23:00,640 --> 00:23:03,240 And nowhere more so than here... 202 00:23:04,760 --> 00:23:06,880 In South Africa. 203 00:23:10,400 --> 00:23:14,240 This is the fynbos, part of the cape floral kingdom, 204 00:23:14,360 --> 00:23:17,560 a great expanse of open heath/ands 205 00:23:17,680 --> 00:23:19,400 just north of the cape. 206 00:23:22,840 --> 00:23:26,320 Here, there are more different species of plant 207 00:23:26,440 --> 00:23:29,360 than anywhere else in the world - 208 00:23:29,480 --> 00:23:33,080 nearly 9,000 - many needing pollinators. 209 00:23:37,600 --> 00:23:40,000 They compete with one another for such help 210 00:23:40,120 --> 00:23:43,360 by flaunting extravagant shapes 211 00:23:43,480 --> 00:23:45,560 and vivid colours... 212 00:23:47,120 --> 00:23:51,720 All promising nectar as a sugary reward. 213 00:23:54,560 --> 00:23:56,480 But there is a plant here 214 00:23:56,600 --> 00:24:00,240 that avoids this crowded competition. 215 00:24:02,200 --> 00:24:04,200 And the rising temperatures of summer 216 00:24:04,320 --> 00:24:06,720 bring just what it needs. 217 00:24:11,240 --> 00:24:12,880 (Flames crackle) 218 00:24:31,000 --> 00:24:34,720 This is the first fire here for 15 years. 219 00:24:44,360 --> 00:24:47,600 Nearly all the plants are destroyed. 220 00:24:53,160 --> 00:24:55,120 Incinerated. 221 00:25:03,080 --> 00:25:05,440 It might seem from the smoke 222 00:25:05,560 --> 00:25:08,560 and the still-smouldering embers that no plant 223 00:25:08,680 --> 00:25:10,640 could survive such an inferno. 224 00:25:21,240 --> 00:25:24,160 But just four days after the flames... 225 00:25:25,720 --> 00:25:28,200 Rising from the ashes... 226 00:25:33,160 --> 00:25:35,200 A fire Lily. 227 00:25:42,840 --> 00:25:46,680 It has been lying dormant underground for 15 years, 228 00:25:46,800 --> 00:25:52,400 but now, awakened by the smoke, it flowers. 229 00:26:02,200 --> 00:26:05,240 The blooms may be small and unshowy, 230 00:26:05,360 --> 00:26:08,040 but that's all they need to be. 231 00:26:09,920 --> 00:26:12,000 In this charred landscape, 232 00:26:12,120 --> 00:26:15,080 pollinators such as these sunbirds 233 00:26:15,200 --> 00:26:18,560 can spot these little red beacons from great distances. 234 00:26:23,800 --> 00:26:26,720 They're the only source of nectar around. 235 00:26:36,880 --> 00:26:40,080 And the more visitors the flowers attract, 236 00:26:40,200 --> 00:26:43,600 the more likely they are to be pollinated. 237 00:26:46,320 --> 00:26:48,680 (Birds tweet) 238 00:26:56,760 --> 00:26:58,720 It's just in time. 239 00:27:03,880 --> 00:27:09,920 Within a few months, the whole landscape is alive once more. 240 00:27:12,920 --> 00:27:18,160 In fact, all these plants need fire to survive. 241 00:27:22,440 --> 00:27:25,040 And as competitors return... 242 00:27:26,560 --> 00:27:28,680 The fire Lily fades. 243 00:27:36,680 --> 00:27:39,320 It now returns underground, 244 00:27:39,440 --> 00:27:44,920 and will rest there as a bulb until another fire awakens it. 245 00:27:53,400 --> 00:27:55,000 - (Birdsong) - (Insects buzz) 246 00:27:55,120 --> 00:27:58,320 By the time the long, hot days of summer arrive, 247 00:27:58,440 --> 00:28:03,320 wildflower meadows are bursting with life. 248 00:28:05,280 --> 00:28:08,040 But Autumn is not far away. 249 00:28:09,560 --> 00:28:13,840 So now, pollinated plants must use their remaining energy 250 00:28:13,960 --> 00:28:16,840 to produce the next generation. 251 00:28:29,280 --> 00:28:33,960 A dandelion clock contains around 200 seeds... 252 00:28:37,920 --> 00:28:40,600 Each with its own tiny parachute. 253 00:28:46,240 --> 00:28:49,600 Few seeds can fly as far as these. 254 00:28:49,720 --> 00:28:53,640 Some are known to have travelled over 60 miles. 255 00:29:00,480 --> 00:29:03,240 But to travel any distance at all, 256 00:29:03,360 --> 00:29:05,960 they need the wind to be just right. 257 00:29:11,640 --> 00:29:14,240 However, before they can get away, 258 00:29:14,360 --> 00:29:16,640 there is a risk. 259 00:29:16,760 --> 00:29:20,240 Voracious hunters live in this Meadow. 260 00:29:22,040 --> 00:29:23,880 (Sniffs) 261 00:29:44,720 --> 00:29:46,960 Tiny harvest mice. 262 00:29:48,600 --> 00:29:52,280 - They love dandelion seeds. - (Creaking) 263 00:29:58,440 --> 00:30:00,280 But they don't like to share. 264 00:30:11,920 --> 00:30:15,040 Finally, the sun warms the ground 265 00:30:15,160 --> 00:30:18,480 and a gentle breeze blows in, 266 00:30:18,600 --> 00:30:22,120 creating an ideal updraught. 267 00:30:24,800 --> 00:30:27,160 (Sniffs) 268 00:30:34,680 --> 00:30:37,280 Air flowing between the bristles 269 00:30:37,400 --> 00:30:40,680 creates a vortex that lifts the seeds up. 270 00:30:44,640 --> 00:30:47,720 Heading off on the gentle breeze, 271 00:30:47,840 --> 00:30:51,400 this seed now starts its travels. 272 00:31:19,440 --> 00:31:22,560 Plants use a variety of different techniques 273 00:31:22,680 --> 00:31:26,120 to spread their seeds as far as possible from themselves, 274 00:31:26,240 --> 00:31:29,400 and one of the most remarkable is this one. 275 00:31:29,520 --> 00:31:34,120 It's called ecballium, and it's a relative of the cucumber. 276 00:31:34,240 --> 00:31:35,960 For several weeks now, 277 00:31:36,080 --> 00:31:39,400 pressure has been building up inside the pods, 278 00:31:39,520 --> 00:31:41,320 until now they're as taut 279 00:31:41,440 --> 00:31:44,000 as a well-pumped-up bicycle tyre. 280 00:31:44,120 --> 00:31:47,080 All they need is just a slight nudge. 281 00:32:04,400 --> 00:32:07,520 The further the plant can fire its seeds, 282 00:32:07,640 --> 00:32:09,640 the better. 283 00:32:11,440 --> 00:32:14,680 If a seedling germinates close to its parent, 284 00:32:14,800 --> 00:32:18,440 the two will have to compete for nutrients and light. 285 00:32:21,760 --> 00:32:23,600 This himalayan balsam 286 00:32:23,720 --> 00:32:27,160 has seed pods that react rather differently - 287 00:32:27,280 --> 00:32:29,040 like catapults. 288 00:32:29,160 --> 00:32:32,320 As they dry out, they begin to strain 289 00:32:32,440 --> 00:32:35,920 along precisely positioned lines of weakness. 290 00:32:36,040 --> 00:32:38,520 And then just the slightest disturbance, 291 00:32:38,640 --> 00:32:40,040 even a single raindrop, 292 00:32:40,160 --> 00:32:42,000 is enough to trigger the mechanism. 293 00:33:02,800 --> 00:33:05,320 (Waves crash) 294 00:33:06,400 --> 00:33:09,280 (Seabirds call) 295 00:33:15,800 --> 00:33:18,640 The east coast of South Africa. 296 00:33:21,600 --> 00:33:24,480 Summer here brings scorching temperatures. 297 00:33:34,160 --> 00:33:37,040 This ceratocaryum has to get its seeds underground 298 00:33:37,160 --> 00:33:39,120 before it gets too hot. 299 00:33:41,800 --> 00:33:45,360 And it has acquired somewhat unlikely allies. 300 00:33:51,160 --> 00:33:53,240 Dung beetles. 301 00:33:56,080 --> 00:34:01,960 They have a particular fondness for antelope droppings. 302 00:34:05,760 --> 00:34:09,040 At this time of the year, these beetles Bury the dung 303 00:34:09,160 --> 00:34:10,760 and lay their eggs on it. 304 00:34:16,760 --> 00:34:18,800 And the fresher... 305 00:34:21,800 --> 00:34:23,200 The better. 306 00:34:28,680 --> 00:34:31,840 Ceratocaryum's spindly stems... 307 00:34:33,040 --> 00:34:35,520 Send their seeds flying. 308 00:34:56,000 --> 00:35:00,000 They're the same size, shape, 309 00:35:00,120 --> 00:35:05,600 and even smell remarkably like antelope dung. 310 00:35:19,880 --> 00:35:23,640 The beetles simply can't resist them. 311 00:35:42,320 --> 00:35:45,880 Dung beetles always Bury dung balls at the same depth, 312 00:35:46,000 --> 00:35:49,800 and it's one which suits the seeds very well. 313 00:35:59,600 --> 00:36:02,880 So effective is the seeds' deception 314 00:36:03,000 --> 00:36:06,400 that the beetles come back for more time and time again. 315 00:36:21,880 --> 00:36:26,240 Most of the ceratocaryum's seeds get safely buried... 316 00:36:28,760 --> 00:36:33,560 Exactly where they need to be. 317 00:36:52,480 --> 00:36:58,480 As the sun begins to retreat, so Autumn arrives. 318 00:37:01,720 --> 00:37:04,400 The cooler, shorter days are the cue 319 00:37:04,520 --> 00:37:06,680 for many seasonal forests 320 00:37:06,800 --> 00:37:09,680 to prepare for the winter shutdown. 321 00:37:12,960 --> 00:37:16,000 The trees start to divert their nutrients 322 00:37:16,120 --> 00:37:17,840 back into their roots. 323 00:37:19,080 --> 00:37:22,680 And there, other organisms await them. 324 00:37:29,960 --> 00:37:31,400 Fungi. 325 00:38:10,640 --> 00:38:14,800 Mushrooms are the familiar face of fungi. 326 00:38:14,920 --> 00:38:17,920 But they are merely the fruiting bodies. 327 00:38:18,040 --> 00:38:21,080 Some of them only last for a few days. 328 00:38:21,200 --> 00:38:24,920 They are, however, evidence of the giant organism 329 00:38:25,040 --> 00:38:27,240 that lies in the soil beneath. 330 00:38:27,360 --> 00:38:29,800 Just a single handful of soil 331 00:38:29,920 --> 00:38:33,240 may contain several thousand metres 332 00:38:33,360 --> 00:38:36,160 of their microscopic filaments. 333 00:38:36,280 --> 00:38:39,720 It's only recently that we have discovered 334 00:38:39,840 --> 00:38:43,600 the extraordinary role that these fungi play 335 00:38:43,720 --> 00:38:45,880 in a forest like this. 336 00:38:48,200 --> 00:38:53,360 Their filaments plug into the tips of the tree's roots, 337 00:38:53,480 --> 00:38:57,880 and nutrients pass between tree and fungus 338 00:38:58,000 --> 00:38:59,440 throughout the year. 339 00:39:00,720 --> 00:39:02,960 Some fungi have the ability 340 00:39:03,080 --> 00:39:05,480 to link with not just a single tree, 341 00:39:05,600 --> 00:39:08,680 but with a whole group of trees, 342 00:39:08,800 --> 00:39:11,320 so that the entire forest 343 00:39:11,440 --> 00:39:14,360 may be linked together by these microscopic threads 344 00:39:14,480 --> 00:39:18,160 to form what you might call a wood wide web. 345 00:39:26,200 --> 00:39:29,960 Hundreds of trees can be interconnected by these webs. 346 00:39:31,480 --> 00:39:34,800 Scientists call it the mycorrhizal network. 347 00:39:36,640 --> 00:39:39,600 And it might look something like this. 348 00:39:48,320 --> 00:39:49,960 They've discovered that trees 349 00:39:50,080 --> 00:39:51,920 not only send nutrients along it, 350 00:39:52,040 --> 00:39:54,840 but chemical and electrical signals, 351 00:39:54,960 --> 00:39:57,600 allowing them to communicate with one another. 352 00:40:00,320 --> 00:40:02,840 But some trees can also be selfish, 353 00:40:02,960 --> 00:40:05,240 and steal from their rivals... 354 00:40:06,440 --> 00:40:08,000 Oi' even wage war, 355 00:40:08,120 --> 00:40:12,800 by sending out toxins that will harm competitors. 356 00:40:19,200 --> 00:40:21,920 It seems, however, that most trees 357 00:40:22,040 --> 00:40:23,800 do try to help each other. 358 00:40:27,080 --> 00:40:30,080 They raise the alarm when attacked by leaf-eaters, 359 00:40:30,200 --> 00:40:34,800 leaving other trees time to produce defensive chemicals. 360 00:40:39,160 --> 00:40:40,960 Those that are dying 361 00:40:41,080 --> 00:40:43,880 may send their food reserves to their neighbours. 362 00:40:45,480 --> 00:40:49,480 And some individuals, known as mother trees, 363 00:40:49,600 --> 00:40:51,960 recognise their own offspring... 364 00:40:53,160 --> 00:40:55,560 And will channel resources to them... 365 00:40:59,160 --> 00:41:01,240 So giving their young 366 00:41:01,360 --> 00:41:03,760 the best possible start in life. 367 00:41:15,120 --> 00:41:16,440 (Birdsong) 368 00:41:24,200 --> 00:41:27,720 As the harshness of winter approaches... 369 00:41:29,520 --> 00:41:33,320 Temperate woodlands from Russia 370 00:41:33,440 --> 00:41:35,160 to Canada... 371 00:41:36,360 --> 00:41:40,520 Are now in a race to shut down. 372 00:41:40,640 --> 00:41:42,600 (Tick/ng) 373 00:42:06,520 --> 00:42:10,600 The green pigment in the leaves starts to break down, 374 00:42:10,720 --> 00:42:14,680 and nutrients are withdrawn into the branches. 375 00:42:16,920 --> 00:42:19,680 The chemical substances that are left behind 376 00:42:19,800 --> 00:42:24,080 then create one of the most spectacular displays of colour 377 00:42:24,200 --> 00:42:26,760 in the whole of nature. 378 00:43:14,240 --> 00:43:15,640 (Tick/ng) 379 00:43:23,400 --> 00:43:26,320 The first freezing nights of winter 380 00:43:26,440 --> 00:43:28,880 bring with them a killer. 381 00:43:32,160 --> 00:43:33,360 Frost. 382 00:43:33,480 --> 00:43:35,200 (Frost crackles) 383 00:43:39,840 --> 00:43:43,840 Stems, when frozen, rupture... 384 00:43:46,360 --> 00:43:51,640 And flowers of ice form in the chilly air. 385 00:44:24,120 --> 00:44:27,920 For some, winter brings dormancy. 386 00:44:29,480 --> 00:44:32,800 For others, it brings death. 387 00:44:43,480 --> 00:44:48,560 Another cycle of the seasons comes to an end. 388 00:44:50,520 --> 00:44:53,720 (Birdsong) 389 00:45:03,920 --> 00:45:06,520 Plants all across the seasonal world 390 00:45:06,640 --> 00:45:09,920 have developed many different strategies for success, 391 00:45:10,040 --> 00:45:15,280 but they all depend on the seasons changing reliably 392 00:45:15,400 --> 00:45:17,680 year after year. 393 00:45:17,800 --> 00:45:20,960 It doesn't matter whether you live for 3,000 years 394 00:45:21,080 --> 00:45:23,040 or just a few months, 395 00:45:23,160 --> 00:45:27,640 everything depends on you getting the timing just right. 396 00:45:31,120 --> 00:45:33,120 But in our changing world, 397 00:45:33,240 --> 00:45:36,920 this is becoming a greater challenge every year... 398 00:45:39,400 --> 00:45:43,040 And even the most Hardy and resilient of plants 399 00:45:43,160 --> 00:45:44,800 are starting to struggle. 400 00:45:54,160 --> 00:45:59,880 These sequoia trees are the giants of the natural world. 401 00:46:00,000 --> 00:46:03,680 The largest living things on the planet. 402 00:46:03,800 --> 00:46:07,960 They can grow to almost 100 metres tall 403 00:46:08,080 --> 00:46:09,760 and 11 metres across. 404 00:46:12,480 --> 00:46:15,960 Their bark alone can be over a half a metre thick. 405 00:46:17,280 --> 00:46:19,840 They're also among the oldest, 406 00:46:19,960 --> 00:46:24,080 some living to over 3,000 years. 407 00:46:24,200 --> 00:46:27,000 And to achieve such age and size, 408 00:46:27,120 --> 00:46:29,960 they need very particular living conditions, 409 00:46:30,080 --> 00:46:31,920 such as a farm here 410 00:46:32,040 --> 00:46:35,480 in the Sierra Nevada mountains of California. 411 00:46:40,400 --> 00:46:44,920 Not only do they need energy from the sun, but, critically, 412 00:46:45,040 --> 00:46:50,280 they also require up to 4,000 litres of water a day, 413 00:46:50,400 --> 00:46:52,960 so they are almost entirely reliant 414 00:46:53,080 --> 00:46:55,640 on the seasonal snowmelt. 415 00:47:02,640 --> 00:47:06,360 But recent years have brought longer, hotter summers, 416 00:47:06,480 --> 00:47:08,160 and their source of water 417 00:47:08,280 --> 00:47:11,120 is becoming increasingly unreliable. 418 00:47:16,760 --> 00:47:19,800 Scientists are discovering that 419 00:47:19,920 --> 00:47:23,200 even these seemingly indestructible giants 420 00:47:23,320 --> 00:47:27,720 are now starting to show signs of vulnerability. 421 00:47:29,440 --> 00:47:32,440 Some are shedding their needles and branches 422 00:47:32,560 --> 00:47:36,400 as a way of conserving precious water. 423 00:47:46,280 --> 00:47:51,520 But for others, climate change has already been fatal. 424 00:47:51,640 --> 00:47:57,080 10% of them have been lost in just the last few years. 425 00:48:07,440 --> 00:48:11,080 A single giant sequoia in its lifetime 426 00:48:11,200 --> 00:48:15,720 can produce 100 million seeds. 427 00:48:15,840 --> 00:48:18,600 These in my hand, from one cone, 428 00:48:18,720 --> 00:48:22,360 are more than enough to start a completely new forest. 429 00:48:25,040 --> 00:48:27,040 But they can only do such a thing 430 00:48:27,160 --> 00:48:31,680 in a world where the seasons change with some reliability. 431 00:48:33,720 --> 00:48:36,200 Today, our climate is changing, 432 00:48:36,320 --> 00:48:40,680 bringing an unprecedented level of unpredictability 433 00:48:40,800 --> 00:48:43,920 all across the seasonal world. 434 00:48:46,280 --> 00:48:51,360 The question is, can we curb climate change sufficiently 435 00:48:51,480 --> 00:48:55,200 to ensure that the seasons will continue? 436 00:48:55,320 --> 00:48:57,840 Only if we can do that 437 00:48:57,960 --> 00:49:00,000 will the future of seasonal plants, 438 00:49:00,120 --> 00:49:03,480 including these magnificent trees, be assured. 439 00:49:26,400 --> 00:49:29,280 David Attenborough: During filming the green planet, 440 00:49:29,400 --> 00:49:30,600 it wasn't only the plants 441 00:49:30,720 --> 00:49:32,880 that struggled to get their timing right. 442 00:49:33,000 --> 00:49:37,720 The increasing unpredictability of the seasons made it 443 00:49:37,840 --> 00:49:39,960 frustratingly difficult for the crew 444 00:49:40,080 --> 00:49:42,320 to be in the right place at the right time. 445 00:49:42,440 --> 00:49:44,640 Whether at the height of summer... 446 00:49:44,760 --> 00:49:50,040 Alistair: We are in the middle of a biblical rainstorm. 447 00:49:50,160 --> 00:49:53,080 Or a quiet autumnal afternoon... 448 00:49:53,200 --> 00:49:55,880 Jonny: This is crazy! Hurricanes are no joke. 449 00:49:56,000 --> 00:49:58,720 They were always kept on their toes. 450 00:49:59,800 --> 00:50:01,120 Jonny: That's really scary! 451 00:50:01,240 --> 00:50:02,600 Ooh! 452 00:50:03,760 --> 00:50:05,760 Sometimes very numb ones. 453 00:50:07,800 --> 00:50:10,920 It's been the most snow they've had for 38 years. 454 00:50:11,040 --> 00:50:13,720 And I think this is now our fifth filming trip 455 00:50:13,840 --> 00:50:17,200 in a row where the seasons haven't done 456 00:50:17,320 --> 00:50:19,760 what they're predictably meant to do every year. 457 00:50:21,200 --> 00:50:23,200 And these challenges continue 458 00:50:23,320 --> 00:50:27,200 in attempting to find and film an elusive plant 459 00:50:27,320 --> 00:50:30,480 with a remarkable survival strategy - 460 00:50:30,600 --> 00:50:32,560 the fire Lily. 461 00:50:42,440 --> 00:50:45,160 Somewhere out there is a tiny, tiny red plant... 462 00:50:46,560 --> 00:50:48,880 In all of that. 463 00:50:57,560 --> 00:51:01,680 Travelling to South Africa at the height of summer... 464 00:51:02,960 --> 00:51:06,920 The crew witnessed many extraordinary flowers 465 00:51:07,040 --> 00:51:08,240 bursting into bloom. 466 00:51:10,000 --> 00:51:14,920 But if they are to see a fire Lily, they need a fire. 467 00:51:17,880 --> 00:51:20,560 None of the team have filmed wildfire before - 468 00:51:20,680 --> 00:51:23,040 not something to be underestimated. 469 00:51:24,480 --> 00:51:27,080 In most cases with wildfires, 470 00:51:27,200 --> 00:51:29,000 when they go wrong, they go wrong radically. 471 00:51:29,120 --> 00:51:30,160 And it's very unforgiving. 472 00:51:30,240 --> 00:51:32,000 If you get caught on the wrong side of a fire 473 00:51:32,040 --> 00:51:34,160 because you want to get that special shot, 474 00:51:34,280 --> 00:51:35,920 there's a possibility you can get killed, 475 00:51:36,040 --> 00:51:37,480 that's really what it comes down to. 476 00:51:37,600 --> 00:51:41,000 And after some understandably studious note-taking... 477 00:51:42,880 --> 00:51:45,480 It's time to put their training to the test. 478 00:51:45,600 --> 00:51:47,080 (Horn beeps) 479 00:51:54,240 --> 00:51:56,240 (Fire crackles) 480 00:51:56,360 --> 00:51:59,320 Alistair: The fire's just racing up a gully behind me. 481 00:51:59,440 --> 00:52:01,000 The heat is intense. 482 00:52:01,120 --> 00:52:02,800 You can't even stand to be, 483 00:52:02,920 --> 00:52:04,720 like, five metres from it. Ifsinsane. 484 00:52:07,240 --> 00:52:09,440 (Fire whooshes) 485 00:52:11,600 --> 00:52:15,920 This is what any fire lilies here should be waiting for. 486 00:52:21,880 --> 00:52:24,040 (Wind roars) 487 00:52:25,200 --> 00:52:26,400 Jeepers. 488 00:52:27,680 --> 00:52:30,600 But fynbos wildfires are starting to become 489 00:52:30,720 --> 00:52:32,560 fiercer than in the past... 490 00:52:34,160 --> 00:52:38,480 Something fire chief reinard geldenhuys knows first-hand. 491 00:52:38,600 --> 00:52:39,920 Nowadays, 492 00:52:40,040 --> 00:52:42,720 we're experiencing more extreme temperature conditions 493 00:52:42,840 --> 00:52:45,320 and more extreme wind conditions, 494 00:52:45,440 --> 00:52:48,160 which exacerbates a fynbos fire. 495 00:52:49,760 --> 00:52:54,480 A fynbos fire in full tilt with a strong wind behind it 496 00:52:54,600 --> 00:52:56,440 is an animal that's just running wild. 497 00:52:57,920 --> 00:52:59,080 It's a very frightening sight 498 00:52:59,200 --> 00:53:00,640 if you're standing in front of it. 499 00:53:06,720 --> 00:53:10,240 Guided by the experience of the fire crew, 500 00:53:10,360 --> 00:53:12,440 the team are able to safely capture 501 00:53:12,560 --> 00:53:14,280 the full fury of the Blaze. 502 00:53:18,280 --> 00:53:22,760 It's given me a complete, new appreciation for fire, 503 00:53:22,880 --> 00:53:24,800 how intensely it burns 504 00:53:24,920 --> 00:53:27,200 and how quickly it roars through this environment. 505 00:53:28,840 --> 00:53:31,600 And the fact that any plants can survive afterwards 506 00:53:31,720 --> 00:53:34,480 is just... yeah, it's crazy. 507 00:53:38,240 --> 00:53:39,840 As destructive as it seems, 508 00:53:39,960 --> 00:53:43,440 the fire has been part of this ecosystem for millennia. 509 00:53:43,560 --> 00:53:47,720 Fires should refresh and regenerate the landscape. 510 00:53:49,240 --> 00:53:51,960 Worryingly, however, this fine balance 511 00:53:52,080 --> 00:53:55,480 between plant and fire is beginning to shift. 512 00:53:56,520 --> 00:54:00,040 More extreme wildfires may spell disaster. 513 00:54:02,160 --> 00:54:03,960 If you disturb the soil in a fynbos system, 514 00:54:04,080 --> 00:54:05,640 you're going to lose a lot of species. 515 00:54:05,760 --> 00:54:09,840 Bigger, hotter fires can burn the soil layer 516 00:54:09,960 --> 00:54:12,360 and burn out all the seeds. 517 00:54:12,480 --> 00:54:14,080 And for the species that have 518 00:54:14,200 --> 00:54:16,800 these really intricate strategies, like the fire Lily, 519 00:54:16,920 --> 00:54:19,280 it really is a difficult game. 520 00:54:21,120 --> 00:54:24,280 Every year is getting hotter and potentially drier, 521 00:54:24,400 --> 00:54:27,200 so it's kind of becoming Russian roulette 522 00:54:27,320 --> 00:54:29,120 for a lot of the species here. 523 00:54:39,520 --> 00:54:41,360 In the fire's aftermath, 524 00:54:41,480 --> 00:54:44,400 the crew must now try to find a tiny flower. 525 00:54:46,240 --> 00:54:49,160 But have any survived the Blaze? 526 00:54:49,280 --> 00:54:50,800 It just looks completely dead. 527 00:54:50,920 --> 00:54:52,280 The whole valley. 528 00:54:58,440 --> 00:55:01,920 There's nothing for it but to get their hands dirty. 529 00:55:03,600 --> 00:55:07,640 Searching in the ash is a grubby business. 530 00:55:07,760 --> 00:55:09,520 (Sighs) 531 00:55:14,360 --> 00:55:16,000 Disgusting. 532 00:55:17,640 --> 00:55:20,600 After scouring this mountainside just days 533 00:55:20,720 --> 00:55:22,200 after it burned, 534 00:55:22,320 --> 00:55:26,640 they finally find the first signs of regeneration. 535 00:55:29,680 --> 00:55:31,880 Wow. That's what it's all about! 536 00:55:32,000 --> 00:55:33,320 That's the fire Lily. 537 00:55:33,440 --> 00:55:37,440 It's like a proper bright red against all the black. 538 00:55:37,560 --> 00:55:39,160 I mean, that's amazing. 539 00:55:39,280 --> 00:55:40,960 There's another one over there, 540 00:55:41,080 --> 00:55:43,200 and there's another one behind those. 541 00:55:44,640 --> 00:55:47,200 This place hasn't burned for 15 years, 542 00:55:47,320 --> 00:55:50,440 so they've been sat underground waiting for this precise moment 543 00:55:50,560 --> 00:55:52,920 for that entire time, and then within two weeks, 544 00:55:53,040 --> 00:55:55,800 they're up and they're flowering. It's incredible. 545 00:55:57,000 --> 00:56:00,720 This time, the fire lilies here succeeded in flowering, 546 00:56:00,840 --> 00:56:03,840 but in the 15 years since they last bloomed, 547 00:56:03,960 --> 00:56:08,200 the earth has experienced ten of the warmest years on record. 548 00:56:09,640 --> 00:56:12,000 You know, there's huge debates about climate change, 549 00:56:12,120 --> 00:56:14,160 how real is it really, and so on. 550 00:56:14,280 --> 00:56:15,760 Erm... 551 00:56:15,880 --> 00:56:17,400 We experience it in the fire. 552 00:56:17,520 --> 00:56:21,320 It's more intense, it burns easier, it burns longer. 553 00:56:22,880 --> 00:56:25,480 In the past, we used to have one big fire per season, 554 00:56:25,600 --> 00:56:28,480 and we said, "yo, that was a big one." 555 00:56:28,600 --> 00:56:31,680 Now we have five to six big ones per season. 556 00:56:33,120 --> 00:56:35,840 If we don't change our ways, we are going to reach a point 557 00:56:35,960 --> 00:56:38,440 where fires are burning with such ferocity 558 00:56:38,560 --> 00:56:40,760 that it will destroy thelandscape. 559 00:56:42,720 --> 00:56:46,440 And in recent times, a rapidly changing climate 560 00:56:46,560 --> 00:56:49,800 has led to some of the biggest fires in living memory, 561 00:56:49,920 --> 00:56:54,280 not just in South Africa, but around the world. 562 00:56:54,400 --> 00:56:57,920 The next five to ten years are going to be pretty scary 563 00:56:58,040 --> 00:57:01,800 to actually see what this has done to the ecosystem. 564 00:57:01,920 --> 00:57:06,280 Let's hope that the next time this fire Lily blooms, 565 00:57:06,400 --> 00:57:09,840 it'll find a world in which it can still survive.