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