1 00:00:56,620 --> 00:00:59,740 This is the boreal forest... 2 00:01:04,820 --> 00:01:07,380 ..the largest forest on Earth. 3 00:01:09,100 --> 00:01:12,740 750 billion trees... 4 00:01:15,500 --> 00:01:18,860 ..smothered by snow throughout the winter. 5 00:01:23,940 --> 00:01:28,780 This is the northernmost boundary of an extraordinary world. 6 00:01:32,500 --> 00:01:37,140 I'm standing at the edge of the Arctic Circle. 7 00:01:37,140 --> 00:01:41,700 To the north of me lies a land dominated for most of the year 8 00:01:41,700 --> 00:01:43,860 by snow and ice. 9 00:01:43,860 --> 00:01:47,620 3,000 miles to the south - the tropics, 10 00:01:47,620 --> 00:01:51,660 bathed the year round in warm sunshine. 11 00:01:51,660 --> 00:01:55,300 And in between, a very different world, 12 00:01:55,300 --> 00:01:58,780 dominated by relentless change. 13 00:02:04,660 --> 00:02:08,660 An endless cycle of four distinct seasons, 14 00:02:08,660 --> 00:02:11,020 each with its own challenges. 15 00:02:12,620 --> 00:02:15,260 The short, freezing days of winter 16 00:02:15,260 --> 00:02:19,220 give way to the urgent awakening of spring. 17 00:02:22,060 --> 00:02:25,620 And the long, hot days of summer 18 00:02:25,620 --> 00:02:28,780 yield to the cooling of autumn. 19 00:02:33,340 --> 00:02:36,180 Opportunities will be brief. 20 00:02:43,660 --> 00:02:45,700 To survive these extremes, 21 00:02:45,700 --> 00:02:49,940 plants have not only got to be hardy and resilient, 22 00:02:49,940 --> 00:02:53,420 but many of them have developed special strategies 23 00:02:53,420 --> 00:02:57,740 in order to meet the demands of this seasonal world. 24 00:02:59,900 --> 00:03:04,180 To succeed, they must get their timing just right. 25 00:03:07,220 --> 00:03:10,860 For months now, this world has been asleep. 26 00:03:12,100 --> 00:03:14,460 But change is coming. 27 00:03:29,820 --> 00:03:32,740 Spring is on its way. 28 00:03:55,780 --> 00:03:59,980 In Canada, the forests are starting to stir. 29 00:04:02,180 --> 00:04:05,620 Throughout the winter, the sugar maples here 30 00:04:05,620 --> 00:04:09,980 have kept stores of nutrients ready for this moment. 31 00:04:12,820 --> 00:04:16,100 Now, as temperatures start to rise, 32 00:04:16,100 --> 00:04:19,660 those nutrients must be brought up from the roots. 33 00:04:27,180 --> 00:04:29,660 Sap is on the rise. 34 00:04:35,180 --> 00:04:37,980 Fuel for new green growth. 35 00:04:49,180 --> 00:04:51,780 But just as growth reaches full speed... 36 00:04:53,340 --> 00:04:55,380 ..robbers arrive. 37 00:05:15,260 --> 00:05:17,860 A sap sucker. 38 00:05:17,860 --> 00:05:22,140 A thief in search of maple syrup. 39 00:05:39,820 --> 00:05:42,780 The tree can tolerate hundreds of wounds. 40 00:05:50,140 --> 00:05:53,940 But if they completely encircle the trunk, 41 00:05:53,940 --> 00:05:57,180 the tree will eventually die. 42 00:06:04,420 --> 00:06:08,300 The sap sucker's break-in hasn't gone unnoticed. 43 00:06:17,420 --> 00:06:23,820 Hummingbirds, squirrels and insects 44 00:06:23,820 --> 00:06:27,140 all invade the sap sucker's territory, 45 00:06:27,140 --> 00:06:29,180 trying to steal a meal. 46 00:06:33,380 --> 00:06:36,380 But unwittingly, they help the tree. 47 00:06:42,300 --> 00:06:44,860 Time spent chasing the competition... 48 00:06:46,580 --> 00:06:49,940 ..means less time to drill new holes. 49 00:07:19,700 --> 00:07:23,580 The tree gets a chance to repair its wounds. 50 00:07:25,780 --> 00:07:28,700 And the sap can rise freely again. 51 00:07:36,060 --> 00:07:41,180 So this year, at least, the tree will once more produce its leaves. 52 00:07:45,780 --> 00:07:48,500 Hundreds of miniature solar panels 53 00:07:48,500 --> 00:07:50,860 that collect energy from the sunlight. 54 00:07:54,340 --> 00:07:58,700 Each leaf is covered by millions of microscopic pores. 55 00:07:59,860 --> 00:08:01,700 Stomata. 56 00:08:04,460 --> 00:08:07,340 They take in carbon dioxide... 57 00:08:08,980 --> 00:08:11,900 ..and release oxygen and water vapour 58 00:08:11,900 --> 00:08:15,580 in a process that produces high-energy fuel. 59 00:08:27,980 --> 00:08:31,060 All the trees here can now use that fuel 60 00:08:31,060 --> 00:08:33,500 to grow over the coming months. 61 00:08:52,780 --> 00:08:57,860 As spring proceeds, the power of the sun increases. 62 00:09:01,540 --> 00:09:03,740 On river banks across Europe, 63 00:09:03,740 --> 00:09:09,140 many plants have been lying dormant underground, 64 00:09:09,140 --> 00:09:11,820 waiting for the earth to warm. 65 00:09:18,300 --> 00:09:20,900 And now a race begins. 66 00:09:28,140 --> 00:09:32,980 Among the first to start are nettles - the sprinters. 67 00:09:38,620 --> 00:09:42,580 Then, only just behind, come the brambles. 68 00:09:43,900 --> 00:09:47,500 They're much more aggressive and have backward-pointed hooks 69 00:09:47,500 --> 00:09:50,460 with which to scramble over their rivals. 70 00:09:53,220 --> 00:09:56,260 Last to come - the climbers. 71 00:09:59,540 --> 00:10:01,860 Hops... 72 00:10:01,860 --> 00:10:03,900 ..and bryony. 73 00:10:07,540 --> 00:10:10,580 They lasso their way towards the light. 74 00:10:39,700 --> 00:10:44,540 Soon, every inch of space and every patch of light has been claimed. 75 00:10:48,020 --> 00:10:49,820 But hidden in the shadows, 76 00:10:49,820 --> 00:10:53,700 another plant has been waiting to make its move. 77 00:11:03,180 --> 00:11:06,260 This... 78 00:11:06,260 --> 00:11:08,300 ..is dodder. 79 00:11:14,460 --> 00:11:16,500 A hunter... 80 00:11:18,140 --> 00:11:20,660 ..with an exceptional sense of smell. 81 00:11:27,820 --> 00:11:31,300 Moving swiftly, it searches for its prey. 82 00:11:34,660 --> 00:11:37,500 It detects the scent of a young nettle. 83 00:11:56,780 --> 00:12:00,260 The dodder punctures the nettle's stem 84 00:12:00,260 --> 00:12:02,780 and sucks out the nutritious sap. 85 00:12:06,620 --> 00:12:09,460 And it doesn't stop at just one victim. 86 00:12:12,700 --> 00:12:15,460 With its energy supply assured, 87 00:12:15,460 --> 00:12:17,500 it multiplies. 88 00:12:26,420 --> 00:12:30,100 It's a parasite with an insatiable appetite. 89 00:13:32,300 --> 00:13:37,940 But remarkably, its victims can now exploit the dodder... 90 00:13:40,020 --> 00:13:42,820 ..when other springtime enemies appear. 91 00:13:46,820 --> 00:13:48,860 Caterpillars. 92 00:14:00,060 --> 00:14:03,700 When under attack, a leaf sends out a signal 93 00:14:03,700 --> 00:14:07,460 telling the rest of the plant to start building defences... 94 00:14:10,380 --> 00:14:14,340 ..foul-tasting toxins that deter the caterpillars. 95 00:14:17,380 --> 00:14:19,780 In an extraordinary twist, 96 00:14:19,780 --> 00:14:23,060 the stems of the dodder interconnecting the plants 97 00:14:23,060 --> 00:14:26,780 are now being used as lines of communication 98 00:14:26,780 --> 00:14:31,340 to relay these warning signals from plant to plant. 99 00:14:37,780 --> 00:14:41,940 They respond by producing their own protective chemicals. 100 00:14:45,940 --> 00:14:51,220 Eventually, the whole river bank becomes one huge defensive network. 101 00:14:52,740 --> 00:14:56,700 And the one-time rivals are now better off together. 102 00:15:18,300 --> 00:15:23,780 The first warm days of spring encourage some plants to flower 103 00:15:23,780 --> 00:15:26,180 and get ahead of the competition... 104 00:15:27,740 --> 00:15:32,380 ..creating beautiful displays throughout the seasonal world. 105 00:15:35,060 --> 00:15:38,380 From the spectacular cherry blossoms of Japan... 106 00:15:41,620 --> 00:15:45,460 ..to the goldfield flowers of California. 107 00:15:49,700 --> 00:15:52,420 But spring flowering is risky. 108 00:15:52,420 --> 00:15:55,260 If they flower too early, it may not be warm enough 109 00:15:55,260 --> 00:15:57,700 for pollinating insects to be active. 110 00:15:59,620 --> 00:16:03,740 But the common daisy gives them every opportunity. 111 00:16:07,580 --> 00:16:11,500 The warmer the flowers are, the more attractive they are - 112 00:16:11,500 --> 00:16:15,980 and they have a remarkable strategy in order to maximise this. 113 00:16:17,900 --> 00:16:21,460 They were closed up tightly throughout the night 114 00:16:21,460 --> 00:16:23,820 as a protection against the elements. 115 00:16:23,820 --> 00:16:27,500 But once they feel the warmth and the light of the sun, 116 00:16:27,500 --> 00:16:29,540 they spring into action. 117 00:16:43,940 --> 00:16:46,700 It's a behaviour called heliotropism. 118 00:16:48,660 --> 00:16:52,580 They turn to keep facing the sun, 119 00:16:52,580 --> 00:16:55,340 absorbing as much heat as they can. 120 00:17:12,100 --> 00:17:15,620 This is a thermal camera, 121 00:17:15,620 --> 00:17:21,060 and it will tell me the difference between the surrounding temperature 122 00:17:21,060 --> 00:17:25,180 and the temperature in the centre of a daisy flower. 123 00:17:25,180 --> 00:17:28,500 The surroundings - 12 degrees. 124 00:17:30,180 --> 00:17:32,300 In the centre of a flower... 125 00:17:34,020 --> 00:17:36,140 ..21. 126 00:17:38,100 --> 00:17:43,620 Pollinators such as bees and wasps prefer the warmed-up flowers 127 00:17:43,620 --> 00:17:46,540 because they can get a share of the heat for themselves. 128 00:17:48,420 --> 00:17:52,580 As a consequence, they can collect more nectar from more flowers, 129 00:17:52,580 --> 00:17:54,620 pollinating as they go. 130 00:17:57,580 --> 00:18:00,940 And the daisies, with the help of their pollinators, 131 00:18:00,940 --> 00:18:04,260 are able to have a particularly long flowering season. 132 00:18:07,420 --> 00:18:10,660 But when the window of opportunity is brief, 133 00:18:10,660 --> 00:18:13,340 even more ingenious tactics are necessary. 134 00:18:26,820 --> 00:18:29,340 Here in south-western Australia, 135 00:18:29,340 --> 00:18:33,380 summer temperatures can soar to up to 40 degrees Celsius. 136 00:18:44,140 --> 00:18:47,340 Now, for a brief moment in the cooler spring, 137 00:18:47,340 --> 00:18:49,540 flowering plants must get busy. 138 00:18:54,980 --> 00:18:58,540 And this hammer orchid, with its strange flower, 139 00:18:58,540 --> 00:19:00,580 is doing exactly that. 140 00:19:04,100 --> 00:19:06,660 It needs to attract a pollinator, 141 00:19:06,660 --> 00:19:10,100 but has no nectar and doesn't even look like a flower. 142 00:19:13,500 --> 00:19:16,660 Unlike these neighbouring huge grass trees. 143 00:19:21,780 --> 00:19:24,780 These produce thousands of tiny white flowers, 144 00:19:24,780 --> 00:19:26,820 all dripping with nectar. 145 00:19:34,260 --> 00:19:37,140 But the orchid has a different strategy. 146 00:19:39,460 --> 00:19:45,060 It synchronises its emergence with the brief mating season 147 00:19:45,060 --> 00:19:47,540 of the thynnid wasp. 148 00:19:53,020 --> 00:19:58,940 The flightless female wasp produces pheromones to attract males. 149 00:20:07,340 --> 00:20:11,100 This male detects a scent that seems to be hers... 150 00:20:19,180 --> 00:20:21,860 ..yet flies right on by. 151 00:20:28,300 --> 00:20:33,140 The orchid not only has the same shape and colour as a female wasp, 152 00:20:33,140 --> 00:20:35,820 but it sits at the same height as she does. 153 00:20:37,780 --> 00:20:39,820 It even mimics her smell. 154 00:20:42,060 --> 00:20:46,380 And the beguiled male attempts to mate with it. 155 00:21:02,340 --> 00:21:05,660 He hammers against the orchid's pollen sacks. 156 00:21:11,020 --> 00:21:14,700 And the wasp leaves, doubtless a little shaken... 157 00:21:17,780 --> 00:21:19,940 ..only to be duped once again. 158 00:21:30,580 --> 00:21:33,940 The pollen on his back now sticks to this different orchid. 159 00:21:35,580 --> 00:21:38,100 And the deception has worked. 160 00:21:41,500 --> 00:21:46,940 The orchid's imitation is even more intoxicating, it seems, 161 00:21:46,940 --> 00:21:48,980 than the real thing. 162 00:22:09,380 --> 00:22:13,860 Eventually, the male wasps tire of the orchid's enticements. 163 00:22:17,900 --> 00:22:21,540 {\an8}And now, the wasps, both male and female, 164 00:22:21,540 --> 00:22:24,700 {\an8}find the flowers of the grass trees to feed. 165 00:22:26,940 --> 00:22:28,980 And there, at long last... 166 00:22:31,340 --> 00:22:33,380 ..they mate. 167 00:22:39,380 --> 00:22:41,420 And as for the hammer orchid? 168 00:22:43,180 --> 00:22:45,380 Pollination is complete. 169 00:22:58,220 --> 00:23:03,620 As summer approaches, the need to flower becomes more urgent. 170 00:23:05,140 --> 00:23:11,340 And nowhere more so than here in South Africa. 171 00:23:15,180 --> 00:23:19,900 This is the fynbos, part of the Cape floral kingdom, 172 00:23:19,900 --> 00:23:24,220 a great expanse of open heathlands just north of the cape. 173 00:23:27,620 --> 00:23:30,460 Here there are more different species of plant 174 00:23:30,460 --> 00:23:32,500 than anywhere else in the world. 175 00:23:34,060 --> 00:23:37,820 Nearly 9,000, many needing pollinators. 176 00:23:42,300 --> 00:23:45,020 They compete with one another for such help 177 00:23:45,020 --> 00:23:49,820 by flaunting extravagant shapes and vivid colours. 178 00:23:51,780 --> 00:23:55,620 All promising nectar as a sugary reward. 179 00:23:59,620 --> 00:24:04,180 But there is a plant here that avoids this crowded competition. 180 00:24:06,700 --> 00:24:11,500 And the rising temperatures of summer bring just what it needs. 181 00:24:35,700 --> 00:24:39,340 This is the first fire here for 15 years. 182 00:24:49,620 --> 00:24:52,220 Nearly all the plants are destroyed. 183 00:24:57,660 --> 00:24:59,700 Incinerated. 184 00:25:08,460 --> 00:25:12,020 It might seem from the smoke and the still-smouldering embers 185 00:25:12,020 --> 00:25:15,180 that no plant could survive such an inferno. 186 00:25:25,740 --> 00:25:28,820 But just four days after the flames... 187 00:25:30,540 --> 00:25:32,580 ..rising from the ashes... 188 00:25:37,900 --> 00:25:39,940 ..a fire lily. 189 00:25:47,340 --> 00:25:52,140 It has been lying dormant underground for 15 years, 190 00:25:52,140 --> 00:25:56,780 but now, awakened by the smoke, it flowers. 191 00:26:06,900 --> 00:26:11,820 {\an8}The blooms may be small and unshowy, but that's all they need to be. 192 00:26:15,020 --> 00:26:19,420 In this charred landscape, pollinators, such as these sunbirds, 193 00:26:19,420 --> 00:26:23,380 can spot these little red beacons from great distances. 194 00:26:28,300 --> 00:26:31,420 They're the only source of nectar around. 195 00:26:42,340 --> 00:26:44,780 And the more visitors the flowers attract, 196 00:26:44,780 --> 00:26:47,580 the more likely they are to be pollinated. 197 00:27:01,300 --> 00:27:03,340 It's just in time. 198 00:27:08,780 --> 00:27:14,420 Within a few months, the whole landscape is alive once more. 199 00:27:17,980 --> 00:27:22,100 In fact, all these plants need fire to survive. 200 00:27:27,380 --> 00:27:31,180 And as competitors return, 201 00:27:31,180 --> 00:27:33,220 the fire lily fades. 202 00:27:41,500 --> 00:27:44,060 It now returns underground 203 00:27:44,060 --> 00:27:49,100 and will rest there as a bulb until another fire awakens it. 204 00:27:59,500 --> 00:28:03,740 By the time the long, hot days of summer arrive, 205 00:28:03,740 --> 00:28:07,900 wild flower meadows are bursting with life. 206 00:28:10,140 --> 00:28:12,660 But autumn is not far away. 207 00:28:14,540 --> 00:28:19,140 So now pollinated plants must use their remaining energy 208 00:28:19,140 --> 00:28:21,660 to produce the next generation. 209 00:28:23,740 --> 00:28:25,780 Seeds. 210 00:28:33,620 --> 00:28:37,900 A dandelion clock contains around 200 seeds... 211 00:28:42,980 --> 00:28:45,380 ..each with its own tiny parachute. 212 00:28:51,460 --> 00:28:54,220 Few seeds can fly as far as these. 213 00:28:54,220 --> 00:28:57,860 Some are known to have travelled over 60 miles. 214 00:29:05,300 --> 00:29:10,380 But to travel any distance at all, they need the wind to be just right. 215 00:29:16,700 --> 00:29:20,340 However, before they can get away, there is a risk. 216 00:29:21,460 --> 00:29:24,540 Voracious hunters live in this meadow. 217 00:29:49,580 --> 00:29:51,620 Tiny harvest mice. 218 00:29:53,500 --> 00:29:55,900 They love dandelion seeds. 219 00:30:02,940 --> 00:30:04,980 But they don't like to share. 220 00:30:16,260 --> 00:30:20,380 Finally, the sun warms the ground 221 00:30:20,380 --> 00:30:23,380 and a gentle breeze blows in, 222 00:30:23,380 --> 00:30:26,180 creating an ideal updraught. 223 00:30:39,660 --> 00:30:43,260 Air flowing between the bristles creates a vortex 224 00:30:43,260 --> 00:30:45,300 that lifts the seeds up. 225 00:30:49,820 --> 00:30:55,940 Heading off on a gentle breeze, this seed now starts its travels. 226 00:31:24,100 --> 00:31:27,220 Plants use a variety of different techniques 227 00:31:27,220 --> 00:31:31,180 to spread their seeds as far as possible from themselves. 228 00:31:31,180 --> 00:31:34,300 And one of the most remarkable is this one. 229 00:31:34,300 --> 00:31:39,060 It's called ecballium, and it's a relative of the cucumber. 230 00:31:39,060 --> 00:31:43,580 For several weeks now, pressure has been building up inside the pods. 231 00:31:43,580 --> 00:31:48,340 Until now, they're as taut as a well-pumped-up bicycle tyre. 232 00:31:48,340 --> 00:31:51,620 All they need is just a slight nudge. 233 00:31:55,860 --> 00:31:57,900 HE LAUGHS 234 00:32:09,460 --> 00:32:14,220 The further the plant can fire its seeds, the better. 235 00:32:15,900 --> 00:32:19,180 If a seedling germinates close to its parent, 236 00:32:19,180 --> 00:32:22,940 the two will have to compete for nutrients and light. 237 00:32:26,380 --> 00:32:32,020 This Himalayan balsam has seed pods that react rather differently, 238 00:32:32,020 --> 00:32:34,140 like catapults. 239 00:32:34,140 --> 00:32:38,340 As they dry out, they begin to strain along precisely positioned 240 00:32:38,340 --> 00:32:40,380 lines of weakness. 241 00:32:40,380 --> 00:32:42,940 And then, just the slightest disturbance, 242 00:32:42,940 --> 00:32:47,140 even a single raindrop, is enough to trigger the mechanism. 243 00:33:20,420 --> 00:33:23,140 The east coast of South Africa. 244 00:33:26,100 --> 00:33:29,060 Summer here brings scorching temperatures. 245 00:33:38,860 --> 00:33:42,300 This Ceratocaryum has to get its seeds underground 246 00:33:42,300 --> 00:33:44,340 before it gets too hot. 247 00:33:46,700 --> 00:33:49,980 And it has acquired somewhat unlikely allies. 248 00:33:56,420 --> 00:33:58,460 Dung beetles. 249 00:34:01,580 --> 00:34:06,540 They have a particular fondness for antelope droppings. 250 00:34:10,460 --> 00:34:13,860 At this time of the year, these beetles bury the dung 251 00:34:13,860 --> 00:34:15,900 and lay their eggs on it. 252 00:34:22,420 --> 00:34:24,460 And the fresher... 253 00:34:26,700 --> 00:34:28,740 ..the better. 254 00:34:33,620 --> 00:34:39,460 Ceratocaryum's spindly stems send their seeds flying. 255 00:35:01,260 --> 00:35:04,620 They're the same size, shape 256 00:35:04,620 --> 00:35:07,780 and even smell remarkably like... 257 00:35:09,100 --> 00:35:11,140 ..antelope dung. 258 00:35:24,620 --> 00:35:28,060 The beetles simply can't resist them. 259 00:35:46,940 --> 00:35:51,220 Dung beetles always bury dung balls at the same depth. 260 00:35:51,220 --> 00:35:54,380 And it's one which suits the seeds very well. 261 00:36:04,140 --> 00:36:07,020 So effective is the seed's deception 262 00:36:07,020 --> 00:36:10,980 that the beetles come back for more time and time again. 263 00:36:26,700 --> 00:36:31,260 Most of the Ceratocaryum seeds get safely buried... 264 00:36:34,700 --> 00:36:38,140 ..exactly where they need to be. 265 00:36:57,580 --> 00:37:03,020 As the sun begins to retreat, so autumn arrives. 266 00:37:06,260 --> 00:37:11,540 The cooler, shorter days are the cue for many seasonal forests 267 00:37:11,540 --> 00:37:14,180 to prepare for the winter shutdown. 268 00:37:17,740 --> 00:37:22,340 The trees start to divert their nutrients back into their roots. 269 00:37:24,100 --> 00:37:27,220 And there, other organisms await them. 270 00:37:34,700 --> 00:37:36,740 Fungi. 271 00:38:15,460 --> 00:38:19,980 Mushrooms are the familiar face of fungi, 272 00:38:19,980 --> 00:38:22,620 but they are merely the fruiting bodies. 273 00:38:22,620 --> 00:38:26,060 Some of them only last for a few days. 274 00:38:26,060 --> 00:38:30,100 They are, however, evidence of the giant organism 275 00:38:30,100 --> 00:38:32,660 that lies in the soil beneath. 276 00:38:32,660 --> 00:38:37,940 Just a single handful of soil may contain several thousand metres 277 00:38:37,940 --> 00:38:41,140 of their microscopic filaments. 278 00:38:41,140 --> 00:38:46,300 It's only recently that we have discovered the extraordinary role 279 00:38:46,300 --> 00:38:49,860 that these fungi play in a forest like this. 280 00:38:52,900 --> 00:38:58,420 Their filaments plug into the tips of the tree's roots 281 00:38:58,420 --> 00:39:03,260 and nutrients pass between tree and fungus throughout the year. 282 00:39:05,340 --> 00:39:10,260 Some fungi have the ability to link with not just a single tree, 283 00:39:10,260 --> 00:39:13,340 but with a whole group of trees, 284 00:39:13,340 --> 00:39:16,740 so that the entire forest may be linked together 285 00:39:16,740 --> 00:39:19,020 by these microscopic threads, 286 00:39:19,020 --> 00:39:22,500 to form what you might call a wood-wide web. 287 00:39:31,020 --> 00:39:34,940 Hundreds of trees can be interconnected by these webs. 288 00:39:36,020 --> 00:39:39,580 Scientists call it the mycorrhizal network. 289 00:39:41,540 --> 00:39:44,020 And it might look something like this. 290 00:39:52,980 --> 00:39:56,460 They've discovered that trees not only send nutrients along it 291 00:39:56,460 --> 00:40:00,100 but chemical and electrical signals, 292 00:40:00,100 --> 00:40:02,980 allowing them to communicate with one another. 293 00:40:05,060 --> 00:40:09,860 But some trees can also be selfish and steal from their rivals. 294 00:40:10,980 --> 00:40:16,620 Or even wage war by sending out toxins that will harm competitors. 295 00:40:24,220 --> 00:40:28,620 It seems, however, that most trees do try to help each other. 296 00:40:31,620 --> 00:40:35,020 They raise the alarm when attacked by leaf-eaters, 297 00:40:35,020 --> 00:40:39,100 leaving other trees time to produce defensive chemicals. 298 00:40:44,060 --> 00:40:48,260 Those that are dying may send their food reserves to their neighbours. 299 00:40:50,060 --> 00:40:54,220 And some individuals known as mother trees 300 00:40:54,220 --> 00:40:57,580 recognise their own offspring, 301 00:40:57,580 --> 00:41:00,140 and will channel resources to them... 302 00:41:04,300 --> 00:41:08,620 ..so giving their young the best possible start in life. 303 00:41:29,060 --> 00:41:32,300 As the harshness of winter approaches... 304 00:41:34,340 --> 00:41:41,340 ..temperate woodlands from Russia to Canada 305 00:41:41,340 --> 00:41:45,180 are now in a race to shut down. 306 00:42:11,420 --> 00:42:15,620 The green pigment in the leaves starts to break down 307 00:42:15,620 --> 00:42:19,060 and nutrients are withdrawn into the branches. 308 00:42:21,460 --> 00:42:24,220 The chemical substances that are left behind 309 00:42:24,220 --> 00:42:29,260 then create one of the most spectacular displays of colour 310 00:42:29,260 --> 00:42:31,340 in the whole of nature. 311 00:43:28,380 --> 00:43:33,660 The first freezing nights of winter bring with them a killer. 312 00:43:36,820 --> 00:43:38,860 Frost. 313 00:43:44,460 --> 00:43:48,460 Stems, when frozen, rupture. 314 00:43:51,420 --> 00:43:55,540 And flowers of ice form in the chilly air. 315 00:44:29,060 --> 00:44:32,460 For some, winter brings dormancy. 316 00:44:34,580 --> 00:44:37,540 For others, it brings death. 317 00:44:48,300 --> 00:44:51,620 Another cycle of the seasons 318 00:44:51,620 --> 00:44:53,660 comes to an end. 319 00:45:08,500 --> 00:45:11,340 Plants all across the seasonal world 320 00:45:11,340 --> 00:45:15,580 have developed many different strategies for success. 321 00:45:15,580 --> 00:45:22,620 But they all depend on the seasons changing reliably year after year. 322 00:45:22,620 --> 00:45:25,380 It doesn't matter whether you live for 3,000 years 323 00:45:25,380 --> 00:45:27,980 or just a few months, 324 00:45:27,980 --> 00:45:32,140 everything depends on you getting the timing just right. 325 00:45:35,820 --> 00:45:38,060 But in our changing world, 326 00:45:38,060 --> 00:45:41,500 this is becoming a greater challenge every year. 327 00:45:44,260 --> 00:45:48,060 And even the most hardy and resilient of plants 328 00:45:48,060 --> 00:45:50,100 are starting to struggle. 329 00:45:59,540 --> 00:46:05,100 These sequoia trees are the giants of the natural world, 330 00:46:05,100 --> 00:46:08,980 the largest living thing on the planet. 331 00:46:08,980 --> 00:46:12,300 They can grow to almost 100 metres tall 332 00:46:12,300 --> 00:46:14,340 and 11 metres across. 333 00:46:17,100 --> 00:46:20,700 Their bark alone can be over a half-a-metre thick. 334 00:46:21,820 --> 00:46:28,620 They're also among the oldest, some living to over 3,000 years. 335 00:46:28,620 --> 00:46:31,580 And to achieve such age and size, 336 00:46:31,580 --> 00:46:34,780 they need very particular living conditions, 337 00:46:34,780 --> 00:46:38,500 such as are found here in the Sierra Nevada mountains 338 00:46:38,500 --> 00:46:40,540 of California. 339 00:46:45,460 --> 00:46:48,140 Not only do they need energy from the sun but, 340 00:46:48,140 --> 00:46:55,540 critically, they also require up to 4,000 litres of water a day. 341 00:46:55,540 --> 00:47:00,220 So they are almost entirely reliant on the seasonal snowmelt. 342 00:47:06,980 --> 00:47:10,740 But recent years have brought longer, hotter summers 343 00:47:10,740 --> 00:47:15,220 and their source of water is becoming increasingly unreliable. 344 00:47:21,900 --> 00:47:23,940 Scientists are discovering 345 00:47:23,940 --> 00:47:27,660 that even these seemingly indestructible giants 346 00:47:27,660 --> 00:47:31,540 are now starting to show signs of vulnerability. 347 00:47:34,340 --> 00:47:37,580 Some are shedding their needles and branches 348 00:47:37,580 --> 00:47:40,300 as a way of conserving precious water. 349 00:47:51,220 --> 00:47:55,100 But for others, climate change has already been fatal. 350 00:47:57,220 --> 00:48:01,340 10% of them have been lost in just the last few years. 351 00:48:12,300 --> 00:48:16,020 A single giant sequoia in its lifetime 352 00:48:16,020 --> 00:48:20,340 can produce 100 million seeds. 353 00:48:20,340 --> 00:48:23,220 These, in my hand, from one cone, 354 00:48:23,220 --> 00:48:26,940 are more than enough to start a completely new forest. 355 00:48:29,540 --> 00:48:34,340 But they can only do such a thing in a world where the seasons change 356 00:48:34,340 --> 00:48:36,380 with some reliability. 357 00:48:38,660 --> 00:48:43,660 Today, our climate is changing, bringing an unprecedented level 358 00:48:43,660 --> 00:48:48,740 of unpredictability all across the seasonal world. 359 00:48:51,060 --> 00:48:56,260 The question is, can we curb climate change sufficiently 360 00:48:56,260 --> 00:49:00,300 to ensure that the seasons will continue? 361 00:49:00,300 --> 00:49:04,220 Only if we can do that will the future of seasonal plants, 362 00:49:04,220 --> 00:49:08,580 including these magnificent trees, be assured. 363 00:49:32,020 --> 00:49:34,220 During filming The Green Planet, 364 00:49:34,220 --> 00:49:38,420 it wasn't only the plants that struggled to get their timing right. 365 00:49:38,420 --> 00:49:41,580 The increasing unpredictability of the seasons 366 00:49:41,580 --> 00:49:43,980 made it frustratingly difficult for the crew 367 00:49:43,980 --> 00:49:46,660 to be in the right place at the right time. 368 00:49:47,780 --> 00:49:49,820 Whether the height of summer... 369 00:49:49,820 --> 00:49:54,660 We are in the middle of a biblical rainstorm. 370 00:49:54,660 --> 00:49:57,660 ..or a quiet autumnal afternoon... 371 00:49:57,660 --> 00:50:00,980 MAN: This is crazy. Hurricanes are no joke. 372 00:50:00,980 --> 00:50:03,300 ..they were always kept on their toes. 373 00:50:04,300 --> 00:50:07,100 That's really scary. Ooh! 374 00:50:08,740 --> 00:50:10,780 Sometimes very numb ones. 375 00:50:12,900 --> 00:50:15,980 It's been the most snow they've had for 38 years, 376 00:50:15,980 --> 00:50:19,820 {\an8}and I think this is now our fifth filming trip in a row 377 00:50:19,820 --> 00:50:23,460 {\an8}where the seasons haven't done what they're predictably meant to do 378 00:50:23,460 --> 00:50:25,780 {\an8}every year. 379 00:50:25,780 --> 00:50:29,780 And these challenges continue in attempting to find and film 380 00:50:29,780 --> 00:50:34,180 an elusive plant with a remarkable survival strategy. 381 00:50:35,900 --> 00:50:37,940 The fire lily. 382 00:50:47,100 --> 00:50:51,100 Somewhere out there is a tiny, tiny red plant... 383 00:50:51,100 --> 00:50:53,140 ..in all of that. 384 00:51:02,980 --> 00:51:05,580 Travelling to South Africa at the height of summer... 385 00:51:08,260 --> 00:51:10,820 ..the crew witnessed many extraordinary flowers 386 00:51:10,820 --> 00:51:12,860 bursting into bloom. 387 00:51:15,060 --> 00:51:19,180 But if they are to see a fire lily, they need a fire. 388 00:51:22,380 --> 00:51:25,500 None of the team have filmed wildfire before - 389 00:51:25,500 --> 00:51:27,660 not something to be underestimated. 390 00:51:29,140 --> 00:51:32,420 In most cases, with wildfires, is that, when they go wrong, 391 00:51:32,420 --> 00:51:34,620 they go wrong radically, and it's very unforgiving. 392 00:51:34,620 --> 00:51:36,940 If you get caught on the wrong side of a fire 393 00:51:36,940 --> 00:51:38,820 because you want to get that special shot, 394 00:51:38,820 --> 00:51:40,740 there's a possibility you can get killed. 395 00:51:40,740 --> 00:51:42,460 That's really what it comes down to. 396 00:51:42,460 --> 00:51:45,580 And after some understandably studious note-taking... 397 00:51:47,340 --> 00:51:50,140 ..it's time to put their training to the test. 398 00:52:00,860 --> 00:52:04,260 The fire's just racing up a gully behind me. 399 00:52:04,260 --> 00:52:07,740 The heat is intense. You just... You can't even stand to be, like, 400 00:52:07,740 --> 00:52:09,780 five metres from it. It's insane. 401 00:52:12,860 --> 00:52:14,900 Whoa! 402 00:52:16,180 --> 00:52:20,500 This is what any fire lilies here should be waiting for. 403 00:52:29,580 --> 00:52:31,620 Jeepers. 404 00:52:32,940 --> 00:52:37,220 But fynbos wildfires are starting to become fiercer than in the past. 405 00:52:38,620 --> 00:52:41,540 Something fire chief Reinard Geldenhuys 406 00:52:41,540 --> 00:52:43,780 knows first-hand. 407 00:52:43,780 --> 00:52:47,260 Nowadays, we're experiencing more extreme temperature conditions 408 00:52:47,260 --> 00:52:49,300 and more extreme wind conditions, 409 00:52:49,300 --> 00:52:52,740 which exacerbates a fynbos fire. 410 00:52:54,740 --> 00:52:58,460 Fynbos fire in full tilt, with a strong wind behind it, 411 00:52:58,460 --> 00:53:01,100 is an animal that's just running wild. 412 00:53:02,420 --> 00:53:05,340 It's a very frightening sight if you're standing in front of it. 413 00:53:11,660 --> 00:53:15,100 Guided by the experience of the fire crew, 414 00:53:15,100 --> 00:53:19,380 the team are able to safely capture the full fury of the blaze. 415 00:53:22,940 --> 00:53:27,740 It's given me a complete new appreciation for fire. 416 00:53:27,740 --> 00:53:30,620 How intensely it burns and how quickly it roars 417 00:53:30,620 --> 00:53:32,660 through this environment. 418 00:53:33,700 --> 00:53:37,020 And the fact that any plants can survive afterwards 419 00:53:37,020 --> 00:53:39,060 is just... Yeah, it's crazy. 420 00:53:42,700 --> 00:53:44,780 As destructive as it seems, 421 00:53:44,780 --> 00:53:48,060 the fire has been part of this ecosystem for millennia. 422 00:53:49,140 --> 00:53:52,380 Fires should refresh and regenerate the landscape. 423 00:53:53,900 --> 00:53:58,380 Worryingly, however, this fine balance between plant and fire 424 00:53:58,380 --> 00:54:01,060 is beginning to shift. 425 00:54:01,060 --> 00:54:04,780 More extreme wildfires may spell disaster. 426 00:54:06,620 --> 00:54:08,820 If you disturb the soil in a fynbos system, 427 00:54:08,820 --> 00:54:11,100 you're going to lose a lot of species. 428 00:54:11,100 --> 00:54:14,300 Bigger, hotter fires can burn the soil there 429 00:54:14,300 --> 00:54:16,340 and burn out all the seeds. 430 00:54:17,380 --> 00:54:20,420 And for the species that have these really intricate strategies, 431 00:54:20,420 --> 00:54:23,860 like the fire lily, it really is a difficult game. 432 00:54:25,620 --> 00:54:29,060 Every year is getting hotter and potentially drier. 433 00:54:29,060 --> 00:54:31,940 So it's kind of becoming Russian roulette 434 00:54:31,940 --> 00:54:33,980 for a lot of the species here. 435 00:54:43,940 --> 00:54:45,980 In the fire's aftermath, 436 00:54:45,980 --> 00:54:48,700 the crew must now try to find a tiny flower... 437 00:54:50,820 --> 00:54:53,780 ..but have any survived the blaze? 438 00:54:53,780 --> 00:54:56,580 It just looks completely dead, the whole valley. 439 00:55:02,900 --> 00:55:06,060 There's nothing for it but to get their hands dirty. 440 00:55:08,420 --> 00:55:11,460 Searching in the ash is a grubby business. 441 00:55:17,620 --> 00:55:19,660 I feel... 442 00:55:19,660 --> 00:55:22,020 ..disgusting. 443 00:55:22,020 --> 00:55:26,380 After scouring this mountainside just days after it burned... 444 00:55:27,580 --> 00:55:31,380 ..they finally find the first signs of regeneration. 445 00:55:34,700 --> 00:55:38,300 Wow. That's what it's all about. That's the fire lily. 446 00:55:38,300 --> 00:55:41,540 It's like a pop of bright red against all the black. 447 00:55:42,740 --> 00:55:45,700 I mean, that's amazing. There's another one over there, 448 00:55:45,700 --> 00:55:47,740 and there's another one behind us. 449 00:55:49,100 --> 00:55:51,580 This place hasn't burned for 15 years, 450 00:55:51,580 --> 00:55:55,340 so they've been sat underground waiting for this precise moment 451 00:55:55,340 --> 00:55:57,500 for that entire time. And then, within two weeks, 452 00:55:57,500 --> 00:56:00,340 they're up and they're flowering. It's incredible. 453 00:56:01,660 --> 00:56:05,260 {\an8}This time, the fire lilies here succeeded in flowering. 454 00:56:05,260 --> 00:56:08,340 {\an8}But in the 15 years since they last bloomed, 455 00:56:08,340 --> 00:56:12,820 {\an8}the Earth has experienced ten of the warmest years on record. 456 00:56:14,340 --> 00:56:16,740 You know, there's huge debates about climate change - 457 00:56:16,740 --> 00:56:19,020 how real is it, really, and so on. 458 00:56:19,020 --> 00:56:22,660 Erm, we experience it in the fire. 459 00:56:22,660 --> 00:56:25,980 It's more intense, burns easier, burns longer. 460 00:56:27,620 --> 00:56:30,900 In the past, we used to have one big fire per season, 461 00:56:30,900 --> 00:56:33,140 and we said, "Ja, that was a big one." 462 00:56:33,140 --> 00:56:36,220 Now we have five to six big ones per season. 463 00:56:37,740 --> 00:56:41,140 If we don't change our ways, we are going to reach a point where 464 00:56:41,140 --> 00:56:45,340 fires are burning with such ferocity that it will destroy the landscape. 465 00:56:47,820 --> 00:56:51,260 And in recent times, a rapidly changing climate 466 00:56:51,260 --> 00:56:54,340 has led to some of the biggest fires in living memory - 467 00:56:54,340 --> 00:56:57,820 not just in South Africa, but around the world. 468 00:56:59,100 --> 00:57:02,940 The next five to ten years are going to be pretty scary 469 00:57:02,940 --> 00:57:06,020 to actually see what this has done to the ecosystem. 470 00:57:07,180 --> 00:57:10,740 Let's hope that the next time this fire lily blooms, 471 00:57:10,740 --> 00:57:14,060 it will find a world in which it can still survive. 472 00:57:19,020 --> 00:57:21,060 Next time on The Green Planet... 473 00:57:22,660 --> 00:57:24,700 ..desert worlds. 474 00:57:26,260 --> 00:57:28,340 A landscape of extremes... 475 00:57:30,060 --> 00:57:32,260 ..where water equals life. 476 00:57:36,460 --> 00:57:38,500 It only takes a drop. 477 00:57:41,780 --> 00:57:45,220 The Open University has produced a poster 478 00:57:45,220 --> 00:57:49,820 that explores the vital role that plants have for our planet. 479 00:57:49,820 --> 00:57:52,940 To order your free copy, call... 480 00:57:56,100 --> 00:57:58,140 ..or go to... 481 00:58:01,860 --> 00:58:04,700 ..and follow the links to the Open University.