[00:33.69]Trees. 
[00:34.61]
[00:34.89]Surely among the most magnificent of all living things. 
[00:40.16]
[00:42.02]Some are the largest organisms on Earth 
[00:45.11]
[00:45.18]dwarfing all others, and these are the tallest of them all. 
[00:50.87]
[01:03.11]The deciduous and coniferous woodlands that grow in the seasonal parts of our planet 
[01:08.40]
[01:08.56]are the most extensive forests on Earth. 
[01:11.99]
[01:20.14]Their sheer extent stuns the imagination. 
[01:24.05]
[01:36.16]The barren snows of the Arctic. 
[01:38.74]
[01:38.82]A thousand miles from the North Pole, and heading south. 
[01:43.49]
[01:46.45]This is the very first place that trees can grow. 
[01:50.08]
[01:52.81]To begin with the conifers are sparse 
[01:55.42]
[01:55.71]but soon they dominate the land. 
[01:58.76]
[02:06.78]This is the Taiga Forest. 
[02:10.14]
[02:11.84]There are as many trees here, as in all the world's rainforests combined. 
[02:17.63]
[02:18.39]The Taiga circles the globe and contains a third of all the trees on Earth. 
[02:23.95]
[02:24.30]It produces so much oxygen, that it refreshes the atmosphere of the entire planet. 
[02:31.27]
[02:35.27]At the Taiga's northern extent 
[02:37.60]
[02:37.74]the growing season can last for just one month a year. 
[02:42.31]
[02:42.85]It can take fifty years for a tree to get bigger than a seedling. 
[02:47.65]
[03:00.74]It's a silent world 
[03:02.65]
[03:03.02]where little stirs 
[03:05.12]
[03:06.80]But there are occasional signs of life. Stories written in the snow. 
[03:12.65]
[03:14.02]The prints of an Arctic fox and the hare it might've been stalking. 
[03:19.38]
[03:24.65]A female polar bear and her two cubs. 
[03:28.56]
[03:38.43]Some animals are so difficult to glimpse that they're like spirits. 
[03:43.48]
[03:43.77]One could live a lifetime in these woods and never see a lynx. 
[03:49.47]
[03:52.58]The cat must roam hundreds of miles in search of prey 
[03:56.38]
[03:56.66]and may never visit the same patch of forest twice. 
[04:00.37]
[04:02.07]It's the very essence of wilderness. 
[04:05.41]
[04:09.88]With so few prey animals here, life for a hunter is particularly hard. 
[04:16.31]
[04:18.57]Creatures are scarce because few can eat conifer needles. 
[04:22.84]
[04:23.67]The moose is an exception. 
[04:25.93]
[04:30.92]Growth is so difficult 
[04:32.80]
[04:32.91]that conifers protect their precious leaves by filling them with resin. 
[04:37.11]
[04:37.24]That reduces water loss, but it also makes them very distasteful. 
[04:42.28]
[04:52.81]At least the conifer's seeds are edible 
[04:56.33]
[04:56.56]but they're protected within armor plated cones 
[04:59.68]
[04:59.98]and it takes a specialist to reach them. 
[05:03.23]
[05:05.50]The crossbill's extraordinary beak 
[05:07.56]
[05:07.75]can prise apart the scales, so that it's tongue can extract the seeds. 
[05:13.19]
[05:16.57]Birds are fortunate. 
[05:18.08]
[05:18.32]When the seasonal crop is gathered, they can fly south 
[05:22.17]
[05:26.55]But one animal is so expert at survival in this frozen forest 
[05:31.36]
[05:31.60]that it stays here and is active all year long. 
[05:35.88]
[05:38.32]In local folklore, the wolverine is a link to the spirit world 
[05:42.88]
[05:43.05]and a cross between a bear and a wolf. 
[05:45.73]
[05:46.05]In reality, it's a huge weasel. 
[05:49.84]
[05:51.87]It's bulk helps to conserve body heat and also broadens it's menu. 
[05:56.42]
[05:56.60]It's so big and powerful, it can even bring down an adult caribou. 
[06:01.83]
[06:03.32]For it's size, it's said that the animal can eat more in one sitting than any other 
[06:08.53]
[06:08.75]which is why it's also known as the glutton. 
[06:12.29]
[06:29.12]Being gluttonous here is a very effective strategy. 
[06:33.23]
[06:33.28]It's wise to eat all you can, when you can 
[06:37.32]
[06:38.82]and when even a glutton can't eat more 
[06:41.79]
[06:41.87]it stores what's left for later, in the surrounding deep freeze. 
[06:47.16]
[06:53.69]Spring in the ice forest. 
[06:56.46]
[07:07.33]The capercaillie can also digest conifer needles 
[07:11.70]
[07:11.89]but feeding is not it's priority at the moment. 
[07:15.37]
[07:17.76]Like gladiators, the males square up for a battle. 
[07:22.09]
[07:32.59]Each may have just a single chance to impress a female. 
[07:37.67]
[07:38.70]Neither can afford a lapse in concentration. 
[07:42.81]
[08:06.31]The injured loser may not survive. 
[08:10.25]
[08:14.83]The inhabitants of this great wilderness 
[08:17.53]
[08:17.53]may live and die without ever having contact with humanity. 
[08:21.95]
[08:22.56]Long may it be that way. 
[08:25.00]
[08:34.46]The northern forest may be the largest on Earth 
[08:37.86]
[08:37.86]but to see coniferous trees that have reached their full potential 
[08:41.93]
[08:42.15]you must travel a thousand miles south of here. 
[08:45.95]
[08:51.31]The Pacific Coast of North America. 
[08:53.97]
[09:00.25]The land of hemlock, douglas fir and giant redwood. 
[09:05.96]
[09:13.33]Here, water is never locked up in ice 
[09:16.76]
[09:16.81]and even if rains fail 
[09:18.57]
[09:18.78]the needles can extract moisture from the fogs that roll in from the sea. 
[09:24.30]
[09:31.97]The Sun's energy powers these forests 
[09:34.80]
[09:34.80]not for one month as it does in the Taiga but for half the year. 
[09:40.27]
[09:48.71]These conifers grow at ten times the rate of those near the Arctic 
[09:53.09]
[09:53.38]and they live for thousands of years. 
[09:56.62]
[10:06.08]One grove of redwoods in California 
[10:08.96]
[10:09.02]contains three of the tallest trees on Earth. 
[10:12.98]
[10:18.03]This one is over a hundred meters high, the size of a thirty story building. 
[10:24.04]
[10:51.18]These forests were growing here long before humans walked the Earth. 
[10:56.41]
[10:56.59]They were in their prime twenty million years ago 
[10:59.81]
[10:59.92]and existed before the Swiss Alps or the Rocky Mountains were even raised. 
[11:05.58]
[11:17.77]There is more living matter in a forest of giant conifers, than in any tropical rainforest 
[11:23.98]
[11:24.48]but it's all contained within the trees. 
[11:27.71]
[11:27.95]These are as inedible as those in the Taiga 
[11:31.34]
[11:31.55]so animals are still scarce, but they are present. 
[11:36.82]
[11:40.07]A pine marten. It's spring, the best time of year for a marten to find food. 
[11:47.24]
[12:02.05]Bird's eggs are a seasonal snack and for a short time, there's plenty of them 
[12:08.80]
[12:10.13]Sometimes perhaps, too many. 
[12:12.95]
[12:16.10]But to live here permanently, the marten needs a more reliable food source. 
[12:21.83]
[12:22.52]Squirrels fit the bill. 
[12:24.83]
[12:25.03]They thrive here on the pine cones and although these are also seasonal 
[12:29.76]
[12:29.84]they can be stored and eaten throughout the year. 
[12:33.52]
[12:37.65]The squirrels are busy mating 
[12:40.53]
[12:44.15]Good news for the hunter. A distracted squirrel, is a vulnerable squirrel. 
[12:49.72]
[12:56.11]But, this time, the amorous couple is safe. 
[12:59.45]
[12:59.65]There is a loner stocking his larder, who will be the easier target. 
[13:04.85]
[13:38.32]Early summer, and great grey owl chicks are fledging. 
[13:43.56]
[13:45.82]Adults can only raise young here 
[13:48.48]
[13:48.54]in years when the seasonal vole crop is big enough to support them. 
[13:53.21]
[13:57.87]The moment has arrived for their first flight. 
[14:01.63]
[14:06.15]Leaping from the world's tallest trees is not for the faint hearted. 
[14:12.42]
[14:36.63]If you're going to fall here it's quite a good idea to do it in stages. 
[14:42.27]
[14:59.84]The ground is no place for an owl. 
[15:04.00]
[15:05.58]If he's to climb to the top of his class he'll need to persevere 
[15:10.41]
[15:12.89]So now, let's have another go. 
[15:16.47]
[15:35.42]The American conifer forests may not be the richest in animal life 
[15:40.68]
[15:40.90]but their trees are extraordinary. 
[15:43.98]
[15:44.50]This giant sequoia, a relative of the redwood, is the largest living thing on Earth. 
[15:50.81]
[15:51.17]Known as General Sherman, it's the weight of ten blue whales. 
[15:56.69]
[16:06.03]Higher up in the nearby mountains, bristlecone pines, the oldest organisms on the planet. 
[16:13.98]
[16:15.46]Some have been here for five thousand years. 
[16:19.18]
[16:19.18]They were alive before the pyramids were built 
[16:22.14]
[16:22.30]and were already three thousand years old when Christ was born. 
[16:27.73]
[16:31.93]Across the Equator, in the southern hemisphere there are forests that mirror those of the north. 
[16:39.65]
[16:40.01]Here in South America 
[16:41.63]
[16:41.67]araucaria trees or monkey puzzles are like the conifers of the Taiga. 
[16:46.86]
[16:47.44]They have waterproof scales, instead of needles 
[16:50.44]
[16:50.46]and their cones look a little different but the principles are the same. 
[16:55.70]
[16:59.86]Slender billed parakeets rather than crossbills, extract their seeds. 
[17:05.93]
[17:13.33]Where the growing season is longerm, there are alerce trees the redwoods of the south. 
[17:20.35]
[17:34.26]As in the frozen north, the Valdivian forests of Chile support very few animals 
[17:40.97]
[17:41.23]but that is the end of the similarity. 
[17:44.73]
[17:47.81]This is a bizarre world of miniature creatures. 
[17:52.63]
[17:54.81]The pudu, the world's smallest deer feeds on the giant leaves of the gunnera plant. 
[18:01.92]
[18:08.70]The female is just thirty centimeters high at the shoulder 
[18:12.66]
[18:12.68]and her infants are hardly bigger than kittens. 
[18:16.65]
[18:32.71]The male must stay alert. There are hunters here who would snatch his young. 
[18:38.98]
[18:40.70]Another miniature. The kodkod cat. 
[18:44.26]
[18:47.66]It's the smallest cat in all the Americas and a young pudu would be a feast for it 
[18:54.02]
[18:55.18]But, with the male on guard, the kodkod must lower his sights. 
[19:00.43]
[19:05.27]Moths are hatching. They're the last of the summer. 
[19:08.99]
[19:09.29]The tiny cat should be able to score with these. 
[19:13.29]
[19:15.69]No one knows why the creatures here are so small 
[19:18.78]
[19:18.84]but at least they can survive on meager rations. 
[19:23.14]
[19:48.19]You might call this a game of cat and moth. 
[19:52.25]
[20:15.07]As winter approaches in Chile spring is arriving in the northern hemisphere. 
[20:21.51]
[20:28.97]These are the deciduous forests of Homme. 
[20:33.20]
[20:33.90]Dormant throughout the winter, they now undergo 
[20:36.82]
[20:36.92]one of the most magical transformations in the natural world. 
[20:41.58]
[20:53.03]By late spring the landscape is wrapped in a vibrant fresh green. 
[20:58.03]
[20:58.41]Here, instead of conifers, there are broad leaved trees 
[21:02.49]
[21:02.71]and that makes the character of this forest entirely different. 
[21:07.28]
[21:11.28]Being broad, these leaves trap much more light than needles 
[21:15.82]
[21:16.08]but they're also thin, soft and edible. 
[21:20.28]
[21:38.49]And others can eat the leaf eaters. 
[21:41.99]
[22:03.28]It's spring in the great broad leaved forests of Eastern Europe and Asiatic Russia. 
[22:10.13]
[22:11.01]The mandarin ducks are courting. 
[22:13.99]
[22:26.81]The female mandarin nests in a tree hole 
[22:30.23]
[22:30.42]and when it's time for everyone to leave she leads the way. 
[22:35.47]
[22:38.05]The ducklings are only twenty four hours old. 
[22:41.81]
[22:43.88]It's a long drop, and a few calls of encouragement are required. 
[22:48.07]
[23:01.30]Two down seven to go. 
[23:04.13]
[23:37.02]There are still two missing. 
[23:39.17]
[24:00.33]All present and correct. 
[24:02.52]
[24:03.28]But they won't be safe until they reach water 
[24:06.13]
[24:06.32]and the forest pool is almost a mile away. 
[24:10.04]
[24:44.48]By June the days are at their longest 
[24:47.57]
[24:47.68]and all across the northern hemisphere the broad leaves are hard at work. 
[24:53.06]
[25:01.98]On the east coast of North America it seems like any other summer's evening 
[25:07.03]
[25:09.20]but tonight is special. 
[25:12.46]
[25:16.01]After seventeen years underground 
[25:18.99]
[25:19.29]creatures are stirring. 
[25:21.94]
[25:27.70]The nymphs of the periodical cicada have been biding their time. 
[25:32.71]
[25:32.92]Now they march like zombies towards the nearest tree, and start to climb. 
[25:39.70]
[25:47.13]At first, there are merely thousands 
[25:49.84]
[25:50.15]but soon, more than a billion swarm all over the forest. 
[25:54.86]
[25:55.05]The biggest insect emergence on the planet is underway. 
[25:59.62]
[26:29.26]They invade the upper branches, where they climb out of their external skeletons 
[26:34.63]
[26:34.73]and assume their adult winged form. 
[26:38.51]
[26:46.43]At first they're white and soft, but they have until dawn to complete their transformation. 
[26:52.53]
[27:06.42]After an absence of seventeen years, the forest is now overrun by cicadas. 
[27:13.00]
[27:20.89]The adults are clumsy and very edible. 
[27:25.37]
[27:34.19]For turtles and other inhabitants of the forest 
[27:37.17]
[27:37.34]this is a feast they're lucky to see once in their lifetime 
[27:40.97]
[27:41.04]and they gorge themselves while they can. 
[27:44.15]
[27:57.11]Times have never been so good. 
[27:59.32]
[27:59.66]The cicadas have no defenses and virtually offer themselves to their attackers. 
[28:05.55]
[28:15.16]The stream of insects is so relentless 
[28:17.97]
[28:18.02]that soon all the predators are full to the point of bursting 
[28:22.71]
[28:33.59]and still the cicadas come. 
[28:36.10]
[28:36.30]With the predators overwhelmed the survivors can achieve their purpose. 
[28:42.00]
[28:44.54]After mating, the adults lay their eggs and then their job is done. 
[28:49.91]
[28:50.35]In just a few days they will all die and the forest will fall silent. 
[28:55.47]
[28:55.87]The cicadas here, will not be heard again for another seventeen years. 
[29:02.03]
[29:11.23]Having fed the predators, the cicadas leave one final gift for the forest itself. 
[29:17.86]
[29:18.01]The nutrients in a generation of cicadas are returned to the soil, all at once 
[29:23.92]
[29:24.15]and the trees enjoy a marked spurt in growth. 
[29:27.67]
[29:28.02]This may be the single largest dose of fertilizer in the natural world. 
[29:33.42]
[29:53.81]In the great broad leaf forests of Eastern Europe 
[29:57.15]
[29:57.28]the days are beginning to shorten, and a primeval sound heralds the onset of autumn. 
[30:05.45]
[30:22.49]Male red deer are starting their rut. 
[30:26.86]
[30:31.92]The air is heavy with the scent of females. 
[30:36.07]
[30:46.95]The rules are simple. 
[30:48.74]
[30:49.17]Winner takes all. 
[30:51.33]
[31:43.28]Across the northern hemisphere the deciduous forests are changing. 
[31:48.24]
[31:48.54]Leaves that have provided food and shelter since the spring, are now shed. 
[31:54.23]
[31:58.48]In the broad leaf forests of Russia winter is particularly severe 
[32:04.84]
[32:09.26]but there will always be some who benefit from hardship. 
[32:14.05]
[32:17.73]Black vultures scavenge from the carcass of a seeker deer 
[32:21.45]
[32:21.53]that has died of cold or starvation. 
[32:24.23]
[32:24.53]These endangered birds are visitors. 
[32:26.86]
[32:26.89]They've come down from the north to escape the even colder conditions in Siberia. 
[32:32.32]
[33:08.32]An Amur leopard. 
[33:10.23]
[33:10.42]The rarest cat on Earth. 
[33:13.11]
[33:13.67]Winter is a difficult time for this hunter. 
[33:16.66]
[33:16.76]There are no leaves for cover and no young prey animals. 
[33:20.86]
[33:21.12]This female has the added pressure, of having to provide for her one year old cub. 
[33:26.71]
[33:26.99]It'll be another twelve months, before he'll be able to fend for himself. 
[33:32.21]
[33:44.23]The bickering vultures have abandoned the carcass. 
[33:48.02]
[33:48.05]It's a valuable discovery for the leopards. 
[33:51.65]
[33:56.14]But the cub doesn't share it's mother's sense of urgency. 
[34:00.89]
[34:29.12]The vultures have left behind plenty of good meat 
[34:32.66]
[34:33.02]but it's stiff with frost. 
[34:35.31]
[34:37.87]The mother works to open the hide, and make feeding a little easier for her cub. 
[34:43.21]
[34:54.38]There are only forty Amur leopards left in the wild 
[34:58.65]
[35:00.80]and that number is still falling. 
[35:03.55]
[35:04.55]The harshness of the winter here hinders their increasing numbers. 
[35:09.06]
[35:09.27]It takes one of these females longer to raise her young to independence 
[35:13.35]
[35:13.41]than it does a leopard in Africa. 
[35:16.08]
[35:23.59]If the mother can sustain her cub for a few more weeks 
[35:27.66]
[35:27.74]spring will bring an increase in prey and her task will lighten. 
[35:33.27]
[35:38.19]For all the inhabitants of this seasonal forest 
[35:41.58]
[35:41.78]the long, cold wait is nearly over. 
[35:45.11]
[35:57.06]Spring in a deciduous woodland is special. 
[36:01.10]
[36:04.84]With no leaves overhead, the rays of the sun strike the forest floor directly 
[36:09.71]
[36:09.87]and their warmth rouses plants from their winter sleep. 
[36:13.92]
[36:20.96]The ground living plants are in a hurry. 
[36:23.32]
[36:23.45]Before long the trees above will come into leaf and steal their light. 
[36:28.25]
[36:37.82]Their flowers decorate the forest floor 
[36:40.45]
[36:40.50]as they advertise their sweet nectar to the newly emerged insects. 
[36:45.52]
[37:02.17]The spring blooms of the deciduous woodlands have no equivalent 
[37:06.24]
[37:06.35]in either the great conifer forests, or the tropical jungles. 
[37:10.81]
[37:15.55]Within a matter of weeks the canopy has closed 
[37:19.42]
[37:19.42]and only a few wheeling shafts of light penetrate the woodland. 
[37:24.41]
[37:32.42]In the treetops, the broad leaves rapidly expand to their full size 
[37:37.04]
[37:37.16]to make the most of summer while it lasts. 
[37:40.82]
[37:46.51]Then, after a few months, the days begin to shorten again 
[37:51.07]
[37:51.29]and the trees must shut down and shed their leaves in preparation 
[37:55.47]
[37:55.47]for the cold dark time ahead. 
[37:58.73]
[38:02.95]Great tracts of North America flush red as the season progresses. 
[38:08.45]
[38:09.71]The effect is so spectacular and so extensive 
[38:13.82]
[38:14.05]that it can be seen from space. 
[38:16.86]
[38:31.26]The threat of winter frost is not the only reason for trees to shed leaves. 
[38:37.27]
[38:41.53]These forests stand in the tropics. 
[38:44.24]
[38:44.49]Here day length never changes 
[38:47.16]
[38:47.33]but the dry season is so severe 
[38:49.57]
[38:49.65]that the trees can't afford to loose the amount of water 
[38:52.69]
[38:52.75]that would evaporate from their broad leaves, so the leaves must be shed. 
[38:58.19]
[39:15.29]The forest resembles a European woodland in mid winter 
[39:19.70]
[39:20.08]but the heat is overpowering, and it's inhabitants, unfamiliar. 
[39:25.38]
[39:29.06]For the creatures of India's teak forests, these are desperate times 
[39:34.74]
[39:35.99]but salvation is at hand. 
[39:38.17]
[39:38.41]The mahwa tree is about to bloom. 
[39:41.44]
[39:45.59]It's flowers are full of liquid making them irresistible. 
[39:49.74]
[39:56.69]The mahwa is an oasis in a hot dry desert. 
[40:01.42]
[40:11.38]Those that fly or climb are not the only ones to get a share. 
[40:16.89]
[40:19.93]Chital deer follow the langur monkeys 
[40:22.92]
[40:23.14]collecting the flowers that fall. 
[40:26.20]
[40:31.54]The monkeys welcome the deer, for deer are unrivaled at spotting predators. 
[40:37.59]
[40:38.97]If they are relaxed, it must be safe to come down to the ground 
[40:42.95]
[40:43.06]and gather the food that lies there 
[40:45.55]
[40:55.93]but it's not wise to travel far from the sentinels. 
[41:00.43]
[41:51.91]Tropical Madagascar. 
[41:53.73]
[41:54.33]The wet season. 
[41:56.25]
[42:02.60]It's now that the baobab trees regrow their leaves 
[42:06.40]
[42:06.59]and collect water to store in their huge trunks, ready for the dry season ahead. 
[42:12.40]
[42:32.97]The prehistoric shape of these trees is rightly famous 
[42:36.44]
[42:36.61]but few have ever witnessed the baobab's real magic 
[42:40.22]
[42:40.46]for that happens at night and high in the treetops. 
[42:44.85]
[42:49.78]Flush with water, the baobab prepares itself for an unforgettable display. 
[42:57.06]
[43:12.93]Once started the foot long flowers can open fully in less than a minute. 
[43:18.64]
[44:01.56]As the flowers open, the creatures of the forest wake. 
[44:06.43]
[44:17.65]The mouse lemurs have been hibernating throughout the dry season. 
[44:21.70]
[44:22.05]With the return of rains it's time to get busy. 
[44:26.29]
[44:30.84]A dozen share this tree hole, but there's plenty of room. 
[44:35.14]
[44:35.16]The world's smallest primate is no bigger than your hand. 
[44:39.91]
[44:45.02]High in the branches above, the baobab's nectar is starting to flow. 
[44:50.78]
[45:04.05]A drink of this sugary energy packed liquid 
[45:07.34]
[45:07.55]is an ideal way for the lemurs to start their day. 
[45:11.82]
[45:15.27]Liquid oozes from the flower's center and trickles down the petals 
[45:20.75]
[45:36.23]But the nectar is not intended for lemurs. 
[45:39.95]
[45:43.36]These giant hawk moths are the drinkers the tree needs to attract. 
[45:49.59]
[45:58.40]As they sip, moving from tree to tree, so they transfer pollen and fertilize the flowers. 
[46:06.20]
[46:19.44]Nectar was an excellent first course for the lemurs 
[46:23.61]
[46:23.83]but moths are the main dish. 
[46:26.89]
[46:28.13]The moths are very important to the lemurs 
[46:30.81]
[46:30.98]for they will replenish the fat reserves that the lemurs need to survive the barren dry season. 
[46:37.64]
[46:45.12]The lemurs might seem to be a pest for the baobab. 
[46:48.50]
[46:48.64]They kill it's pollinators and rob it of it's nectar 
[46:51.93]
[46:52.03]but they do give something in return. 
[46:54.73]
[46:54.83]For, as the wrestle with the moths, their fur inevitably becomes dusted with pollen 
[47:00.12]
[47:00.35]so they, too, become pollinators. 
[47:04.05]
[47:25.27]As the alternation of wet and dry seasons brings change to some tropical forests 
[47:31.80]
[47:31.93]so the progression of summer to winter dictates life in more temperate regions. 
[47:38.09]
[47:46.64]Whether trees have needles or broad leaves 
[47:50.06]
[47:50.19]it is their ability to survive annual change, that has enabled them to cover 
[47:55.92]
[47:55.92]such vast areas of the Earth 
[47:58.50]
[47:58.68]and made the seasonal forests 
[48:00.84]
[48:01.03]the greatest forests of all. 
[48:06.38]