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00:00The End
00:30In the lands between the Arctic Circle and the tropics,
00:50each year brings a great change between winter and summer,
00:53and this in turn imposes an annual rhythm on the lives of animals and plants.
00:57Up in the north, in the great evergreen forests, conditions in midwinter are cripplingly severe.
01:12Life, if it is to flourish, has three needs.
01:15It needs light, warmth and moisture.
01:19And the reason that trees like these don't grow much farther north
01:23is not only because of the extreme cold,
01:25but because with the long months of winter darkness,
01:29there is simply not enough light in the year for them to grow.
01:32Here in northern Norway, 300 miles, 500 kilometers north of the Arctic Circle,
01:38there is just enough light, but it does get extremely cold.
01:4370 degrees of frost have been measured in these northern forests,
01:47and during the winter there are very heavy falls of snow.
01:50The cold not only threatens to freeze the liquid within the trees,
01:57it also denies them one of their essential supplies, water.
02:01Although snow and ice lie all around,
02:03the trees can't tap that water while it's frozen.
02:06So in winter, this land is effectively as parched as a desert,
02:11and the pine trees have as great a need to conserve their water as a cactus.
02:15All plants lose some water from the surface of their leaves,
02:23but the long, thin pine needles are protected by a thick rind
02:26that is almost impermeable.
02:28And the pores through which they breathe,
02:30and from which they could lose water by evaporation,
02:33are kept out of the wind by being placed in lines
02:36along the groove that runs the length of the needle,
02:39each in a tiny pit ringed with a ridge.
02:41These dry, waxy leaves are almost inedible,
02:49but the seeds in the cones are a different matter.
02:51And what's more, they're one of the few kinds of food
02:54available in the forest during the winter.
02:59The crossbill has a special beak,
03:02which enables it to separate the brown segments of the closed cone
03:05and prise out the nutritious seeds.
03:07This winter feast is never certain.
03:16Some years, every branch of the trees will be laden with cones.
03:20In others, there will only be a handful.
03:22Then, the seed-eaters must move on or die.
03:27The few remaining cones will then have a chance
03:30to shed their seeds into the snow
03:31at a time when there are few animals around.
03:39Even so, there are some.
03:45Voles make their runways through the snow
03:47and industriously collect what they can.
03:49Moose get little nourishment from pine trees
03:56apart from the shaggy moss
03:58that here and there hangs from the branches.
04:00They chew the sappy twigs and bark of birch,
04:16but there's precious little to be found,
04:18certainly not enough in itself to keep them going.
04:21And if it wasn't for the fat reserves
04:22they built up during the summer,
04:24few would survive.
04:26The winter forest can support very few plant-eaters,
04:33but they're just enough to provide meals
04:35for one or two hardy hunters.
04:37The great grey owl has legs well-suited
04:59for grappling with its prey in the snow,
05:01particularly long and covered with warm feathers.
05:04It regularly patrols the snow
05:06for it can't afford to miss
05:08a single opportunity of a meal.
05:09And this is an incautious move.
05:38Mm-hmm.
05:39Mm-hmm.
05:52Lynx seek bigger prey.
06:22The female has young which, though large, are not yet skilled enough to hunt for themselves,
06:35so they are relying on her.
06:47The cost efficiency of hunting is precisely calculated.
06:53If the lynx doesn't catch a hare within 200 yards, the amount of meat it might provide
06:57is not enough to make the expenditure of energy worthwhile, and the lynx gives up.
07:07Bigger prey are worth much longer chases, and the lynx pursue roe deer with great persistence.
07:25A single deer will provide food for the whole lynx family.
07:39In this bleak land, even the most ferocious and capable hunters do not scorn to scavenge.
07:48An eagle owl will take cold deer flesh just as eagerly as the warm bodies of voles.
07:59A wolverine, the biggest of the weasel family, and more than a match for an eagle owl.
08:13OIL
08:23Covert
08:38The coniferous forest grows right round the globe in a belt that, in places, is 1,200 miles across.
08:52From Scandinavia, it extends across northern Europe and Siberia to the shores of the Pacific.
09:01During the last ice age, when the seas were lower, the Bering Strait did not exist,
09:06so the trees continued without interruption into North America.
09:10They stretch right across northern Canada to the Atlantic,
09:14and because of this one-time continuity, all the trees in this vast forest
09:19and all its permanent inhabitants in America, Asia and Europe are very much the same.
09:27But when spring comes, visitors journey up from warmer parts,
09:31and the forest on each continent takes on its own individual character.
09:36In Scandinavia, a hawk owl, a nomad that has spent the winter in the gentler conditions farther south,
09:46comes cruising up north again, looking for food and a nest site.
09:55Unlike other owls, it's primarily a daytime hunter,
09:58and relies not so much on its acute hearing as its sharp eyesight,
10:03as it waits for the melting snow to reveal rodents.
10:06As it is, the first off I always have Catalyst.
10:09The first year I can see on my list from the sale of different sends a travesty path,
10:13so I think the time it starts adding stars and empire,
10:13andutar Zhang Maherland when the blue lines are faster than the place.
10:15But if I never Josper showed,
10:17I quickly heard the Dionne story on Hennes is in my list.
10:20This time tonight's Siggler's search of the 300-ļæ½Anthor and Iļæ½sa.
10:21In Pć”ćÆ 2017, I will watch one of the final stars.
10:26In Pijnč¹,
10:31and פ×,
10:33it plays a reference for every day to the middle of agres.
10:34In pine trees from Norway to Siberia, the cock Capacaylae is starting to claim his territory.
10:42This giant grouse is one of the few creatures that eats pine needles.
10:48His hen takes them too.
11:04Now is the time for nesting.
11:08The hawk owl is in search of a hole in a tree, for it's already found, its partner.
11:16But many of the tree holes are already occupied,
11:19for great numbers of owls of several different species have travelled up to feed on the crop of voles.
11:28No owl can dig a hole for itself.
11:30They rely mainly on woodpeckers,
11:32and none of that family are more expert carpenters than the black woodpecker of northern Europe.
11:38The sharp beak with which they dig out insects also serves as an excellent chisel,
11:43but even so, most woodpeckers prefer to work in dead trees where the wood may be a little bit softer.
11:49There are ants near this tree too,
11:52which is an added asset for the woodpeckers rely on them for food during the winter.
12:00Not all owls use nest holes.
12:10The eagle owl nests on the ground, often among rocks.
12:15It already has a clutch of three eggs,
12:17for being a permanent resident of these forests, it paired early.
12:20Plants now have their chance to breed.
12:34The wood anemones are already in flower, and so are the pines.
12:38Each tree produces both male and female flowers,
12:41which mature at slightly different times,
12:43so that the female flowers are likely to be fertilised by pollen from other trees.
12:50Now it is as warm as it ever will be in the northern forests.
12:55Summer visitors are arriving, and the trees echo with their song.
13:04This willow warbler, singing so vigorously in Scandinavia,
13:08has come all the way from the savannah country south of the Sahara.
13:12So has the wind chap.
13:13And the lure that has brought them so far
13:18is the sudden emergence of myriads of insects.
13:32This bedraggled creature is hardly recognisable,
13:35for its wings have not yet expanded.
13:37It's a pine beauty moth,
13:38and its first priority is to get away from the forest floor,
13:42which is full of danger.
13:43But not all the moths have such a clear run.
13:52Shrews are among the first to feed on them.
13:57Up among the pine needles,
13:58the pine beauty pumps fluid out of its body
14:01and into the veins of its wings.
14:08Here the moths will lay their eggs
14:14so that their caterpillars can feed on the young shoots.
14:18The wood ants have missed their chance to catch the adult moth,
14:21but now they're looking for the caterpillars among the branches.
14:26The colour and the pattern of the caterpillar
14:28conceals it from birds which hunt by sight,
14:30but is no protection against ants
14:32which search by smell and touch.
14:38Finally, the body is hauled down to the nest
15:05for all to consume.
15:06The caterpillars of the sawfly
15:15are also swarming on the pine shoots.
15:18They do have a defence against ants,
15:20a chemical one.
15:22As they chew,
15:23they store some of the resin from the pine needles
15:25in a pouch inside their mouth.
15:27When a foraging ant discovers them,
15:29they dab a spot of this resin on its head,
15:32like this.
15:36The resin damages the ants' eyes and antennae,
15:40so disorientating it that it can hardly walk straight.
15:44Even if it finds its way back to the nest,
15:47it smells so strongly and so strangely
15:49that the other ants treat it as an intruder and kill it.
15:52The ants themselves are food for others.
16:03The wryneck is a member of the woodpecker family
16:06that has specialised in eating ants
16:08and particularly relishes their cocoons.
16:10Like its cousins,
16:16the wryneck nests in holes in trees,
16:19but it doesn't excavate them for itself.
16:21It's yet another tenant of vacated woodpecker holes.
16:24With a long tongue,
16:36you can even collect insects from the bark
16:38without leaving your nest.
16:42Here in the far north,
16:44close to the Arctic Circle,
16:46the sun during the summer
16:47hardly sinks below the horizon
16:48and the nights are brief.
16:50The eagle owl hunts just as effectively
16:58in the twilight as in the dark.
17:01It has a rabbit.
17:02The season is a good one
17:03and game is abundant.
17:07Down in the nest on the forest floor,
17:10there's only one chick left.
17:11The other two may have been taken by foxes.
17:14Eagle owls often kill rival species
17:21and this chick's last meal
17:22was a short-eared owl,
17:24which it's not yet finished.
17:26The single survivor
17:27has a superabundance of food.
17:30It has grown fast
17:31and its adult feathers
17:32are already appearing through its down.
17:35The tail of a red squirrel
17:37is left over from a previous meal
17:39and it even takes that too.
17:44The voles are swarming
17:56on the forest floor.
17:58Last winter,
17:59the pines produced
17:59great quantities of seed
18:01so many adult voles
18:02survived till spring
18:04and now they're all breeding
18:05at an extraordinary rate.
18:07This female produced her four young
18:09only three weeks ago
18:10but she's already pregnant again
18:12and will soon abandon
18:13this family
18:14and start a new one.
18:15All the owls,
18:43some visitors,
18:45some residents,
18:46scour the forest for voles.
18:57Teng Malm's owl,
18:58up in a tree hole,
18:59has three chicks,
19:00all flourishing
19:01and all demanding voles.
19:03There's a very good night.
19:06This one was just one day
19:07and we're able to win
19:08if you get the
19:08way that you're not
19:09about.
19:10We'll find a little name
19:11so much.
19:12We're able to win
19:12business.
19:13It's this one day
19:15and we're able to win
19:16and I'm out of the world.
19:16We'll be able to win
19:17in the world.
19:18We're able to win
19:18for every day
19:19and we're able
19:20to win
19:20the bush.
19:30The number of voles varies considerably.
19:35It gradually builds up over a period of five to six years
19:39until finally there are so many that they eat out their food supply
19:43and the population crashes.
19:45These changes have their effect on the owl population.
19:49More voles mean better fed owls which produce bigger clutches of eggs
19:52and rear more chicks.
19:54And as the number of owls increases, so they spread out into new territory.
19:58I'm in Finland, very close to the Russian border.
20:04In fact, those pine forests behind me are actually in Russia.
20:09But the frontier is no barrier to the bird they call the phantom of the north,
20:13the great grey owl.
20:15And in years when the vol population is high,
20:19the owl comes across these frontiers and into the Finnish pine forest.
20:24And I know they're here already because I've just picked up this.
20:27This is an owl pellet.
20:30All owls, as part of their natural digestion,
20:34throw up the fur and their bones of their prey.
20:37And this, I can see, has actually got vole skulls in it.
20:43But to discover exactly what the state of the vole population is at the moment,
20:48I'll have to look inside the nest of a great grey owl.
20:52And to do that, I'll need this.
20:56All owls are fairly ferocious,
21:00and the great grey owl certainly can be.
21:03So as part of the standard equipment of looking for owl's nests,
21:07you need this.
21:08Up there is one of their nests,
21:15and the female has just flown off.
21:17She's perching in that tree over there,
21:19keeping a very close eye on me.
21:22If I go up and have a look in the nest,
21:24I may be able to get some idea as to how the vole cycle is going.
21:29There's just one chick.
21:48If the voles had been at the height of their population,
21:53there would probably be about four chicks in such a nest as this.
21:57But the fact that there's only one makes it pretty clear
22:00that the vole population is already beginning to crash.
22:04So it's very likely that the female and her mate
22:09will soon be on their way back to Russia.
22:17There's now just a month left of the short northern summer.
22:21Many of the birds that came up here to harvest the insects and to breed
22:24will soon be moving back again to avoid the severities of the coming winter.
22:30Some, like the redwing, will go to open pasture land down south.
22:35The brambling prefers beech woodland
22:38and will leave almost as soon as it's finished its summer molt.
22:40The hawk owl is driven south by hunger,
22:50for as the forest gets colder,
22:52there is less and less food to be found.
22:56As it flies south,
22:58so the trees beneath change character.
23:00The ranks of dark conifers are replaced
23:02by the brighter green of the broadleaved trees,
23:06oak and ash,
23:08birch and beech.
23:09Deliccfish.
23:18Trimcish.
23:27Trimcfish.
23:32Trimcish.
23:33Trimcish.
23:34Trimcish.
23:35Down here, the weather's warmer,
23:36the summers are longer and the woodlands are free of frost not for just two or
23:41three months in the year but for eight or nine and the shape of the trees is
23:46very different instead of their branches drooping down and so shedding the snow
23:51these branches spread out widely carrying tier upon tier of leaves with
23:56which to catch the abundant energy of the Sun and the leaves are very different
24:00they're not covered with a thick protective rind but are thin delicate
24:05structures during the summer water is more accessible so there is less need to
24:10take rigorous measures to conserve it indeed during hot days the trees
24:15evaporate large quantities to keep cool so the pores through which they breathe
24:19are numerous and not in pits as they are in the pines
24:24these succulent soft leaves unlike pine needles are relished as food by all
24:32kinds of creatures
24:39large animals like deer take many of them but the greatest quantity by far is
24:45gathered by insects
24:54the forest canopy in late summer has more birds in it than at any other time
25:16of the year they're returning migrants newly arrived from the north resident
25:21breeders gathering food to feed their second families of the season and young
25:25fledglings starting to forage for themselves and still not sure what is
25:29edible and what isn't nearly all of them are hunting for insects and the crop
25:34they take is huge
25:37not surprisingly the insects have evolved many ways of protecting themselves they
25:54snip off half-eaten leaves so as to give the minimum sign of their presence they
25:58disguise themselves as a blob of cuckoo spit or a bird dropping but if they move as
26:03eventually they must their concealment is lost
26:17some hang in places which are difficult to reach
26:20this might baffle a fledgling but an adult great tit is both experienced and agile
26:26the tree creeper specializes in insects that live on bark
26:39a poplar hawk moth tries to defend itself by pretending to be fierce
26:47the nuthatch habitually works its way down the trunk and that way may see
27:06insects that have been overlooked by tree creepers that habitually come up it
27:10one of the most expert of all bark feeders and in some ways the most
27:32specialized of all the birds living in the tall trees of these forests are the
27:36woodpeckers the greatest spotted woodpecker is typical of them its hearing is excellent
27:41and it locates the grubs it seeks by the tiny sounds they make as they move inside
27:46the bark
27:50its tail feathers have strong quills and serve as props for its body
27:55its bill has a resilient pad at the base which cushions its brain from the shock of
28:00its drilling its feet give it a grip in all directions with two toes pointing forwards
28:08and two backwards each continent has its own range of woodpeckers
28:13Europe has ten species but here in North America there are over twice as many
28:18this one a sap sucker drills holes in trees not for insects but for sap
28:23he digs lines of these wells in many different kinds of trees
28:27each little hole points slightly downwards so that the sap doesn't trickle out
28:32but collects in a small pool inside and the sap sucker collects it with its tongue
28:37and so do other birds
28:42a hummingbird
28:44most of its family live in the tropics and feed on nectar
28:47but this one comes north in the summer and finds tree sap just as acceptable
28:54flies too come to the sweet sap
28:58in late summer the parent sap suckers lead their fledglings to the wells and leave them to feast
29:20not only on the sap but on the insects it attracts
29:23this american woodpecker uses its drilling skills to bore neat sockets in dead tree trunks
29:32acorns are its main food but during the season there are far more acorns than the woodpeckers can eat immediately
29:38but they don't leave them for others
29:41several birds share a communal acorn treasury like this one
29:45they hammer the acorns into the hole so firmly that few other creatures can get them out
29:50and the store will keep the acorn woodpeckers supplied throughout the rest of the year
30:01the ripening acorns herald the end of summer and the beginning of autumn
30:05trees and bushes proffer their seeds to the forest animals
30:09some are wrapped in soft and tasty flesh to tempt the animals to eat them
30:13and so transport them to new sites
30:16others are packed with nourishment not for animals but to provide food for the germinating seedling
30:23but the animals eat them just the same
30:25even the hard and unpromising looking acorns of the american pin oak are collected by raccoons
30:31the squirrels habit of burying acorns for the winter store has been the beginning of many a note
30:46the black bear on occasion will eat fish and voles and even carrion but much of its diet is vegetable
30:53it will dig for roots and even eat pine cones but it has a very sweet tooth and just now it relishes the fruit
31:06all sorts of mammals are now clambering around in the trees in search of fruit
31:23the possum a strange primitive mammal of the americas related more closely to kangaroos than to rats
31:29eats almost anything
31:35few of them can get to the very tops of the trees or the very thinnest twig
31:39but a chipmunk can
31:44the chills of autumn presage the coming of winter
31:48the delicate leaves worked efficiently throughout the warm and moist summer
31:52but they're not suited to cold weather
31:54frost will damage them
31:56their abundant pores would lose too much water
31:58so the green chlorophyll in them is broken down and withdrawn into the tree
32:03revealing the red and brown waste products
32:06and the leaves fall
32:08and they too provide food for another woodland community
32:13the inhabitants of the leaf litter
32:15there may be a hundred thousand box mites in every cubic yard
32:23and there are many other creatures too chewing their way through the dead leaves
32:28extracting what nutriment they can
32:30and leaving the remainder to be dealt with by fungi and bacteria
32:42they themselves are hunted by monsters in miniature pseudo scorpions
32:46horrific in close-up but perhaps fortunately the size of a pinhead
32:53they are shortening to the dead leaves
32:54they buy into the rareastre
32:55so they often
33:09they won't come.
33:10Snails are giants in comparison, and since they carry their shells around with them,
33:33they might seem to be fairly well protected against any creatures smaller than a bird.
33:38But one particular beetle has specialised equipment for dealing with them.
33:44Its head and jaws are long and thin.
34:08Almost hidden in the leaves of these American woods are some spectacularly coloured little creatures hardly bigger than worms.
34:22They're amphibians, salamanders. Almost every range of mountains in the United States has its own species with its own particular colours.
34:34But being nocturnal, they're rarely seen.
34:44Shrews eat most small living things they come across, and they're formidable hunters, for they're one of the few mammals that has a poisonous bite.
35:02The salamander's only defence is to produce an acrid liquid from glands on its tail.
35:16The first time a shrew encounters this, it usually takes no notice and eats the salamander.
35:22But apparently the taste is not very nice, for on later encounters, like this one,
35:26one sniff is enough to remind the shrew that the meal won't be a good one, and it leaves the salamander alone.
35:32The summer visitors have departed. The woods have fallen silent. The days are shortening, and the temperature falling.
35:48Theling of the olive oil. The liquid is filled with red water, which fills the river and the water.
36:03Here are the flowers to the soil, and the leaves are full of water and water.
36:08The wholerinacidon is the rocks, and the leaves are when it comes across.
36:11Th ŠæŠ»Š°Ń gas is the same, and it's beautiful.
36:15Eventually, the land is gripped tight by frost.
36:45It's late winter, the once resplendent trees are now mere skeletons, and life in these
36:55woodlands has come almost to a complete standstill.
36:59The trees, without their leaves, can't grow.
37:02The birds that came visiting up here during the summer have now retreated south, and some
37:07of these small mammals have crawled into holes and gone to sleep.
37:12Their heartbeat has almost stopped, their bodies have become as cold as stone.
37:17They're hibernating.
37:19But that sleep doesn't last throughout the winter.
37:23They wake up every four or five days and go and look for food, like, for example, those
37:28small chipmunks over there.
37:31Not only warmth, but intense cold will bring them out, for although their body temperature
37:35falls while they're hibernating, if it drops to freezing point, they will die.
37:40So in really cold spells, they must get up and warm themselves with a little exercise, even
37:45though it dangerously depletes their fat reserves.
37:49But in these American woodlands, there is one spectacular sleeper, who dozes for months
37:54on end.
37:55Just look at this.
38:05A black bear.
38:09She retired to this den in early autumn, and after a month or so of drowsiness produced
38:13her cubs.
38:15In the colder northern parts of these woods, she may spend six or seven months here, during
38:19which time she suckles her cubs, but neither feeds herself nor urinates nor defecates.
38:25So she spends the majority of her life half asleep.
38:32When spring at last comes, the brown carpet of rotting leaves is suddenly flooded with colour.
38:40The plants that live close to the ground now make haste to sprout and flower and soak up
38:45the spring sunshine before the trees above produce their own leaves and cut out the light.
38:55The bear's den is empty, but the owners haven't gone far.
39:09There's still not much to eat, only a few leaves, nor will there be until the first of the berries
39:13come into fruit in summer.
39:15But meanwhile, at least the sun is warm.
39:25Another mother spends the spring up in a tree, a wood duck, and she is about to leave.
39:37The hole has provided a secure nest, but all ducklings follow their mothers as soon as
39:42they hatch.
39:51And now new forms appear from among the dead leaves.
40:19MUSIC PLAYS
40:25I'm sorry.
40:55Spring showers soak the woodlands and create just the moist, warm conditions needed by the fungi to produce their fruiting bodies.
41:03These must be mature and ready to discharge their microscopic spores by the time the dry winds of summer begin to blow,
41:10so that their spores, like dust, will be carried all through the forest.
41:14Once, the woods of North America stretched over the eastern half of the continent in an almost continuous band hundreds of miles deep.
41:26Today, the majority has been felled to make space for farmland and cities, but enough remains to make plain their splendor.
41:33And now we've come farther south still.
41:39I'm on the borders of Florida and Georgia in the southern United States.
41:44And here, it's very hot in the summer, and the winters are very mild, with only a few frosts and none of them severe.
41:50So some of the broadleaved trees here, like for example this oak, don't shed all their leaves in the autumn, but keep them throughout the year and continue growing.
42:02And these aren't the only evergreens that are here either.
42:06There are pines.
42:07In some parts, where the soil is very rocky or sandy and poor in nutrients, the pines will grow because nothing else can survive there.
42:16But this pine forest owes its existence to another factor altogether.
42:31Oak saplings are killed within minutes by fire.
42:37But the terminal buds of young pines are surrounded by a shock of needles.
42:42They burn at a relatively low temperature.
42:45And by the time the flames have consumed them, the main fire has swept by.
42:50And the bud at the top of the stem, from which new growth will come, is still unharmed.
42:58Fires like these are not just the work of careless people.
43:01They occur naturally.
43:02The spark that regularly sets fire to these forests is lightning.
43:08In this part of the southern states, violent thunderstorms are common.
43:11And lightning often strikes the taller trees, scoring a deep groove down the length of the trunk as it flashes down to earth.
43:18And this, at my feet, is the tinder which set it aflame.
43:26These are pine needles.
43:29And they're so full of resin and they're so dry that they flame up very easily.
43:34But the fire they produce is not very hot.
43:37And it's also very short-lived.
43:38So that if any creature can survive fire for just one or two minutes, then it can survive a fire like this.
43:48The rattlesnake, like many other ground-living animals, regularly takes refuge from the midday sun in holes.
43:55So now it knows exactly where to go to escape the fire.
43:59But this hole is already occupied by its digger and owner.
44:23A gopher tortoise.
44:25Rattlesnake and tortoise do not normally interfere with one another.
44:55And that seems to be the way things are going to stay.
45:03But in the back of the burrow lies another refugee, an indigo snake.
45:07And it, on occasion, eats rattlesnakes.
45:10Rattlesnakes.
45:25But the fire is passing.
45:33And the rattlesnake can return to the forest.
45:42Some insects don't avoid fire.
45:45They actively seek it.
45:46Beetles find it difficult to lay their eggs in the pines because the trees swamp them with resin.
45:51But a tree killed by fire can't resist.
45:55And these beetles take advantage of the situation.
45:58They have pits behind their legs which are sensitive to infrared rays.
46:02And therefore they can detect the slightest rise in temperature.
46:05And with these to guide them, they travel from all over the forest to the wake of the fire.
46:09And arrive in hundreds.
46:11Quickly, they mate.
46:23The females crawl all over the scorched trunks, seeking crevices in the bark into which they can lay their eggs.
46:30So ensuring that their grubs will have some nice nutritious bark to chew.
46:34As insects assemble in the burnt forest, the insect eaters follow.
46:41The oak toad almost exactly matches the colour of the charred forest floor.
46:48Other more conspicuous hunters wait on newly emerged shoots.
46:51Within a couple of months of a summer fire, the forest has more than recovered.
47:02It is rejuvenated.
47:04The fire has cleared away the old growth on the ground.
47:07And by reducing the pine needles to ash, has released their nutrients into the soil.
47:11And now the ground sprouts more flowers than at any other time.
47:21Because of regular fires, big bushes can't establish themselves here.
47:33So swampy areas are not colonised and sucked dry by them, as happens elsewhere.
47:39And open marshes remain where pitcher plants can grow and where frogs can swim and breed.
47:45Indeed, one species of frog lives nowhere else but in these pools in the American pine barrens.
47:51The woodpeckers here can't excavate their nest in dead trees, as do woodpeckers elsewhere.
48:12For in this fire-ravaged forest, they would risk incineration.
48:16So the red-cockaded woodpecker drills its holes in living pines.
48:21But the wood is so hard, it takes several woodpeckers about two years to dig the hole.
48:29Resinous sap seeps out around the hole where the outer layers of the tree have been breached.
48:34So the birds make their hole low down on the trunk,
48:38where the inner sap-free heartwood is thick enough to accommodate the entire nest.
48:42The flow of resin is diverted to the outside by drilling pits like sap wells above and below the hole.
48:49It's in these laboriously excavated holes that the red-cockaded woodpecker raises its young.
49:02The holes are very conspicuous, for each is surrounded by a sheet of yellow congealed resin.
49:14The rat-snake is a great robber of nests and stealer of chicks.
49:22It's an extremely skilful tree-climber.
49:40Since the woodpecker's hole in the living tree has to be fairly low down on the trunk,
49:44it is within easy reach of the snake and therefore might seem to be in considerable danger.
49:51But now the other function of all that resin,
49:54deliberately produced around the nest by the woodpecker,
49:56is about to become clear.
49:58The woodpecker's hole in the living tree-climber.
50:28The shackles in the resin seem to irritate the snake beyond endurance,
50:31and it arches its body away.
50:37Eventually, it's too much.
50:43So fire, one way or another,
50:45influences the whole community of animals and plants in the pine forests of the south.
50:51This injury was also caused by fire,
50:54and this is also a coniferous tree,
50:57but a very different one.
51:00To start with, it's over 40 feet across along its base,
51:04and it's 267 and a half feet high.
51:10This is a giant sequoia.
51:13It's thought to be about 2,500 years old,
51:19but the largest individual tree of all is this one,
51:23known as the General Sherman.
51:26It's just taller,
51:27and it's estimated to weigh 1,385 tons,
51:33and that makes it the most massive living organism in the world.
51:36Although these trees are growing almost as far south as the southern pines,
51:43the climate here, 2,000 meters up in the Sierra Nevada mountains,
51:47is much colder,
51:49and snow lies on the ground for almost half the year.
51:52It's as though by climbing to this height,
51:54we have returned climatically to the great forests of the north.
51:58During the Ice Age,
51:59these sequoias grew over much of North America,
52:02but when some 8,000 years ago the earth began to warm,
52:06they died out except for these isolated groups high up in the mountains.
52:19We've traveled some 2,000 miles southwards
52:23since we started at the tree line near the Arctic Circle,
52:27and in all that vast territory,
52:29the majority of the forest trees have been conifers.
52:33So it seems only right and proper
52:35that we should end with these,
52:38the noblest of them all.
52:40As a group,
52:41the conifers owe much of their success
52:43to their ability to cope with the changeable northern climate.
52:48They can survive both the short, dark days of winter
52:51with their bitter cold,
52:53as well as the long, sunny days of summer
52:54with their raging fires.
52:56But if we continue a further 1,000 miles southwards,
53:00we come to the tropics,
53:02and there the climate is radically different.
53:05It's no longer very variable,
53:07but remarkably constant,
53:08with much the same amounts of light
53:10and rain and heat
53:12throughout the year.
53:14There the other great group of forest trees,
53:17the broad-leaved trees,
53:19come into their own.
53:20That is the jungle,
53:22and that's where we will be
53:23in the next program.
53:24And that's where we will be in the next program.
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