BBC.The.Green.Planet.3of5.Seasonal.Worlds.1080p.HDTV.x265.AAC.MVGroup.org.eng Subtitles

00:00:50,200 --> 00:00:53,This is the boreal forest...

00:00:58,440 --> 00:01:01,..the largest forest on Earth.

00:01:02,680 --> 00:01:06,750 billion trees...

00:01:09,160 --> 00:01:12,..smothered by snow throughout
the winter.

00:01:17,640 --> 00:01:22,This is the northernmost boundary
of an extraordinary world.

00:01:26,200 --> 00:01:30,I'm standing at the edge
of the Arctic Circle.

00:01:30,840 --> 00:01:35,To the north of me lies a land
dominated for most of the year

00:01:35,320 --> 00:01:37,by snow and ice.

00:01:37,600 --> 00:01:41,3,000 miles to the south -
the tropics,

00:01:41,280 --> 00:01:45,bathed the year round
in warm sunshine.

00:01:45,320 --> 00:01:48,And in between,
a very different world,

00:01:48,960 --> 00:01:52,dominated by relentless change.

00:01:58,320 --> 00:02:02,An endless cycle
of four distinct seasons,

00:02:02,320 --> 00:02:04,each with its own challenges.

00:02:06,200 --> 00:02:09,The short, freezing days of winter

00:02:09,000 --> 00:02:12,give way to the urgent awakening
of spring.

00:02:15,720 --> 00:02:19,And the long, hot days of summer

00:02:19,280 --> 00:02:22,yield to the cooling of autumn.

00:02:26,920 --> 00:02:29,Opportunities will be brief.

00:02:37,280 --> 00:02:39,To survive these extremes,

00:02:39,360 --> 00:02:43,plants have not only g***t to be
hardy and resilient,

00:02:43,600 --> 00:02:47,but many of them have developed
special strategies

00:02:47,080 --> 00:02:51,in order to meet the demands
of this seasonal world.

00:02:53,560 --> 00:02:57,To succeed, they must get
their timing just right.

00:03:00,880 --> 00:03:04,For months now,
this world has been asleep.

00:03:05,720 --> 00:03:08,But change is coming.

00:03:23,400 --> 00:03:26,Spring is on its way.

00:03:49,400 --> 00:03:53,In Canada, the forests are
starting to stir.

00:03:55,920 --> 00:03:59,Throughout the winter,
the sugar maples here

00:03:59,360 --> 00:04:03,have kept stores of nutrients
ready for this moment.

00:04:06,440 --> 00:04:09,Now, as temperatures start to rise,

00:04:09,720 --> 00:04:13,those nutrients must be brought
up from the roots.

00:04:20,880 --> 00:04:23,Sap is on the rise.

00:04:28,800 --> 00:04:31,Fuel for new green growth.

00:04:42,840 --> 00:04:45,But just as growth reaches
full speed...

00:04:47,000 --> 00:04:49,..robbers arrive.

00:05:08,880 --> 00:05:11,A sap sucker.

00:05:11,440 --> 00:05:15,A thief in search of maple syrup.

00:05:33,560 --> 00:05:36,The tree can tolerate
hundreds of wounds.

00:05:43,840 --> 00:05:47,But if they completely encircle
the trunk,

00:05:47,600 --> 00:05:50,the tree will eventually die.

00:05:58,080 --> 00:06:01,The sap sucker's break-in
hasn't gone unnoticed.

00:06:11,000 --> 00:06:17,Hummingbirds, squirrels and insects

00:06:17,480 --> 00:06:20,all invade the sap sucker's
territory,

00:06:20,720 --> 00:06:22,trying to steal a meal.

00:06:27,000 --> 00:06:30,But unwittingly, they help the tree.

00:06:36,000 --> 00:06:38,Time spent chasing the
competition...

00:06:40,280 --> 00:06:43,..means less time to drill
new holes.

00:07:13,360 --> 00:07:17,The tree gets a chance to repair
its wounds.

00:07:19,400 --> 00:07:22,And the sap can rise freely again.

00:07:29,800 --> 00:07:34,So this year, at least, the tree
will once more produce its leaves.

00:07:39,360 --> 00:07:42,Hundreds of miniature solar panels

00:07:42,200 --> 00:07:44,that collect energy from
the sunlight.

00:07:48,080 --> 00:07:52,Each leaf is covered by millions
of microscopic pores.

00:07:53,520 --> 00:07:55,Stomata.

00:07:58,120 --> 00:08:00,They take in carbon dioxide...

00:08:02,720 --> 00:08:05,..and release oxygen and
water vapour

00:08:05,600 --> 00:08:09,in a process that produces
high-energy fuel.

00:08:21,640 --> 00:08:24,All the trees here can now use
that fuel

00:08:24,600 --> 00:08:27,to grow over the coming months.

00:08:46,440 --> 00:08:51,As spring proceeds,
the power of the sun increases.

00:08:55,120 --> 00:08:57,On river banks across Europe,

00:08:57,360 --> 00:09:02,many plants have been lying dormant
underground,

00:09:02,800 --> 00:09:05,waiting for the earth to warm.

00:09:11,920 --> 00:09:14,And now a race begins.

00:09:21,760 --> 00:09:26,Among the first to start
are nettles - the sprinters.

00:09:32,280 --> 00:09:36,Then, only just behind,
come the brambles.

00:09:37,560 --> 00:09:41,They're much more aggressive
and have backward-pointed hooks

00:09:41,240 --> 00:09:44,with which to scramble
over their rivals.

00:09:46,880 --> 00:09:49,Last to come - the climbers.

00:09:53,200 --> 00:09:55,Hops...

00:09:55,520 --> 00:09:57,..and bryony.

00:10:01,200 --> 00:10:04,They lasso their way
towards the light.

00:10:33,440 --> 00:10:38,Soon, every inch of space and every
patch of light has been claimed.

00:10:41,600 --> 00:10:43,But hidden in the shadows,

00:10:43,480 --> 00:10:47,another plant has been waiting
to make its move.

00:10:56,800 --> 00:10:59,This...

00:10:59,920 --> 00:11:01,..is dodder.

00:11:08,160 --> 00:11:10,A hunter...

00:11:11,840 --> 00:11:14,..with an exceptional
sense of smell.

00:11:21,480 --> 00:11:24,Moving swiftly, it searches
for its prey.

00:11:28,280 --> 00:11:31,It detects the scent of
a young nettle.

00:11:50,440 --> 00:11:53,The dodder punctures the nettle's
stem

00:11:53,880 --> 00:11:56,and s***s out the nutritious sap.

00:12:00,320 --> 00:12:03,And it doesn't stop at just
one victim.

00:12:06,280 --> 00:12:09,With its energy supply assured,

00:12:09,080 --> 00:12:11,it multiplies.

00:12:20,080 --> 00:12:23,It's a parasite with an insatiable
appetite.

00:13:25,920 --> 00:13:31,But remarkably, its victims can now
exploit the dodder...

00:13:33,720 --> 00:13:36,..when other springtime enemies
appear.

00:13:40,480 --> 00:13:42,Caterpillars.

00:13:53,760 --> 00:13:57,When under attack, a leaf sends out
a signal

00:13:57,360 --> 00:14:01,telling the rest of the plant
to start building defences...

00:14:04,080 --> 00:14:07,..foul-tasting toxins that deter
the caterpillars.

00:14:10,960 --> 00:14:13,In an extraordinary twist,

00:14:13,440 --> 00:14:16,the stems of the dodder
interconnecting the plants

00:14:16,720 --> 00:14:20,are now being used as
lines of communication

00:14:20,520 --> 00:14:24,to relay these warning signals
from plant to plant.

00:14:31,520 --> 00:14:35,They respond by producing
their own protective chemicals.

00:14:39,640 --> 00:14:44,Eventually, the whole river bank
becomes one huge defensive network.

00:14:46,400 --> 00:14:50,And the one-time rivals
are now better off together.

00:15:11,920 --> 00:15:17,The first warm days of spring
encourage some plants to flower

00:15:17,360 --> 00:15:19,and get ahead of the competition...

00:15:21,480 --> 00:15:25,..creating beautiful displays
throughout the seasonal world.

00:15:28,800 --> 00:15:32,From the spectacular
cherry blossoms of Japan...

00:15:35,280 --> 00:15:39,..to the goldfield flowers
of California.

00:15:43,400 --> 00:15:46,But spring flowering is risky.

00:15:46,160 --> 00:15:48,If they flower too early, it may not
be warm enough

00:15:48,880 --> 00:15:51,for pollinating insects
to be active.

00:15:53,320 --> 00:15:57,But the common daisy gives
them every opportunity.

00:16:01,280 --> 00:16:05,The warmer the flowers are,
the more attractive they are -

00:16:05,160 --> 00:16:09,and they have a remarkable strategy
in order to maximise this.

00:16:11,640 --> 00:16:15,They were closed up tightly
throughout the night

00:16:15,120 --> 00:16:17,as a protection against the
elements.

00:16:17,520 --> 00:16:21,But once they feel the warmth and
the light of the sun,

00:16:21,160 --> 00:16:23,they spring into action.

00:16:37,640 --> 00:16:40,It's a behaviour called
heliotropism.

00:16:42,280 --> 00:16:46,They turn to keep facing the sun,

00:16:46,160 --> 00:16:48,absorbing as much heat as they can.

00:17:05,680 --> 00:17:09,This is a thermal camera,

00:17:09,360 --> 00:17:14,and it will tell me the difference
between the surrounding temperature

00:17:14,720 --> 00:17:18,and the temperature in the centre
of a daisy flower.

00:17:18,840 --> 00:17:22,The surroundings - 12 degrees.

00:17:23,840 --> 00:17:25,In the centre of a flower...

00:17:27,600 --> 00:17:29,..21.

00:17:31,840 --> 00:17:37,Pollinators such as bees and wasps
prefer the warmed-up flowers

00:17:37,280 --> 00:17:40,because they can get a share
of the heat for themselves.

00:17:42,080 --> 00:17:46,As a...