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(VARIOUS ANIMAL NOISES)

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High in the canopy of the South Amecan
rainforest, a fruit is falling.

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It has come from a plant sitting on a branch
of one of the giant trees.

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Now it will rot and release a thousand seeds.

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If the seedlings are to survive, they will
have to gain a position like their parents.

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Somehow, they've got to
get up into the canopy and the sunshine.

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The shoots that come from the seeds, like all
shoots, can sense the light  -  they can see.

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Each, as you might expect, sprouts upwards.

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00:01:51,880 --> 00:01:55,350
But now these infant plants
behave very strangely.

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They don't head for the brightest light,
as most seedlings do,

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they seek the densest shade.

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And that usually lies
around the trunk of the nearest tree.

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Each seedling is fuelled entirely by the store
of food its parents deposited within the seed.

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That is enough to enable it
to travel about six feet.

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If it doesn't find what it's looking for
within that distance, it will die of starvation.

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These have made it to first base.

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They've reached a vertical surface, a tree trunk.

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As soon as one touches it,
its behaviour changes dramatically.

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It starts growing upwards,
and as it does, it puts out its first leaves.

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Now, for the first time,
it can manufacture food for itself.

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With each additional leaf,
the young plant increases in strength.

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It holds these small,
circular leaves flat against the bark.

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As it gains height,
it produces bigger and bigger ones.

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And now, fifty feet above the forest floor,

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and many months since it first emerged
as a slim green shoot from its seed,

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this extraordinarily active plant has changed
the shape of its leaves once again.

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They've developed the slits and the holes
that give it the name of cheese plant.

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The small, round leaves pressed up against
this trunk, and the stem that bore them,

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have now shrivelled and died.

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The cheese plant has reached its true home,
the forest canopy,

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and these are its adult leaves.

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Cheese plant leaves unfurl
from pointed spikes like rolled umbrellas,

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but there are many ways of unpacking the green
sheets plants must open to catch the sun.

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These are ferns.

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A tropical alocasia.

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The needle - shaped leaves of a larch.

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The broad, five - fingered hand of a chestnut.

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Sycamore.

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Leaves are the factories
in which plants make their food.

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They are powered by sunshine,

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and they use the simplest of raw materials:
air, water and a few minerals.

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The process is the unique talent of plants.
No animals can do such a thing,

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so all animals, too, depend, first -  or
second - hand, on the food produced here.

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This is the very basis of life.

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Air seeps into the leaves
through pores on their surface.

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It circulates within and reaches tiny granules
that contain a green substance, chlorophyll.

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This is the key facilitator,
that uses the energy of the sun

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to bond carbon dioxide to hydrogen,
derived from water

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and produces carbohydrate,
sugars and starches.

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These, dissolved in sap, are then carried
from the leaf into the body of the plant,

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even during the night,
when the leaf factory has shut down.

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Come the dawn, the sun reappears
and the process starts up again.

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In open country, in a hedgerow, perhaps,

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there is so much light that,
as the sun climbs higher,

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a plant has little difficulty
in getting all it needs.

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In thick forest, it's not so easy.

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A plant growing beneath the canopy
has to continually move its leaves

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to catch what it can
from the shifting shafts of the sunlight.

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Above, the trees position their leaves
with such accuracy

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that they form a close - fitting mosaic.

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The canopy is so efficient at gathering light
that very little filters down here.

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There are leaves, of course  -  this is
the young sapling of one of the canopy trees,

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but it is growing hardly at all.

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It's waiting for the chance that one of the adult
trees will fall, releasing a flood of light.

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Then it can grow, and it'll race upwards
to try and claim the vacant space.

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It can wait ten, twenty years for that chance,

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but until it comes, there's simply
not enough light for it to grow any further.

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For most, of course, that chance
will never come. Most will die as saplings.

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But some plants that spend their whole
lives here on the dim forest floor  -

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this begonia, for example.

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It produces big leaves,
flowers and sets seeds, all in this dim light.

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How?

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The secret is in the leaves.

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To start with, they have red undersides.

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That means light falling on the surface
of the leaf and going through it is not lost

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but reflected back into the body of the leaf.

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So when sunlight does,
for a short time, fall on the leaf,

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the plant is able to take
maximum advantage of it.

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Another species of begonia
has a different light - gathering trick.

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Small patches on their leaves are transparent,
and act as tiny lenses,

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gathering the feeble light and focusing it
onto the grains of chlorophyll within.

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But plants need something else as well as
light in order to make food for themselves.

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They need water
and the nutrients that are dissolved in it.

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And that, of course,
they suck up from the ground.

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The roots with which they do so
probe downwards, seeking moisture.

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To get that, they have to position themselves
with just as much accuracy

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as the leaves do when finding light.

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Having found water, they put out thin rootlets,
and from them, a fur of tiny hairs,

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so multiplying thousands of times the surface
area through which water can be sucked in.

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So the soil in a woodland
is a tangle of precisely - placed rootlets

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from many different kinds of plants,

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each individual doing its best to ensure
that it gets its fair share of moisture.

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If the rainfall is reasonably good
for much of the year,

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if the water in the ground
can dissolve enough nutrients from the soil,

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then some plants will become very big indeed.

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Growing seventy feet tall, like this sycamore,
brings it great advantages.

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It allows it to overtop its neighbours,
so it can get all the sunshine it needs,

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and it enables it to spread out
a huge surface area of leaves,

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and through their pores
it can suck in carbon dioxide from the air.

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But it also brings considerable problems.

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As well as carbon dioxide,
the leaves need water in order to make food.

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And water in the leaf
can easily evaporate through the pores.

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Indeed, 90% of the water sucked in by the roots

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is lost through the surface of the leaves
at the top of the tree.

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But pumping water up here to this height
can cause considerable problems.

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To pump this jet of water
seventy feet up in the air, here,

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it takes that huge, big, noisy engine down there.

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But this tree pumps up
about 100 gallons every hour,

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and manages to do so in total silence.

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How?

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The answer is to be found in the tree's trunk.

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The central part of this is wood.

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Around the outside of this pillar
there are ranks of hair - thin pipes.

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Those immediately beneath the bark
carry the food - laden sap down from the leaves.

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Farther inside the trunk,
there's another set of tubes.

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These are the ones that carry the water up.

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They are continuous pipes
that extend the whole length of the trunk.

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As the water evaporates in the leaves above,

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the long, thin threads of it
are pulled up the tubes, into the branches,

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and ultimately into the leaves themselves.

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Some of it is used in the food - making process,

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the rest evaporates
through the leaf pores as vapour.

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Of course, leaves can't absorb water directly.

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Indeed, water lying on their surface
can cause problems by clogging up the pores.

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So some leaves have shapes
which help to reduce that problem.

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Plants growing in the rainforests
of the tropics have particular difficulties,

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for here the rain drenches down in torrents.

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They have to be tough to withstand the pounding.

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They also have to have gutters
to carry away the water.

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Many have pointed tips at the end,

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ensuring the water doesn't linger on the leaf
but drains rapidly and completely away

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and doesn't interfere
with the intake of air through the leaf pores.

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Others use dense hairs to keep their pores free.

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But rainfall is the least of the dangers
that threaten leaves.

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Leaves are breakfast, lunch and supper
for these proboscis monkeys in Borneo.

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They eat pretty well nothing else.

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Maybe a few flower petals now and then,
perhaps a little fruit,

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but otherwise entirely leaves.

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But leaves have a great drawback as food  - 
they are not, in fact, very nutritious.

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So these monkeys have to spend hours
and hours and hours every day,

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stripping the trees of their leaves.

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Leaf sap, loaded with starch and sugars,
is certainly nutritious.

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The problem comes
from the walls of the cells that enclose that sap.

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They are made of cellulose, and mammals'
digestive juices can't deal with that.

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Bacteria, however, can, and those animals,
like these monkeys, that eat a lot of leaves,

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have to sit around after feeding,

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to give time for the bacterial colonies
in their stomachs to deal with their difficult meals.

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Despite these drawbacks,

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Iots of mammals, and even some birds
and reptiles, have taken to this diet.

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But, in fact, such big leaf - eaters
are in the minority.

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The plants' most numerous attackers
by far are insects.

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All around me in this Borneo rainforest, millions
of tiny mouths are munching away invisibly.

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To give you some idea
of the lengths to which an insect will go

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in order to get a vegetarian meal in safety,
look at this.

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Clearly it's a badly - damaged leaf,

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but where is the creature
that's doing the damage?

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This is it, a tiny caterpillar.

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It's soft, it's defenceless, it's clearly
an excellent mouthful for many a bird.

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So if it is to survive,
it has to take steps to protect itself.

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It starts by making a semi - circular cut
into the leaf from the margin.

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But when the cut is only half - complete,
it starts from the other end.

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It spins silk across the hinge.
That, as it dries, contracts,

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and helps the caterpillar
pull over the segment to form a roof.

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To make its tent a little more commodious,
it cuts a pleat,

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pulls it across, and now it's got a little wigwam.

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The whole process only takes a few hours

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and is usually done at night,
when there are no birds around.

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Now the caterpillar can feed in safety,

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shaving off the soft surface layers of the leaf
out of the sight of any hungry bird,

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and at significant cost to the plant.

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The damage and loss inflicted on plants
by animals both large and small

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is huge and never - ending.

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Plants, of course,
do what they can to defend themselves.

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Some develop long, ferocious,
needle - sharp spines.

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These, you might think,
would be sufficient to deter anything.

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But not so.

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This tongue is so mobile that it can pick out
the soft leaves from between the spines.

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This hide is so tough that even
the sharpest spines don't puncture it easily.

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And these rubbery lips seem able to survive
the most prickly of mouthfuls.

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The attacker, of course, is a giraffe,

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and it can reach leaves
fifteen feet above the ground.

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It's the tallest of all living animals.

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Such intensive grazing
makes it very difficult for plants here

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to grow much bigger than stunted bushes.

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Thanks to their thorny defences,
some acacias do succeed in growing to maturity.

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Then they develop the umbrella shape
so characteristic of the East African grasslands.

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And now, at last, the acacia tree
has some parts that even a giraffe can't reach:

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the branches up to the top in the centre.

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There, the acacia can save precious energy

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and reduce the scale of its thorny armaments.

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On the outside, the thorns are as long
and as dense as anywhere,

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but in the middle of the crown,
there are no thorns whatsoever.

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The techniques employed by plants
to defend themselves are very varied indeed.

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Some involve extremely refined armaments.

196
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This is one of the commonest plants
of the European countryside.

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In summer, many might think its tall stems
are only too abundant in the hedgerows.

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Beneath its leaves,
it produces sprays of tiny flowers.

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We can all recognise these as nettles,
and learned to do so when we were young,

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for the good reason
that they have painful stings.

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But this sting is actually
quite a complex weapon. Watch.

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Ow!

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It's a hollow hair made of silica,
the mineral from which we make glass,

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and it's filled with poison.

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Its tip is so sharp
that the slightest touch cuts human skin,

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and so fragile it breaks at that touch
and releases poison into the wound.

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The result is a painful swelling.

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It's not just young humans
who learn to avoid nettles, so do young rabbits.

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00:23:49,920 --> 00:23:53,515
This one already knows
that green leaves are good to eat.

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It's yet to learn
that some can defend themselves.

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The nose has little protective fur and that hurt.

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It's better to stick to grass.

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00:24:14,160 --> 00:24:17,789
With such an effective armoury,
nettles grow unmolested,

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and rapidly establish themselves
in great thickets.

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00:24:21,600 --> 00:24:24,672
But there are two kinds of nettles growing here.

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The kind on the right is slightly different.

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Its leaves look just like those
of a stinging nettle, but its white, tubular flowers

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are quite different
from those small brown ones of the true nettle.

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In fact, this is a relative of mint and thyme,
this is the deadnettle,

220
00:24:48,280 --> 00:24:51,795
and it has no sting of any kind.

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But even an adult rabbit
seems not to know the difference,

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and it certainly doesn't risk a sting.

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The deadnettle,
without going to the expense and trouble

224
00:25:01,720 --> 00:25:06,874
of producing poisoned hypodermic needles,
has found protection in mimicry.

225
00:25:08,840 --> 00:25:11,912
And this is another mimic.

226
00:25:15,840 --> 00:25:20,960
A tortoise in the desert of Southern Africa
is always on the lookout for a juicy mouthful,

227
00:25:21,120 --> 00:25:24,999
but it walks right over
as good a one as it might find all day

228
00:25:25,160 --> 00:25:28,630
and feeds instead on a few shrivelled leaves.

229
00:25:31,040 --> 00:25:34,476
The pebble plant
mimics its surroundings so accurately

230
00:25:34,640 --> 00:25:38,758
that it even varies its colour
to match that of the gravel around it.

231
00:25:38,920 --> 00:25:41,912
Few animals even notice it.

232
00:25:44,720 --> 00:25:51,319
The passionflower uses mimicry to defend itself
in perhaps the most extraordinary way of all.

233
00:25:51,480 --> 00:25:54,392
It's much pestered by heliconius butterflies.

234
00:25:54,560 --> 00:25:59,680
This is because its leaves
are the favourite food of heliconius caterpillars.

235
00:25:59,840 --> 00:26:02,798
So the female butterflies
always lay their eggs on the plants,

236
00:26:02,960 --> 00:26:05,030
in order that their youngsters, when they hatch,

237
00:26:05,200 --> 00:26:09,637
will find their favourite food
immediately in front of them.

238
00:26:11,800 --> 00:26:15,873
The egg is a little bright yellow globe.

239
00:26:25,680 --> 00:26:27,477
There's another one.

240
00:26:31,240 --> 00:26:34,232
The caterpillars are particularly voracious.

241
00:26:34,400 --> 00:26:40,635
They will tackle leaves, stems, shoots and buds,
pretty well every part of the passionflower.

242
00:27:02,800 --> 00:27:05,268
Because her young need so much food,

243
00:27:05,440 --> 00:27:10,639
a female heliconius won't lay on a passionflower
if there are eggs already there.

244
00:27:10,800 --> 00:27:14,190
And before she starts,
she makes a careful survey.

245
00:27:14,360 --> 00:27:18,399
This female has decided not to lay here.

246
00:27:18,560 --> 00:27:22,314
Hardly surprising  -  the leaves
are already covered with eggs.

247
00:27:22,480 --> 00:27:24,596
Except that they are not eggs.

248
00:27:24,760 --> 00:27:31,836
These yellow spots are imitations,
fakes produced by the plant as a deterrent.

249
00:27:32,000 --> 00:27:36,710
Another species of passionflower
produces even more convincing bogus eggs,

250
00:27:36,880 --> 00:27:38,598
on the stalks of the leaves,

251
00:27:38,760 --> 00:27:42,753
surely one of the subtlest of strategies
based on mimicry.

252
00:27:47,000 --> 00:27:50,788
Bracken has adopted
a rather more straightforward defence.

253
00:27:55,520 --> 00:28:00,230
You might think a nutritious - looking
carpet of young leaves like this

254
00:28:00,400 --> 00:28:04,393
would show lots of signs of damage by grazers.

255
00:28:04,560 --> 00:28:06,198
I can see none.

256
00:28:06,360 --> 00:28:13,311
The fact is that bracken
is full of a cocktail of toxins so powerful

257
00:28:13,480 --> 00:28:20,591
that any mammal that eats it, such as rabbit
or cattle, is liable to go blind or to get cancer.

258
00:28:20,760 --> 00:28:24,912
When they're young,
the leaves are packed with cyanide,

259
00:28:25,080 --> 00:28:29,471
which deters most things, including insects.

260
00:28:29,640 --> 00:28:35,237
But as the plant matures, it starts
to synthesise even more complex poisons

261
00:28:35,400 --> 00:28:37,960
that deter almost every living creature.

262
00:28:38,120 --> 00:28:45,470
As a result, the plant sprawls unchecked
and covers vast areas of European hillsides.

263
00:28:47,240 --> 00:28:53,713
Ferocious spines, painful stings,
poisonous sap, near - perfect disguise;

264
00:28:53,880 --> 00:28:57,350
plants seem to have evolved
every conceivable defence for their leaves,

265
00:28:57,520 --> 00:29:03,072
which by their very nature have to be spread
wide to catch the light, so are very visible.

266
00:29:03,240 --> 00:29:08,439
But this plant, the sensitive mimosa,
common beside tropical roadsides,

267
00:29:08,600 --> 00:29:13,754
has perhaps the most radical
and certainly the most dramatic solution of all.

268
00:29:25,280 --> 00:29:28,909
One touch makes it fold its leaflets.

269
00:29:30,360 --> 00:29:34,319
Another tap and it flops to the ground.

270
00:29:34,480 --> 00:29:40,953
How does that help? Well, watch how
a hungry leaf - eating grasshopper gets on.

271
00:29:41,120 --> 00:29:44,829
Obviously, there's a splendid meal ahead.

272
00:29:49,760 --> 00:29:51,910
But before it even takes a bite...

273
00:29:54,680 --> 00:29:56,830
..the meal vanishes.

274
00:30:25,600 --> 00:30:28,194
This ability to move fast

275
00:30:28,360 --> 00:30:34,230
is used by one astonishing plant
to turn the tables on animals.

276
00:30:34,400 --> 00:30:38,791
It grows here in this swampy pine forest
in Northern Carolina.

277
00:30:38,960 --> 00:30:42,589
Animals don't eat it, it eats animals.

278
00:30:42,760 --> 00:30:45,228
And there's one right here.

279
00:30:47,040 --> 00:30:48,678
Watch.

280
00:30:59,360 --> 00:31:01,874
This is Venus's flytrap.

281
00:31:02,040 --> 00:31:05,077
It shapes its traps from the ends of its leaves.

282
00:31:05,240 --> 00:31:09,119
One or two hairs on their surface act as triggers.

283
00:31:09,280 --> 00:31:10,872
Here comes a meal.

284
00:31:15,200 --> 00:31:18,829
Touch the hair, and the trap is sprung.

285
00:31:21,040 --> 00:31:24,874
There's now no escape.

286
00:31:25,040 --> 00:31:30,433
The beetle's struggles stimulate the plant
to close the trap even more tightly.

287
00:31:30,600 --> 00:31:35,310
It now produces digestive acids
from glands on the inner surface of the leaf

288
00:31:35,480 --> 00:31:38,438
which first kill
and then dissolve its victim's body.

289
00:31:39,920 --> 00:31:45,392
Growing in the same Carolina swamp,
there's another carnivorous plant.

290
00:31:45,560 --> 00:31:48,472
These are the trumpet pitchers.

291
00:31:48,640 --> 00:31:50,358
Like the Venus's flytrap,

292
00:31:50,520 --> 00:31:54,718
they find so little nutriment
in this impoverished, waterlogged soil,

293
00:31:54,880 --> 00:31:58,873
that they supplement it
with the bodies of animals.

294
00:31:59,040 --> 00:32:02,396
Their traps are also formed from leaves,

295
00:32:02,560 --> 00:32:08,829
but leaves that have been folded lengthways
to make a vertical tube which fills with water.

296
00:32:18,560 --> 00:32:22,758
These spectacular trumpets
may look like flowers, but they're not.

297
00:32:22,920 --> 00:32:28,392
Though, in a sense, this bright yellow top
serves the same purpose as a petal,

298
00:32:28,560 --> 00:32:31,279
it's an advertisement of a delicious reward.

299
00:32:31,440 --> 00:32:34,830
And the reward itself is under here.

300
00:32:37,520 --> 00:32:39,078
A sweet nectar.

301
00:32:39,240 --> 00:32:46,999
But if an insect comes to collect it and strays
into the mouth of the trumpet, then it's doomed.

302
00:33:01,200 --> 00:33:03,760
The inside of the throat of the trumpet

303
00:33:03,920 --> 00:33:09,278
is covered with microscopic
downward - pointing spines.

304
00:33:12,120 --> 00:33:16,716
As long as it stays on the rim, the ant is all right,

305
00:33:16,880 --> 00:33:23,035
but if it strays off it...
it falls into a pond of water and drowns.

306
00:33:23,200 --> 00:33:29,275
The tiny corpse dissolves and the marsh pitcher
absorbs the resulting soup.

307
00:33:33,520 --> 00:33:38,275
And where one ant goes,
others are likely to follow.

308
00:33:53,880 --> 00:33:56,758
The marsh pitcher attracts other animals, too.

309
00:33:56,920 --> 00:34:01,516
This frog may be hoping to eat some
of the insects before the pitcher does.

310
00:34:01,680 --> 00:34:05,673
But if it loses its footing, the plant will eat it.

311
00:34:10,480 --> 00:34:13,597
Marsh pitchers have comparatively simple traps.

312
00:34:13,760 --> 00:34:17,355
The pitcher plants proper
produce more elaborate ones.

313
00:34:17,520 --> 00:34:20,990
And they live on the other side of the world.

314
00:34:24,600 --> 00:34:28,275
The headquarters of the pitcher plants
are in South - East Asia.

315
00:34:28,440 --> 00:34:34,356
There are 76 different species of them,
30 of which grow only on the island of Borneo.

316
00:34:34,520 --> 00:34:37,239
And they include the biggest of them all,

317
00:34:37,400 --> 00:34:42,076
a truly spectacular plant
appropriately called nepenthes rajah.

318
00:34:42,240 --> 00:34:49,669
That grows only on this great mountain,
Kinabalu, and they're all around me.

319
00:34:57,000 --> 00:35:05,635
I guess...this one contains...
two or three pints of liquid.

320
00:35:05,800 --> 00:35:11,636
It's so big that it catches not just insects
but even small rodents,

321
00:35:11,800 --> 00:35:17,477
and one was recorded that had in it
the body of a drowned rat.

322
00:35:17,640 --> 00:35:22,156
So if ever there was
a carnivore among plants, this is it.

323
00:35:26,160 --> 00:35:31,393
The traps of this Asian family of pitcher plants
are, once again, modified leaves.

324
00:35:31,560 --> 00:35:37,112
But they're not simply folded into a tube,
the process is more complex.

325
00:35:37,280 --> 00:35:43,276
A shoot appears that looks just the same
as those that turn into normal leaves.

326
00:35:49,000 --> 00:35:53,596
Over a period of several days,
flanges develop near the end

327
00:35:53,760 --> 00:35:56,832
and open out to form the blade of a leaf.

328
00:36:00,440 --> 00:36:05,560
But then the tip of the midrib
continues to grow.

329
00:36:16,080 --> 00:36:20,596
Once it touches the ground,
it begins to inflate.

330
00:36:45,640 --> 00:36:51,510
The lid opens to expose the plant's lethal pond.

331
00:37:07,520 --> 00:37:15,154
Some of the bigger species may produce
half a dozen of these huge, elegant traps.

332
00:38:05,040 --> 00:38:10,194
The shape and placing of the pitchers
varies from species to species,

333
00:38:10,360 --> 00:38:12,669
but essentially they're all the same.

334
00:38:12,840 --> 00:38:14,751
They attract prey with nectar,

335
00:38:14,920 --> 00:38:19,152
they have slippery sides,
so many of their visitors tumble into them,

336
00:38:19,320 --> 00:38:25,395
and the fluid within contains juices
which actively dissolves the bodies.

337
00:38:35,000 --> 00:38:38,595
So leaves, one way or another,
either by catching insects

338
00:38:38,760 --> 00:38:43,675
or, much more usually, by absorbing gases
and harnessing the energy of sunlight,

339
00:38:43,840 --> 00:38:45,717
manufacture food for a plant.

340
00:38:45,880 --> 00:38:49,156
But leaves are actually quite delicate structures.

341
00:38:49,320 --> 00:38:54,997
This plant, the giant arum of Borneo,

342
00:38:55,160 --> 00:38:58,470
develops the biggest undivided leaf of all.

343
00:38:58,640 --> 00:39:04,431
It can have a surface area
of up to 3 square metres, 34 square feet.

344
00:39:04,600 --> 00:39:11,039
The arum keeps these vast leaves outstretched
by pumping the cells within them full of water.

345
00:39:11,200 --> 00:39:16,593
If there's not enough water, or if it gets so cold
the water freezes and bursts the cell walls,

346
00:39:16,760 --> 00:39:18,352
the leaf will collapse.

347
00:39:18,520 --> 00:39:21,956
Of course, neither is likely
here in the tropical rainforest,

348
00:39:22,120 --> 00:39:25,476
one reason why such immense leaves
can develop here.

349
00:39:25,640 --> 00:39:29,553
But elsewhere in the world,
plants don't have it so easy.

350
00:39:39,360 --> 00:39:43,069
In northern lands,
where the winters can be very severe,

351
00:39:43,240 --> 00:39:48,314
many trees have to take drastic measures
to protect themselves.

352
00:39:50,560 --> 00:39:54,838
As the days grow shorter and colder
and autumn approaches,

353
00:39:55,000 --> 00:40:01,109
the trees prepare to cut their losses
and suspend their activities.

354
00:40:03,320 --> 00:40:06,471
They start to shut down their food factories

355
00:40:06,640 --> 00:40:10,553
and withdraw the valuable chlorophyll
from the leaves.

356
00:40:10,720 --> 00:40:13,029
As the green pigment drains away,

357
00:40:13,200 --> 00:40:17,239
waste products that have accumulated
over the year are revealed

358
00:40:17,400 --> 00:40:20,517
and the leaves begin to change colour.

359
00:40:20,680 --> 00:40:23,478
In New England
and the Appalachian Mountains,

360
00:40:23,640 --> 00:40:30,273
day after day, whole hillsides
of maples and aspens begin to flush red.

361
00:41:29,560 --> 00:41:32,711
As the leaves dry out, they're sealed off.

362
00:41:32,880 --> 00:41:38,477
A hard, corky partition develops
within the base of the leaf stalks.

363
00:41:38,640 --> 00:41:43,634
Now the slightest breath of air will detach them.

364
00:42:11,160 --> 00:42:14,789
The loss is great but it's not total.

365
00:42:14,960 --> 00:42:18,270
The leaves falling to the ground will soon decay.

366
00:42:18,440 --> 00:42:22,831
That will release much of the nutriments
used in constructing them,

367
00:42:23,000 --> 00:42:27,994
and in spring, the trees, through their
rootlets just below the surface of the earth,

368
00:42:28,160 --> 00:42:31,675
will be able to reclaim
much of what they have lost.

369
00:42:33,560 --> 00:42:39,476
So by the time winter grips the land,
the trees are reduced to skeletons.

370
00:42:39,640 --> 00:42:45,636
Growth has virtually stopped,
the processes of life are barely ticking over.

371
00:42:56,680 --> 00:43:00,753
This alternation of growing in summer
and shutting down in winter

372
00:43:00,920 --> 00:43:05,198
Ieaves its mark in the tree's trunk  - 
annual rings.

373
00:43:05,360 --> 00:43:10,070
The white wood are large, open cells
that were laid down in the summer,

374
00:43:10,240 --> 00:43:16,554
and the dark wood small, dense cells
laid down more slowly in autumn and winter.

375
00:43:16,720 --> 00:43:18,631
So by counting the rings,

376
00:43:18,800 --> 00:43:25,353
I can be absolutely certain that this beech
lived for over two hundred years before it fell.

377
00:43:25,520 --> 00:43:29,593
And that's longer than any animal lives.

378
00:43:33,200 --> 00:43:39,992
The record for longevity, however,
is much greater than that, and is held elsewhere.

379
00:43:54,240 --> 00:44:00,270
Here, 10,000 feet up
in the White Mountains of Eastern California,

380
00:44:00,440 --> 00:44:05,753
grow the oldest living things on earth,
the bristlecone pines.

381
00:44:07,160 --> 00:44:10,914
This part is already dead.

382
00:44:11,080 --> 00:44:15,756
But here there is life and growth.

383
00:44:15,920 --> 00:44:21,472
Those rings in the trunk
tell us exactly how old these trees are.

384
00:44:21,640 --> 00:44:26,236
Because conditions here are so extreme
and it gets so very cold in winter,

385
00:44:26,400 --> 00:44:29,392
some years there's very little growth at all.

386
00:44:29,560 --> 00:44:34,554
As a consequence,
the rings are very much more close together.

387
00:44:34,720 --> 00:44:37,951
This is a cross - section of one of these trees.

388
00:44:38,120 --> 00:44:43,148
The outermost ring
is the year in which it died, 1958.

389
00:44:43,320 --> 00:44:46,869
Count 100 rings inwards, 1858.

390
00:44:47,040 --> 00:44:50,077
Another century, 1758.

391
00:44:50,240 --> 00:44:57,396
Around here is the ring it was developing
when Columbus arrived on this continent in 1492.

392
00:44:57,560 --> 00:45:02,918
It was in the full vigour of its youth
when the Pharaohs ruled Egypt.

393
00:45:04,400 --> 00:45:11,238
So we can be sure that when the first
human farmers were beginning to plant seeds,

394
00:45:11,400 --> 00:45:15,109
this ancient, ravaged tree was just sprouting.

395
00:45:15,280 --> 00:45:19,319
It's over 4,000 years old.

396
00:45:21,160 --> 00:45:25,995
Pine leaves are obviously very different
from the leaves of oak and maple.

397
00:45:26,160 --> 00:45:30,119
Instead of being broad and flat
and easily damaged by frost,

398
00:45:30,280 --> 00:45:33,113
they are needle - shaped and very tough.

399
00:45:33,280 --> 00:45:37,796
Instead of having pores all over
the flat surface, as oak and maple do,

400
00:45:37,960 --> 00:45:44,069
these pores are restricted to a groove
which runs down the length of the needle.

401
00:45:44,240 --> 00:45:49,917
It's partly filled by a tough, waxy deposit,

402
00:45:50,080 --> 00:45:53,436
and beneath that there are lines of small pores.

403
00:45:53,600 --> 00:45:57,388
Very few compared with those
scattered all over an oak leaf.

404
00:46:03,200 --> 00:46:05,191
Even at the height of summer,

405
00:46:05,360 --> 00:46:09,990
Ieaves like these can't manufacture food
as swiftly as broad leaves do.

406
00:46:10,160 --> 00:46:14,199
But on the other hand,
the needle - producing trees, the conifers,

407
00:46:14,360 --> 00:46:18,478
don't discard them every year,
but keep them very much longer,

408
00:46:18,640 --> 00:46:21,632
with all the saving of energy that implies.

409
00:46:21,800 --> 00:46:25,076
The conifer's policy is slow but sure,

410
00:46:25,240 --> 00:46:31,759
and it's produced not only the oldest plants
but other record - holders.

411
00:46:33,760 --> 00:46:41,519
And this is the most massive living thing
on earth, the giant sequoia.

412
00:47:03,200 --> 00:47:09,036
They don't live as long as bristlecone pines
but almost, over 3,000 years.

413
00:47:09,200 --> 00:47:12,715
They grow up to 300 feet tall,

414
00:47:12,880 --> 00:47:15,474
and every year they put on as much wood

415
00:47:15,640 --> 00:47:20,156
as there is in a 60 - foot tree
of normal proportions,

416
00:47:20,320 --> 00:47:26,350
so that the really big ones
weigh over 1,000 tons.

417
00:47:52,040 --> 00:47:56,670
Although they may be loaded with snow
for months in the winter,

418
00:47:56,840 --> 00:47:59,035
and baked dry in the summer,

419
00:47:59,200 --> 00:48:05,992
the conifers have produced the largest and
the longest - living of all organisms on earth.

420
00:48:06,160 --> 00:48:10,073
And like all plants, they've done it
with the simplest of ingredients,

421
00:48:10,240 --> 00:48:12,708
with water and minerals from the earth,

422
00:48:12,880 --> 00:48:17,715
carbon dioxide
from the atmosphere and light.

423
00:48:18,305 --> 00:48:24,946
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