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No part of the earth is more hostile to life
than the frozen wastes around the poles.

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850 miles north of the Arctic Circle,
this is Ellesmere Island.

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No animal can live permanently
on these ice-fields,

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and even plants
face almost insuperable problems,

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for the four things they must have
are in cripplingly short supply.

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Water: it's true there's
a lot of frozen water all around me,

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but water has to be liquid
for plants to make any use of it.

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Nutrients: there's virtually none
in this frost-shattered rock.

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Warmth and light:
for six months of the year, it's dark,

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and in the brief summer, as now,
the sun doesn't rise high in the sky,

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and devastating winds can carry away
what little warmth it brings.

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And yet, there are plants here.

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Some live actually inside the rock.

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This thin green line is made by algae,
microscopic plants.

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They're so small, they can live actually
between the grains of this sandstone.

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And there at least,
they're out of this desiccating wind.

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On the surface of the rocks are lichens.

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They grow incredibly slowly, and may take
50 years to cover a square centimetre.

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But they can survive

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even if there are only two days a year
when it's warm enough for them to grow.

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In spite of these bleak conditions,
there are, in fact, flowers to be found here,

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but you have to look hard to find them.

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Here's one. It's a kind of mustard,

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but it's much smaller
than its more southerly relatives.

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But by being so small,
it manages to keep out of the crippling wind.

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In midsummer, for a few weeks, enough water
melts from the glaciers for streams to flow.

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And then, miniature gardens burst into bloom.

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The searing wind compels them all
to keep close to the ground.

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None keeps closer than this.

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It is in fact a tree, a willow.

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These are its catkins.

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But the trunk grows horizontally, not vertically,
and it can stretch almost as far along the ground

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as its more southerly relatives stand up above it.

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Even so, it still produces enough leaves
to sustain a few grazers, musk ox.

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Nothing is wasted up here.

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Not a moment of sunshine,
not the tiniest shelter, not a scrap of food.

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When a musk ox dies, its decaying body
releases a rich flush of nourishment into the soil,

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and tiny gardens appear
in the shelter of its bones.

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The arctic poppy, like all plants,
needs warmth to grow.

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But it is unusually efficient at collecting it.

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As the midsummer sun skims round the horizon,
all 360 degrees in 24 hours without setting,

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the poppy turns its flowers to track it.

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The slanting sun may not be strong,

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but it is at least continuous
during the few weeks of high summer.

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The heat the poppy gathers
by staring continuously at the sun

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enables it to develop seeds
in the centre of each flower

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before summer comes to an end and the sun
disappears below the horizon for months.

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Conditions may be just as severe on the high
peaks of the Alps, 2,000 miles to the south,

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at least during the winter.

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But here, spring brings a greater benefit
than in the Arctic.

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The sun rises higher in the sky and is warm
enough to melt all but the highest snow-fields.

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As it melts, it reveals the snowbell,
already in flower.

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The plant formed its flower buds last autumn,

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before the increasing cold shut down
its activities for the winter.

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The buds stayed dormant until spring sunshine,
filtering down through the snow,

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triggered them into action,

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and they opened even before
the snowy blanket above them had melted.

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In summer, the high meadows,
newly freed from snow, fill with flowers.

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Because for so much of the time it's so cold,
the vegetation here decays only very slowly.

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So a peaty soil forms.

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But it's only a thin layer
over solid rock and boulders,

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and trees find it very hard to get root.

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Not only that, but avalanches
regularly sweep these slopes,

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carrying away saplings
before they can get firmly established.

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So shallow-rooted plants have these parts
of the mountains largely to themselves,

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and in summer
they bring a rich display of colour.

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But for every thousand feet you climb,
the temperature drops by about three degrees.

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Plants living in the high mountains
have to be able to survive extreme cold.

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It's very important
to keep out of the worst of the chilling winds,

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and many plants here
form small rounded humps.

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And that brings them a number of advantages.

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Growing into the shape of a cushion
is an excellent way of conserving heat.

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No plants do it more spectacularly than these,
high in the mountains of Tasmania.

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These are the largest cushion plants in the world,
they grow to over 12 feet across.

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Any one square yard
contains over 100,000 shoots,

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so I guess this one cushion around me
contains several million.

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This rounded shape
does more than just reduce wind chill.

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The air temperature around me
here at about 3,500 feet high,

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is only a degree or so above freezing.

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But if I put this temperature probe
on the surface of this cushion,

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I can see that there it is several degrees warmer.

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The cushion, in fact, acts as a solar panel,
absorbing heat directly from the sun,

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so that even on very cold days,

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providing it's not covered in snow
and is exposed to direct sunshine,

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it can photosynthesise and grow.

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The plants that form these spectacular cushions
come from several families,

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sedges and rushes, daisies and dandelions.

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One cushion may contain several species,

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tightly packed together
and growing to exactly the same height.

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For one kind to grow higher
than those around it would be suicidal.

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In the New Zealand Alps,

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one of these cushion-forming species also
protects itself by developing a blanket of hair.

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Its colonies form conspicuous white humps
on the mountainside.

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New Zealand farmers, whose flocks sometimes
stray up onto these high slopes,

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call such cushions vegetable sheep.

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This tall pillar growing on Mount Kenya
also covers itself in a blanket.

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It's a giant lobelia.

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Its long leaves are fringed with dense hairs.

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Its flowers are hidden away from the frost
beneath this downy covering.

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There is no point having bright petals if they
can't be seen, and these are just simple tubes.

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But the lobelia's pollinator, a sunbird,
knows where they are and how to reach them.

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During the day, it can get quite warm, as Mount
Kenya stands almost exactly on the equator,

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but up here at 14,000 feet,
once the sun goes down it gets bitterly cold.

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Then the lobelia will have real need
of its hairy blanket.

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There are other giants here, too -
tree-groundsels,

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relatives of the little yellow weed
that grows in European gardens.

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They have a different way
of dealing with the cold nights.

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Their dead leaves remain attached to the stem,
so that they act like lagging,

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and prevent the liquids in the pipes
running up inside the trunk from freezing solid.

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Conditions here can change
with extraordinary speed.

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One moment the equatorial sun
is blazing down from a cloudless sky,

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the next, a chilling wind begins to blow
and the great mountain collects a cloud cover.

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As well as the tree-groundsel,

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there's another member of the family
that grows close to the ground like a cabbage.

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As night falls, it makes its own preparations
for surviving the bitter cold.

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The most precious and vulnerable
part of the plant

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is the bud in its centre
from which all growth comes.

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That must be protected at all costs,

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and folding the thick leaves over it
does the trick.

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The temperature has now fallen
by as much as thirty degrees.

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Water in the muddy swamps
is beginning to freeze.

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As it does so, it expands
and the ground begins to heave.

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It's impossible for small plants
to keep a root-hold under these conditions.

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The Mount Kenya moss doesn't even try.

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It grows into balls that are lifted up by the ice
pinnacles and it rolls around during the night.

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The sun returns,
the temperature rockets upwards,

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the threat of death by freezing has passed,
at least for now.

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The cabbage groundsels
stretch out their leaves to catch the light

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and start making food once more.

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The ice in the swamps melts,
and the streams flow again.

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This is just as well, for now the plants,
baking under the sun,

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are losing a lot of water
by evaporation from their leaves.

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Excessive water loss, of course,

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is the other great disaster
that can kill the hardiest of plants.

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If the sap-filled vessels in the trunks
of the tree-groundsels had frozen,

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their leaves would now be baked dry.

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Here we are still in Africa,
but about 14,000 feet lower down.

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I'm on the southern edge of the Namib Desert.

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Here, plants can't get water,
not because it's frozen,

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but because rain hardly ever falls,
only about one or two inches in a year.

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Most of the time,
it's bone-dry and devastatingly hot.

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Yet, almost unbelievably, there are trees
standing out in the sands, totally unsheltered,

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with no sign of moisture
anywhere around them.

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Water storage is the great trick here.

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These green, succulent leaves are full of it,

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and so are these bloated branches.

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The local bushmen
used to cut off these branches,

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hollow out the spongy tissue
and use them as containers for arrows,

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which is why this tree is called the quiver tree.

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Its branches are covered with a blindingly white
powder which reflects the heat,

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and its leaves have thick rinds
with very few pores,

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which minimises the amount of water
they lose through evaporation.

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The trunk, even of an old tree
ravaged by the years,

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remains smooth and impermeable.

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But even the quiver tree
can't seal itself off totally from its surroundings.

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Living involves breathing, and some
water vapour is inevitably lost in that process.

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But this tree has a way of reducing that:

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self-amputation.

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It can cut off a leaf rosette and seal the stump.

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This branch will never grow leaves again,

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but with luck, the tree will just survive
with a reduced number of leaves

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and put out new shoots
when conditions improve.

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Most of the plants in this desert,
however, are less conspicuous,

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and there are rather more of them
than you might suppose.

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This little plant
has fused its leaves together in pairs

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to form a set of cones,
which is why it's called conophytum.

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The white surface of each cone
is the skin of last year's leaf.

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The plant is now waiting for the rains to arrive.

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Let's see what happens
if I make them arrive just a little early.

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One of the greatest of all water reservoirs

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is held by the saguaro cactus
that grows in Arizona and New Mexico.

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One of these giants
can hold several tons of liquid.

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They don't risk losing precious water
through the leaves, for they have none.

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Instead, the task of making food
has been taken over by the stem,

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which has become green with chlorophyll
and keeps its pores well protected in grooves.

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The 50-foot-high columns
are crowned with tufts of flowers.

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The pleats in the trunks
enable the plants to expand rapidly

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and suck up rain falling in a sudden storm
before it evaporates in the heat and disappears.

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Such a store is very precious.
Lots of desert animals would raid it if they could.

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00:20:14,814 --> 00:20:21,731
They can't because cacti, like desert succulents
everywhere, defend themselves with spines.

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The other way of protecting yourself
against robbers is to hide underground.

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You might think that these are pebbles.
You would be wrong.

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This is a window plant.

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These little studs
are the flat tops of the pillar-like leaves.

186
00:21:01,374 --> 00:21:07,051
And these tops are transparent.
They allow the light to pass through them,

187
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where it's transmitted
by a series of lined-up crystals

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down to the bottom of the leaf,
where there's green pigment.

189
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So, although this little plant
is several inches under the ground,

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it can catch the sunlight and turn it into food.

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And in the driest times of all,
when sandstorms blow across the Namib,

192
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it may be covered up completely.

193
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Many plants take refuge underground
at the hottest time of year,

194
00:21:40,414 --> 00:21:42,609
and survive as bulbs and tubers,

195
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swollen with their stores of food and water
gathered during the good times.

196
00:21:51,254 --> 00:21:58,410
Underground is undoubtedly the coolest place
to be, but it's not necessarily the safest.

197
00:22:04,534 --> 00:22:06,604
Mole rats.

198
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They burrow ceaselessly,
searching at random for their food.

199
00:22:18,974 --> 00:22:21,124
Some bulbs they eat immediately,

200
00:22:21,294 --> 00:22:26,209
but others they take away down their tunnels
and stack in special larders.

201
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Being carried away and put in store
is not necessarily a disaster for the plants.

202
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Mole rats seldom eat all their reserves,

203
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and as they extend their burrows,
more distant larders may get forgotten.

204
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Then the bulbs will sprout,
and benefit from a new location.

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This plant is totally dead.

206
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It didn't store its food underground in bulbs.

207
00:23:22,494 --> 00:23:26,009
Instead, it adopted a very different
and drastic strategy.

208
00:23:26,174 --> 00:23:30,565
It condensed its entire life
into a few short weeks.

209
00:23:30,734 --> 00:23:36,047
And its last act was to release into the sand
a few hundred seeds.

210
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They're easy enough to find.

211
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And there are some.

212
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They can wait here in this hot sand,
apparently lifeless,

213
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for one year, two years,
even twenty years.

214
00:23:58,734 --> 00:24:03,649
But when the rains do come,
their moment arrives.

215
00:24:15,574 --> 00:24:21,729
One day the land is so dry
the withered plants crunch to pieces underfoot.

216
00:24:22,734 --> 00:24:27,125
Two or three weeks later and it's ablaze.

217
00:24:39,014 --> 00:24:42,723
Arid lands around the world,
not only here in South Africa,

218
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but in Australia and Arizona,

219
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all respond to rain by rapidly producing
dazzling displays of colour.

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The sudden flush of flowers and leaves
attracts lots of plant-eaters.

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For them, too, the pressures of desert living
are momentarily relaxed.

222
00:25:43,774 --> 00:25:47,608
It may seem a paradox
that some of the harshest environments

223
00:25:47,774 --> 00:25:50,572
should produce such unrivalled glories,

224
00:25:50,734 --> 00:25:54,852
but the desert soil
will not remain moist for long,

225
00:25:55,014 --> 00:25:59,929
and in that short time, plants must
not only grow leaves but produce seeds,

226
00:26:00,094 --> 00:26:02,562
so the need for pollination is urgent.

227
00:26:02,734 --> 00:26:08,047
Those with the most brilliant flowers
have the best chance of attracting an insect.

228
00:26:08,214 --> 00:26:12,730
This is competitive advertising
at its most intense.

229
00:26:18,374 --> 00:26:22,003
So, a few days of rain once every year or so

230
00:26:22,174 --> 00:26:27,851
are enough to enable plants to survive
in some of the driest places on earth.

231
00:26:51,014 --> 00:26:54,927
And this is one of the wettest places on earth.

232
00:26:55,094 --> 00:27:00,373
Here it rains almost every day,
and sometimes for days on end.

233
00:27:00,534 --> 00:27:05,210
I'm in South America,
on the top of an immense sandstone plateau

234
00:27:05,374 --> 00:27:11,847
9,000 feet high, five miles across,
surrounded by huge vertical cliffs.

235
00:27:12,014 --> 00:27:15,290
This is Mount Roraima.

236
00:27:20,974 --> 00:27:24,603
Plants cut off up here
from the hot rainforest below

237
00:27:24,774 --> 00:27:28,323
adapt to their surroundings
in their own individual way,

238
00:27:28,494 --> 00:27:32,806
so there are species here
that occur nowhere else in the world.

239
00:27:34,534 --> 00:27:39,813
The near-continuous rains produce torrents
that cascade over the edge of the plateau

240
00:27:39,974 --> 00:27:43,489
and form some of the highest
waterfalls on earth.

241
00:27:47,534 --> 00:27:51,971
Much of this extraordinary landscape
is naked rock.

242
00:27:52,134 --> 00:27:55,968
Only here and there
do clumps of plants get a root-hold,

243
00:27:56,134 --> 00:27:59,922
and even when they succeed,
life is very difficult for them.

244
00:28:00,094 --> 00:28:03,291
Their main problem is lack of nutrients.

245
00:28:03,454 --> 00:28:07,572
These rushing streams wash away
everything in their path,

246
00:28:07,734 --> 00:28:10,294
and are flowing over bare rock.

247
00:28:10,454 --> 00:28:15,244
Only in a few places
does a little gravely sediment accumulate.

248
00:28:15,414 --> 00:28:20,613
So many of the plants that grow up here
have to have ways of augmenting their food.

249
00:28:20,774 --> 00:28:24,210
And some of them do it by eating animals.

250
00:28:26,654 --> 00:28:32,684
This is about the simplest way
in which a plant can catch and eat an insect.

251
00:28:32,854 --> 00:28:34,890
This is the marsh pitcher,

252
00:28:35,054 --> 00:28:38,967
and this particular species
lives only on Mount Roraima.

253
00:28:39,134 --> 00:28:43,969
There are four others, but they, too,
live on other mountains just near here,

254
00:28:44,134 --> 00:28:46,204
and nowhere else in the world.

255
00:28:46,374 --> 00:28:48,365
And this is how they do it.

256
00:28:50,294 --> 00:28:56,324
The leaf, joined at its margins to form a tube,
is covered by downward-pointing hairs.

257
00:28:56,494 --> 00:29:00,772
Easy to slide down, very difficult to climb up.

258
00:29:01,494 --> 00:29:06,124
One slip and it's drowning
and dissolution for the insect...

259
00:29:07,134 --> 00:29:10,171
..and then digestion by the plant.

260
00:29:13,254 --> 00:29:17,611
The pond in a bromeliad is normally
a safe haven for aquatic insects,

261
00:29:17,774 --> 00:29:23,406
but a bladderwort is hunting
inside Roraima's bromeliads.

262
00:29:32,054 --> 00:29:34,807
Not content with prey in this pond,

263
00:29:34,974 --> 00:29:40,526
the bladderwort is looking
for new hunting grounds elsewhere.

264
00:29:49,934 --> 00:29:53,893
It explores with long, sensitive tendrils.

265
00:30:00,214 --> 00:30:03,331
It has found another bromeliad...

266
00:30:06,574 --> 00:30:10,886
..and descends into this new territory.

267
00:30:18,694 --> 00:30:21,492
Now, it prepares to hunt.

268
00:30:33,454 --> 00:30:39,324
Its traps, the bladders from which
it gets its name, are tiny capsules.

269
00:30:39,494 --> 00:30:45,410
Glands inside them extract water,
so creating a partial vacuum.

270
00:30:56,494 --> 00:31:00,533
Each bladder has a little door
fringed with bristles.

271
00:31:00,694 --> 00:31:04,084
A mosquito larva has only to touch
one of these triggers,

272
00:31:04,254 --> 00:31:08,327
and the door will implode
and sweep the prey inside.

273
00:31:10,134 --> 00:31:11,726
The glands pump out water,

274
00:31:11,894 --> 00:31:17,605
so, at one and the same time, the bladderwort
starts its meal and re-sets its trap,

275
00:31:17,774 --> 00:31:22,211
which is ready for another customer
within two hours.

276
00:31:29,254 --> 00:31:31,848
Roraima also has sundews.

277
00:31:32,014 --> 00:31:37,532
Like sundews elsewhere, they catch insects
in a way that is a family speciality.

278
00:31:43,334 --> 00:31:46,371
The sparkling drops on the leaf hairs
are not sweet,

279
00:31:46,534 --> 00:31:49,207
but insects nonetheless are attracted to them.

280
00:31:49,374 --> 00:31:56,325
They are, however, extremely sticky,
as any inquisitive insect immediately discovers.

281
00:32:01,174 --> 00:32:07,249
The hairs move swiftly. One can turn
through 180 degrees in less than a minute.

282
00:32:07,414 --> 00:32:12,249
So even though an insect may have been
caught by only one or two hairs,

283
00:32:12,414 --> 00:32:17,249
others nearby quickly fold over it,
and soon it is held fast.

284
00:32:46,454 --> 00:32:50,970
The sundews on Roraima, like the bladderwort
and the carnivorous pitcher,

285
00:32:51,134 --> 00:32:54,092
occur only on these plateaus.

286
00:32:55,094 --> 00:32:59,246
Indeed, about a third of the species
on the mountain evolved here

287
00:32:59,414 --> 00:33:02,087
and are found nowhere else.

288
00:33:03,814 --> 00:33:08,763
The water that sluices over these rocks
has caused problems for Roraima's plants

289
00:33:08,934 --> 00:33:12,210
by preventing the accumulation of nutrients.

290
00:33:18,734 --> 00:33:24,286
After it leaves the mountain, it joins the biggest
of all river systems, the Amazon,

291
00:33:24,454 --> 00:33:30,086
and then, lying in swamps and lakes,
it will create a different set of difficulties.

292
00:33:30,254 --> 00:33:33,530
But again, there are plants
that have solved them.

293
00:33:40,534 --> 00:33:43,731
Access to light is the great problem here.

294
00:33:43,894 --> 00:33:47,603
Those plants that can command the surface
can rule the lake.

295
00:33:47,774 --> 00:33:52,973
And none does so on a greater scale
and more aggressively than this,

296
00:33:53,134 --> 00:33:56,365
the giant Amazon water-lily.

297
00:34:05,574 --> 00:34:08,532
Its gigantic leaves are armoured with spines

298
00:34:08,694 --> 00:34:13,131
that protect them against any fish
that might try to make a meal of them.

299
00:34:30,294 --> 00:34:34,492
Their huge expanse is kept outstretched
and floating on the surface

300
00:34:34,654 --> 00:34:38,533
by a lattice of buoyant, air-filled struts.

301
00:34:45,174 --> 00:34:52,091
The crinkles in the surface swiftly flatten out
as the leaf expands to its full size.

302
00:34:58,614 --> 00:35:03,972
The edges are turned up so that the leaf
can shoulder aside any competition.

303
00:35:06,654 --> 00:35:10,966
Fully grown, a single leaf is six feet across.

304
00:35:13,094 --> 00:35:18,168
Virtually no other plants can live
in the black, shaded water beneath these leaves.

305
00:35:18,334 --> 00:35:23,647
They cover the surface so completely, and the
support of their air-filled girders is so effective,

306
00:35:23,814 --> 00:35:26,806
that birds, most famously the lily-trotter,

307
00:35:26,974 --> 00:35:32,446
can spend their entire lives
walking around on them, collecting insects.

308
00:35:33,614 --> 00:35:37,812
The giant lily's flowers
are on an equally monumental scale.

309
00:35:37,974 --> 00:35:40,124
They're about a foot across.

310
00:35:52,054 --> 00:35:55,012
The life of any one bloom is short.

311
00:35:55,174 --> 00:35:59,884
It opens in the evening
and gives off a strong perfume.

312
00:36:00,854 --> 00:36:02,651
During the night it closes,

313
00:36:02,814 --> 00:36:07,763
and it stays closed for the whole of the next day,
slowly flushing pink.

314
00:36:09,134 --> 00:36:12,365
On its second evening, it opens again.

315
00:36:17,134 --> 00:36:20,285
Then it closes for the last time.

316
00:36:22,734 --> 00:36:26,044
Why does it behave in this extraordinary way?

317
00:36:26,974 --> 00:36:32,526
It's a neat way of avoiding any chance
of being fertilised by its own pollen.

318
00:36:32,694 --> 00:36:37,404
The perfume it produces on its first evening
attracts beetles.

319
00:36:41,534 --> 00:36:47,131
They bring with them pollen from other lilies,
so this flower is about to be fertilised.

320
00:36:53,374 --> 00:36:56,491
But then the lily closes its petals.

321
00:36:57,174 --> 00:37:02,692
The beetles will be held captive
inside for 24 hours.

322
00:37:10,254 --> 00:37:16,853
The following evening, the beautiful prison
opens its gates and the inmates are free to go.

323
00:37:22,814 --> 00:37:28,207
The flower has showered the beetles
with its own pollen during their long stay.

324
00:37:30,734 --> 00:37:35,012
Now red and odourless,
the flower is no longer attractive to beetles,

325
00:37:35,174 --> 00:37:39,326
so they'll go in search of white flowers
on another plant,

326
00:37:39,494 --> 00:37:43,646
carrying the pollen and bringing about
cross-fertilisation.

327
00:37:49,174 --> 00:37:54,931
Its mission completed, the flower withdraws
back to its watery world.

328
00:38:09,454 --> 00:38:14,608
As swiftly-flowing streams
enter the still water of a lake,

329
00:38:14,774 --> 00:38:20,007
so they slow down
and shed their load of sediment.

330
00:38:20,174 --> 00:38:24,645
So, day after day, the lake fills up.

331
00:38:24,814 --> 00:38:31,925
As the waters get shallower, so it becomes
possible for different, bigger plants to grow.

332
00:38:35,254 --> 00:38:39,884
The trees in the forefront of this invasion
here in the southern United States

333
00:38:40,054 --> 00:38:42,488
are likely to be swamp cypresses.

334
00:38:42,654 --> 00:38:45,930
The bases of their trunks
are broad and cone-shaped,

335
00:38:46,094 --> 00:38:49,803
so that they are able to squat firmly
on the lake floor.

336
00:38:54,374 --> 00:38:59,402
But they also have a way of creating
an ever-widening platform for themselves,

337
00:38:59,574 --> 00:39:03,123
and getting a head start on their competitors.

338
00:39:03,774 --> 00:39:09,451
Mud will be deposited wherever the current
that is carrying it in suspension slows down.

339
00:39:09,614 --> 00:39:13,846
The cypresses encourage
that to happen around them

340
00:39:14,014 --> 00:39:18,087
by growing their roots
into a maze of flanges and spires.

341
00:39:18,254 --> 00:39:21,326
But the problems of a freshwater swamp are tiny

342
00:39:21,494 --> 00:39:26,693
compared with those of the salty swamps
of the coast, where the mangroves live.

343
00:39:33,454 --> 00:39:39,643
Here I'm closer to the sea
and the ground is even more unstable.

344
00:39:39,814 --> 00:39:45,810
So the mangroves that grow here have to take
more extreme measures to stand upright,

345
00:39:45,974 --> 00:39:50,843
and they develop this great tangle of prop-roots.

346
00:39:51,014 --> 00:39:56,611
Twice in every 24 hours,
their land is invaded by the sea.

347
00:40:12,494 --> 00:40:18,330
Estuary mud is particularly fine and sticky.
Aerating it is virtually impossible,

348
00:40:18,494 --> 00:40:23,887
and when the tide is out, the mangroves breathe
through large pores on their arching prop-roots.

349
00:40:24,054 --> 00:40:27,285
But now, when the tide is in, they can't do that.

350
00:40:27,454 --> 00:40:32,972
They have no alternative but, in effect,
to hold their breath for several hours.

351
00:40:38,294 --> 00:40:41,092
Eventually, the tide begins to turn,

352
00:40:41,254 --> 00:40:46,726
and as the water ebbs away,
the mangroves slowly begin to breathe again.

353
00:40:47,494 --> 00:40:51,169
Submersion is longest
at the very edge of the sea.

354
00:40:51,334 --> 00:40:56,249
It's the first part of the swamp to be covered,
and the last to be exposed.

355
00:40:56,414 --> 00:40:59,167
Here, the mangroves sprout fields of snorkels,

356
00:40:59,334 --> 00:41:03,612
each carrying pores
through which the roots can take in air.

357
00:41:09,094 --> 00:41:12,803
It's especially tricky for young plants
to get started here.

358
00:41:12,974 --> 00:41:15,852
The adult trees deal with that hazard

359
00:41:16,014 --> 00:41:20,690
by keeping hold of their young
until the very last moment.

360
00:41:41,654 --> 00:41:47,445
This long spike, green though it is,
is in fact a root.

361
00:41:47,614 --> 00:41:51,846
The seed has germinated
while it's still attached to the tree.

362
00:41:52,014 --> 00:41:59,853
And now the young plant is about to stake
its claim for territory in a quite literal way.

363
00:42:00,014 --> 00:42:05,293
A shoot that falls when the tide is out
has a chance of sticking in the mud.

364
00:42:10,374 --> 00:42:14,845
If the tide is in and the water deeper,
then the shoot won't reach the bottom.

365
00:42:15,014 --> 00:42:20,725
But all is by no means lost.
On the contrary. The young plant floats away.

366
00:42:23,294 --> 00:42:26,923
Like this it may be carried
into a different estuary.

367
00:42:28,934 --> 00:42:33,610
There, when the tide goes out,
it may, with luck, snag its tip in the mud.

368
00:42:33,774 --> 00:42:36,607
So it may end up far away from its parents

369
00:42:36,774 --> 00:42:41,529
and colonise newly-formed mudflats
on the very margins of the sea.

370
00:42:51,854 --> 00:42:56,211
Rocky coasts present plants
with yet other problems.

371
00:42:57,174 --> 00:43:03,522
The rocks are firm enough - the perils come
from the pounding waves and surging currents.

372
00:43:03,694 --> 00:43:08,529
No flowering plant has evolved a solution
to the difficulties of living here,

373
00:43:08,694 --> 00:43:10,525
but algae have.

374
00:43:11,254 --> 00:43:16,692
They have the simplest structure of all plants,
they've never developed rigid stems,

375
00:43:16,854 --> 00:43:20,733
but in the sea, the water itself provides support.

376
00:43:20,894 --> 00:43:25,524
Their holdfasts grip the rock so firmly
that if the current does rip them up,

377
00:43:25,694 --> 00:43:29,448
it's likely to be the rock that breaks,
not the plant.

378
00:43:37,214 --> 00:43:43,813
They have long, cable-like stems that are
rubbery and flexible but immensely strong.

379
00:43:44,534 --> 00:43:47,731
The great blades
in which they manufacture their food

380
00:43:47,894 --> 00:43:52,763
are kept near the sunlight by huge,
gas-filled floats.

381
00:43:57,574 --> 00:44:00,452
Such algae can reach immense lengths.

382
00:44:00,614 --> 00:44:03,606
They can grow in waters almost 100 feet deep,

383
00:44:03,774 --> 00:44:09,770
but because they stream out in the current,
their total length can be several times that.

384
00:44:15,094 --> 00:44:19,053
One species has fronds
that measure over 300 feet,

385
00:44:19,214 --> 00:44:23,253
about as long as the tallest of land-living trees.

386
00:44:23,414 --> 00:44:30,172
These thickets can with justice be regarded
as the marine equivalent of the terrestrial forests.

387
00:44:32,334 --> 00:44:35,485
Farther out to sea, the water becomes so deep

388
00:44:35,654 --> 00:44:42,093
that even these giant algae can't maintain a hold
on the sea floor and still reach the light.

389
00:44:43,254 --> 00:44:49,489
The open water of the deep ocean
is the domain of the simplest plants of all,

390
00:44:49,654 --> 00:44:53,249
the microscopic single-celled algae.

391
00:44:57,534 --> 00:45:02,005
These, perhaps the least considered
by humanity of all plants,

392
00:45:02,174 --> 00:45:05,246
have the four essentials of life in abundance.

393
00:45:05,414 --> 00:45:09,771
The water around them never drops
more than a degree or so below freezing,

394
00:45:09,934 --> 00:45:15,452
they're always within reach of sunlight,
and they're constantly provided with nutrients

395
00:45:15,614 --> 00:45:19,163
as currents bring up rich ooze
on an immense scale.

396
00:45:19,334 --> 00:45:23,964
And they've colonised
not only salt water, but fresh.

397
00:45:39,454 --> 00:45:43,652
These simple plants are the basis
of all life in water,

398
00:45:43,814 --> 00:45:47,807
just as higher plants
are the basis of all life on land.

399
00:45:47,974 --> 00:45:51,728
Two-thirds of the surface of this planet
is covered by water

400
00:45:51,894 --> 00:45:55,204
and most of it
is beyond the reach of flowering plants.

401
00:45:55,374 --> 00:45:58,764
So floating algae in the seas and the lakes

402
00:45:58,934 --> 00:46:02,609
play a greater part in enriching
our atmosphere with oxygen

403
00:46:02,774 --> 00:46:07,131
than all the land-based plants put together.

404
00:46:12,854 --> 00:46:18,690
So we end as we began,
with the simplest of plants, algae.

405
00:46:19,054 --> 00:46:21,010
Plants, whether very simple

406
00:46:21,174 --> 00:46:26,407
or highly complex, like these growing in the
rainforest along the coast of tropical Australia,

407
00:46:26,574 --> 00:46:29,134
have colonised the whole planet.

408
00:46:29,294 --> 00:46:33,128
They live not only in such
favourable environments as these

409
00:46:33,294 --> 00:46:36,730
but on frozen rocks and gravels
of the polar lands

410
00:46:36,894 --> 00:46:39,886
and in the searingly hot sands of the deserts.

411
00:46:40,054 --> 00:46:43,490
They've developed ways of surviving
fire and hurricanes.

412
00:46:43,654 --> 00:46:45,963
They can withstand the attacks of animals

413
00:46:46,134 --> 00:46:50,412
and even, on occasion,
find ways of eating animals themselves.

414
00:46:50,574 --> 00:46:57,127
But one thing plants can't withstand,
and that's the determined onslaught of humans.

415
00:46:57,294 --> 00:47:00,092
Ever since we arrived on this planet as a species,

416
00:47:00,254 --> 00:47:04,850
we've cut them down, dug them up,
burnt them and poisoned them.

417
00:47:05,014 --> 00:47:08,131
Today we're doing so
on a greater scale than ever.

418
00:47:08,294 --> 00:47:13,846
Even this small, precious patch of rainforest
in northern Queensland is under threat.

419
00:47:19,054 --> 00:47:21,966
We destroy plants at our peril.

420
00:47:22,134 --> 00:47:26,093
Neither we nor any other animal
can survive without them.

421
00:47:26,254 --> 00:47:32,853
The time has now come for us to cherish
our green inheritance, not to pillage it.

422
00:47:33,014 --> 00:47:36,211
For without it, we will surely perish.

423
00:47:37,305 --> 00:47:43,728
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