The Living Planet (1984–…): Season 1, Episode 3 - The Northern Forests - full transcript
THE LIVING PLANET
A PORTRAIT OF THE EARTH
In the lands between the
Arctic Circle and the tropics,
each year brings a great change
between winter and summer,
imposing a rhythm in the
lives of animals and plants.
Up north in the great
evergreen forests,
conditions in mid-winter
are cripplingly severe.
THE NORTHERN FORESTS
Life, if it is to flourish,
has three needs:
Light, warmth and moisture.
And the reason trees like these
don't grow much farther north
is not only the extreme cold,
but with the long months
of winter darkness,
there is not enough light in
the year for them to grow.
Here in northern Norway, 300 miles,
500km north of the Arctic Circle,
there is just enough light,
but it does get extremely cold.
70 degrees of frost
have been measured here,
and in winter there are
very heavy snowfalls.
The cold threatens to freeze
the liquid within the trees,
and denies them one of their
essential supplies: Water.
Although snow and ice lie all around,
the trees can't tap that
water while it's frozen.
So this land is effectively
as parched as a desert,
and the pine trees have as great a
need to conserve water as a cactus.
All plants lose some water
through their leaves,
but pine needles are protected
by a near-impermeable rind.
The pores through which they breathe,
and from which water can evaporate,
are kept out of the wind
by being placed in lines,
along the groove that runs
the length of the needle,
each in a tiny pit
ringed with a ridge.
These dry,
waxy leaves are almost inedible,
but the seeds in the cones are not,
and are one of the few kinds of food
available in the forest in winter.
The crossbill's special beak enables
it to separate the cone's segments
and prise out the nutritious seeds.
This winter feast is never certain.
Some years every branch of the
trees will be laden with cones,
in others there will only be a handful.
Then the seed-eaters must move on or die.
The few remaining cones can then
shed their seeds into the snow
when there are few animals around.
Even so, there "are" some.
Voles make their runways through
the snow and collect what they can.
Moose get little
nourishment from pine trees,
apart from the shaggy moss
that hangs from the branches.
They chew the sappy
twigs and bark of birch,
but there's not enough
to keep them going.
If it wasn't for the fat reserves they
built up in summer, few would survive.
The winter forests can
support very few plant-eaters,
but there are just enough to
feed one or two hardy hunters.
The great grey owl's legs are
ideal for grabbing prey in snow:
Long and covered with warm feathers.
It regularly patrols the snow,
for it can't afford to miss a
single opportunity of a meal.
And this is an incautious move.
Lynx seek bigger prey.
The female has young,
which, though large,
are not yet skilled enough to hunt
for themselves, so they rely on her.
The cost-efficiency of hunting
is precisely calculated.
If the lynx doesn't catch
a hare within 200 yards,
the meat it might provide is not enough to
warrant the effort, and the lynx gives up.
Bigger prey are worth
much longer chases,
and the lynx pursue roe
deer with great persistence.
A single deer will provide
food for the whole lynx family.
In this bleak land, even the most
ferocious and capable hunters
do not scorn to scavenge.
An eagle owl will
take cold deer flesh
just as eagerly as the
warm bodies of voles.
A wolverine,
the biggest of the weasel family,
and more than a match
for an eagle owl.
The coniferous forest
grows right round the globe
in a belt that, in places,
is 1,200 miles across.
From Scandinavia, it extends
across northern Europe and Siberia
to the shores of the Pacific.
During the last ice age,
when the seas were lower,
the Bering Strait did not exist, so
the trees continued into North America,
across northern Canada
to the Atlantic.
Consequently,
all the trees in this vast forest
and its permanent inhabitants in America,
Asia and Europe, are much the same.
But when spring comes, visitors
journey up from warmer parts
and each forest takes on its
own individual character.
In Scandinavia, a hawk owl, a nomad
that has spent the winter farther south,
comes cruising up north again
looking for food and a nest site.
Unlike other owls,
it's primarily a daytime hunter,
and relies not so much on its
acute hearing as its sharp eyesight
as it waits for the melting
snow to reveal rodents.
In pine trees,
from Norway to Siberia,
the cock capercaillie
claims his territory.
This giant grouse is one of the few
creatures that eats pine needles.
His hen takes them too.
Now is the time for nesting. The hawk
owl is in search of a hole in a tree,
for it's already found its partner.
But many tree holes are occupied,
for great numbers of owls have
travelled up to feed on the voles.
No owl can dig a hole for itself.
They rely mainly on woodpeckers,
and none is a more expert carpenter
than the black woodpecker
of northern Europe.
Their sharp beak serves
as an excellent chisel,
but most prefer to work in dead
trees where the wood is softer.
There are ants near this tree too, which
the woodpeckers rely on for food in winter.
Not all owls use nest holes. The eagle
owl nests on the ground, among rocks.
It already has a clutch of three eggs, for,
being a permanent resident of these forests,
it paired early.
Plants now have their
chance to breed.
The wood anemones are already
in flower, as are the pines.
Each tree produces male
and female flowers,
which mature at different times,
so the female flowers are likely to be
fertilised by pollen from other trees.
Now it is as warm as it ever
will be in the northern forests.
Summer visitors are arriving,
and the trees echo with their song.
This willow warbler, singing
so vigorously in Scandinavia,
has come all the way from the
savannah country south of the Sahara.
So has the winchat.
And the lure that has brought them so far is
the sudden emergence of myriads of insects.
This bedraggled creature
is hardly recognisable,
for its wings have not yet
expanded. It's a pine beauty moth,
and its first priority is to leave the
forest floor which is full of danger.
But not all the moths
have such a clear run.
Shrews are among the
first to feed on them.
Up among the pine needles, the pine
beauty pumps fluid out of its body
and into the veins of its wings.
Here the moths will lay their eggs so their
caterpillars can feed on the young shoots.
The wood ants have missed their
chance to catch the adult moth,
but now they're looking for the
caterpillars among the branches.
The colour and the pattern of the caterpillar
conceals it from birds which hunt by sight,
but is no protection against ants
which search by smell and touch.
Finally the body is hauled down
to the nest for all to consume.
The caterpillars of the sawfly are
also swarming on the pine shoots.
They do have a defence
against ants: A chemical one.
As they chew, they store some of
the resin from the pine needles
in a pouch inside their mouth.
When a foraging ant discovers them,
they dab a spot of this
resin on its head, like this.
The resin damages the
ant's eyes and antennae,
so disorientating it
that it can hardly walk.
Even if it finds its way back to the
nest, it smells so strongly and strangely
that the other ants treat it
as an intruder and kill it.
The ants themselves
are food for others.
The wryneck is a member of the woodpecker
family that has specialised in eating ants,
and particularly
relishes their cocoons.
Like its cousins, the wryneck
nests in holes in trees,
but it doesn't excavate
them for itself.
It is yet another tenant of
vacated woodpecker holes.
With a long tongue you can even
collect insects from the bark
without leaving your nest.
Here in the far north,
close to the Arctic Circle,
the sun during the summer hardly sinks
below the horizon and the nights are brief.
The eagle owl hunts just as effectively
in the twilight as in the dark.
It has a rabbit. The season is
a good one and game is abundant.
Down in the nest on the forest
floor, there is only one chick left.
The other two may have
been taken by foxes.
Eagle owls often kill rival species, and
this chick's last meal was a short-eared owl,
which it's not yet finished.
The single survivor has
a superabundance of food.
It has grown fast and its adult feathers
are already appearing through its down.
The tail of a red squirrel is
left over from a previous meal,
and it even takes that too.
The voles are swarming
on the forest floor.
Last winter, the pines produced
great quantities of seed,
so many adult voles
survived till spring
and now they're all breeding
at an extraordinary rate.
This female produced her four
young only three weeks ago,
but she is already pregnant again and will
soon abandon this family and start a new one.
All the owls, some visitors,
some residents,
scour the forest for voles.
Tengmalm's owl, up in a tree hole,
has three chicks,
all flourishing and
all demanding voles.
The number of voles
varies considerably.
It gradually builds up over a period of five
to six years until finally there are so many
that they eat out their food
supply and the population crashes.
These changes have their
effect on the owl population.
More voles mean better-fed owls,
which produce bigger clutches
of eggs and rear more chicks.
And as the number of owls increases,
so they spread out into new territory.
I'm in Finland,
very close to the Russian border.
In fact, those pine forests
behind me are actually in Russia.
But the frontier is no barrier to the
bird they call the phantom of the north,
the great grey owl, and in years
when the vole population is high,
the owl comes across these frontiers
and into the Finnish pine forests.
And I know they are here already
because I have just picked up this.
This is an owl pellet. All owls,
as part of their natural digestion,
throw up the fur and
bones of their prey.
And this, I can see,
has actually got vole skulls in it.
But to discover exactly what the state
of the vole population is at the moment,
I'll have to look inside the
nest of a great grey owl,
and to do that I'll need this.
All owls are fairly ferocious and
the great grey owl certainly can be,
so as part of the standard equipment
of looking for owl nests you need this.
Up there is one of their nests,
and the female has just flown off.
She's perching in that tree over
there, keeping a very close eye on me.
If I go up and have
a look in the nest,
I may be able to get some idea as
to how the vole cycle is going.
And... come on...
there is just one chick.
If the voles had been at the
height of their population,
there would probably be four
chicks in such a nest as this,
but the fact there is only
one makes it pretty clear
that the vole population is
already beginning to crash.
So it is very likely
the female and her mate
will soon be on their
way back to Russia.
There's now just a month left
of the short northern summer.
Many of the birds that came up here
to harvest the insects and to breed
will soon be moving back again to avoid
the severities of the coming winter.
Some, like the redwing, will go
to open pastureland down south.
The brambling prefers beech woodland,
and will leave almost as soon as
it has finished its summer moult.
The hawk owl is driven
south by hunger,
for as the forest gets colder,
there is less food to be found.
As it flies south, so the
trees beneath change character.
The ranks of dark conifers are replaced by
the brighter green of the broadleaved trees:
Oak and ash, birch and beech.
Down here, the weather's warmer,
the summers are longer,
and the woodlands are free of frost,
not for just two or three months
in the year, but for eight or nine,
and the shape of the
trees is very different.
Instead of their branches drooping
down, and so shedding the snow,
these branches spread out widely,
carrying tier upon tier of leaves with which
to catch the abundant energy of the sun.
And the leaves are very different. They are
not covered with a thick, protective rind,
but are thin, delicate structures. During
the summer water is more accessible,
so there is less need to take
rigorous measures to conserve it.
Indeed, during hot days the trees
evaporate large quantities to keep cool.
So the pores through which
they breathe are numerous,
and not in pits as
they are in the pines.
These succulent, soft leaves,
unlike pine needles,
are relished as food by
all kinds of creatures.
Large animals, like deer,
take many of them,
but the greatest quantity by
far is gathered by insects.
The forest canopy in late
summer has more birds in it
than at any other time of the year.
There are returning migrants
newly arrived from the north,
resident breeders gathering food to feed
their second families of the season,
and young fledglings starting
to forage for themselves
and still not sure what
is edible and what isn't.
Nearly all of them are hunting for
insects, and the crop they take is huge.
Not surprisingly, the insects have evolved
many ways of protecting themselves.
They snip off half-eaten leaves so as to
give the minimum sign of their presence.
They disguise themselves as a blob
of cuckoo spit or a bird dropping,
but if they move, as eventually they
must, their concealment is lost.
Some hang in places which
are difficult to reach.
This might baffle a fledgling, but an adult
great tit is both experienced and agile.
The tree creeper specialises
in insects that live on bark.
A poplar hawk moth tries to defend
itself by pretending to be fierce.
The nuthatch habitually
works its way down the trunk,
and that way may see insects
that have been overlooked
by tree creepers that
habitually come up it.
One of the most expert
of all bark-feeders,
and in some ways the most
specialised of all the birds
living in the tall trees of these
forests, are the woodpeckers.
The greater spotted
woodpecker is typical of them.
Its hearing is excellent and
it locates the grubs it seeks
by the tiny sounds they make
as they move inside the bark.
Its tall feathers have strong quills
and serve as props for its body.
Its bill has a resilient pad at
the base which cushions its brain
from the shock of its drilling.
Its feet give it a
grip in all directions,
with two toes pointing
forwards and two backwards.
Each continent has its
own range of woodpeckers.
Europe has ten species, but here in North
America there are over twice as many.
This one, a sapsucker, drills holes
in trees not for insects, but for sap.
It digs lines of these wells
in many kinds of trees.
Each little hole points slightly downwards
so that the sap does not trickle out
but collects in a small pool inside,
and the sapsucker collects
it with its tongue.
And so do other birds.
A hummingbird. Most of its family live
in the tropics and feed on nectar,
but this one comes north in the summer
and finds tree sap just as acceptable.
Flies, too, come to the sweet sap.
In late summer, the parent sapsuckers
lead their fledglings to the wells
and leave them to feast not only on
the sap but on the insects it attracts.
This American woodpecker
uses its drilling skills
to bore neat sockets
in dead tree trunks.
Acorns are its main food,
but during the season,
there are far more acorns than the
woodpeckers can eat immediately.
But they don't leave them for others.
Several birds share communal acorn treasury,
like this one. They hammer the
acorns into the holes so firmly
that few other creatures
can get them out,
and the store will keep the acorn
woodpeckers supplied throughout the year.
The ripening acorns herald the end of
summer and the beginning of autumn.
Trees and bushes proffer their
seeds to the forest animals.
Some are wrapped in
soft and tasty flesh
to tempt the animals to eat them
and so transport them to new sites.
Others are packed with nourishment,
not for animals,
but to provide food for
the germinating seedling,
but the animals eat them just the same.
Even the hard and unpromising-looking
acorns of the American pin oak
are collected by racoons.
The squirrel's habit of burying
acorns for a winter store
has been the start of many an oak.
The black bear, on occasion, will
eat fish and voles and even carrion,
but much of its diet is vegetable. It will
dig for roots and even eat pine cones,
but it has a very sweet tooth and
just now it relishes the fruit.
All sorts of mammals are now clambering
around in the trees in search of fruit.
The possum, a strange primitive
animal of the Americas
related more closely to kangaroos
than to rats, eats almost anything.
Few of them can get to the very tops
of the trees or the thinnest twig,
but a chipmunk can.
The chills of autumn presage
the coming of winter.
The delicate leaves worked efficiently
throughout the warm moist summer,
but they are not suited to cold
weather. Frost will damage them.
Their abundant pores
would lose too much water.
So the green chlorophyll in them is
broken down and withdrawn into the tree,
revealing the red and brown waste
products, and the leaves fall.
And they, too, provide food
for another woodland community,
the inhabitants of the leaf litter.
There may be 100,000 box
mites in every cubic yard.
And there are many other creatures too,
chewing their way through the dead leaves,
extracting what nutriment they can
and leaving the remainder to be
dealt with by fungi and bacteria.
They themselves are hunted by monsters
in miniature, pseudoscorpions,
horrific in close-up, but, perhaps
fortunately, the size of a pinhead.
Snails are giants in comparison and, since
they carry their shells around with them,
they might seem to be fairly well protected
against any creatures smaller than a bird.
But one particular beetle has specialised
equipment for dealing with them.
Its head and jaws are long and thin.
Almost hidden in the leaves
of these American woods
are some spectacularly coloured little
creatures hardly bigger than worms.
They are amphibians: Salamanders.
Almost every mountain range in the US
has its own species with its own colours,
but, being nocturnal,
they're rarely seen.
Shrews eat most small living things they
come across, and they are formidable hunters,
for they are one of the few
mammals that has a poisonous bite.
The salamander's only defence is to produce
an acrid liquid from glands on its tail.
The first time a
shrew encounters this,
it usually takes no notice
and eats the salamander,
but apparently the taste is not very nice,
for on later encounters, like this one,
one sniff reminds the shrew
the meal won't be a good one
and it leaves the salamander alone.
The summer visitors have departed.
The woods have fallen silent.
The days are shortening and
the temperature falling.
Eventually the land is
gripped tight by frost.
It's late winter. The once-resplendent
trees are now mere skeletons
and life in these woodlands has
come almost to a standstill.
The trees, without their leaves,
can't grow.
The birds that came visiting up here
during the summer have now retreated south,
and some of these small mammals have
crawled into holes and gone to sleep.
Their heartbeat has almost stopped, their
bodies have become as cold as stone.
They're hibernating. But that sleep
doesn't last throughout the winter.
They wake up every four or five
days and go and look for food.
Like, for example,
those small chipmunks over there.
Not only warmth but intense
cold will bring them out,
for although their body temperature
falls while they hibernate,
if it drops to freezing point,
they will die.
So in really cold spells, they must get up
and warm themselves with a little exercise,
even though it dangerously
depletes their fat reserves.
But in these American woodlands
there is one spectacular sleeper
who dozes for months on end.
Just look at this.
A black bear.
She retired to this
den in early autumn,
and after a month or so of
drowsiness, produced her cubs.
In the colder northern parts of these woods,
she may spend six or seven months here,
during which time
she suckles her cubs
but neither feeds herself
nor urinates nor defecates.
So she spends the majority
of her life half-asleep.
When spring at last comes,
the brown carpet of rotting leaves
is suddenly flooded with colour.
The plants that live close to the ground
now make haste to sprout and flower
and soak up the spring sunshine before
the trees above produce their own leaves
and cut out the light.
The bear's den is empty,
but the owners haven't gone far.
There's still not much to eat,
only a few leaves,
nor will there be until the first of
the berries come into fruit in summer,
but meanwhile at
least the sun is warm.
Another mother spends
the spring up in a tree:
A wood duck,
only she is about to leave.
The hole has provided a secure nest,
but all ducklings follow their
mothers as soon as they hatch.
And now new forms appear
from among the dead leaves.
The spring showers soak the woodlands
and create just the moist,
warm conditions needed by the fungi
to produce their fruiting bodies.
These must be mature and ready to
discharge their microscopic spores
by the time the dry winds
of summer begin to blow,
so that their spores, like dust, will
be carried all through the forest.
Once, the woods of North America stretched
over the eastern half of the continent
in an almost continuous
band hundreds of miles deep.
Today, the majority has been felled
to make space for farmland and cities,
but enough remains to make
plain their splendour.
And now we've come
farther south still.
I'm on the borders of Florida and
Georgia in the southern United States,
and here it's very hot in the summer
and the winters are very mild,
with only a few frosts,
and none of them severe.
So some of the broadleaved
trees here, like this oak,
don't shed all their
leaves in the autumn
but keep them throughout the
year and continue growing.
And these aren't the only evergreens
that are here, either. There are pines.
In some parts where the soil is very
rocky or sandy and poor in nutrients,
the pines will grow because
nothing else can survive there.
But this pine forest owes its
existence to another factor altogether.
Oak saplings are killed
within minutes by fire.
But the terminal buds of young pines
are surrounded by a shock of needles.
They burn at a relatively
low temperature,
and by the time the flames have consumed
them, the main fire has swept by
and the bud at the top of the stem,
from which new growth will come,
is still unharmed.
Fires like these are not just the work
of careless people, they occur naturally.
The spark that regularly sets fire
to these forests is lightning.
In this part of the southern States,
violent thunderstorms are common
and lightning often
strikes the taller trees,
scoring a deep groove down the length of
the trunk as it flashes down to earth.
And this at my feet is the
tinder which set it aflame.
These are pine needles, and they're
so full of resin and they're so dry
that they flame up very easily.
But the fire they produce is not very
hot, and it's also very short-lived,
so that if any creature can survive
fire for just one or two minutes,
then it can survive a fire like this.
The rattlesnake, like many
other ground-living animals,
regularly takes refuge from
the midday sun in holes,
so now it knows exactly where
to go to escape the fire.
But this hole is already
occupied by its digger and owner,
a gopher tortoise.
Rattlesnake and tortoise do not
normally interfere with one another...
and that seems to be the
way things are going to stay.
But in the back of the burrow lies
another refugee, an indigo snake,
and it, on occasion,
eats rattlesnakes.
But the fire is passing and the
rattlesnake can return to the forest.
Some insects don't avoid fire,
they actively seek it.
Beetles find it difficult to
lay their eggs in the pines
because the trees swamp them with resin.
But a tree killed by fire can't resist,
and these beetles take
advantage of the situation.
They have pits behind their legs
which are sensitive to infra-red rays,
and therefore they can detect the
slightest rise in temperature,
and with these to guide them, they
travel from all over the forest
to the wake of the fire
and arrive in hundreds.
Quickly they mate.
The females crawl all
over the scorched trunks,
seeking crevices in the bark into
which they can lay their eggs,
so ensuring that their grubs will have
some nice nutritious bark to chew.
As insects assemble in the burnt
forest, the insect-eaters follow.
The oak toad almost exactly matches
the colour of the charred forest floor.
Other more conspicuous hunters
wait on newly emerged shoots.
Within a couple of months of a summer
fire, the forest has more than recovered,
it is rejuvenated. The fire has cleared
away the old growth on the ground,
and by reducing the pine needles to ash
has released their nutrients into the soil,
and now the ground sprouts more
flowers than at any other time.
Because of regular fires, big bushes
can't establish themselves here,
so swampy areas are not colonised and
sucked dry by them as happens elsewhere,
and open marshes remain
where pitcher plants can grow
and where frogs can swim and breed.
Indeed, one species of
frog lives nowhere else
but in these pools in the
American pine barrens.
Woodpeckers here can't excavate their nest
in dead trees as do woodpeckers elsewhere,
for in this fire-ravaged forest
they would risk incineration,
so the red-cockaded woodpecker
drills its holes in living pines.
But the wood is so hard, it takes several
woodpeckers about two years to dig the hole.
Resinous sap seeps
out around the hole
where the outer layers of
the tree have been breached.
So the birds make their
hole low down on the trunk
where the inner sap-free heartwood is thick
enough to accommodate the entire nest.
The flow of resin is
diverted to the outside
by drilling pits like sap
wells above and below the hole.
It's in these laboriously
excavated holes
that the red-cockaded
woodpecker raises its young.
The holes are very conspicuous,
for each is surrounded
by a sheet of yellow congealed resin.
The rat snake is a great robber
of nests and stealer of chicks.
It's an extremely
skilful tree climber.
Since the woodpecker's hole in the living
tree has to be fairly low down on the trunk,
it is within easy reach of the snake
and therefore might seem to
be in considerable danger.
But now the other function
of all that resin,
deliberately produced around the nest by
the woodpecker, is about to become clear.
The chemicals in the resin seem to
irritate the snake beyond endurance,
and it arches its body away.
Eventually it's too much.
So fire, one way or another, influences
the whole community of animals and plants
in the pine forests of the south.
This injury was also caused by fire,
and this is also a coniferous tree,
but a very different one.
To start with, it's over 40
feet across along its base
and it's 267,5 feet high.
This is a giant sequoia.
It's thought to be
about 2,500 years old,
but the largest individual tree of all is
this one, known as the General Sherman.
It's just taller and it's
estimated to weigh 1,385 tons,
which makes it the most massive
living organism in the world.
Although these trees are growing almost
as far south as the southern pines,
the climate here, 2,000 metres up
in the Sierra Nevada mountains,
is much colder and snow lies on the
ground for almost half the year.
It's as though,
by climbing to this height,
we have returned climatically to
the great forests of the north.
During the Ice Age, these sequoias
grew over much of North America.
But when, some 8,000 years ago,
the earth began to warm,
they died out except for these isolated
groups high up in the mountains.
We've travelled some
2,000 miles southwards
since we started at the tree
line near the Arctic Circle,
and in all that vast territory the majority
of the forest trees have been conifers,
so it seems only right and proper
that we should end with these,
the noblest of them all.
As a group, the conifers
owe much of their success
to their ability to cope with
the changeable northern climate.
They can survive both the short, dark
days of winter with their bitter cold,
as well as the long sunny days of
summer with their raging fires.
A PORTRAIT OF THE EARTH
In the lands between the
Arctic Circle and the tropics,
each year brings a great change
between winter and summer,
imposing a rhythm in the
lives of animals and plants.
Up north in the great
evergreen forests,
conditions in mid-winter
are cripplingly severe.
THE NORTHERN FORESTS
Life, if it is to flourish,
has three needs:
Light, warmth and moisture.
And the reason trees like these
don't grow much farther north
is not only the extreme cold,
but with the long months
of winter darkness,
there is not enough light in
the year for them to grow.
Here in northern Norway, 300 miles,
500km north of the Arctic Circle,
there is just enough light,
but it does get extremely cold.
70 degrees of frost
have been measured here,
and in winter there are
very heavy snowfalls.
The cold threatens to freeze
the liquid within the trees,
and denies them one of their
essential supplies: Water.
Although snow and ice lie all around,
the trees can't tap that
water while it's frozen.
So this land is effectively
as parched as a desert,
and the pine trees have as great a
need to conserve water as a cactus.
All plants lose some water
through their leaves,
but pine needles are protected
by a near-impermeable rind.
The pores through which they breathe,
and from which water can evaporate,
are kept out of the wind
by being placed in lines,
along the groove that runs
the length of the needle,
each in a tiny pit
ringed with a ridge.
These dry,
waxy leaves are almost inedible,
but the seeds in the cones are not,
and are one of the few kinds of food
available in the forest in winter.
The crossbill's special beak enables
it to separate the cone's segments
and prise out the nutritious seeds.
This winter feast is never certain.
Some years every branch of the
trees will be laden with cones,
in others there will only be a handful.
Then the seed-eaters must move on or die.
The few remaining cones can then
shed their seeds into the snow
when there are few animals around.
Even so, there "are" some.
Voles make their runways through
the snow and collect what they can.
Moose get little
nourishment from pine trees,
apart from the shaggy moss
that hangs from the branches.
They chew the sappy
twigs and bark of birch,
but there's not enough
to keep them going.
If it wasn't for the fat reserves they
built up in summer, few would survive.
The winter forests can
support very few plant-eaters,
but there are just enough to
feed one or two hardy hunters.
The great grey owl's legs are
ideal for grabbing prey in snow:
Long and covered with warm feathers.
It regularly patrols the snow,
for it can't afford to miss a
single opportunity of a meal.
And this is an incautious move.
Lynx seek bigger prey.
The female has young,
which, though large,
are not yet skilled enough to hunt
for themselves, so they rely on her.
The cost-efficiency of hunting
is precisely calculated.
If the lynx doesn't catch
a hare within 200 yards,
the meat it might provide is not enough to
warrant the effort, and the lynx gives up.
Bigger prey are worth
much longer chases,
and the lynx pursue roe
deer with great persistence.
A single deer will provide
food for the whole lynx family.
In this bleak land, even the most
ferocious and capable hunters
do not scorn to scavenge.
An eagle owl will
take cold deer flesh
just as eagerly as the
warm bodies of voles.
A wolverine,
the biggest of the weasel family,
and more than a match
for an eagle owl.
The coniferous forest
grows right round the globe
in a belt that, in places,
is 1,200 miles across.
From Scandinavia, it extends
across northern Europe and Siberia
to the shores of the Pacific.
During the last ice age,
when the seas were lower,
the Bering Strait did not exist, so
the trees continued into North America,
across northern Canada
to the Atlantic.
Consequently,
all the trees in this vast forest
and its permanent inhabitants in America,
Asia and Europe, are much the same.
But when spring comes, visitors
journey up from warmer parts
and each forest takes on its
own individual character.
In Scandinavia, a hawk owl, a nomad
that has spent the winter farther south,
comes cruising up north again
looking for food and a nest site.
Unlike other owls,
it's primarily a daytime hunter,
and relies not so much on its
acute hearing as its sharp eyesight
as it waits for the melting
snow to reveal rodents.
In pine trees,
from Norway to Siberia,
the cock capercaillie
claims his territory.
This giant grouse is one of the few
creatures that eats pine needles.
His hen takes them too.
Now is the time for nesting. The hawk
owl is in search of a hole in a tree,
for it's already found its partner.
But many tree holes are occupied,
for great numbers of owls have
travelled up to feed on the voles.
No owl can dig a hole for itself.
They rely mainly on woodpeckers,
and none is a more expert carpenter
than the black woodpecker
of northern Europe.
Their sharp beak serves
as an excellent chisel,
but most prefer to work in dead
trees where the wood is softer.
There are ants near this tree too, which
the woodpeckers rely on for food in winter.
Not all owls use nest holes. The eagle
owl nests on the ground, among rocks.
It already has a clutch of three eggs, for,
being a permanent resident of these forests,
it paired early.
Plants now have their
chance to breed.
The wood anemones are already
in flower, as are the pines.
Each tree produces male
and female flowers,
which mature at different times,
so the female flowers are likely to be
fertilised by pollen from other trees.
Now it is as warm as it ever
will be in the northern forests.
Summer visitors are arriving,
and the trees echo with their song.
This willow warbler, singing
so vigorously in Scandinavia,
has come all the way from the
savannah country south of the Sahara.
So has the winchat.
And the lure that has brought them so far is
the sudden emergence of myriads of insects.
This bedraggled creature
is hardly recognisable,
for its wings have not yet
expanded. It's a pine beauty moth,
and its first priority is to leave the
forest floor which is full of danger.
But not all the moths
have such a clear run.
Shrews are among the
first to feed on them.
Up among the pine needles, the pine
beauty pumps fluid out of its body
and into the veins of its wings.
Here the moths will lay their eggs so their
caterpillars can feed on the young shoots.
The wood ants have missed their
chance to catch the adult moth,
but now they're looking for the
caterpillars among the branches.
The colour and the pattern of the caterpillar
conceals it from birds which hunt by sight,
but is no protection against ants
which search by smell and touch.
Finally the body is hauled down
to the nest for all to consume.
The caterpillars of the sawfly are
also swarming on the pine shoots.
They do have a defence
against ants: A chemical one.
As they chew, they store some of
the resin from the pine needles
in a pouch inside their mouth.
When a foraging ant discovers them,
they dab a spot of this
resin on its head, like this.
The resin damages the
ant's eyes and antennae,
so disorientating it
that it can hardly walk.
Even if it finds its way back to the
nest, it smells so strongly and strangely
that the other ants treat it
as an intruder and kill it.
The ants themselves
are food for others.
The wryneck is a member of the woodpecker
family that has specialised in eating ants,
and particularly
relishes their cocoons.
Like its cousins, the wryneck
nests in holes in trees,
but it doesn't excavate
them for itself.
It is yet another tenant of
vacated woodpecker holes.
With a long tongue you can even
collect insects from the bark
without leaving your nest.
Here in the far north,
close to the Arctic Circle,
the sun during the summer hardly sinks
below the horizon and the nights are brief.
The eagle owl hunts just as effectively
in the twilight as in the dark.
It has a rabbit. The season is
a good one and game is abundant.
Down in the nest on the forest
floor, there is only one chick left.
The other two may have
been taken by foxes.
Eagle owls often kill rival species, and
this chick's last meal was a short-eared owl,
which it's not yet finished.
The single survivor has
a superabundance of food.
It has grown fast and its adult feathers
are already appearing through its down.
The tail of a red squirrel is
left over from a previous meal,
and it even takes that too.
The voles are swarming
on the forest floor.
Last winter, the pines produced
great quantities of seed,
so many adult voles
survived till spring
and now they're all breeding
at an extraordinary rate.
This female produced her four
young only three weeks ago,
but she is already pregnant again and will
soon abandon this family and start a new one.
All the owls, some visitors,
some residents,
scour the forest for voles.
Tengmalm's owl, up in a tree hole,
has three chicks,
all flourishing and
all demanding voles.
The number of voles
varies considerably.
It gradually builds up over a period of five
to six years until finally there are so many
that they eat out their food
supply and the population crashes.
These changes have their
effect on the owl population.
More voles mean better-fed owls,
which produce bigger clutches
of eggs and rear more chicks.
And as the number of owls increases,
so they spread out into new territory.
I'm in Finland,
very close to the Russian border.
In fact, those pine forests
behind me are actually in Russia.
But the frontier is no barrier to the
bird they call the phantom of the north,
the great grey owl, and in years
when the vole population is high,
the owl comes across these frontiers
and into the Finnish pine forests.
And I know they are here already
because I have just picked up this.
This is an owl pellet. All owls,
as part of their natural digestion,
throw up the fur and
bones of their prey.
And this, I can see,
has actually got vole skulls in it.
But to discover exactly what the state
of the vole population is at the moment,
I'll have to look inside the
nest of a great grey owl,
and to do that I'll need this.
All owls are fairly ferocious and
the great grey owl certainly can be,
so as part of the standard equipment
of looking for owl nests you need this.
Up there is one of their nests,
and the female has just flown off.
She's perching in that tree over
there, keeping a very close eye on me.
If I go up and have
a look in the nest,
I may be able to get some idea as
to how the vole cycle is going.
And... come on...
there is just one chick.
If the voles had been at the
height of their population,
there would probably be four
chicks in such a nest as this,
but the fact there is only
one makes it pretty clear
that the vole population is
already beginning to crash.
So it is very likely
the female and her mate
will soon be on their
way back to Russia.
There's now just a month left
of the short northern summer.
Many of the birds that came up here
to harvest the insects and to breed
will soon be moving back again to avoid
the severities of the coming winter.
Some, like the redwing, will go
to open pastureland down south.
The brambling prefers beech woodland,
and will leave almost as soon as
it has finished its summer moult.
The hawk owl is driven
south by hunger,
for as the forest gets colder,
there is less food to be found.
As it flies south, so the
trees beneath change character.
The ranks of dark conifers are replaced by
the brighter green of the broadleaved trees:
Oak and ash, birch and beech.
Down here, the weather's warmer,
the summers are longer,
and the woodlands are free of frost,
not for just two or three months
in the year, but for eight or nine,
and the shape of the
trees is very different.
Instead of their branches drooping
down, and so shedding the snow,
these branches spread out widely,
carrying tier upon tier of leaves with which
to catch the abundant energy of the sun.
And the leaves are very different. They are
not covered with a thick, protective rind,
but are thin, delicate structures. During
the summer water is more accessible,
so there is less need to take
rigorous measures to conserve it.
Indeed, during hot days the trees
evaporate large quantities to keep cool.
So the pores through which
they breathe are numerous,
and not in pits as
they are in the pines.
These succulent, soft leaves,
unlike pine needles,
are relished as food by
all kinds of creatures.
Large animals, like deer,
take many of them,
but the greatest quantity by
far is gathered by insects.
The forest canopy in late
summer has more birds in it
than at any other time of the year.
There are returning migrants
newly arrived from the north,
resident breeders gathering food to feed
their second families of the season,
and young fledglings starting
to forage for themselves
and still not sure what
is edible and what isn't.
Nearly all of them are hunting for
insects, and the crop they take is huge.
Not surprisingly, the insects have evolved
many ways of protecting themselves.
They snip off half-eaten leaves so as to
give the minimum sign of their presence.
They disguise themselves as a blob
of cuckoo spit or a bird dropping,
but if they move, as eventually they
must, their concealment is lost.
Some hang in places which
are difficult to reach.
This might baffle a fledgling, but an adult
great tit is both experienced and agile.
The tree creeper specialises
in insects that live on bark.
A poplar hawk moth tries to defend
itself by pretending to be fierce.
The nuthatch habitually
works its way down the trunk,
and that way may see insects
that have been overlooked
by tree creepers that
habitually come up it.
One of the most expert
of all bark-feeders,
and in some ways the most
specialised of all the birds
living in the tall trees of these
forests, are the woodpeckers.
The greater spotted
woodpecker is typical of them.
Its hearing is excellent and
it locates the grubs it seeks
by the tiny sounds they make
as they move inside the bark.
Its tall feathers have strong quills
and serve as props for its body.
Its bill has a resilient pad at
the base which cushions its brain
from the shock of its drilling.
Its feet give it a
grip in all directions,
with two toes pointing
forwards and two backwards.
Each continent has its
own range of woodpeckers.
Europe has ten species, but here in North
America there are over twice as many.
This one, a sapsucker, drills holes
in trees not for insects, but for sap.
It digs lines of these wells
in many kinds of trees.
Each little hole points slightly downwards
so that the sap does not trickle out
but collects in a small pool inside,
and the sapsucker collects
it with its tongue.
And so do other birds.
A hummingbird. Most of its family live
in the tropics and feed on nectar,
but this one comes north in the summer
and finds tree sap just as acceptable.
Flies, too, come to the sweet sap.
In late summer, the parent sapsuckers
lead their fledglings to the wells
and leave them to feast not only on
the sap but on the insects it attracts.
This American woodpecker
uses its drilling skills
to bore neat sockets
in dead tree trunks.
Acorns are its main food,
but during the season,
there are far more acorns than the
woodpeckers can eat immediately.
But they don't leave them for others.
Several birds share communal acorn treasury,
like this one. They hammer the
acorns into the holes so firmly
that few other creatures
can get them out,
and the store will keep the acorn
woodpeckers supplied throughout the year.
The ripening acorns herald the end of
summer and the beginning of autumn.
Trees and bushes proffer their
seeds to the forest animals.
Some are wrapped in
soft and tasty flesh
to tempt the animals to eat them
and so transport them to new sites.
Others are packed with nourishment,
not for animals,
but to provide food for
the germinating seedling,
but the animals eat them just the same.
Even the hard and unpromising-looking
acorns of the American pin oak
are collected by racoons.
The squirrel's habit of burying
acorns for a winter store
has been the start of many an oak.
The black bear, on occasion, will
eat fish and voles and even carrion,
but much of its diet is vegetable. It will
dig for roots and even eat pine cones,
but it has a very sweet tooth and
just now it relishes the fruit.
All sorts of mammals are now clambering
around in the trees in search of fruit.
The possum, a strange primitive
animal of the Americas
related more closely to kangaroos
than to rats, eats almost anything.
Few of them can get to the very tops
of the trees or the thinnest twig,
but a chipmunk can.
The chills of autumn presage
the coming of winter.
The delicate leaves worked efficiently
throughout the warm moist summer,
but they are not suited to cold
weather. Frost will damage them.
Their abundant pores
would lose too much water.
So the green chlorophyll in them is
broken down and withdrawn into the tree,
revealing the red and brown waste
products, and the leaves fall.
And they, too, provide food
for another woodland community,
the inhabitants of the leaf litter.
There may be 100,000 box
mites in every cubic yard.
And there are many other creatures too,
chewing their way through the dead leaves,
extracting what nutriment they can
and leaving the remainder to be
dealt with by fungi and bacteria.
They themselves are hunted by monsters
in miniature, pseudoscorpions,
horrific in close-up, but, perhaps
fortunately, the size of a pinhead.
Snails are giants in comparison and, since
they carry their shells around with them,
they might seem to be fairly well protected
against any creatures smaller than a bird.
But one particular beetle has specialised
equipment for dealing with them.
Its head and jaws are long and thin.
Almost hidden in the leaves
of these American woods
are some spectacularly coloured little
creatures hardly bigger than worms.
They are amphibians: Salamanders.
Almost every mountain range in the US
has its own species with its own colours,
but, being nocturnal,
they're rarely seen.
Shrews eat most small living things they
come across, and they are formidable hunters,
for they are one of the few
mammals that has a poisonous bite.
The salamander's only defence is to produce
an acrid liquid from glands on its tail.
The first time a
shrew encounters this,
it usually takes no notice
and eats the salamander,
but apparently the taste is not very nice,
for on later encounters, like this one,
one sniff reminds the shrew
the meal won't be a good one
and it leaves the salamander alone.
The summer visitors have departed.
The woods have fallen silent.
The days are shortening and
the temperature falling.
Eventually the land is
gripped tight by frost.
It's late winter. The once-resplendent
trees are now mere skeletons
and life in these woodlands has
come almost to a standstill.
The trees, without their leaves,
can't grow.
The birds that came visiting up here
during the summer have now retreated south,
and some of these small mammals have
crawled into holes and gone to sleep.
Their heartbeat has almost stopped, their
bodies have become as cold as stone.
They're hibernating. But that sleep
doesn't last throughout the winter.
They wake up every four or five
days and go and look for food.
Like, for example,
those small chipmunks over there.
Not only warmth but intense
cold will bring them out,
for although their body temperature
falls while they hibernate,
if it drops to freezing point,
they will die.
So in really cold spells, they must get up
and warm themselves with a little exercise,
even though it dangerously
depletes their fat reserves.
But in these American woodlands
there is one spectacular sleeper
who dozes for months on end.
Just look at this.
A black bear.
She retired to this
den in early autumn,
and after a month or so of
drowsiness, produced her cubs.
In the colder northern parts of these woods,
she may spend six or seven months here,
during which time
she suckles her cubs
but neither feeds herself
nor urinates nor defecates.
So she spends the majority
of her life half-asleep.
When spring at last comes,
the brown carpet of rotting leaves
is suddenly flooded with colour.
The plants that live close to the ground
now make haste to sprout and flower
and soak up the spring sunshine before
the trees above produce their own leaves
and cut out the light.
The bear's den is empty,
but the owners haven't gone far.
There's still not much to eat,
only a few leaves,
nor will there be until the first of
the berries come into fruit in summer,
but meanwhile at
least the sun is warm.
Another mother spends
the spring up in a tree:
A wood duck,
only she is about to leave.
The hole has provided a secure nest,
but all ducklings follow their
mothers as soon as they hatch.
And now new forms appear
from among the dead leaves.
The spring showers soak the woodlands
and create just the moist,
warm conditions needed by the fungi
to produce their fruiting bodies.
These must be mature and ready to
discharge their microscopic spores
by the time the dry winds
of summer begin to blow,
so that their spores, like dust, will
be carried all through the forest.
Once, the woods of North America stretched
over the eastern half of the continent
in an almost continuous
band hundreds of miles deep.
Today, the majority has been felled
to make space for farmland and cities,
but enough remains to make
plain their splendour.
And now we've come
farther south still.
I'm on the borders of Florida and
Georgia in the southern United States,
and here it's very hot in the summer
and the winters are very mild,
with only a few frosts,
and none of them severe.
So some of the broadleaved
trees here, like this oak,
don't shed all their
leaves in the autumn
but keep them throughout the
year and continue growing.
And these aren't the only evergreens
that are here, either. There are pines.
In some parts where the soil is very
rocky or sandy and poor in nutrients,
the pines will grow because
nothing else can survive there.
But this pine forest owes its
existence to another factor altogether.
Oak saplings are killed
within minutes by fire.
But the terminal buds of young pines
are surrounded by a shock of needles.
They burn at a relatively
low temperature,
and by the time the flames have consumed
them, the main fire has swept by
and the bud at the top of the stem,
from which new growth will come,
is still unharmed.
Fires like these are not just the work
of careless people, they occur naturally.
The spark that regularly sets fire
to these forests is lightning.
In this part of the southern States,
violent thunderstorms are common
and lightning often
strikes the taller trees,
scoring a deep groove down the length of
the trunk as it flashes down to earth.
And this at my feet is the
tinder which set it aflame.
These are pine needles, and they're
so full of resin and they're so dry
that they flame up very easily.
But the fire they produce is not very
hot, and it's also very short-lived,
so that if any creature can survive
fire for just one or two minutes,
then it can survive a fire like this.
The rattlesnake, like many
other ground-living animals,
regularly takes refuge from
the midday sun in holes,
so now it knows exactly where
to go to escape the fire.
But this hole is already
occupied by its digger and owner,
a gopher tortoise.
Rattlesnake and tortoise do not
normally interfere with one another...
and that seems to be the
way things are going to stay.
But in the back of the burrow lies
another refugee, an indigo snake,
and it, on occasion,
eats rattlesnakes.
But the fire is passing and the
rattlesnake can return to the forest.
Some insects don't avoid fire,
they actively seek it.
Beetles find it difficult to
lay their eggs in the pines
because the trees swamp them with resin.
But a tree killed by fire can't resist,
and these beetles take
advantage of the situation.
They have pits behind their legs
which are sensitive to infra-red rays,
and therefore they can detect the
slightest rise in temperature,
and with these to guide them, they
travel from all over the forest
to the wake of the fire
and arrive in hundreds.
Quickly they mate.
The females crawl all
over the scorched trunks,
seeking crevices in the bark into
which they can lay their eggs,
so ensuring that their grubs will have
some nice nutritious bark to chew.
As insects assemble in the burnt
forest, the insect-eaters follow.
The oak toad almost exactly matches
the colour of the charred forest floor.
Other more conspicuous hunters
wait on newly emerged shoots.
Within a couple of months of a summer
fire, the forest has more than recovered,
it is rejuvenated. The fire has cleared
away the old growth on the ground,
and by reducing the pine needles to ash
has released their nutrients into the soil,
and now the ground sprouts more
flowers than at any other time.
Because of regular fires, big bushes
can't establish themselves here,
so swampy areas are not colonised and
sucked dry by them as happens elsewhere,
and open marshes remain
where pitcher plants can grow
and where frogs can swim and breed.
Indeed, one species of
frog lives nowhere else
but in these pools in the
American pine barrens.
Woodpeckers here can't excavate their nest
in dead trees as do woodpeckers elsewhere,
for in this fire-ravaged forest
they would risk incineration,
so the red-cockaded woodpecker
drills its holes in living pines.
But the wood is so hard, it takes several
woodpeckers about two years to dig the hole.
Resinous sap seeps
out around the hole
where the outer layers of
the tree have been breached.
So the birds make their
hole low down on the trunk
where the inner sap-free heartwood is thick
enough to accommodate the entire nest.
The flow of resin is
diverted to the outside
by drilling pits like sap
wells above and below the hole.
It's in these laboriously
excavated holes
that the red-cockaded
woodpecker raises its young.
The holes are very conspicuous,
for each is surrounded
by a sheet of yellow congealed resin.
The rat snake is a great robber
of nests and stealer of chicks.
It's an extremely
skilful tree climber.
Since the woodpecker's hole in the living
tree has to be fairly low down on the trunk,
it is within easy reach of the snake
and therefore might seem to
be in considerable danger.
But now the other function
of all that resin,
deliberately produced around the nest by
the woodpecker, is about to become clear.
The chemicals in the resin seem to
irritate the snake beyond endurance,
and it arches its body away.
Eventually it's too much.
So fire, one way or another, influences
the whole community of animals and plants
in the pine forests of the south.
This injury was also caused by fire,
and this is also a coniferous tree,
but a very different one.
To start with, it's over 40
feet across along its base
and it's 267,5 feet high.
This is a giant sequoia.
It's thought to be
about 2,500 years old,
but the largest individual tree of all is
this one, known as the General Sherman.
It's just taller and it's
estimated to weigh 1,385 tons,
which makes it the most massive
living organism in the world.
Although these trees are growing almost
as far south as the southern pines,
the climate here, 2,000 metres up
in the Sierra Nevada mountains,
is much colder and snow lies on the
ground for almost half the year.
It's as though,
by climbing to this height,
we have returned climatically to
the great forests of the north.
During the Ice Age, these sequoias
grew over much of North America.
But when, some 8,000 years ago,
the earth began to warm,
they died out except for these isolated
groups high up in the mountains.
We've travelled some
2,000 miles southwards
since we started at the tree
line near the Arctic Circle,
and in all that vast territory the majority
of the forest trees have been conifers,
so it seems only right and proper
that we should end with these,
the noblest of them all.
As a group, the conifers
owe much of their success
to their ability to cope with
the changeable northern climate.
They can survive both the short, dark
days of winter with their bitter cold,
as well as the long sunny days of
summer with their raging fires.