Throughout the world coniferous forests are found in areas having the lowest temperatures permissible for the growth of trees. The largest expanses are found at the far north of the Northern Continent, bordering the tundra.
Throughout the world coniferous forests are found in areas having the lowest temperatures permissible for the growth of trees. The largest expanses are found at the far north of the Northern Continent, bordering the tundra.
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The coniferous forests of the Northern Continent represent the greatest
expanse of uninterrupted forest in the world. Coniferous trees do well
at high latitudes
because they are evergreen, and photosynthesis can take place immediately
conditions are right for growth without having first to produce leaves,
as is the case
with deciduous trees. In this way the conifers compensate for the short
growing season, which is about 50 to 80 days depending on the latitude.
Fruiting and
reproduction are also in tune with the climate. Conifers, unlike deciduous
trees, do not produce fruiting bodies that are pollinated and ripen within
a single year. The fertilization of a female cone may take more than a
year to complete, and as many as three more years may elapse before the
cone matures
and the seeds are ripe for dispersal.
The lack of leaf litter and the prevailing cold conditions which inhibit
the natural decay of the forest's pine needle carpet - material that is
slow to
decompose in any case - results in only a thin underlying layer of topsoil
and little or no undergrowth. The indigenous mammals are largely herbivorous
and exist mainly on diets comprising mosses, pine needles, bark and seed
cones. Insectivorous birds are rare compared with those that feed on cone-seeds
and
buds.
Throughout the region forest fires are not uncommon, usually occurring
in spring, when the trees are low in sap. Large areas can be devastated
at a time. Recolonization
is firstly by deciduous trees such as birches, alders and rowans that are
only later replaced by the climatic vegetation of spruce, larch, cedar
or pine.
The coniferous tree's typical tall, pointed shape is ideal for bearing
the weight of the winter snowfall and allows the snow to be shed cjuickly
when
it melts in spring. Their surface-spreading root systems are perfectly
adapted to the shallow soils that are characteristic of the habitat.
In the north of the region, where the underlying soil is frozen all year
and is therefore impervious to water, there are many lakes, streams and
bogs with
their own localized flora of mosses and sedges. The forest is more open
and blends into the neighbourine tundra. Larger patches of tundra mosses
and lichens
appear on high ground. Near rivers in this transitional area the forest
remains thick and extends far northwards along sheltered valleys into the
tundra. At
the southern edge of the coniferous belt, the conifers grade imperceptibly
into deciduous woodland.
Throughout the world, smaller areas of coniferous forest are found outside
their normal latitudinal extent, particularly on the slopes of mountains,
where the altitude produces climatic con¬ditions similar to those experienced
near
the poles.
During the Age of Man the coniferous forests experienced considerable environmental
damage, due mainly to clearance for agriculture and also in the course
of commercial forestry. This effectively exposed large areas of land to
the erosional effects
of wind and rain, destroying the soil structure and consequently reducing
its water-retention capacity. The coniferous forests took some time to
recover
from this damage, for the normal successive recolonization could not take
place immediately.
The evolution of the hornheads
The ancestral hornhead, Protocornudens, which existed between 35 and 40 million years ago was smaller and more antelope-like in appearance. The horny head plate did not appear until some time later.
The ornate horn structure plays an important part both in courtship and in male's dominance struggles. |
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The hornhead's horn formation grows gradually
throughout adolescence and early adulthood and in the case of helmeted
hornhead takes its final form around three years of age. |
The browsers are the largest animals living in the coniferous forest regions.
They feed mainly on young twigs and needles in the summer and subsist
on bark, mosses and lichens during the rest of the year.
Across the northern continent the most prolific species are those that
are derived from the gigantelopes of the African sub-continent.
These northern animals, although much heavier than their distant antelope
ancestors, are
still
not nearly as huge as the African gigantelopes. Only the shaggy
tundra-dwelling
forms of the far north can compare in size with these.
This difference in size between the two different northern forms
is due to two separate periods of migration. The first took place
about
forty
million
years ago, before the great mountain barriers between Africa and
Europe were thrown up and at about the time that the rabbuck was
ousting the
antelope from
its traditional home on the African plains. The gigantelopes, then
at an early stage of evolution, were forced to spread northwards
into the coniferous
forest,
where they later flourished and developed into the hornheads, Cornudens spp.
The second migration took place more recently, about ten million
years ago, when the African gigantelopes had reached their present
elephantine
proportions.
The erosion of the mountain chain that once separated the Indian
sub-continent from the rest of Asia opened up new paths to the
north and led to their
gradual colonization of the Tundra and the evolution of the woolly
gigantelopes, Megalodorcas sp.
Soon after their arrival in the coniferous forest the ancestral
hornheads' jaws and horns began to evolve in response to their
new environment.
In common with all the now almost extinct ruminants, most of these
creatures
possessed
no upper incisor teeth. They cropped grass by working their lower
incisors against a bony pad on the roof of the mouth. However,
this system is
not particularly effective for browsing from forest trees. The
first change
that took place
was that the horny head plate became extended forward to form a
sort of beak. The lower lip became muscular and grew forward to
meet it,
thus extending
the
mouth some distance beyond the front teeth. This fairly primitive
arrangement is still found in several species, for example the
helmeted hornhead,
Cornudens horridus. In more advanced forms, however, the lower
jaw is also extended
so that the lower front teeth meet the horny beak instead. These
adaptations are
the result of evolutionary pressure that enabled only those forms
that could feed successfully on the twigs, bark and lichens of
the coniferous
trees to
survive. The elaborate horn formation above the eyes is also used
for defence.
The horn structure has been carried one stage further in the water
hornhead, Cornudens rastrostrius, that inhabits lakesides and the
banks of rivers.
In this creature the horny plate extends forward into a broad rake-like
structure,
with which the animal grazes on soft water weeds that it finds
on the beds of ponds and streams. It has two broad hooves on each
foot,
set
widely
apart and connected by a web of skin, which prevents the animal
from sinking into
soft mud and sand. The water homhead, in its way of life, must
surely resemble the hadrosaurs - the duckbilled dinosaurs of the
latter
part of the Age
of Reptiles.
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The relationship between predator and prey
The broadbeak is the most massive predatory bird found in the coniferous forests.
The combined rear limbs and tail of modern beaver form an ideal structure for gripping a pine tree's rough bark.
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Parops lepidorostrus
Although closely related to the broadbeak it more nearly resembles their common ancestor, the starling.
The modern beaver's swimming stroke involves the whole body.
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As in all other habitats the animals of the coniferous forest fall
into the familiar food-chain pattern of predator and prey
with the carnivorous
animals
forming the final link. Here, as in the temperate woodlands,
the fiercest and commonest hunters are the predator rats. They hunt
beneath the
trees in small
packs, tracking down the rabbuck and the hornhead, singling
out the weak and elderly individuals and running them to exhaustion.
The
predator rats
take
it in turn to attack, savaging their prey with powerful front
teeth. Homheads have such powerful horns that, when they are the quarry,
it is almost as
dangerous for the hunter as it is for the hunted.
A predator unique to the coniferous forest is the pamthret,
Vulpemustela acer, a large weasel-like creature and one of
the few true carnivores
still in existence.
Its size - up to two metres in length - makes it by far the
largest predatory animal found in the region and it probably
owes its
survival to its low,
powerful build and its ability to run through the sparse
undergrowth easily, bursting
out suddenly upon its prey. Pamthrets live in small family
groups and normally hunt in pairs.
Not all the predators are mammals; birds also kill their
share of the small animal population. The broadbeak, Pseudofraga sp., one
of the
larger birds
of prey, has a wing span of over a metre and lives in the
western
forests of the Northern Continent. It is descended from the
starlings, which
expanded to fill the gap left when many of the ancient predatory
birds became extinct
during the Age of Man. It has a rounded tail and broad, blunt
wings, which enable it to fly swiftly and manoeuvre in the
tight spaces
between the
trees.
It has a straight, powerful bill and strong talons, which
it uses to grip its prey. The broadbeak's closest living
relative,
Parops
lepidorostrus,
is a totally
different creature. It is only ten centimetres long and lives
mainly on
insects that it extracts from the bark of trees with its
thin beak.
With so many predators in the coniferous forest it is not
surprising that the smaller mammals should have evolved such
a variety
of defensive ploys
to ensure
their survival. The spine-tailed squirrel, Humisciurus
spinacaudatus,
is an excellent example of their ingenuity. It has a long,
broad, flat tail
with
quills developed on its underside, which when at rest lie
flat over the ground. However, when the animal is alarmed
it throws
its tail
over its
back and the
sudden increase in skin tension erects the quills. This presents
an almost impenetrable barrier and can be turned to deflect
an attack from either
side.
One large rodent that became adapted to a semi-aquatic way
of life during the Age of Mammals, partly as a defence against
predators,
was the beaver.
After
man the beaver, Castor spp., became even better adapted to
life in water. Its tail and hind feet have become fused together
into
one
large paddle,
which,
when powered by its backbone, produces a powerful up-and-down
swimming
stroke. Its ears, eyes and nose are placed high up on its
head and remain above water
when the rest of the animal is submerged. Surprisingly the
paddle does not impair the creature's movement on land and
is used as
a grasping
limb, enabling
it to climb partway up trees, increasing its potential supply
of food and building materials.
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Birds and mammals that feed on and in the trees of the coniferous forests
Each spring the chiselheads select a new tree and construct a labyrinth of tunnels and nesting chambers in preparation for winter.
The chiselhead's deeply-rooted incisor teeth form effective burrowing tools. |
The trevel's long-claved fingers and toes enable it to cling firmly to the bark of trees. Hanging by its tail, the trevel can feed from cones growing in places that cannot be reached by animals of similar size and weight.
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Throughout the Age of Mammals the rodents were one of
the most successful animal groups in the coniferous
forests. Their powerful
teeth enabled
them to cope
with the tough vegetable matter found there and their
warm,
furry coats helped them to retain body heat during
hibernation,
The chiselhead, Tenebra vermiforme, a rodent and a
relation of the temperate woodland chirits, is highly
adapted
to life in
the coniferous
forest. Its
huge incisor teeth and wormlike body enable it to burrow
deep into the living wood,
where it can remain protected from the cold in winter.
Although in some ways the animal is at an advanced
stage of development,
its
parasitic way
of life
is really quite primitive. Its staple diet is the bark
of trees, which it strips off completely, leaving the
tree totally
denuded.
This, combined
with the massive
damage it does by burrowing, kills the tree within
a few years.
As the chiselheads only colonize live trees they must
be continually on the move and every spring, after
hibernation, the young
of the new generation
migrate
to find new territories. During migration they are
very vulnerable and many are taken by predators before
they
can complete
the journey. The balance
between
burrower and predator is highly critical and it needs
only
a slight reduction in the number of predators to produce
an increase
in
the population of
burrowers that would lead to the total destruction
of vast areas of coniferous forest.
No other small rodent found in the coniferous forest
is quite so destructive. Most live on shoots, bark
and the
seeds found
in cones.
Many are ground
dwellers and feed from the cones where they fall. Others
are lightly built and agile
enough to scramble along the branches to where the
cones are actually growing.
One large vole-like rodent, the trevel, Scandemys longicaudata,
is unusual in having a prehensile tail. Too heavy to
reach the cones
growing on the
slenderest branches, it feeds on them instead by hanging
by its tail from a sturdy neighbouring
branch and reaching out with its front paws. Like other
rodents of this general size it gathers more than is
necessary for
its immediate
needs
and stores the
rest for the lean winter months. Its hibernation nest
is a long, drooping structure woven together from grass,
strips
of bark
and pine needles.
Built hanging from
the end of a branch it is large enough to accommodate
the animal
together with sufficient food to see it through the
winter.
Of the many seed-eating birds found in the coniferous
forest, the largest by far is the common pine chuck,
Paraloxus
targa. The two
sexes of
this species
are quite different, both in appearance and in their
mode of life. The male is much more powerfully built
and is
equipped with a massive
beak,
which it
uses for breaking open pine cones to feed on the seeds.
The female, much smaller and drabber, totally lacks
the male's
heavy beak
and is really
a scavenger
supplementing her diet with carrion, insects, grubs
and birds' eggs. Most probably the common pine chuck's
ancestor
was
a
bird similar
in appearance
to the present-day
female and the male has evolved its own distinctive
features primarily for display and its eating habits
are a secondary
development.
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INTRODUCTION BY DESMOND MORRIS 9
Cell Genetics : Natural Selection : Animal Behaviour
: Form and Development :
Food Chains
The Origins of Life : Early Living Forms : The Age of
Reptiles :
The Age of Mammals : The Age of Man
The World after Man
TEMPERATE WOODLANDS AND GRASSLANDS 36
The Rabbucks : The Predators : Creatures of the Undergrowth
:
The Tree Dwellers : Nocturnal Animals : The Wetlands
CONIFEROUS FORESTS 50
The Browsing Mammals : The Hunters and the Hunted : Tree Life
TUNDRA AND THE POLAR REGIONS 58
The Migrants : The Meaching and its Enemies : The Polar
Ocean :
The Southern Ocean : The Mountains
The Sand Dwellers : Large Desert Animals : The North American Deserts
The Grass-eaters : Giants of the Plains : The Meat-eaters
The Tree-top Canopy ; Living in the Trees : The Forest
Floor :
Living with Water : Australian Forests : The Australian Forest Undergrowth
ISLANDS AND ISLAND CONTINENTS 100
South American Forests : South American Grasslands :
The Island of Lemuria :
The Islands of Batavia : The Islands of Pacaus
The Destiny of Life
Glossary : The Tree of Life : Index : Acknowledgements
