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| Rainforest in the
Blue Mountains, Australia. |
Rainforests
A rainforest is a forest that receives heavy rainfall.
The most notable rainforests are in the tropics or
subtropics, mostly in the Intertropical Convergence
Zone. The biggest rainforest is the Amazon rainforest,
which is mostly in Brazil. Forests like this have
extraordinary biodiversity. Biologists say over half of
all plant and animal species live in the rainforest.
Also more than 1/4 of all medicines come from here. Even
though they only cover 6% of the Earth's land area they
are still an important source of oxygen.
The rainforest gets an average of 50 to 250 inches
(1.2-6.3m) of rain through the year. It is warm all year
round, rarely getting above 34°C (94 °F) or getting
below 20 °C (68 °F). It has an average humidity of 77 to
88%. Tropical rainforests occur in three major
geographical areas around the world. These areas are: |
- Parts of South and Central America –
the Amazon River basin, and Costa Rica.
- Africa – Congo River basin, with a
small area in West Africa; also eastern Madagascar.
- South Asia and Australasia – west
coast of India, Assam, Southeast Asia, New Guinea, and
Queensland, Australia.
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A less-used term is temperate rainforest. For temperate rain
forests of North America, annual precipitation is over 140
cm (55 in), and the mean annual temperature is between 4 and
12 °C (39 and 54 °F). However, definitions in other
countries differ considerably. For example, Australian
definitions are ecological-structural rather than climatic: |
- Closed canopy of trees which
excludes at least 70% of the sky.
- Forest is composed mainly of tree
species which do not require fire for regeneration, but
with seedlings able to regenerate under shade and in
natural openings.
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This definition would not suit the forests of western North
America, and so the term "temperate rainforest" is not so
widely agreed. The weather in a rainforest would be humid,
which is wet but warm like a greenhouse. The bottom most
layer receives 2% of the sunlight. Only plants adapted to
low light can grow in this region. The understory layer lies
between the canopy and forest floor. It is a home to a
number of birds, snakes and lizards as well as predators
such as jaguars and leopards. The leaves are much bigger at
this level and insect life is abundant. |
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Characteristics
The characteristics of the tropical rainforests are: |
- Land is mostly under 700 metres down
to below sea level.
- Climate:
- High rainfall.
- High temperature.
- Equable: not much variation.
- Vegetation: 90% or more Angiosperms.
- Tall canopy trees.
- Lianas (climbing plants).
- Epiphytes.
- Leaves large, complete margins, with
drip tips.
- Flowers and fruits large.
- Pollination mainly by insects.
- Leguminaceae are the most common
plant family.
- Evergreens: leaves may be shed, but
not seasonally.
- Animals:
- High diversity: many different
species
- Many insects which eat plants, and
many anti-insect defenses by plants
- Many arboreal (tree-living) mammals
|
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| Aerial view of the
Amazon rainforest, taken from a plane. |
The five layers
Tropical rainforests are typically dominated by different
plants and animals at different levels. The top layer is the
emergent layer. Then there is the canopy layer. Under the
tall canopy is the understory. The understory is made up of
smaller trees, vines and shrubs. The next layer is called
the shrub layer, and has mainly bushes. The bottom layer is
the forest floor. This is made up of the small plants on the
ground.
Emergent layer
The emergent layer is the farthest from the ground. High in
the trees eagles perch. Their keen eyes search constantly
for small monkeys and other prey. Butterflies, parrots,
toucans, and hundreds of other colourful birds constantly
fly through the tops of the trees.
Canopy layer
The canopy is like a huge green roof over the forest. The
trees grow up thin and straight, like pillars seeking the
sun. They do not put out branches until they are very tall.
Then, they spread out like an umbrella in the sunlight. The
trees are so close together that very little light
penetrates through to the lower layers. Many kinds of
monkeys, birds, and insects live in the layer. The animals
that call this layer home often never touch the ground
throughout their entire lives. They find everything they
need existing within the canopy. Water can be accessed from
the boles of trees, if not, the leaves and epiphytes that
grow in the canopy can supply that need. The animals eat the
leaves and fruit of the trees, insects, or other animals.
The tall canopy trees must be able to reach the sunlight
high in the air and still get nutrients from the thin soil
on the forest floor. Their roots do not go deep into the
soil because there is nothing there for the plants to reach.
Instead, the roots spread out in all directions along or
just under the ground. That way they can quickly make use of
the nutrients from the recycled plants and animals that have
fallen to the floor.
Understory layer
The understory is usually a dark, humid place, under the
canopy. There is very little light and no breeze because
they are blocked out by the canopy. The plants under the
canopy must be able to live with very little sunlight.
Bushes, large green plants, and small trees make up this
layer. Often they will only grow in open patches where a big
tree has fallen down. Other plants, like vines, grow on the
big trees.
Shrub Layer
The shrub layer is mainly made out of bushes. It contains
most of the rainforests orchids, because the orchids use
water from the forest floor, vegetation from the understory
and sunlight that is reflected from the canopy layer leaves.
It is the smallest layer of the rainforest, yet contains
over 84% of the rainforest's orchids. It is normally very
dark in the shrub layer, apart from little spots of sunlight
that comes through empty spaces of the emergent layer.
Despite not having very much sunlight, the shrub layer is
very humid [wet and warm]. Many insects live in the shrub
layer such as scorpions, beetles and tarantulas. Many people
categorize the rainforest into 4 layers not 5. They consider
the shrub layer to be part of the understory.
Forest floor
The ground level is called the forest floor. Snakes, Tapirs,
Jaguars, Tamanduas, and Gorillas are just a few of the
species that live here. It is dark on the rainforest floor.
Insects, giant centipedes, spiders, ants, and beetles are
also very abundant here. The floor of the rainforest is
often very open and easy to walk across. That is because so
little light reaches the floor that very few plants can grow
there. |
|
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| A Kermode bear from
the Great Bear Rainforest. |
Plants and animals
One type of plant in the rainforest does not need soil.
These plants are called epiphytes, or air plants. Air
plants live on the branches of trees in the canopy or
understory, with their roots out in the air. In the
humid rainforest, they collect water from the rain that
falls on them.
One kind of air plant is a flower called an orchid.
There are thousands of different kinds of orchids in the
rainforest. Some air plants store water in pools in and
around their roots. These pools can become homes for
frogs and salamanders. Frogs usually need to lay their
eggs in ponds, but some rainforest tree frogs lay their
eggs in the pools in air plants. That way, the frogs
never have to go down to the ground. Some plants are
made for medicine for humans.
Millions of kinds of insects live in the rainforest. It
never gets cold enough to kill them. There are bees,
butterflies, termites, beetles, and many kinds of flies.
There are ants everywhere. One kind of ant is the army
ant. Army ants do not have nests. They march out in a
line every day to hunt for other insects, which they
eat. At night they hook themselves together to form a
living nest around their queen and larvae, or baby ants.
Snakes live in the trees and on the forest floor. They
eat frogs, eggs, birds, insects, and small animals. Some
of the snakes, like the fer-de-lance of Latin America,
are poisonous, but others are not. One large
non-poisonous snake is the anaconda of South America. It
is one of the largest snakes in the world. It kills its
prey by wrapping itself around the animal and squeezing
it until it cannot breathe.
Monkeys are a very common animal in the rainforest. Most
live their lives up in the canopy and the understory.
They have long arms to swing from branch to branch, and
some use their tails to hold onto the trees while they
eat. They are fast and agile, jumping easily from tree
to tree for food. Different monkeys eat different
things. They can eat nuts, flowers, roots, and frogs.
Their hoots and howls are heard throughout the
rainforest, even when they cannot be seen among the
trees.
Many colorful birds also live among the canopy of the
rain forest, and there are also animals that live on the
forest floor. The tapir is a forest animal that looks
like a large pig. It is actually related to the horse
and the rhinoceros. They live in South American and
Asian rain forests, eating leaves, twigs, and fruit.
Tapirs are among the animals hunted by the big cats of
the rain forest. Jaguars, leopards, and tigers are the
largest predators of rain forests. These cats have
beautiful fur coats that have been hunted for the fur
trade for years. The spotted coats of the jaguar and
leopards were especially popular for fur coats. Today
most countries are trying to protect their big cats, but
many are still hunted illegally.
These are only a few of the animals and plants in the
rainforest. About half of all of the different kinds, or
species, of plants and animals in the entire world live
in rain forests. Many of the plants and animals,
especially insects, do not even have scientific names,
because they have never been classified by a biologist. |
 |
| General distribution
of temperate rainforests. |
People of the rainforest
There are many tribes of people who have lived in the
rainforests for thousands of years. These forest
dwellers usually belong to one of two groups. They are
usually hunter/gatherers or slash-and-burn farmers.
Hunter/gatherers
Hunter/gatherers live as they do in every other region
of the world. They kill animals and gather what the
forest provides for part of their food. Unlike in the
Arctic, tools are always available. Unlike in the
desert, water is always available. The people do not
need clothes to protect them from the weather. The
forest even provides a way to make hunting easier. Many
of the people hunt with poisoned arrows. The poisons
come from the plants of the forest. That makes the
animals easier to kill.
Slash-and-burn farmers
Most of the forest people are slash-and-burn farmers.
They raise crops in small clearings as well as hunting
and gathering in the forest. This provides them with
food year-round. They start by cutting (slashing) down
the trees and the other plants in an area. They let the
dead plants dry out, then they burn them. The ash from
the burned plants goes into the soil and makes it
fertile for a little while. This is called
slash-and-burn farming.
The small clearings grow food crops for a few years,
then the family or group moves on and clears a new
field. The old field is left to be overgrown by the
forest. In a few years, it once again looks like the
rain forest that surrounds it.
This type of farming does not harm the rain forest when
only a few people are doing it. The small clearings
become rain forest again without any damage. The land is
used and recycled for use again some other time. The
rain forest easily regrows to fill in the clearings
after the people leave. That is changing today. Today,
the rain forests are getting smaller because too many
people are burning them. |
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| Worldwide tropical
rainforest climate zones. |
Rainforests in danger
There are some serious problems concerning the
rainforests that need to be fixed. Rainforests are being
cut down too quickly. Every year an area about the size
of West Virginia is being destroyed. This is a problem
for everyone.
Rainforests are so large and thick that for many years
very few people lived or went there. Today, however,
that is changing. Millions of poor, often hungry, people
live near the rainforests of the world. These people are
desperate for a better life, and they think they can
find it in the forests.
Settlers can get into the rainforests because modern
machines have opened roads deep into the jungle. The
roads are usually built by businesses who want to cut
down trees or dig up minerals in the forest. Governments
build other roads for trade and to allow settlers into
the forest. Poor people come into the forest by the
thousands on the roads and take land to raise food. They
burn off the trees and plants to make a field. Then they
plant crops for food and to sell. All around them other
farmers do the same, so there is no forest left to grow
back.
The new farms can only grow crops for a few years in the
poor soil. The farmers then sell the land to a cattle
rancher or just leave and clear a new piece of land. The
soil is so poor that it will not even grow grass to feed
cattle for more than a few more years. By then, the
ground is hard packed and grows only a few weeds. The
rainforest is destroyed and nothing can be done with the
land.
If this continues long enough, the forests will be
destroyed and the farmers will have no place to move.
Then those people will starve , because there will be no
land left where they can grow food. Forcing them to stop
cutting down the forest will not help, because they
would just starve now instead of later. New ways need to
be found for these people to live on the rainforest land
without destroying it.
Also, no one knows how destroying the rainforests will
change the earth. We know that less rain will fall once
the trees are gone. That may cause some rivers, which
supply water to cities around the rainforest, to dry up
during part of the year. Also, burning trees puts carbon
into the air. Carbon absorbs heat from the sun. Will the
burning of so many trees change the air and make the
climate on the earth warmer? Experts are arguing about
it, but it might be happening.
The rainforests are also the source of many things that
are useful to human beings. As many as one out of every
four drugs bought at the store were discovered in
rainforest. Coffee, chocolate, bananas, corn, tea, sweet
potatoes, Brazil nuts, rubber, and tapioca all came from
the rainforest. Very valuable wood is taken from the
trees of the rainforest. Mahogany, teak, and balsa wood
come from there. Those trees can not be grown without
the thick, wet, warm rainforests. Thus, the loss of the
rainforests would hurt other people besides those that
must live there.
Tropical rainforests are located in a band around the
equator (Zero degrees latitude), mostly in the area
between the Tropic of Cancer (23.5° N latitude) and the
Tropic of Capricorn (23.5° S latitude). This 3,000 mile
(4800 km) wide band is called the "tropics." |
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 Kiddle: Rainforests
Wikipedia: Rainforests |
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