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T. Sibona. F.A.O |
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The tropical rain
forest is a forest of tall trees in a region of year-round
warmth. An average of 50 to 260 inches (125 to 660 cm.) of
rain falls yearly. Rain forests belong
to the tropical wet climate group. The temperature in a rain
forest rarely gets higher than 93 °F (34 °C) or
drops below 68 °F (20 °C); average humidity is
between 77 and 88%; rainfall is often more than 100 inches a
year. There is usually a brief season of less rain. In
monsoonal areas, there is a real dry season. Almost all rain
forests lie near the equator. Rainforests now
cover less than 6% of Earth's land surface. Scientists
estimate that more than half of all the world's plant and
animal species live in tropical rain forests. Tropical
rainforests produce 40% of Earth's oxygen. A tropical rain
forest has more kinds of trees than any other area in the
world. Scientists have counted about 100 to 300 species in
one 2 1/2-acre (1-hectare) area in South America. Seventy
percent of the plants in the rainforest are
trees. About 1/4 of all the
medicines we use come from rainforest plants.
Curare
comes from a tropical vine, and is used as an anesthetic and
to relax muscles during surgery. Quinine, from the cinchona
tree, is used to treat malaria. A person with lymphocytic
leukemia has a 99% chance that the disease will go into
remission because of the rosy periwinkle. More than 1,400
varieties of tropical plants are thought to be potential
cures for cancer. All tropical rain
forests resemble one another in some ways. Many of the trees
have straight trunks that don't branch out for 100 feet or
more. There is no sense in growing branches below the canopy
where there is little light. The majority of the trees have
smooth, thin bark because there is no need to protect the
them from water loss and freezing temperatures. It also
makes it difficult for epiphytes
and plant parasites to get a hold on the trunks. The bark of
different species is so similar that it is difficult to
identify a tree by its bark. Many trees can only be
identified by their flowers. Despite these
differences, each of the three largest rainforests--the
American, the African, and the Asian--has a different group
of animal and plant species. Each rain forest has many
species of monkeys, all of which differ from the species of
the other two rain forests. In addition, different areas of
the same rain forest may have different species. Many kinds
of trees that grow in the mountains of the Amazon rain
forest do not grow in the lowlands of that same forest.
Layers of
the Rainforest There are four very
distinct layers of trees in a tropical rain forest. These
layers have been identified as the emergent,
upper canopy, understory, and forest floor.
Plant
Life Besides these four
layers, a shrub/sapling layer receives about 3 % of the
light that filters in through the canopies. These stunted
trees are capable of a sudden growth surge when a gap in the
canopy opens above them. The air beneath the
lower canopy is almost always humid. The trees themselves
give off water through the pores (stomata) of their leaves.
This process, called transpiration, can account for as much
as half of the precipitation in the rain forest. Rainforest plants
have made many adaptations to their environment. With over
80 inches of rain per year, plants have made adaptations
that helps them shed water off their leaves quickly so the
branches don't get weighed down and break. Many plants have
drip tips and grooved leaves, and some leaves have oily
coatings to shed water. To absorb as much sunlight as
possible on the dark understory, leaves are very large. Some
trees have leaf stalks that turn with the movement of the
sun so they always absorb the maximum amount of light.
Leaves in the upper canopy are dark green, small and
leathery to reduce water loss in the strong sunlight. Some
trees will grow large leaves at the lower canopy level and
small leaves in the upper canopy. Other plants grow in the
upper canopy on larger trees to get sunlight. These are the
epiphytes such as orchids and bromeliads. Many trees have
buttress and stilt roots for extra support in the shallow,
wet soil of the rainforests. Over 2,500 species
of vines grow in the rainforest. Lianas start off as small
shrubs that grow on the forest floor. To reach the sunlight
in the upper canopy it sends out tendrils to grab sapling
trees. The liana and the tree grow towards the canopy
together. The vines grow from one tree to another and make
up 40% of the canopy leaves. The rattan vine has spikes on
the underside of its leaves that point backwards to grab
onto sapling trees. Other "strangler" vines will use trees
as support and grow thicker and thicker as they reach the
canopy, strangling its host tree. They look like trees whose
centers have been hollowed out. Dominant species do
not exist in tropical rainforests. Lowland dipterocarp
forest can consist of many different species of
Dipterocarpaceae, but not all of the same species. Trees of
the same species are very seldom found growing close
together. This bio diversity and separation of the species
prevents mass contamination and die-off from disease or
insect infestation. Bio diversity also insures that there
will be enough pollinators to take care of each species'
needs. Animals depend on the staggered blooming and fruiting
of rainforest plants to supply them with a year-round source
of food.
Animal
Life Many species of
animal life can be found in the rain forest. Common
characteristics found among mammals and birds (and reptiles
and amphibians, too) include adaptations to a life in the
trees, such as the prehensile
tails of New World monkeys. Other characteristics are bright
colors and sharp patterns, loud vocalizations, and diets
heavy on fruits. Insects make up the
largest single group of animals that live in tropical
forests. They include brightly colored butterflies,
mosquitoes, camouflaged stick insects, and huge colonies of
ants. The Amazon river
basin rainforest contains a wider variety of plant and
animal life than any other biome in the world. The second
largest population of plant and animal life can be found in
scattered locations and islands of Southeast Asia. The
lowest variety can be found in Africa. There may be 40 to
100 different species in 2.5 acres ( 1 hectare) of a
tropical rain forest.
When early explorers
first discovered the rainforests of Africa, Southeast Asia
and South America, they They were amazed by the dense
growth, trees with giant buttresses, vines and epiphytes .
The tropical vegetation grew so dense that it was difficult
to cut one's way through it. It was thought at the time that
the soil of a rainforest must be very fertile, filled with
nutrients, enabling it to support the immense trees and
other vegetation they found. Today we know that
the soil of the tropical rainforests is shallow, very poor
in nutrients and almost without soluble minerals. Thousands
of years of heavy rains have washed away the nutrients in
the soil obtained from weathered rocks. The rainforest has a
very short nutrient
cycle.
Nutrients generally stay in an ecosystem by being recycled
and in a rainforest are mainly found in the living plants
and the layers of decomposing leaf litter. Various species
of decomposers like insects, bacteria, and fungi make quick
work of turning dead plant and animal matter into nutrients.
Plants take up these nutrients the moment they are released.
A study in the
Amazon rainforest found that 99% of nutrients are held in
root mats. When a rainforest is burned or cut down the
nutrients are removed from the ecosystem. The soil can only
be used for a very short time before it becomes completely
depleted of all nutrients.
Where the
Rainforests Are Found The tropical rain
forest can be found in three major geographical areas around
the world.
by Michael
G. 2001 In an average year
the climate in a tropical rain forest is very humid because
of all the rainfall. A tropical rainforest gets about 150 cm
of rain per year. It gets lots of rain because it is very
hot and wet in rain forests. The hotter the air, the more
water vapor it can hold. It rains usually about 1/8 of an
inch per day. This climate is
found near the equator. That means that there is more direct
sunlight hitting the land and sea there than anywhere else.
The sun warms the land and sea and the water evaporates into
the air. The warm air can hold a lot of water vapor. As the
air rises, it cools. That means it can hold less water
vapor. Then as warm meets cold, condensation takes place and
the vapor forms droplets and clouds form. The clouds then
produce rain. It rains more than ninety days a year and the
strong sun usually shines between the storms. The water
cycle repeats often along the equator. The main plants in
this biome are trees. This is important because in the rain
forest, some rain never gets past the trees and to the
smaller plants and ground below. Trees in this climate reach
a height of more than 164 feet. They form a canopy. The
forest floor is called understory. The canopy also keeps
sunlight from reaching the plants in the understory. Between
the canopy and understory is a lower canopy made up of
smaller trees. These plants do receive some filtered
sunlight. The tropical rain
forest is classified under the Köppen Classification
system as Af, meaning tropical forest. The A
is given to tropical climates that are moist for all months
and which have average temperatures above 18 degrees
Celsius. The f stands for sufficient precipitation
for all months. The latitude range for my climate is
15° to 25° North and South of the
equator. The annual
precipitation of a rain forest is greater than 150 cm. In a
rain forest there is a short dry season. In only a month the
rainforest receives 4 inches of rain. The rain forest
climate is different from a lot of other climates. In other
climates, the evaporation is carried away to fall as rain in
far off areas, but in the rain forests, 50 percent of the
precipitation comes from its own evaporation. A lot of the
rain that falls on the rain forest never reaches the ground,
instead it stays on the trees because the leaves act as a
shield. The average
temperature of a rain forest is about 77° Fahrenheit.
The rain forest is about the same temperature year round.
The temperature never drops below 64° Fahrenheit. Rain
forests are so hot because they are found near the equator.
The closer to the equator you are, the more solar radiation
there is. The more solar radiation there is, the hotter it
is. Rain forest are never found in climates which have
temperatures 32° Fahrenheit and below because the plant
life will not be able to live in the frost. All the plants
will die out if the rain forest is cooler. The plants that make
up the understory of a rain forest have adapted to the small
amount of sunlight that they receive. Ferns and mosses do
well, along with epiphytes. These are plants that grow on
other plants. They can be found growing on branches of tall
trees. There are many different plant species found in the
rain forest. by Michael G. 2001
bibliography: "Introduction",
http://www.hqlist.demon.nl/gvg/ctkoppen.htm
(Nov 2000) "Köppen
Biomes", http://www.tesarta.com/www/resources/library/biomes.html
(Dec 2000) "Rainfall",
http://encarta.msn.com/find/print.asp?&pg=8&ti=00531000&sc=29&pt=1
(Dec.2000) "Temperature",
http://encarta.msn.com/find/print.asp?&pg=8&ti=00531000&sc=29&pt=1
(Dec.2000) Allaby, Michael,
Biomes of the world volume 7 Oxford: Anndromedia Limited1999
Kellert, Stephen R.
Macmillion Encyclopedia of the Environment. Simon and
Schuster and Prentice Hall International. 1997 "Rainforest
Climate", http://passporttoknowledge.com/rainforest/GEOsystem/Rainforests/climate.html
(March 2001) Stralhler, Arthur N.
Strahler, Alan H. Elements of Physical Geography .
John Wiley & Sons. 1997.
Rainforests
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