Tropical Rain Forests
The tropical rain forest biome is
one of the most productive areas on earth. More than half of
the different kinds animals and plants in the world live in the
tropical rain forests. The abundant sunlight, warm temperatures,
and daily rain lead to a fast turnover of nutrients, and plant
growth is rapid. This is a land without winter, so the
growing season lasts all year. There are flowers and fruit all
These forests have been in existence
for between 70 million and 100 million years, so this biome is
very old. During this time the animals and plants have had the
opportunity to adapt to each other very closely, and so there
are many niches (roles in using a special part of the available
resources) that unique organisms fill. Special insects pollinate
special kinds of orchids, for instance.
A hundred million years of rain
also affects the soil. Looking at the plant life, it is easy
to think that the soil is rich, but it is actually nutrient poor.
Plants cannot grow on sunlight and rain alone: they need small
quantities of minerals as well. These minerals include calcium,
magnesium, and phosphorus. Over the years the rain has washed
these out of the soil, so all the nutrients are actually in the
living plants and animals.
Competition for the minerals is fierce.
If a leaf falls from a tall tree, or a piece of fruit is knocked
off a branch, it may fall to the forest floor. Immediately the
detritivores (bacteria and fungi that eat (break down) dead material)
get to work and start digesting the fallen piece of organic matter.
Their digestive processes make the minerals available again,
and the net of shallow plant roots lies ready to soak them up
and send them up into the trees and vines. This means that the
nutrient "wealth" of the forest is all being used by
the life forms living there. If the rain forest is cut down,
nothing remains but a thin layer of low fertility soil.
Rain forests consist of a number
of layers. Seen from above, the rain forest looks like
a bumpy green carpet, but it actually has a number of levels.
The emergent layer has the tallest trees, which stand
up individually above the trees crowded together below them.
These trees get a lot of light, but they also have to deal with
the wind. They make good perches for eagles and other predatory
canopy consists of a thick growth of tall trees which
capture much of the sunlight. Their branches touch, their leaves
seem to fill every space where light may fall. Their branches
bear colorful fruits. Epiphytes (plants that "grow in air")
perch on the branches as well, and vines climb up from the forest
floor to claim a share of the sun. Many of the animals live in
the canopy, eating fruit, flowers, and leaves. Meat eaters go
where the plant eaters are, and prey on the monkeys and colorful
birds. Insects are everywhere. This part of the rain forest is
filled with life. It supports life forms and communities
as the surface of the earth usually does.
The understory consists of small trees, shrubs, and
bushes. These plants are adapted to low light levels, and their
large, tender leaves capture as much light energy as they can.
The shrubs support vines, mosses, and fragile amphibians, such
a frogs, which enjoy the humid atmosphere.
The forest floor receives only about 2% of the light
that falls onto the trees of the canopy. There are few plants
down here in the twilight. The floor is littered with dead leaves,
twigs, animals and fallen fruit, all of which are being digested
by diligent insects and other detritivores. A few animals also
live here, including wild pigs. They eat whatever has fallen
from the rich communities above them. There is no underbrush
for them to deal with, so travel in this dim world is easy.
from a Corel CD-ROM : for viewing only, not for downloading. More
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