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GENERAL
CHARACTERISTICS:
Rainforests are one of the most important ecosystems in the world,
and their importance to the well being of our planet is an established
scientific fact. Extraordinary in terms of their biological diversity,
tropical rainforests are a major resource for medicinal plants and
thousands of forest products. They are home to countless species and
many unique indigenous cultures, and play a key role in the global
ecosystem in regulating weather and producing significant amounts of the
world's oxygen.
 Tropical
rain forests are found only in a relatively small area on earth, between
the latitudes 22.5 degrees North (Tropic of Capricorn) and 22.5 degrees
South of the equator (Tropic of Cancer). Originally covering much vaster
areas, rain forests in the world, though man's activities, have been
reduced only about 2% of the earth's surface, (about 2.41 millions
square miles or 625 million hectares). The largest continuous rain
forest is found in the Amazon river basin in South America, much of
which lies in Brazil. Indonesia and the Congo Basin in Africa are also
home to extensive rain forests as well.
Geographically, the distribution of rain forests is seen in four areas
based on four forested continental regions: 1) The Ethiopian/Afrotropical
(30%)
2) Australasian (9%)
3) Oriental or Indomalayan/Asian (16%)
4) Neotropical (45%)
Biological diversity is the hallmark of tropical rain forests worldwide
but they also share other defining characteristics as well, including
a warm, year-round climate with temperatures ranging from 72-93F
(22-34C) and high precipitation levels between 80 and 430 inches of rain
each year).
BIODIVERSITY:
It
is estimated that over 50 % of all life on earth is found in the
rainforests. The number of species is staggering and may go as high as
50 million. This great biodiversity is a direct function of the
favorable year round climate and high precipitation. Other ecosystems in
the world, temperate forests and woodlands, pale in comparison to
rainforests where biodiversity is concerned.
RAIN FOREST STRUCTURE:
Tropical rain forests have a characteristic
structure that is made up of a number of vertical layers that reach up
from the forest floor to the very tops of the tallest trees. The primary
layers are: 1) Ground Level, 2) Understory, 3) Canopy and 4) Overstory.
An estimated 70-90 percent of life in rain forests exist in the trees,
high above the shaded forest floor. Each layer has its own
characteristic and unique plant and animal species
The
Ground Level
is the forest floor, and in most true rain forests, the overhead
vegetation of the layers above prevent very little light from reaching
it. Growth on the ground floor is typically sparse, and there is little
jungle like vegetation to impede movement. Typically as little as 5
percent or less of the light falling on the rain forests in the world
make it to the ground level. The dominant features are decaying tree
trunks, seedlings, saplings, fungus and low-growing sparse vegetation.
It is the site of much decomposition, an important process for the
health of the rain forest ecosystem.
The
Canopy
refers to the dense ceiling of tree branches with
leaves that is formed by the closely spaced trees and can reach to 130
feet above the forest floor. An interesting feature of the canopy trees,
which make up the largest proportion of vegetation in the rainforest, is
the fact that despite overlapping tree branches, trees of the canopy
rarely interlock or even touch. Instead they are usually separated by
very small distances, sometimes only a few feet. Because of this animals
that dwell in the rain forest canopies survive by having the abilities
to climb, leaf, glide or fly.The
dominant function of this level of the rain forest, as well as the
Overstory, is the conversion of sunlight to energy through the process
known as photosynthesis. This is the process whereby plants convert
atmospheric carbon dioxide and water into oxygen and simple sugars. The
canopy of rain forests is a true high energy production system and is
one of the most important biological engines on Earth for the production
of oxygen and absorption of carbon dioxide, a greenhouse gas. Without
rain forests and their buffering effects, the global warming now
being experienced would accelerate greatly.
The
Understory is the layer of the canopy characterized by multiple leaf
and branches and is the lower part of the canopy. The lowest part of the
understory has a shrub layer that extends no higher than 20 feet or so
above the ground and is usually made up of tree saplings and shrubs and
smaller plants.
The Overstory
is that part of the canopy that consists of the
crowns of the most emergent trees. These can soar 20 to 100 feet above
the rest of the canopy and some of the highest trees can reach to over
200 feet.
RIVER
SYSTEMS IN RAIN FORESTS:
Some of
the largest rivers in the world are found in tropical rainforests. These
include the Amazon, Orinoco, Negro, Zaire, Madeira and Mekong rivers.
These giant rivers are truly immense, and some have thousands of
tributaries extending for thousands of miles.
Amazing also in their biodiversity, the rivers of the rain forests
are increasingly under threat from man and his activities, including
pollution, hydroelectric projects, siltation from deforestation and
overfishing and commercial exploitation.
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