Zoo Guides: The Rainforest/ZOO Guides - The Rainforest.iso/pc/raintext/intro.txt

Text File | 1994-06-16 | 8KB | 146 lines

The Rainforest cREMedia 1994 All Rights Reserved.

What are rainforests?

Rainforests occur in both temperate and tropical regions. Tropical rainforests
occur in three major regions: Asia, Africa and in Central and South America.
The name 'tropische Regenwald' meaning 'tropical rainforest' was first defined
in 1898 by A Schimper, a German botanist. Most of the world's rainforests fall
either side of the Equator between the Tropic of Capricorn and the Tropic of
Cancer. Forests close to the Equator which receive year round drenchings are
known as evergreen equatorial rainforests.

Rain in these areas falls at a rate of between 160 and 400 inches a year; there
is no winter, days and nights are equal in length and a consistently high
temperature of around 80 degrees is maintained.

The further a rainforest is from the equator the greater are the changes in
temperature and rainfall. Seasonal changes give rise to semi-deciduous
rainforests in which most, and sometimes all, the trees lose their leaves during
the dry season.

Tropical 'moist' forests are called monsoon forests in South East Asia. Although
extremely rich in wildlife and vegetation they do, however, contain fewer animal
and plant species than the evergreen equatorial rainforests. There is no clear
demarcation line between equatorial evergreen forests and the tropical moist
forests as they blend one into the other without noticeable change although
trees tend to be smaller in stature in moist tropical forests.

Rainforest layers

Rainforests are usefully divided into four layers; the emergent layer, the canopy,
the understory and the forest floor. Each level is home to a unique variety of
animals many of whom rarely cross between the different layers.

The emergent layer gets its name because trees emerge randomly from the
main forest roof. Most of the trees at this level reach 160 feet but some attain
heights of 200 feet or more. Pavilion trees are able to withstand burning sun,
strong winds and torrential rainshowers.

The crowns of trees in the canopy form an almost closed roof on the forest
below. It is often further divided into upper and lower canopy. Because the top
of the canopy basks in almost constant sunlight and can absorb light more
easily trees tend to have smaller leaves than those at a lower level. Usually
trees are very straight and reach heights of between 100 and 150 feet.

The lower canopy is the richest layer in terms of animal and plant life. Most of
the mammals that live in the canopy are nocturnal.

The understory extends from the forest floor up to about 80 feet and contains a
mix of saplings, tall shrubs, vines and palms. Leaves are often long and
pointed, the ends of which form 'drip tips' allowing excess water to run off
quickly. Little sunlight filters into the understory which makes it dark and humid.

Plant growth on the forest floor is very limited because only between 1-2% of
sunlight filters down to this level. The floor of the rainforest teems with life.
Millions of termites, beetles, centipedes and ants can be found in one acre of
rainforest.

Lowland rainforest

Scientists have identified more than 40 types of lowland rainforest. They cover a
greater land area than other types of rainforest, the two largest regions being in
Africa and South America. These forests are found at altitudes of under 1,000 ft,
although in Amazonia some forests below 6,000 ft are also called 'lowland
rainforests'. Some lowland rainforests contain swamp forests. Life is so
abundant in lowland rainforests that a single acre may hold as many as 15,000
separate plant and animal species. Trees in lowland rainforests can grow to
heights of 150 ft or more which are often supported by enormous buttress roots.

Montane rainforest

Montane rainforests are divided into two types; lower montane growing at
elevations above sea level of between 1,000 and 3,000 ft, and upper montane
rainforests growing at an altitude of between 3,000 and 10,000 ft. Montane
forests are given the name 'cloud' forest because they are constantly shrouded
in mist. Rainfall increases and temperature decreases at these higher
elevations. Trees become shorter and grow crooked rather than upright, and
their leaves are smaller. Tropical species give way to those found more
commonly in temperature forests such as oak, beech and conifer trees.

Mangrove rainforest

Mangrove forests are found at the edge of the sea where regular flooding
occurs. Mangrove trees live in a silt-rich soil and use pitchfork-like roots which
grow out from the lower part of their trunks for additional support. These roots,
known as stilt or prop roots, trap debris which provide the trees with nutrients
but are also important for stabilizing the shoreline. Mangrove forests range in
stature from shrubs a few few high to trees which can reach heights of 80 ft.
Mangroves are home to many bird species and molluscs.





Custodians of the forests

Indigenous people are the true custodians of the forest. They know which forest
plant and animal species are safe to use as food and medicines, knowledge
which may help us in our search for cures for disease and illness and food for
our growing world population. Every single year a tribe in Brazil alone has
become extinct this century. According to a report by the World Bank, Brazil's
Indian population was five million in 1500. Today it is under 200,000. Attempted
'pacification' of tribespeople has proved fatal to many.

The introduction of diseases, sometimes deliberately, such as influenza and
smallpox to which they have no immunity, has wiped out hundreds. In 1977, a
measles epidemic wiped out half of the Yanomami tribe of the Amazon region.

In the 1980s the government of Brazil had been promised an enormous grant
by the World Bank to build five hydroelectric dams on the Xingu river.
The natives of South America affected by this began actively protesting  to
protect their homelands.

In 1988 one of the Kayapo Indian leaders, Paulinho Paiakan, travelled to
Washington DC to discuss the plans with leaders of the World Bank. This
meeting received worldwide attention and preceded a major protest gathering
the following year at Altimira on the Xingu river. Meeting together were various
Indian tribe leaders, including Paiakan, ecologists, environmentalists and
government officicials. The Indians successfully highlighted their plight and the
World Bank agreed to postpone their funding of the proposed dams.

What do the rainforests give us?

Many of the foods found in our kitchen at home were first discovered in the
rainforest. Although most are now cultivated outside of the rainforests, some
even in our back gardens, wild populations still grow in the forest. When crops
are struck by disease scientists sometimes need to go back to plants grown in
the wild to procure disease resistant strains which when bred with cultivated
varieties may transfer resistance to disease.

There are still hundreds of fruits and crops eaten only by native people but that
we may one day find on our supermarket shelves.

One quarter of the medicines used by doctors today originate from rainforest
plant species. There are still many more that are unknown to us. Indigenous
people have learned to use thousands of plants as medicines. The US National
Cancer Institute has  identified 3,000 plants which may turn up potential cures
for cancer, half of which come from tropical rainforests.

Some pharmaceutical companies are conducting research into chemicals
extracted from rainforest plants to find cures for a variety of diseases. Besides
food and medicines the rainforest also provides us with many other items
including oils, dyes, waxes, flavorings, fibers and rubber. These are only a very
few of the many resources that are obtainable through sustainable extraction.