Rainforests are
forests characterized by high
rainfall, with definitions setting minimum normal annual rainfall between 1750–2000 mm (68-78 inches). The
monsoon trough, alternately known as the
intertropical convergence zone, plays a significant role in creating
Earth's tropical rain forests.
From 40 to 75% of all
species on
Earth are
indigenous to the rainforests.
It has been estimated that many millions of species of plants, insects, and
microorganisms are still undiscovered. Tropical rainforests have been called the "jewels of the Earth", and the "world's largest
pharmacy", because of the large number of natural
medicines discovered there. Rainforests are also responsible for 28% of the worlds
oxygen turn over, often misunderstood as oxygen production, processing it through
photosynthesis from
carbon dioxide and storing it as
carbon through
biosequestration.
The
undergrowth in a rainforest is restricted in many areas by the lack of
sunlight at ground level. This makes it possible to walk through the forest. If the
leaf canopy is destroyed or thinned, the ground beneath is soon colonized by a dense, tangled growth of
vines,
shrubs, and small
trees called a
jungle. There are two types of rainforest,
tropical rainforest and
temperate rainforest.
Tropical
Many of the world's rainforests are associated with the location of the monsoon trough, also known as the intertropical convergence zone.
Tropical rainforests are rainforests in the
tropics, found near the
Equator (between the
Tropic of Cancer and
Tropic of Capricorn) and present in
southeast Asia (
Myanmar to
Philippines,
Indonesia,
Papua New Guinea, and northeastern
Australia),
Sub-Saharan Africa from
Cameroon to the
Congo (
Congo Rainforest),
South America (e.g. the
Amazon Rainforest),
Central America (e.g.
Bosawás, southern
Yucatán Peninsula-
El Peten-
Belize-
Calakmul), and on many of the
Pacific Islands (such as
Hawaii). Tropical rainforests have been called the "Earth's
lungs," although it is now known that rainforests contribute little net
oxygen additions to the
atmosphere through
photosynthesis.
Temperate
Temperate rainforests are rainforests in
temperate regions. They can be found in
North America (in the
Pacific Northwest, the
British Columbia Coast, and in the
inland rainforest of the
Rocky Mountain Trench east of
Prince George), in
Europe (parts of the
British Isles such as the coastal areas of
Ireland,
Scotland, southern
Norway, parts of the western
Balkans along the
Adriatic coast, as well as in the North West of
Spain and coastal areas of the eastern
Black Sea, including
Georgia and coastal
Turkey), in
East Asia (in
southern China,
Taiwan, much of
Japan and
Korea, and on
Sakhalin Island and the adjacent
Russian Far East coast), in
South America (southern
Chile) and also
Australia and
New Zealand.
Layers
A tropical rainforest is typically divided into four main layers, each with different plants and animals adapted for life in that particular area: the emergent, canopy, understory, and
forest floor layers.
Emergent layer
The
emergent layer contains a small number of very large
trees called
emergents, which grow above the general
canopy, reaching heights of 45–55 m, although on occasion a few species will grow to 70–80 m tall. They need to be able to withstand the hot temperatures and strong winds in some areas.
Eagles,
butterflies,
bats, and certain
monkeys inhabit this layer.
Canopy layer
The
canopy layer contains the majority of the largest trees, typically 30–45 m tall. The densest areas of
biodiversity are found in the forest canopy, a more or less continuous cover of foliage formed by adjacent treetops. The canopy, by some estimates, is home to 50 percent of all plant species, suggesting that perhaps half of all life on Earth could be found there.
Epiphytic plants attach to
trunks and
branches, and obtain water and minerals from rain and debris that collects on the supporting plants. The fauna is similar to that found in the emergent layer, but more diverse. A quarter of all insect species are believed to exist in the rainforest canopy. Scientists have long suspected the richness of the canopy as a habitat, but have only recently developed practical methods of exploring it. As long ago as 1917,
naturalist William Beebe declared that "another continent of life remains to be discovered, not upon the Earth, but one to two hundred feet above it, extending over thousands of square miles." True exploration of this habitat only began in the 1980s, when scientists developed methods to reach the canopy, such as firing ropes into the trees using
crossbows. Exploration of the canopy is still in its infancy, but other methods include the use of
balloons and
airships to float above the highest branches and the building of cranes and walkways planted on the forest floor. The science of accessing tropical forest canopy using airships, or similar aerial platforms, is called dendronautics.
Understory layer
The
understory layer lies between the canopy and the forest floor. The understory (or understorey) is home to a number of
birds,
snakes, and
lizards, as well as
predators such as
jaguars,
boa constrictors, and
leopards. The leaves are much larger at this level. Insect life is also abundant. Many seedlings that will grow to the canopy level are present in the understory. Only about 5 percent of the sunlight shining on the rainforest reaches the understory. This layer can also be called a
shrub layer, although the shrub layer may also be considered a separate layer.
Forest floor
The
forest floor, the bottom-most layer, receives only 2 percent of sunlight. Only plants
adapted to low light can grow in this region. Away from
riverbanks,
swamps, and clearings where dense undergrowth is found, the forest floor is relatively clear of vegetation because of the low sunlight penetration. It also contains
decaying plant and animal matter, which disappears quickly due to the warm, humid conditions promoting rapid decay. Many forms of
fungi grow here which help decay the animal and plant waste. It takes up to 20 minutes for rain to actually touch the ground from the trees.
Flora and fauna
More than half of the world's species of plants and animals are found in the rainforest. Rainforests support a very broad array of
fauna including
mammals,
reptiles,
birds, and
invertebrates. Mammals may include
primates,
felids, and other families. Reptiles include
snakes,
turtles,
chameleons, and other families while birds include such families as
vangidae and
Cuculidae. Dozens of families of invertebrates are found in rainforests.
Fungi are also very common in rainforest areas as they can feed on the decomposing remains of plant and animal life. These species are rapidly disappearing due to
deforestation, habitat loss, and biochemical releases into the atmosphere.
Soils
Despite the growth of
vegetation in a tropical rainforest,
soil quality is often quite poor. Rapid
bacterial decay prevents the accumulation of
humus. The concentration of
iron and
aluminium oxides by the
laterization process gives the
oxisols a bright red color and sometimes produces
minable deposits such as
bauxite. Most trees have roots near the surface as there are not many nutrients below the ground; most of the trees minerals come from the top layer of decomposing leaves (mainly) and animals. On younger substrates, especially of
volcanic origin, tropical soils may be quite fertile. If the trees are cleared, the rain can get at the exposed soil, washing it away. Eventually streams will form, then rivers. Flooding becomes imminent.
Effect on global climate
A natural rainforest emits and absorbs vast quantities of
carbon dioxide. On a global scale, long-term fluxes are approximately in balance, so that an undisturbed rainforest would have a small net impact on atmospheric carbon dioxide levels, though they may have other climatic effects (on
cloud formation, for example, by recycling
water vapor). No rainforest today can be considered to be undisturbed.
[Lewis, S.L. , Phillips, O.L., Baker, T.R., Lloyd, J. et al. 2004 “Concerted changes in tropical forest structure and dynamics: evidence from 50 South American long-term plots” Phil. Trans. R. Soc. Lond. 359] Human induced deforestation plays a significant role in causing rainforests to release carbon dioxide,
[ Malhi, Y and Grace, J. 2000 " Tropical forests and atmospheric carbon dioxide”, Tree 15] as do natural processes such as
drought that result in tree death. Some climate models run with interactive vegetation and predict a large loss of Amazonian rainforest around 2050 due to drought, leading to forest dieback and the subsequent feedback of releasing more carbon dioxide.
Human uses
Tropical rainforests provide timber as well as animal products such as meat and hides. Rainforests also have value as tourism destinations and for the ecosystem services provided. Many foods originally came from tropical forests, and are still mostly grown on
plantations in regions that were formerly primary forest. Also, plant derived medicines are commonly used for fever, fungal infections, burns, gastrointestinal problems, pain, respiratory problems, and wound treatment.
Native peoples
On January 18, 2007,
FUNAI reported that it had confirmed the presence of 67 different
uncontacted tribes in Brazil, up from 40 in 2005. With this addition,
Brazil has now overtaken the island of
New Guinea as the country having the largest number of uncontacted tribes. The province of Irian Jaya or
West Papua in the island of New Guinea is home to an estimated 44 uncontacted tribal groups.
Central African rainforest is home of the
Mbuti pygmies, one of the hunter-gatherer peoples living in equatorial rainforests characterised by their short height (below one and a half metres, or 59 inches, on average). They were the subject of a study by
Colin Turnbull,
The Forest People, in 1962. Pygmies who live in Southeast Asia are, amongst others, referred to as “
Negritos.”
Deforestation
Jungle burned for agriculture in southern
Mexico.
and
temperate rainforests have been subjected to heavy
logging and agricultural clearance throughout the 20th century and the area covered by rainforests around the world is shrinking. Biologists have estimated that large numbers of species are being driven to
extinction (possibly more than 50,000 a year; at that rate, says
E. O. Wilson of
Harvard University, a quarter or more of all species on Earth could be exterminated within 50 years) due to the removal of habitat with destruction of the rainforests.
Another factor causing the loss of rainforest is expanding urban areas.
Littoral rainforest growing along
coastal areas of eastern
Australia is now rare due to
ribbon development to accommodate the demand for
seachange lifestyles.
The forests are being destroyed at a rapid pace. Almost 90% of
West Africa's rainforest has been destroyed. Since the arrival of humans 2000 years ago,
Madagascar has lost two thirds of its original rainforest. At present rates, tropical rainforests in
Indonesia would be logged out in 10 years and
Papua New Guinea in 13 to 16 years.
Several countries, notably
Brazil, have declared their deforestation a national emergency. Amazon deforestation jumped by 69% in 2008 compared to 2007's twelve
months, according to official government data. Deforestation could wipe out or severely damage nearly 60% of the
Amazon Rainforest by 2030, says a new report from
WWF.
However, a January 30, 2009
New York Times article stated, "By one estimate, for every
acre of rain forest cut down each year, more than 50 acres of new forest are growing in the tropics..." The new forest includes secondary forest on former farmland and so-called degraded forest.
From a new recent report in September 2009, new opportunities are beginning to discover they could save the rainforest. In Brazil, Environment Minister Carlos Minc announced proudly that the rate of deforestation of the Amazon fell by 46 percent last year. That means the lowest logging level since the country began to keep annual statistics 21 years ago. But not only Brazil has reduced deforestation as a whole also slowed the loss of forest down. The annual decline is now over two thousand. Deforestation decreases in a country as it becomes richer and more industrialized. Therefore, there are exceptions in a group of countries where deforestation has become so profitable that it is an important part in the growth of prosperity. New goal is to stop felling the forest, but also in managing the forest long-term, which occurs on a larger scale. More police officers guarding the rainforest, and stifle the illegal logging..
See also
