Rainforests are characterized by a closed and continuous tree canopy, moisture-dependent vegetation, the presence of and and the absence of wildfire. Rainforests can be generally classified as tropical rainforests or temperate rainforests, but other types have been described.
Estimates vary from 40% to 75% of all biotic community species being indigenous to the rainforests.
Rainforests as well as endemic rainforest species are rapidly disappearing due to deforestation, the resulting habitat loss and air pollution.
Definition
Rainforests are characterized by a closed and continuous tree canopy, high humidity, the presence of moisture-dependent vegetation, a moist layer of leaf litter, the presence of epiphytes and lianas and the absence of wildfire. The largest areas of rainforest are tropical or temperate rainforests, but other vegetation associations including
Laurel forest, littoral rainforest,
cloud forest, vine thicket and even dry rainforest have been described.
Tropical rainforest
Tropical rainforests are characterized by a warm and wet climate with no substantial dry season: typically found within 10 degrees north and south of the
equator. Mean monthly temperatures exceed during all months of the year.
[Susan Woodward. Tropical broadleaf Evergreen Forest: The rainforest. Retrieved on 14 March 2008.] Average annual
is no less than and can exceed although it typically lies between and .
[Newman, Arnold. The Tropical Rainforest : A World Survey of Our Most Valuable Endangered Habitat : With a Blueprint for Its Survival. New York: Checkmark, 2002. Print.]
Many of the world's tropical forests are associated with the location of the monsoon trough, also known as the Intertropical Convergence Zone.[Hobgood (2008). Global Pattern of Surface Pressure and Wind. Ohio State University. Retrieved on 8 March 2009.] The broader category of tropical moist forests are located in the Equator between the Tropic of Cancer and Tropic of Capricorn. Tropical rainforests exist in Southeast Asia (from Burma) to the Philippines, Malaysia, Indonesia, Papua New Guinea and Sri Lanka; also in Sub-Saharan Africa from the Cameroon to the Congo (Congo Rainforest), South America (e.g. the Amazon rainforest), Central America (e.g. Bosawás, the southern Yucatán Peninsula-El Peten-Belize-Calakmul), Australia, and on Pacific Islands (such as Hawaii). Tropical forests have been called the "Earth's ", although it is now known that rainforests contribute little net oxygen addition to the atmosphere through photosynthesis.[Broecker, Wallace S. (2006). "Breathing easy: Et tu, O2." Columbia University Columbia.edu]
Temperate rainforest
Tropical forests cover a large part of the globe, but temperate rainforests only occur in a few regions around the world.
Temperate rainforests are rainforests in
temperateness regions. They occur in
North America (in the Pacific Northwest in
Alaska,
British Columbia, Washington,
Oregon and
California), in
Europe (parts of the
British Isles such as the coastal areas of
Ireland and
Scotland,
southern Norway, parts of the western
Balkans along the
Adriatic Sea coast, as well as in Galicia and coastal areas of the eastern
Black Sea, including Georgia and coastal
Turkey), in
East Asia (in southern China, Highlands of
Taiwan, much of
Japan and
Korea, and on
Sakhalin and the adjacent Russian Far East coast), in
South America (southern
Chile) and also in
Australia and
New Zealand.
Dry rainforest
Dry rainforests have a more open canopy layer than other rainforests,
and are found in areas of lower rainfall (). They generally have two layers of trees.
Layers
A tropical rainforest typically has a number of layers, each with different plants and animals adapted for life in that particular area. Examples include the emergent, canopy,
understory and
forest floor layers.
Emergent layer
The
emergent layer contains a small number of very large
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 that occur above the canopy in some areas.
,
Butterfly,
and certain
inhabit this layer.
Canopy layer
The
canopy layer contains the majority of the largest trees, typically to 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.
Epiphyte attach to trunks and
, 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,
Natural history 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." A 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
.
Canopy research is still in its infancy, but other methods include the use of balloons and
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 or
understorey layer lies between the canopy and the forest floor. It is home to a number of
,
and
, as well as
predation such as
, boa constrictors and
. The leaves are much larger at this level and insect life is abundant. Many
that will grow to the canopy level are present in the understory. Only about 5% of the sunlight shining on the rainforest canopy reaches the understory. This layer can 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% of the sunlight. Only plants
Adaptation to low light can grow in this region. Away from
,
and clearings, where dense undergrowth is found, the forest floor is relatively clear of vegetation because of the low sunlight penetration. It also contains
decomposition plant and animal matter, which disappears quickly, because the warm, humid conditions promote rapid decay. Many forms of
Fungus growing here help decay the animal and plant waste.
Flora and fauna
It is unknown how many species are found in the world's tropical rainforests, however a very large proportion of the vascular plants are native to them.
Rainforests support a very broad array of
fauna, including
,
,
,
and
. Mammals may include
,
felidae and other families. Reptiles include
,
,
and other families; while birds include such families as
vanga and
cuckoo. Dozens of families of invertebrates are found in rainforests.
Fungus are also very common in rainforest areas as they can feed on the decomposing remains of plants and animals.
The great diversity in rainforest species is in large part the result of diverse and numerous physical refuges,
File:Ursus americanus kermodei, Great Bear Rainforest 1.jpg|A Kermode bear from the Great Bear Rainforest, Canada
File:Mudumalai by N A Nazeer (cropped).jpg|A Bengal tiger in Mudumalai National Park, India
File:Standing jaguar.jpg|A jaguar in the Amazon Rainforest, South America
File:MonkeyJungle 03.JPG|Western lowland gorilla in the African rainforest
File:Pongo tapanuliensis.jpg|Orangutans in Tanjung Puting, Indonesia
File:Anaconda jaune 34.JPG|Yellow anaconda reside in the Amazon basin
File:Lion-tailed macaque by N A Naseer.jpg|Lion-tailed macaque in Silent Valley National Park, India
File:Amazon macaw.jpg|A macaw in the Amazon rainforest
Some species of fauna show a trend towards declining populations in rainforests, for example, reptiles that feed on amphibians and reptiles. This trend requires close monitoring.[Barquero-González, J.P., Stice, T.L., Gómez, G., & Monge-Nájera, J. (2020). Are tropical reptiles really declining? A six-year survey of snakes in a tropical coastal rainforest: role of prey and environment. Revista de Biología Tropical, 68(1), 336–343.] The seasonality of rainforests affects the reproductive patterns of amphibians, and this in turn can directly affect the species of reptiles that feed on these groups,[Oliveira, M.E., & Martins, M. (2001). When and where to find a pitviper: activity patterns and habitat use of the lancehead, Bothrops atrox, in central Amazonia, Brazil. Herpetological Natural History, 8(2), 101 -110. ] particularly species with specialized feeding, since these are less likely to use alternative resources.[Terborgh, J., & Winter, B. (1980). Some causes of extinction. Conservation Biology, 2, 119 -133.]
Soils
Despite the growth of
vegetation in a tropical rainforest,
soil quality is often quite poor. Rapid
decay prevents the accumulation of
humus. The concentration of
iron and
aluminium by the
Laterite process gives the
a bright red colour and sometimes produces
mineral deposits such as
bauxite. Most trees have roots near the surface because there are insufficient nutrients below the surface; most of the trees' minerals come from the top layer of decomposing leaves and animals. On younger substrates, especially of
Volcano origin, tropical soils may be quite fertile. If rainforest trees are cleared, rain can accumulate on the exposed soil surfaces, creating run-off, and beginning a process of soil
erosion. Eventually, streams and rivers form and flooding becomes possible. There are several reasons for the poor soil quality. First is that the soil is highly acidic. The roots of plants rely on an acidity difference between the roots and the soil in order to absorb nutrients. When the soil is acidic, there is little difference, and therefore little absorption of nutrients from the soil. Second, the type of clay particles present in tropical rainforest soil has a poor ability to trap nutrients and stop them from washing away. Even if humans artificially add nutrients to the soil, the nutrients mostly wash away and are not absorbed by the plants. Finally, these soils are poor due to the high volume of rain in tropical rainforests washes nutrients out of the soil more quickly than in other climates.
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 vapour). No rainforest today can be considered to be undisturbed.
Human-induced
deforestation plays a significant role in causing rainforests to release carbon dioxide,
as do other factors, whether human-induced or natural, which result in tree death, such as burning and drought.
Some climate models operating with interactive vegetation predict a large loss of Amazonian rainforest around 2050 due to
drought,
forest dieback and the subsequent release of 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
in regions that were formerly primary forest.
[Myers, N. (1985). The primary source. W. W. Norton & Company, New York, pp. 189–193.] Also, plant-derived medicines are commonly used for fever, fungal infections, burns, gastrointestinal problems, pain, respiratory problems, and wound treatment.
At the same time, rainforests are usually not used
sustainably by non-native peoples but are being exploited or removed for agricultural purposes.
Native people
On 18 January 2007, FUNAI reported also 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.
The tribes are in danger because of the deforestation, especially in Brazil.
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 59inches, on average). They were the subject of a study by Colin Turnbull, The Forest People, in 1962.[ The Tribal Peoples , ThinkQuest] Pygmies who live in Southeast Asia are, amongst others, referred to as "Negrito".
There are many tribes in the rainforests of the Malaysian state of Sarawak. Sarawak is part of Borneo, the third largest island in the world. Some of the other tribes in Sarawak are: the Kayan, Kenyah people, Kejaman, Kelabit people, Punan Bah, Tanjong, Sekapan, and the Lahanan. Collectively, they are referred to as Dayaks or Orangulu which means "people of the interior".
About half of Sarawak's 1.5 million people are Dayaks. Most Dayaks, it is believed by anthropologists, came originally from the South-East Asian mainland. Their mythologies support this.
Deforestation
Tropical and temperate rainforests have been subjected to heavy
logging and
illegal logging for their valuable
and agricultural clearance (
slash-and-burn,
clearcutting) throughout the 20th century and the area covered by rainforests around the world is shrinking.
[ Entire rainforests set to disappear in next decade, The Independent 5 July 2003] 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 . Littoral zone rainforest growing along areas of eastern Australia is now rare due to ribbon development to accommodate the demand for seachange lifestyles.
Forests are being destroyed at a rapid pace.[ Brazil: Amazon Forest Destruction Rate Has Tripled, FoxNews.com, 29 September 2008][ China is black hole of Asia's deforestation, AsiaNews.it, 24 March 2008] According to Rainforest Rescue, an important reason for the increasing deforestation rate, especially in Indonesia, is the expansion of oil palm plantations to meet growing demand for cheap vegetable fats and . In Indonesia, palm oil is already cultivated on nine million hectares and, together with Malaysia, the island nation produces about 85 percent of the world's palm oil.
Several countries,[ Amazon deforestation rises sharply in 2007, Usatoday.com, 24 January 2008] notably Brazil, have declared their deforestation a national emergency.
However, a 30 January 2009 New York Times article stated, "By one estimate, for every acre of rainforest 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.
See also
Further reading
-
Butler, R. A. (2005) A Place Out of Time: Tropical Rainforests and the Perils They Face. Published online: Rainforests.mongabay.com
-
Richards, P. W. (1996). The tropical rain forest. 2nd ed. Cambridge University Press
-
Whitmore, T. C. (1998) An introduction to tropical rain forests. 2nd ed. Oxford University Press.
External links
