- Tropical rainforest
Tropical rainforests are generally found near the
equator. They are common in Asia, Australia, Africa, South America, Central America, and on many of the Pacific Islands. Within the World Wildlife Fund's biomeclassification, tropicalrainforests are considered a type of tropical wet forest(or tropical moist broadleaf forest) and may also be referred to as "lowland equatorial evergreen rainforests". Minimum normal annual rainfall between convert|1750|mm|in and convert|2000|mm|in occurs in this climate region. Mean monthly temperatures exceed convert|18|C|F during all months of the year. [Susan Woodward. [http://www.radford.edu/~swoodwar/CLASSES/GEOG235/biomes/rainforest/rainfrst.html Tropical Broadleaf Evergreen Forest: The Rainforest.] Retrieved on 2008-03-14.] Rainforests are home to half of all the living animaland plantspecies on the planet.The Regents of the University of Michigan. [http://www.globalchange.umich.edu/globalchange1/current/lectures/kling/rainforest/rainforest.html The Tropical Rain Forest.] Retrieved on 2008-03-14.] Tropical rain forests are called the "world's largest pharmacy" because over one-quarter of modern medicines originate from its plants. [Rainforest Concern. [http://www.rainforestconcern.org/rainforest_facts/why_the_importance/ Why are rainforests important?] Retrieved on 2008-03-14.] The undergrowth in a rainforest is restricted in many areas by the lack of sunlight at ground level. [Michael Ritter. [http://www.uwsp.edu/geo/faculty/ritter/geog101/textbook/biogeography/biomes_tropical_forests_page_1.html The Forest Biome.] Retrieved on 2008-03-14.] This makes it possible for people and other animals to walk through the forest. If the leaf canopy is destroyed or thinned for any reason, the ground beneath is soon colonized by a dense tangled growth of vines, shrubs and small trees called a jungle. [cite encyclopedia | title = Tropical Rain Forest | encyclopedia = Glossary of Meteorology | publisher = American Meteorological Society| url = http://amsglossary.allenpress.com/glossary/search?p=1&query=tropical+rain+forest | accessdate = 2008-05-14 ]
The rainforests are home to more
speciesor populations than all other biomes combined. Approximately 80% of the world's known biodiversitycould which be found in tropical rainforests. [ [http://www.reuters.com/article/environmentNews/idUSMAN18800220080620 U.N. calls on Asian nations to end deforestation] , Reuters] The leafy tops of tall trees-extending from 50 to 80 metersabove the forestfloor-forms an understory. Organic matter that falls to the forest floor quickly decomposes, and the nutrients are recycled.
Rainforests are characterized by high
rainfall. This often results in poor soilsdue to leaching of soluble nutrients. Oxisols, infertile, and deeply weathered, have developed on the ancient Gondwanan shields. Rapid bacterial decay prevents the accumulation of humus. The concentration of ironand aluminiumoxides by the laterization process gives the oxisols a bright red color and sometimes produces mineraldeposits (e.g. bauxite). On younger substrates, especially of volcanicorigin, tropical soilsmay be quite fertile, as are the soils of many seasonally flooded forests, which are annually replenished with fertile silt.
Tropical rain forests have been subjected to heavyvague
loggingand agricultural clearance throughout the 20th century, and the area covered by rainforests around the world is rapidlywhich shrinking. [ [http://www.guardian.co.uk/environment/2008/sep/01/forests.brazil Brazil: Deforestation rises sharply as farmers push into Amazon] , The Guardian, September 1, 2008] [ [http://www.asianews.it/index.php?l=en&art=5728 China is black hole of Asia's deforestation] , Asia News, 24 March, 2008]
It has been estimated Who|date=September 2008 that many hundreds of millions of new
speciesof plants, insects, and microorganisms are still undiscovered and, as yet, unnamed by science. Rainforests are also often called the "Earth's lungs," however there is no scientific basis for such a claim as tropical rainforests are known to be essentially oxygenneutral, with little or no net oxygen production. [Broeker, W.S., 2006 "Breathing easy, Et tu, O2" Columbia University http://www.columbia.edu/cu/21stC/issue-2.1/broecker.htm.] [Moran, E.F., "Deforestation and Land Use in the Brazilian Amazon", Human Ecology, Vol 21, No. 1, 1993“It took more than 15 years for the "lungs of the world" myth to be corrected. Rainforests contribute little net oxygen additions to the atmosphere through photosynthesis.”] Tall, broad-leaved evergreen treesare the dominant plants, forming a leafy canopy over the forest floor. Taller trees, called emergents, may rise above the canopy. The upper portion of the canopy often supports a rich flora of epiphytes, including orchids, bromeliads, mosses, and lichens, who live attached to the branches of trees. The undergrowth or understory in a rain forestis often restricted by the lack of sunlight at ground level, and generally consists of shade-tolerant shrubs, herbs, ferns, small trees, and large woody vines which climb into the trees to capture sunlight. The relatively sparse under story vegetation makes it possible for people and other animals to walk through the forest. In deciduousand semi-deciduous forests, or forests where the canopy is disturbed for some reason, the ground beneath is soon colonized by a dense tangled growth of vines, shrubs and small trees called jungle.
temperatureranges from 15°C to 50°C and 125 to 660 cm of rainfall yearly.
The rainforest is divided into five different parts, each with different plants and animals, adapted for life in the particular area. These are: the floor layer, the shrub layer, the understory layer, the canopy layer and the emergent layer. Only the emergent layer is unique to tropical rainforests, while the others are also found in temperate rainforests.
The emergent layer contains a small number of very large trees which grow above the general canopy, reaching heights of 45-55 m, although on occasion a few species will grow to 70 m or 80 m tall. They need to be able to withstand the hot temperatures and strong winds.
Eagles, butterflies, batsand certain monkeys inhabit this layer.
The canopy is host to the largest percentage of animals, such as treefrogs, monkeys, birds, gorillas, orangutangs and insects. The canopy is the layer containing many trees just underneath the emergent.
Tropical rainforests are unable to support
human populations [Bailey, R.C., Head, G., Jenike, M., Owen,B., Rechtman, R., Zechenter, E., 1989 "Hunting and gathering in tropical rainforest: is it possible." American Anthropologist, 91:1 59-82] . Food resources within the forest are extremely dispersed due to the high biological diversity and what food does exist is largely restricted to the canopy and requires considerable energy to obtain. Some groups of hunter-gatherers have exploited rainforest on a seasonal basis but dwelt primarily in adjacent savanna and open forestenvironments where food is much more abundant.Other peoples described as rainforest dwellers are hunter-gatherers who subsist in large part by trading high value forest products such as hides, feathers, and honey with agricultural people living outside the forest. [Bailey, R.C., Head, G., Jenike, M., Owen, B., Rechtman, R., Zechenter, E., 1989 "Hunting and gathering in tropical rainforest: is it possible." American Anthropologist, 91:1 59-82]
Conversion to Agricultural Land
With the invention of agriculture humans were able to clear sections of rainforest to produce crops, converting it to open farmland. Such people, however, obtain their food primarily from farm plots cleared from the forest [Bailey, R.C., Head, G., Jenike, M., Owen,B., Rechtman, R., Zechenter, E., 1989 "Hunting and gathering in tropical rainforest: is it possible." American Anthropologist, 91:1 59-82 ] [Philip L. Walker, Larry Sugiyama, Richard Chacon. (1998) '"Diet, Dental Health, and Cultural Change among Recently Contacted South American Indian Hunter-Horticulturalists" in "Human Dental Development, Morphology, and Pathology". University of Oregon Anthropological Papers, No . 54] and hunt and forage within the forest to supplement this. Agriculture on formerly forested land is not without difficulties. Rainforest soils are often thin and leached of many minerals, and the heavy rainfall can quickly leach nutrients from area cleared for cultivation. People such as the
Yanomamoof the Amazon, utilise slash-and-burnagriculture to overcome these limitations and enable them to push deep into what were previously rainforest environments. However these are not rainforest dwellers, rather they are dwellers in cleared farmland [Bailey, R.C., Head, G., Jenike, M., Owen,B., Rechtman, R., Zechenter, E., 1989 "Hunting and gathering in tropical rainforest: is it possible." American Anthropologist, 91:1 59-82] [Philip L. Walker, Larry Sugiyama, Richard Chacon. (1998) '"Diet, Dental Health, and Cultural Change among Recently Contacted South American Indian Hunter-Horticulturalists" in "Human Dental Development, Morphology, and Pathology". University of Oregon Anthropological Papers, No . 54] that make forays into the rainforest and up to 90% of the typical Yanamomo diet comes from farmed plants [Philip L. Walker, Larry Sugiyama, Richard Chacon. (1998) '"Diet, Dental Health, and Cultural Change among Recently Contacted South American Indian Hunter-Horticulturalists" in "Human Dental Development, Morphology, and Pathology". University of Oregon Anthropological Papers, No . 54]
Cultivated foods and spices
Coffee, chocolate, banana, mango, papaya, macadamia, avocado, and sugarcaneall originally came from tropical rainforest and are still mostly grown on plantations in regions that were formerly primary forest. In the mid-1980s and 90s, 40 million tons of bananas were consumed worldwide each year, along with 13 million tons of mangoes. Central American coffee exports were worth US$3 billion in 1970. Much of the genetic variation used in evading the damage caused by new pests is still derived from resistant wild stock. Tropical forests have supplied 250 cultivated kinds of fruit, compared to only 20 for temperate forests. Forests in New Guineaalone contain 251 tree species with edible fruits, of which only 43 had been established as cultivated crops by 1985. [Myers, N. 1985. The primary source W. W. Norton and Co., New York, pp. 189-193.]
Pharmaceutical and biodiversity resource
Tropical rain forests are called "the world's largest pharmacy" because of the large amount of natural medicines discovered in rainforests that are derived from rainforest plants. For example, rain forests contain the "basic ingredients of
hormonal contraceptionmethods, cocaine, stimulants, and tranquilizing drugs" (Banks 36). Curare(a paralyzing drug) and quinine(a malariacure) are also found there.
Tourismin the Tropical rainforest has increased over the years Fact|date=September 2008 having both positive and negative effects.. People travel both nationallyand internationallyto experience rain forests firsthand.
As tourism becomes more popular in the tropical rainforests there are many different negative impacts that come from it, these being depletion of natural
resources, pollution, and moreFact|date=September 2008. Taking walks/hikes in the forest, off-roading or biking and camping all can trample vegetation, introduce weedsand change plant composition. Bringing in any outside influences that come in contact to the plants and nature of the forest can destroy or leave a major impression on the plants. There are also many other environmental impacts on the forest caused by tourism such as: changes in soilcondition, increased soil erosion, alterations of faunal composition, increase and introduction of weeds, development of social trails or paths through the forest, changes in water quality, habituation of native fauna, alterations of plant life and composition, and spread of soil pathogens.
Despite the negative effects of tourism in the tropical rainforests, there are also several important positive effects.
*An increase in tourism has increased economic support, allowing more revenue to go into the protection of the habitat. Tourism can contribute directly to the conservation of sensitive areas and habitat. Revenue from park-entrance fees and similar sources can be utilised specifically to pay for the protection and management of environmentally sensitive areas. Revenue from taxation and tourism provides an additional incentive for governments to contribute revenue to the protection of the forest.
*Tourism also has the potential to increase public appreciation of the environment and to spread awareness of environmental problems when it brings people into closer contact with the environment. Such increased awareness can induce more environmentally conscious behavior. Tourism has had a positive effect on wildlife preservation and protection efforts, notably in Africa but also in South America, Asia, Australia, and the South Pacific. [Fotiou, S. (2001, October). Environmental Impacts of Tourism. Retrieved November 30, 2007, fromhttp://www.uneptie.org/pc/tourism/sust-tourism/env-conservation.htm]
Rainforests provide numerous animal products including honey, game meat, and associated trophies such as hides and ivory.
In addition to extractive human uses rainforests also have non-extractive uses that are frequently summarized as
ecosystem services. Rain forests play an important role in maintaining biological diversity, modulating precipitation, infiltration and flooding, increasing scientific knowledge and in the spiritual well-being of humans. Such ecosystem services are of use to humans without the need for any modification or management of the forest itself.
*Mann, Charles C., "1491 New Revelations of the Americas Before Columbus" New York: Knopf, 2005 ISBN 0739464418
Tropical and subtropical moist broadleaf forests
Temperate rain forest
List of tropical and subtropical moist broadleaf forests ecoregions
* [http://www.ran.org Rainforest Action Network]
* [http://www.worldwildlife.org/wildplaces/amazon/index.cfm?sc=AWY0707WCG00&searchen=google Info on Amazon Rainforest, the largest rainforest in the world]
* [http://www.blueplanetbiomes.org/rainforest.htm Rain Forest Info from Blue Planet Biomes]
* [http://passporttoknowledge.com/rainforest/main.html Passport to Knowledge Rainforests]
There have been many conservation efforts:
* [http://www.worldwildlife.org World Wildlife Fund]
** [http://www.worldwildlife.org/wildplaces/amazon/you_do.cfm Amazon - What you can do]
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Look at other dictionaries:
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