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in Columbia
A tropical rainforest is defined as a forest in a tropical region, generally between the Tropics and Cancer and Capricorn, with a large amount of rainfall. By contrast, there are tropical dry forests and temperate rainforests. Tropical rainforests are known for being rich in both plant and animal life, a condition expressed by the term biodiversity.

There is about 1.2 billion hectares of tropical forest in the world. Tropical rainforests cover half the worlds woodlands, 14 percent of the world’s land surface and 6 percent of the Earth’s total surface area. Some rainforests have remained virtually unchanged for millions of years. In the same period lakes have appeared and dried up, volcanoes have produced new mountains worn down by erosion and grasslands have become deserts.

The first tropical rainforests began to form roughly 140 million years ago, during the age of the dinosaurs, when the climate of nearly the entire world was tropical. Flowering plants also evolved during this period, and with them their symbiotic relationship with wasps, beetles, bees, flies, butterflies, and moths who pollinated the flowers.▸

Scientists define five different tropical habitats: 1) primary forests with trees 115 to 180 feet high; 2) secondary forests with trees 50 to 60 feet high; 3) Cecropia, mainly with palms up to 50 feet high; 4) scrub and shrubs up to 6.5 feet high; 5) pasture up to 1.5 feet.

There are a number of different kinds of rainforests: montane rainforests in the mountains, lowland rainforests in lowlands, riverine rainforests along rivers, esturine rainforests near estuaries and cloud forests where clouds collide with the slopes of tropical mountains. The word jungle is often times misused as a synonym for rainforest. A jungle refers to dense growth adjacent to an open area.

Based on discoveries made of a 300-million-year-old fossilized forest found in a coal seem in Illinois, club mosses grew over a meter thick and 40 meters high in primordial rainforests.

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above canopy
Websites and Resources: Rainforest Action Network ; Rainforest Foundation ; World Rainforest Movement ; Wikipedia article Wikipedia ; Forest Peoples Programme ; Rainforest Alliance ; Rainforest Portal ; Prince’s Rainforest Project ; Nature Conservancy ; National Geographic ;

Books: “The Private Life of Plants: A Natural History of Plant Behavior” by David Attenborough (Princeton University Press, 1997); “Portraits of the Rainforest” by Adrian Forsythe. National Geographic articles used in these articles: “Rainforest Canopy, the High Frontier” by Edward O. Wilson, December 1991 [▸]; “Tropical Rainforests: Nature's Dwindling Treasures”, by Peter T. White, January 1983[∩];

Websites and Resources on Rainforest Animals: Rainforest Animals ; Rainforest Animal Photos ; Rainforest Plant Photos ; Rainforest Animal Photos ; Rainforest Plants ; Enchanted Learning ; Amazon Plants Plants ; Biology of Plants ; ; Life Cycle of Plants / ; Scientific American articles on plants ; Dave’s Garden ; Wikipedia article Wikipedia ; Picture Gallery in German

The Yokohama-based International Tropical Timber Organization (ITTO), with 59 members representing most of the world’s tropical forests, was formed under the auspices of the United Nations in 1986 when worries about the destruction of tropical forest were becoming a concern. Its mission is to promote forest management and retain the “inherent values” of the forest “while revenues are earned, people employed and communities sustained by the production of timber and other forest products and services.

Rainforest Canopy

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Rainforest strata
The upper branches of the rainforest trees and the vegetation found in them is referred to as the canopy. It extends for about 5 or 7 meters deep from the tops of the trees. The vastness and complexity of system is one reason why the rainforest contains over half of all the worlds species.

The trees that make up the canopy vary in height between 100 and 150 feet, with a few towering 200 feet or more. The trees have trunks free of branches for the first sixty feet or so and nearly horizontal upper branches. Scientists have estimated that the total surface of the leaves and branches on the world's forest canopies is equal to the total surface of the earth.

Virgin rainforests are made up of a nearly continuous canopy of trees with flattened crowns. Describing what it is like be up there, David Attenborough wrote: "Suddenly the humid twilight is replaced by fresh air and sunshine. Around you stretches a limitless meadow of leaves...dimpled like the surface of enormously enlarged cauliflower. Here and there, standing 10 meters or more over the rest, rises a single giant tree...Up here the wind blows freely through their crowns...the air is warm and humid."

Life and Soil in the Rainforest Canopy

The canopy captures 90 percent of sunlight, conducts the bulk of the photosynthesis activity and is home to nearly all the animals, plants, insects and birds. Many creatures live their entire lives and die in the canopy without every setting foot on the ground. While many species in the canopy are very similar to each other, they often have very little in common with species found near the ground.

Once a tree has grown tall enough to become part of the canopy it serves as a host for palm trees, parasitic vines like figs and flowering plants. Many forms of life rely on “soil” found on tree branches rather than on the ground soil.

On the 100-foot-high branches of some large trees there is foot-thick soil with earthworms. This soil made up of wind-borne dust, fallen leaves, decomposed fungi and moss, other detritus (decayed organic material), animal droppings and plant and animal remains. The mixture is like a bog, and especially thick where the branches come together.

Living on top of this soil are leafy plants such as orchids, philodendrons, ferns, bromeliads, and flora related to azaleas, violets and pepper plants. Growing on the leaves and the undersides of the branches are lichens and mosses. And living among all this are birds, insects, small mammals, worms, caterpillars, spiders, butterflies, hummingbirds, lizards and salamanders.▸

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Mid-Level and Low-Level Rainforest Life

The area below the canopy is sometimes called the understory. Very little light penetrates the canopy and the species of trees below it include adolescent canopy trees working their way up and mature tree species that thrive in the twilight region.

Lower down are at the height of human beings is a lower canopy of saplings and herbaceous plants. The layer of leaves, not as dense as the canopy but still significant. These are produced by the small trees and palms and other plants adept at living in dim light. The lower canopy is kind of like a way station for animals on their way between the canopy and the ground.

There isn't much visible activity going on in the rainforest at ground level, which sometimes receive only one percent of the sunlight that reaches the canopy. The canopy is so thick that people who work in the rainforest almost never see the sky and rain from a cloudburst take ten minutes before it reaches the ground.

But that doesn’t mean there isn’t stuff going on. David Attenborough wrote: "It is very hot and stagnant and loaded with moisture. Such conditions suit the process of decay. bacteria and mold work unceasingly. Fungi proliferate, spreading their filaments through the leaf litter and erecting their bodies. The speed of decomposition is extraordinarily rapid."

The canopy trees block all but one percent of the sunlight. Despite rainfall of up to 16 feet a year saplings on the floor of primary forests only grow around an third of an inch a year. At that rate it would take 3,000 years to reach the canopy.

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Rainforest Soils

Tropical rainforest soil is very thin and low in nutrients. With no winters or frosts to kill insects or microorganisms, and with lots of heat and humidity to help them grow and multiply, organic matter such as fallen leaves and twigs decomposes so quickly that only a thin layer of organic material covers the soils.

The soils are heavily leached of nutrients by rain water. But in many cases that doesn't matter much because the nutrients are absorbed by other life forms before the rain has a chance to carry them away. Trees absorb the nutrients with thick mats of rootlets that grow close to the surface of the soil.

Rainforest soils are generally terrible for agriculture, producing crops for one to three years before being depleted of nutrients (See Slash and Burn Agriculture). How is it then that a tropical rainforest is so rich in life. The secret is a quick turnover of nutrients.

When leaves, trees, plants of animals die they fall to the forest floor where they are quickly recycled into mulch by insects and fungi. Bacteria then plays a crucial part converting the mulch and litter into nutrients consumed by plants. The air at ground level in a tropical rainforest, according to Harvard biologist and ant specialist Edmond Wilson is "humid and saturated with odors of healthy decay."▸

Only two organisms can break down dead plants into useable nutrients: bacteria and fungi. In wet, humid, dark and hot conditions in the rainforest fungi and bacteria can break down cellulose very quickly. Since there is little wind in the forests. leaves tend to fall straight down. Thus, many plants fed on nutrient they themselves deposited. Termites also play a major roll converting cellulose to nutrients that can be consumed by other animals. The termites themselves a favorite food of many animals.

See Deforestation

Carbon Cycle

Carbon Cycle and Greenhouse Gas Emmissions

Plants, animals and bacteria and fungi in the soil all play vital roles in the carbon cycle — the circulation of carbon between air, land, water and life forms, both plant and animal. Carbon’s ability to bond with most nonmetals has made it the basis of all organic compounds found in both plants and animals.

Terrestrial vegetation uses 60 billion metric tons of carbon a year to grow, producing oxygen in the process. Carbon dioxide is soluble in water and constantly being exchanged between the air and water. To grow plants remove carbon dioxide through the air via photosynthesis to produce energy and build tissue. Respiration by bacteria and fungi that feed on organic matter returns carbon dioxide to the atmosphere. Some carbon is removed from the system and stored for as long as millions of years locked up in ocean depths or crustal rock and as coal, oil and natural gas.

The World Bank estimates that an acre of rain forest converted to crops is worth $100 to $250. It’s worth far more under a system that puts a value on carbon. An average acre stores about 200 tons of carbon; assuming a low price of $10 a ton, that acre is suddenly worth $2,000. The Amazon is often called the “earth’s lungs” for its ability to generate vast amounts of oxygen and soak up huge amounts of carbon dioxide through photosynthesis.

By some estimates deforestation and destruction of the world’s rainforests is responsible for around 17 to 20 percent of mankind’s greenhouse gas emissions — about the same as China’s or the U.S.’s emissions, and more than the emissions generated by all of the world’s cars and trucks.. [Source: Reuters]

greenhouse effect

Measuring Carbon Storage Capacity of Rainforests

Michael Lemonick wrote in National Geographic, “One obstacle has been the lack of a reliable way of measuring how much carbon is stored in different forests without inspecting every acre from the ground. That's where the maps shown here fit in. They were made by a team led by Gregory Asner, a tropical ecologist with the Carnegie Institution. Satellites, Asner explains, can track forest loss, but not whether it's primary forest or secondary regrowth — whether it consists of huge, old-growth trees or of scrawny saplings that store less carbon.

Asner's team can now do that by surveying the forest from a plane with lidar, a laser-ranging instrument similar to radar. The device shoots an infrared laser pulse toward the ground 100,000 times a second and records how long it takes to reflect back. Some of the light bounces off the forest canopy, but some makes it all the way to the ground. "It's kind of like an MRI," says Asner. "We can figure out not just the height of the canopy, but also the 3-D structure of the forest," and thus how much carbon it's storing. You still need on-the-ground measurements to spot-check the lidar, Asner says, and satellites to get the big picture. But all three together just might offer a way of keeping carbon trading honest — and tropical forests intact. email a friend iconprinter friendly icon

Temperate Cool Rainforests Store More Carbon than Tropical Rainforests, Book Finds

Cool rainforests store more carbon per acre than tropical rainforests, according to a new book that synthesizes the work of 30 international scientists."Temperate and Boreal Rainforests of the World: Ecology and Conservation," published by Island Press, documents that in 2007 the 250 million acres of temperate and high-latitude forests stored 196 gigatons of carbon--the equivalent of six times the amount of carbon dioxide humans emit each year by burning fossil fuels. The book's editor said policymakers need to focus on "the world's forgotten rainforests." [Source: Juliet Eilperin, Washington Post, November 18, 2010]


Juliet Eilperin wrote in the Washington Post, Conservation groups and world leaders have traditionally devoted their efforts to preserving tropical forests as carbon sinks, because in addition to curbing warming they host an array of species and give developing countries a financial incentive for cutting greenhouse gas emissions.

Tropical rainforests get between 60 and 160 inches of rain a year; temperate and boreal forests receive between 40 and 100 inches of rain annually but stay much cooler, with average annual temperatures of between 43 and 52 degrees Fahrenheit. Cool rainforests are found in 10 regions of the world, including America's Pacific Northwest; inland British Columbia and parts of Idaho and Montana; Eastern Russia and Southern Siberia; and Chile and Argentina.

"In some regions, like portions of Europe, nearly all rainforests are gone while others are headed in that direction if we don't act soon," said Dominick DellaSala, chief scientist and president of the Geos Institute in Ashland, Ore. "Decades of logging has created a national ecological debt crisis that is being passed on to future generations from which we are borrowing on their biological inheritance."

These temperate and boreal forests store carbon in the massive trunks of their trees, as well as in their dense soil and foliage. Old-growth temperate forests such as some in the U.S. and Australia, DellaSalla said, store more carbon per acre than any other kind of forest in the world. Ten percent of the world's temperate forests are in the Pacific Northwest and Alaska, while another 25 percent are along the coastline of Canada's British Columbia.

tropical rain forests

America's cool rainforests are just a fraction of their historic size: between 15-20 percent of old-growth rainforests remain in the Pacific Northwest, and less than 4 percent of the region's coastal redwoods still exist.

Rainforest Weather

Compared to the changing weather conditions in temperate forest, the condition in tropical rainforests remains pretty much the same: being close the equator the amount of sunlight and warmth are almost the same everyday. The main variations are the rainfall amounts which often time change between the wet and dry season.

Rainforests receive anywhere from 80 inches to extremes of 400 inches of rain a year. Generally, a third of the rain evaporates, a third is absorbed by roots and greenery and third runs off. Even during strong thunderstorms sometimes little rain penetrates the canopy and reaches the ground. Instead it is absorbed by plants and collects in pools in the leaves and branches in the upper reaches of the rainforest.

The heat in the tropics is strong enough to melt the paint on the walls of steel hulled ships. The shade provided by all the trees in the rainforest, however, keeps the temperatures lower than they otherwise would be. The humidity though makes being in the forest very uncomfortable for many people.

rain in the rain forest

The temperature and humidity are relatively constant at ground level in the tropical rainforest, but varies in the upper branches of the trees. Sunlight bakes the vegetation there, occasionally raising the temperature of the surrounding air to a full 10̊ higher than the ground level temperatures The relative humidity in the upper levels of the rainforest can range from as high as 100 percent at night to less than 30 percent at midday. ▸

Fluctuating temperatures and humidity, intense sunlight, torrential rains and winds can create "unpredictable microclimates" and eddies of wind that move trees and pump air and nutrients into canopy in an "accordion-like" fashion. [Source: Carol Kaesuk Yoon, New York Times, November 22, 1994; "Forest Canopies" Dr. Nadkarni, Academic Press]

Effects of Global Warming on the Rainforest

In rainforests global warming could actually cause a cooling trend in the day as more clouds might be generated by a warming affect. More clouds could cause higher temperatures at night as clouds keep warm air from escaping into space. This in turn could cause more rain. In deforested areas however global warming could cause not only hotter temperature but also less precipitation as there are less trees to give off water by transpiration.

Global warming is already believed to be affecting the world’s rainforests. Studies have shown that even pristine areas untouched by deforestation, logging and other human intrusions are showing changes. One study published in Nature found that tree growth patterns during the past 20 years have been dramatically different growth patterns in previous 20-year period, with large trees in the Amazon rainforests growing more quickly and smaller trees growing more slowly. Scientist theorize that extra carbon dioxide is “fertilizing” the trees, accelerating their growth and blocking out the sun for smaller trees and other plants.

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Global warming could set off a chain reaction with deforestation resulting in more carbon dioxide in the atmosphere and the increased heating causing the rainforest to dry and shrink resulting in even more carbon dioxide in the atmosphere.

Image Source: Mongabay ; Wikimedia Commons

Text Sources: “The Private Life of Plants: A Natural History of Plant Behavior” by David Attenborough (Princeton University Press, 1997); National Geographic articles. Also the New York Times, Washington Post, Los Angeles Times, Smithsonian magazine, Natural History magazine, Discover magazine, Times of London, The New Yorker, Time, Newsweek, Reuters, AP, AFP, Lonely Planet Guides, Compton’s Encyclopedia and various books and other publications.

Last updated March 2011

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