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Welcome to my jungle ... before it's gone. (Rainforests).

What does hot fudge have in common with paint thinner, or chewing gum with some lifesaving medicines? Many of their ingredients come only from tropical rainforests.

Rainforests occupy merely 7 percent of Earth's land area, but harbor at least 50 percent of all plant and animal species on the planet. Rainforests are also indispensable in maintaining the complex balance of Earth's climate. But humans are decimating these dense tropical jungles at a startling rate. A new study by U.S. and Brazilian scientists based on 20 years of satellite images shows that Amazon deforestation has accelerated since 1995 to nearly 5 million acres a year. "That's equivalent to seven football fields a minute!" says study leader William Laurance of the Smithsonian Tropical Research Institute.

Many scientists now think that unless the trend is drastically reversed, all rainforests could vanish from Earth by 2050.


Appropriately named, rainforests get more rain than any other habitat--"around 400 inches of rainfall per year, so they're wet almost year round," says Mohamed Bakarr, a senior technical director at Conservation International in Washington, DC.

Called the "emerald circle," a lush belt of greenery encircles Earth's equator--the tropical rainforests of Asia, Africa, and Central and South America. They date back 70 to 100 million years, according to fossil records. The Amazon River Basin rainforest blankets nearly 5.18 million square kilometers (2 million square miles) of Brazil, Ecuador, and Peru--nearly one half of all tropical rainforests worldwide.


Elaborate layers of rainforest foliage let water filter down from 61-meter (200-foot)-tall trees to short shrubs on the forest floor. Large leaves at the top are specialized to trap rainwater, Bakarr explains: "Then water percolates slowly down to the soil." A maze of roots siphons water from soil to feed shrubs, plants, vines, and trees, "so you don't get much soil erosion." he says. But take away the healthy maze of roots that prevents erosion, and the result is excess water runoff, eroded soil, and an unstable rainforest.

Open pores on the surfaces of leaves release unused water into the atmosphere as vapor in a process called transpiration--as if trees and plants were sweating in the tropical sun. Water vapor then collects in clouds until it rains again, completing the rainforest water cycle (see diagram).


Along with other types of woodlands, tropical rainforests help maintain Earth's livable climate by regulating the exchange of water and carbon between Earth and sky. Not only do trees and plants soak up moisture and release water vapor; they absorb hot sunlight and remove carbon dioxide (C[O.sub.2])--a gas that in excess contributes to global warming--from the atmosphere (see SW 9/3/01).

Trees act as natural carbon sponges. "Forest growth may absorb as much as 25 percent of all carbon released by fossil fuel [oil, gas, coal] burning," explains Susan Trumbore, an earth system scientist at the University of California, Irvine. Through the process of photosynthesis, trees use sunlight to convert C[O.sub.2] and water into plant food. Then they respire, or release, some absorbed carbon into the air.

But trees also store large quantities of carbon in leaves and wood as they grow; young growing forests store more carbon than they emit. "When a plot of land in the Amazon is cut and burned, for example, it releases carbon stored over centuries," says Trumbore. "It takes only one year's worth of emissions from three SUVs to equal the amount of carbon stored in two acres of rainforest." Result: even more C[O.sub.2] floods the atmosphere.

Rainforests also support mind-boggling numbers of plants and animals endemic--found nowhere else--to these warm, wet regions. "Planet Earth could hardly be called healthy if it lost half of all species of plants and animals," says Dian Jukofsky, director of neotropical communications at the Rainforest Alliance in New York City. One 10.3 sq km (4 sq mi) plot of rainforest contains 400 bird species, 100 species of reptiles, and 60 amphibian species, estimates The National Academy of Sciences.

The Amazon rainforest alone contains roughly 30,000 species of plants. Many plants provide chemicals essential for medicines used to treat illnesses ranging from motion sickness to cancer. Even more common are rainforest fruits, nuts, and oils that help feed the world: bananas, coffee, orange juice, Brazil nuts, mangoes, and of course chocolate, to name a few.


The sheer size of the Amazon rainforest has already been slashed by nearly 25 percent, says environmental scientist James Alcock at Penn State University--nearly 2,000 trees are cut down per minute! In some cases, highways, railroads, and grazing land replace the forest, especially as the Brazilian government tries to boost the agricultural, timber, and mining sectors of its economy. "The scariest thing is that many highways, railroads, and dams will penetrate right into the pristine heart of the Amazon," says William Laurance.

The Timber industry relies on rainforest trees to provide woods like teak and mahogany for furniture and houses. Farmers clear land for grazing cattle by burning tracts of trees. "Most clear-cutting in the tropics is to convert land to agriculture," says Richard Donovan, chief of forestry for the Rainforest Alliance. But many wildlife species also lose out because their habitat is gone--roughly 100 species a day, claims the World Resources Institute. "If they can't find a new home, they're history," Donovan says.

To help reverse the crisis, he oversees the SmartWood program. "When a forest operation goes to cut down a tree, we ask that they understand how the tree will grow again and create conditions for new trees to grow." While many trees can regrow in 20 to 30 years, others like mahogany and teak take hundreds of years. "No one suggests that Brazil forego development in the Amazon," says Laurance. "But there are far less destructive ways to exploit the region. We are pushing for slower deforestation and more efficient use of existing agricultural lands than cattle ranching."


Nobody knows for sure. Researchers at Iowa State University were surprised to find that despite 40 years of tree-burning in the Amazon, rainfall has increased by 20 percent. "We expect this pattern may reverse," says study researcher Eugene Takle. "Then there may be drought never before experienced in this region."

"Because of the way tropical rainforests work, they're dependent on trees to return water to the air," explains James Alcock. In other words, a healthy rainforest is a vast, self-contained recycling system. "The interdependence of climate and forest means risks to the forests are much closer at hand than what we might expect," he adds. He thinks the Amazon rainforest could pass the point of no return within 10 to 15 years unless immediate actions are taken to curb the crisis. Otherwise, we face the death of one of Earth's invaluable treasures.


In most tropical rainforest, trees, shrubs, and vines coexist in several layers, or strata. Each layer is home to a dazzling array of rainforest creatures.


SUN WORSHIPERS: The tallest trees--mostly broad-leaved, hardwood evergreens--tower 61-meters (200-feet) high. In the Amazon Basin water cycle, foliage transpires or releases half of all rainfall. Twenty-five percent evaporates; the remainder runs off into rivers.


UP ON THE ROOF: The canopy acts as a "roof" over two bottom layers. Like a leafy umbrella 30 to 46 m (100 to 150 ft) high, this layer collects the most sunlight and rain to fuel new forest growth. The trees have mostly oval pointed leaves, and attract snakes, frogs, and flying squirrels.


LOW LIGHT: Little sunlight reaches the understory, which hovers 3 to 6 m(10 to 20 ft) above the forest floor. Plants rarely grow to 3.6 m (12 ft) and boast larger leaves to absorb the low light. Residents include jaguars, parakeets, tree frogs, and lots of insects.


ROCK BOTTOM: Few plants grow on the dark forest floor--totally shaded by overhanging shrubs and vines. Still, this layer bursts with nutrients as leaves and other debris quickly decompose, or break down. Taller tree roots lie shallow within the soil to quickly absorb nutrients and water.



Even if you don't live near a rainforest, there's a lot you can do as a consumer to help slow their demise:

* Look for certified rainforest products. Chiquita bananas recently got a "thumbs up" from the Rainforest Alliance's Better Banana Project--a seal of good farming practices.

* Conserve natural resources like water and energy. It may be impossible to believe, but it's true: A cleaner planet where you live improves the climate that endangers rainforests.

* Don't buy trinkets made from endangered plants and animals. The more you know about a product, the better equipped you are to save the rainforests.



A terrarium is a landscape in a jar. It contains its own soil, plants, air, food, and water.


large clear plastic or glass container with tight-fitting lid * aquarium gravel * potting soil * small tropical plants * stones, shells, or plastic/ceramic animals


1 Line the container with a 2.5-centimeter (1-inch) layer of gravel. Then fill the bottom 1/4 of the container with soil.

2 Make a hole in the soil for each plant. Set in the plant and press sod over the roots.

3 Soak a sponge in water and squeeze it around the plants until the soil is slightly moist. Repeat. But don't over-water plants.

4 Clean dirt particles off the sides of the terrarium. Add decorations and close the lid.

5 Set terrarium aside for one day. Don't place in direct sunlight; it will overheat. After a day your terrarium should have a bit of water condensed inside its walls. If not, squeeze more water onto the soil. If the walls are completely fogged, remove the lid for a few hours.

6 Once you balance the moisture, the terrarium will create its own "rain cycle."

CONCLUSIONS: Why don't you need to remove leaves that die and fall off your plants? How is condensation in a terrarium like rain?

Lesson Plans


Cross-Curricular Connection

Social Studies: Divide the class into two groups: environmentalists and industrialists. Research each group's interest in and plans for the rainforests. Debate. Then discuss possible compromises.

Did You Know?

* The U.S. National Cancer Institute has identified 3,000 plants that have cancer-fighting properties--70 percent of these plants grow in the rainforest. Twenty-five percent of the active ingredients found in today's cancer-fighting drugs are derived from organisms endemic to rainforests.

* Most of the nutrients of a rainforest ecosystem are stored in its vegetation rather than in its soil.

* In most tropical countries only one tree is replanted for every 10 cut. And in some countries, the rate is 1 tree planted for 30 cut.

National Science Education Standards

Grades 5-8: populations and ecosystems * diversity and adaptations of organisms * structure of the Earth system * populations, resources, and environments * natural hazards * risks and benefits

Grades 9-12: the cell * interdependence of organisms * energy in the Earth system * natural resources * natural and human-induced hazards * environmental quality


To learn more about rainforests visit the Web sites of these organizations.

Rainforest Action Network:

Rainforest Alliance:

Conservation International:

Earth Foundation:

Environmental Defense Fund:


Directions: Answer the following questions in complete sentences.

1. What is a rainforest?

2. What are rainforest strata? Name them.

3. How and why are rainforests destroyed?

4. Even if you don't live near a rainforest, how does its destruction affect your life?


Answers will vary but should include the following points and definitions.

1. Rainforests get around 400 inches of rainfall per year, more than any other habitat on Earth. They're located in the "emerald circle," a lush belt of greenery that encircles Earth's equator. The majority of rainforests is found in Central and South America, Africa, Southeast Asia, and date back 70 to 100 million years.

2. The strata are rainforest layers. They are the emergent layer, canopy layer, understory layer, and forest floor.

3. Rainforests are destroyed through clear cutting and burning of trees, they're most often destroyed for logging, highway and railroad construction, and for farming and grazing land.

4. Rainforests help maintain Earth's climate by regulating the exchange of water and carbon between Earth and sky. Without these regions, more C[O.sub.2] -- a prime culprit in global warming -- remains in the atmosphere. Also, a wide diversity of plants is endemic to rainforests. Many of these plants provide chemicals essential for medicines used to treat illnesses. Rainforests also provide food products such as bananas, coffee, orange juice, nuts, mangoes, and chocolate.
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Article Details
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Author:de Seve, Karen
Publication:Science World
Article Type:Statistical Data Included
Date:Mar 11, 2002
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