A rainforest is an area of tall trees and a high amount of rainfall.
6 - 12
Biology, Ecology, Geography
A rainforest is an area of tall, mostly evergreen trees and a high amount of rainfall. Rainforests are Earth’s oldest living ecosystems, with some surviving in their present form for at least 70 million years. They are incredibly diverse and complex, home to more than half of the world’s plant and animal species—even though they cover just 6% of Earth’s surface. This makes rainforests astoundingly dense with flora and fauna; a 10-square-kilometer (4-square-mile) patch can contain as many as 1,500 flowering plants, 750 species of trees, 400 species of birds and 150 species of butterflies. Rainforests thrive on every continent except Antarctica. The largest rainforests on Earth surround the Amazon River in South America and the Congo River in Africa. The tropical islands of Southeast Asia and parts of Australia support dense rainforest habitats. Even the cool evergreen forests of North America’s Pacific Northwest and Northern Europe are a type of rainforest. Rainforests’ rich biodiversity is incredibly important to our well-being and the well-being of our planet. Rainforests help regulate our climate and provide us with everyday products. Unsustainable industrial and agricultural development, however, has severely degraded the health of the world’s rainforests. Citizens, governments, intergovernmental organizations, and conservation groups are working together to protect these invaluable but fragile ecosystems. Rainforest Structure Most rainforests are structured in four layers: emergent, canopy, understory, and forest floor. Each layer has unique characteristics based on differing levels of water, sunlight, and air circulation. While each layer is distinct, they exist in an interdependent system: processes and species in one layer influence those in another. Emergent Layer The top layer of the rainforest is the emergent layer. Here, trees as tall as 60 meters (200 feet) dominate the skyline. Foliage is often sparse on tree trunks, but spreads wide as the trees reach the sunny upper layer, where they photosynthesize the sun’s rays. Small, waxy leaves help trees in the emergent layer retain water during long droughts or dry seasons. Lightweight seeds are carried away from the parent plant by strong winds. In the Amazon rainforest, the towering trees of the emergent layer include the Brazil nut tree and the kapok tree. The Brazil nut tree, a vulnerable species, can live up to 1,000 years in undisturbed rainforest habitats. Unlike many rainforest species, both the Brazil nut tree and the kapok tree are deciduous—they shed their leaves during the dry season. Animals often maneuver through the emergent layer’s unstable topmost branches by flying or gliding. Animals that can’t fly or glide are usually quite small—they need to be light enough to be supported by a tree’s slender uppermost layers. The animals living in the emergent layer of the Amazon rainforest include birds, bats, gliders, and butterflies. Large raptors, such as white-tailed hawks and harpy eagles, are its top predators. In rainforests on the island of New Guinea, pygmy gliders populate the emergent layer. Pygmy gliders are small rodents that get their name from the way flaps of skin between their legs allow them to glide from branch to branch. Bats are the most diverse mammal species in most tropical rainforests, and they regularly fly throughout the emergent, canopy, and understory layers. One of the world’s largest species of bat, the Madagascan flying fox (found on the African island of Madagascar), for instance, is an important pollinator that mainly feeds on juice from fruit, but will chew flowers for their nectar. Canopy Layer Beneath the emergent layer is the canopy, a deep layer of vegetation roughly 6 meters (20 feet) thick. The canopy’s dense network of leaves and branches forms a roof over the two remaining layers. The canopy blocks winds, rainfall, and sunlight, creating a humid, still, and dark environment below. Trees have adapted to this damp environment by producing glossy leaves with pointed tips that repel water. While trees in the emergent layer rely on wind to scatter their seeds, many canopy plants, lacking wind, encase their seeds in fruit. Sweet fruit entices animals, which eat the fruit and deposit seeds on the forest floor as droppings. Fig trees, common throughout most of the world’s tropical rainforests, may be the most familiar fruit tree in the canopy. With so much food available, more animals live in the canopy than any other layer in the rainforest. The dense vegetation dulls sound, so many—but not all—canopy dwellers are notable for their shrill or frequent vocalizing. In the Amazon rainforest, canopy fruit is snatched up in the large beaks of screeching scarlet macaws and keel-billed toucans, and picked by barking spider and howler monkeys. The silent two-toed sloth chews on the leaves, shoots, and fruit in the canopy. Thousands and thousands of insect species can also be found in the canopy, from bees to beetles, borers to butterflies. Many of these insects are the principal diet of the canopy’s reptiles, including the "flying" draco lizards of Southeast Asia. Understory LayerLocated several meters below the canopy, the understory is an even darker, stiller, and more humid environment. Plants here, such as palms and philodendrons, are much shorter and have larger leaves than plants that dominate the canopy. Understory plants’ large leaves catch the minimal sunlight reaching beyond the dense canopy. Understory plants often produce flowers that are large and easy to see, such as Heliconia, native to the Americas and the South Pacific. Others have a strong smell, such as orchids. These features attract pollinators even in the understory’s low-light conditions. The fruit and seeds of many understory shrubs in temperate rainforests are edible. The temperate rainforests of North America, for example, bloom with berries. Animals call the understory home for a variety of reasons. Many take advantage of the dimly lit environment for camouflage. The spots on a jaguar (found in the rainforests of Central and South America) may be mistaken for leaves or flecks of sunlight, for instance. The green mamba, one of the deadliest snakes in the world, blends in with foliage as it slithers up branches in the Congo rainforest. Many bats, birds, and insects prefer the open airspace the understory offers. Amphibians, such as dazzlingly colored tree frogs, thrive in the humidity because it keeps their skin moist. Central Africa’s tropical rainforest canopies and understories are home to some of the most endangered and familiar rainforest animals—such as forest elephants, pythons, antelopes, and gorillas. Gorillas, a critically endangered species of primate, are crucial for seed dispersal. Gorillas are herbivores that move throughout the dark, dense rainforest as well as more sun-dappled swamps and jungles. Their droppings disperse seeds in these sunny areas where new trees and shrubs can take root. In this way, gorillas are keystone species in many African rainforest ecosystems. Forest Floor Layer The forest floor is the darkest of all rainforest layers, making it extremely difficult for plants to grow. Leaves that fall to the forest floor decay quickly. Decomposers, such as termites, slugs, scorpions, worms, and fungi, thrive on the forest floor. Organic matter falls from trees and plants, and these organisms break down the decaying material into nutrients. The shallow roots of rainforest trees absorb these nutrients, and dozens of predators consume the decomposers! Animals such as wild pigs, armadillos, and anteaters forage in the decomposing brush for these tasty insects, roots and tubers of the South American rainforest. Even larger predators, including leopards, skulk in the darkness to surprise their prey. Smaller rodents, such as rats and lowland pacas (a type of striped rodent indigenous to Central and South America), hide from predators beneath the shallow roots of trees that dominate the canopy and emergent layer. Rivers that run through some tropical rainforests create unusual freshwater habitats on the forest floor. The Amazon River, for instance, is home to the boto, or pink river dolphin, one of the few freshwater dolphin species in the world. The Amazon is also home to black caimans, large reptiles related to alligators, while the Congo River is home to the caimans’ crocodilian cousin, the Nile crocodile. Types of Rainforests Tropical RainforestsTropical rainforests are mainly located between the latitudes of 23.5°N (the Tropic of Cancer) and 23.5°S (the Tropic of Capricorn)—the tropics. Tropical rainforests are found in Central and South America, western and central Africa, western India, Southeast Asia, the island of New Guinea, and Australia. Sunlight strikes the tropics almost straight on, producing intense solar energy that keeps temperatures high, between 21° and 30°C (70° and 85°F). High temperatures keep the air warm and wet, with an average humidity of between 77% and 88%. Such humid air produces extreme and frequent rainfall, ranging between 200-1000 centimeters (80-400 inches) per year. Tropical rainforests are so warm and moist that they produce as much as 75% of their own rain through evaporation and transpiration. Such ample sunlight and moisture are the essential building blocks for tropical rainforests’ diverse flora and fauna. Roughly half of the world’s species can be found here, with an estimated 40 to 100 or more different species of trees present in each hectare. Tropical rainforests are the most biologically diverse terrestrial ecosystems in the world. The Amazon rainforest is the world’s largest tropical rainforest. It is home to around 40,000 plant species, nearly 1,300 bird species, 3,000 types of fish, 427 species of mammals, and 2.5 million different insects. Red-bellied piranhas and pink river dolphins swim its waters. Jewel-toned parrots squawk and fly through its trees. Poison dart frogs warn off predators with their bright colors. Capuchin and spider monkeys swing and scamper through the branches of the rainforest’s estimated 400 billion trees. Millions of mushrooms and other fungi decompose dead and dying plant material, recycling nutrients to the soil and organisms in the understory. The Amazon rainforest is truly an ecological kaleidoscope, full of colorful sights and sounds. Temperate Rainforests Temperate rainforests are located in the mid-latitudes, where temperatures are much more mild than the tropics. Temperate rainforests are found mostly in coastal, mountainous areas. These geographic conditions help create areas of high rainfall. Temperate rainforests can be found on the coasts of the Pacific Northwest in North America, Chile, the United Kingdom, Norway, Japan, New Zealand, and southern Australia. As their name implies, temperate rainforests are much cooler than their tropical cousins, averaging between 10° and 21°C (50° and 70°F). They are also much less sunny and rainy, receiving anywhere between 150-500 centimeters (60-200 inches) of rain per year. Rainfall in these forests is produced by warm, moist air coming in from the coast and being trapped by nearby mountains. Temperate rainforests are not as biologically diverse as tropical rainforests. They are, however, home to an incredible amount of biological productivity, storing up to 500-2000 metric tons of leaves, wood, and other organic matter per hectare (202-809 metric tons per acre). Cooler temperatures and a more stable climate slow down decomposition, allowing more material to accumulate. The old-growth forests of the Pacific Northwest, for example, produce three times the biomass (living or once-living material) of tropical rainforests. This productivity allows many plant species to grow for incredibly long periods of time. Temperate rainforest trees such as the coast redwood in the U.S. state of California and the alerce in Chile are among the oldest and largest tree species in the world. The animals of the temperate rainforest are mostly made up of large mammals and small birds, insects, and reptiles. These species vary widely between rainforests in different world regions. Bobcats, mountain lions, and black bears are major predators in the rainforests of the Pacific Northwest. In Australia, ground dwellers such as wallabies, bandicoots, and potoroos (small marsupials that are among Australia’s most endangered animals) feast on the foods provided by the forest floor. Chile’s rainforests are home to a number of unique birds such as the Magellanic woodpecker and the Juan Fernández firecrown, a hummingbird species that has a crown of color-changing feathers. People and the Rainforest Rainforests have been home to thriving, complex communities for thousands of years. For instance, unique rainforest ecosystems have influenced the diet of cultures from Africa to the Pacific Northwest. MbutiThe Mbuti, a community indigenous to the Ituri rainforest in Central Africa, have traditionally been hunter-gatherers. Their diet consists of plants and animals from every layer of the rainforest. From the forest floor, the Mbuti hunt fish and crabs from the Ituri River (a tributary of the Congo), as well as gather berries from low-lying shrubs. The giant forest hog, a species of wild boar, is also frequently targeted by Mbuti hunters, although this species is hunted for sale more often than food. From the understory, the Mbuti may gather honey from bee hives, or hunt monkeys. From the canopy and emergent layers, Mbuti hunters may set nets or traps for birds. Although they are a historically nomadic society, agriculture has become a way of life for many Mbuti communities today as they trade and barter with neighboring agricultural groups such as the Bantu for crops such as manioc, nuts, rice, and plantains. ChimbuThe Chimbu people live in the highland rainforest on the island of New Guinea. The Chimbu practice subsistence agriculture through shifting cultivation. This means they have gardens on arable land that has been cleared of vegetation. A portion of the plot may be left fallow for months or years. The plots are never abandoned and are passed on within the family. Crops harvested in Chimbu garden plots include sweet potatoes, bananas, and beans. The Chimbu also maintain livestock, particularly pigs. In addition to their own diet, pigs are valuable economic commodities for trade and sale. TlingitThe temperate rainforest of the northwest coast of North America is the home of the Tlingit. The Tlingit enjoy a diverse diet, relying on both marine and freshwater species, as well as game from inland forests. Due to bountiful Pacific inlets, rivers, and streams, the traditional Tlingit diet consists of a wide variety of aquatic life: crab, shrimp, clams, oysters, seals, and fish such as herring, halibut, and, crucially, salmon. Kelps and other seaweeds can be harvested and eaten in soups or dried. One familiar Tlingit saying is “When the tide is out, our table is set.” In more inland areas, historic Tlingit hunters may have targeted deer, elk, rabbit, and mountain goats. Plants gathered or harvested include berries, nuts, and wild celery. YanomamiThe Yanomami are a people and culture native to the northern Amazon rainforest, spanning the border between Venezuela and Brazil. Like the Chimbu, the Yanomami practice both hunting and shifting-cultivation agriculture. Game hunted by the Yanomami include deer, tapirs (an animal similar to a pig), monkeys, birds, and armadillos. The Yanomami have hunting dogs to help them search the understory and forest floor for game. The Yanomami practice slash-and-burn agriculture to clear the land of vegetation prior to farming. Crops grown include cassava, banana, and corn. In addition to food crops, the Yanomami also cultivate cotton, which is used for hammocks, nets, and clothing. Benefits of Rainforests Ecological Well-BeingRainforests are critically important to the well-being of our planet. Tropical rainforests encompass approximately 1.2 billion hectares (3 billion acres) of vegetation and are sometimes described as the Earth’s thermostat. Rainforests produce about 20% of our oxygen and store a huge amount of carbon dioxide, drastically reducing the impact of greenhouse gas emissions. Massive amounts of solar radiation are absorbed, helping regulate temperatures around the globe. Taken together, these processes help to stabilize Earth’s climate. Rainforests also help maintain the world’s water cycle. More than 50% of precipitation striking a rainforest is returned to the atmosphere by evapotranspiration, helping regulate healthy rainfall around the planet. Rainforests also store a considerable percentage of the world’s freshwater, with the Amazon Basin alone storing one-fifth. Human Well-BeingRainforests provide us with many products that we use every day. Tropical woods such as teak, balsa, rosewood, and mahogany are used in flooring, doors, windows, boatbuilding, and cabinetry. Fibers such as raffia, bamboo, kapok, and rattan are used to make furniture, baskets, insulation, and cord. Cinnamon, vanilla, nutmeg, and ginger are just a few spices of the rainforest. The ecosystem supports fruits including bananas, papayas, mangos, cocoa and coffee beans. Rainforests also provide us with many medicinal products. According to the U.S. National Cancer Institute, 70% of plants useful in the treatment of cancer are found only in rainforests. Rainforest plants are also used in the creation of muscle relaxants, steroids, and insecticides. They are used to treat asthma, arthritis, malaria, heart disease, and pneumonia. The importance of rainforest species in public health is even more incredible considering that less than one percent of rainforest species have been analyzed for their medicinal value. Even rainforest fungi can contribute to humanity’s well-being. A mushroom discovered in the tropical rainforest of Ecuador, for example, is capable of consuming polyurethane—a hard, durable type of plastic used in everything from garden hoses to carpets to shoes. The fungi can even consume the plastic in an oxygen-free environment, leading many environmentalists and businesses to invest in research to investigate if the fungi can help reduce waste in urban landfills. Threats to Rainforests Rainforests are disappearing at an alarmingly fast pace, largely due to human development over the past few centuries. Once covering 14% of land on Earth, rainforests now make up only 6%. Since 1947, the total area of tropical rainforests has probably been reduced by more than half, to about 6.2 to 7.8 million square kilometers (3 million square miles). Many biologists expect rainforests will lose 5-10% of their species each decade. Rampant deforestation could cause many important rainforest habitats to disappear completely within the next hundred years. Such rapid habitat loss is due to the fact that 40 hectares (100 acres) of rainforest are cleared every minute for agricultural and industrial development. In the Pacific Northwest’s rainforests, logging companies cut down trees for timber while paper industries use the wood for pulp. In the Amazon rainforest, large-scale agricultural industries, such as cattle ranching, clear huge tracts of forests for arable land. In the Congo rainforest, roads and other infrastructure development have reduced habitat and cut off migration corridors for many rainforest species. Throughout both the Amazon and Congo, mining and logging operations clear-cut to build roads and dig mines. Some rainforests are threatened by massive hydroelectric power projects, where dams flood acres of land. Development is encroaching on rainforest habitats from all sides. Economic inequalities fuel this rapid deforestation. Many rainforests are located in developing countries with economies based on natural resources. Wealthy nations drive demand for products, and economic development increases energy use. These demands encourage local governments to develop rainforest acreage at a fraction of its value. Impoverished people who live on or near these lands are also motivated to improve their lives by converting forests into subsistence farmland. Rainforest Conservation Many individuals, communities, governments, intergovernmental organizations, and conservation groups are taking innovative approaches to protect threatened rainforest habitats. Many countries are supporting businesses and initiatives that promote the sustainable use of their rainforests. Costa Rica is a global pioneer in this field, investing in ecotourism projects that financially contribute to local economies and the forests they depend on. The country also signed an agreement with an American pharmaceutical company, Merck, which sets aside a portion of the proceeds from rainforest-derived pharmaceutical compounds to fund conservation projects. Intergovernmental groups address rainforest conservation at a global scale. The United Nations’ REDD (Reducing Emissions from Deforestation and forest Degradation) Program, for example, offers financial incentives for reducing carbon emissions created by deforestation to 58 member countries. The Democratic Republic of the Congo used REDD funds to create an online National Forest Monitoring System that tracks and maps data on logging concessions, deforestation in protected areas, and national forestry sector measures. REDD funds were also used to investigate best practices in solving land disputes in Cambodia, which lacks proper forest zoning and boundary enforcement. Nonprofit organizations are tackling rainforest conservation through a variety of different approaches. The Rainforest Trust, for example, supports local conservation groups around the world in purchasing and managing critically important habitats. In Ecuador, the Rainforest Trust worked with the Fundación Jocotoco to acquire 495 more hectares (1,222 more acres) for the Río Canandé Reserve, considered to have one of the highest concentrations of endemic and threatened species in the world. Partnering with Burung Indonesia, the Trust created a 8,900-hectare (22,000-acre) reserve on Sangihe Island to protect the highest concentration of threatened bird species in Asia. The Rainforest Alliance is a nonprofit organization that helps businesses and consumers know that their products conserve rather than degrade rainforests. Products that bear the Rainforest Alliance seal contain ingredients from farms or forests that follow strict guidelines designed to support the sustainable development of rainforests and local communities. The Alliance also allows tourism businesses use of their seal after they complete an education program on efficiency and sustainability. In turn, this seal allows tourists to make ecologically smart vacation plans.
Drip Tips Many plants in the humid rain forest canopy are pointed, so that rain can run off the tips of the leaves. These “drip tips” keep the leaves dry and free of mold.
Jungles and Rain Forests Jungles and rain forests are very, very similar. The main difference is that rain forests have thick canopies and taller trees. Jungles have more light and denser vegetation in the understory.
Slow Rain Rain forests are so densely packed with vegetation that a drop of rain falling from the forest’s emergent layer can take 10 minutes to reach the forest floor.
Species-Rich, Soil-Poor The soil of most tropical rain forests contains few nutrients. The rich biodiversity in the canopy and quick decomposition from fungi and bacteria prevent the accumulation of nutrient-rich humus. Nutrients are confined to the rain forest’s thin layer of topsoil. For this reason, most of the towering trees in tropical rain forests have very shallow, widespread root systems called “buttress roots.”
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May 20, 2022
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