Where are tropical rainforests found?
Tropical rainforests are located around the equator where temperatures stay near 80 degrees year round. Rainforests receive 160 to 400 inches (400-1000 cm) of rain each year. The largest rainforests are in Brazil (South America), Zaire (Africa) and Indonesia (South East Asia). Other tropical rainforest places are in Hawaii and the islands of the Pacific & Caribbean.
What is the tropical rainforest?
The Tropical Rainforest is a forest occurring in tropical areas of heavy rainfall. It is abundant with many species of wildlife and vegetation. Rainforests cover less than two percent of the Earth’s surface. They are home to some 50 to 70 percent of all life forms on our planet. Rainforests are the most productive and most complex ecosystems on Earth.
What is the structure of vegetation in the rainforest?
The image shows a typical cross section in the rainforest.
- Emergents are the tallest trees and are usually over 50 metres tall. The Kapok tree is an example of an emergent.
- The sea of leaves blocking out the sun from the lower layers is called the canopy. The canopy contains over 50% of the rainforest wildlife. This includes birds, snakes and monkeys. Lianas (vines) climb to the canopy to reach this sun light.
- The under canopy mainly contains bare tree trunks and lianas.
- The shrub layer has the densest plant growth. It contains shrubs and ferns and other plants needing less light. Saplings of emergents and canopy trees can also be found here.
- The forest floor is usually dark and damp. It contains a layer of rotting leaves and dead animals called litter. This decomposes rapidly (within 6 weeks) to form a thin humus, rich in nutrients.
How did the tropical rainforest get like this?
The high rainfall and year-round high temperatures are ideal conditions for vegetation growth. The wide range of plants encourage a huge variety of insects, birds and animals.igh rainfall and year-round high temperatures are ideal conditions for vegetation growth. The wide range of plants encourage a huge variety of insects, birds and animals.
How has vegetation adapted to the climate?
In the tropical rainforest most trees in the rainforest have wide buttress roots. This is to support them as they grow incredibly tall (over 200ft in some cases) as there is great competition for sunlight. Lianas (vines) grow around trees as they bid to reach sunlight. The leaves of many trees are waxy and have drip tips to allow water to run off them (so that water does not gather on leaves and cause them to rot, it also allows water to reach the roots on the forest floor). Leaf stems are also flexible to allow leaves to move with the sun to maximise photosynthesis.
What is the impact of humans on the tropical rainforest?
Deforestation (cutting down trees) is a major problem caused by humans in the tropical rainforest. Global Rates of Deforestation:
- 2.47 acres (1 hectare) per second: equivalent to two U.S. football fields
- 150 acres (60 hectares) per minute
- 214,000 acres (86,000 hectares) per day: an area larger than New York City
- 78 million acres (31 million hectares) per year: an area larger than Poland
The image shows some of the causes and effects of deforestation in the Amazon Rainforest.
Slash and burn
Most clearances are still by the local people and tribes needing land on which to grow crops. They clear the forest by ‘slash and burn’. Vegetation is cut down and then burned. The ash acts like a fertiliser adder nutrients to the soil. When the soil begins to turn infertile (usually after 3-5 years) the people move on. This is called shifting cultivation. It is a sustainable method of farming in the rainforest. It ensures the forest will recover.
The Transamazon Highway has allowed increased access to the Amazon Rainforest.
Commercial logging is the major cause of primary rainforest destruction in South East Asia and Africa. World wide, it is responsible for the destruction of 5 million ha. per year. Logging roads enable landless people to enter the forest. In Africa, 75% of land being cleared by peasant farmers is land that has been previously logged.
Ranching is a major cause of deforestation, particularly in Central and South America. In Central America, two-thirds of lowland tropical forests have been turned into pasture since 1950.
An unlimited supply of water and ideal river conditions have led to the development of hydro electric power stations (HEP Stations).
There are nearly 3 million landless people in Brazil alone. The government has cleared large areas of the Amazon Rainforest and encouraged people to move there. The scheme has not been successful. Farmers stay on the same land and attempt to farm it year after year. Nutrients in the soil are quickly exhausted as there is no longer a humus layer to provide nutrients. The soil becomes infertile and nothing will grow.
The mining of iron ore, bauxite , gold, oil and other minerals have benefited many LEDCs. However, it has also devastated large areas of rainforest e.g. The Amazon.
Deforestation is causing many problems at a range of scales:
- About 80% of the rainforests nutrients comes from trees and plants. That leaves 20% of the nutrients in the soil. The nutrients from the leaves that fall are instantly recycled back up into the plants and trees. When a rainforest is clear-cut, conditions change very quickly. The soil dries up in the sun. When it rains, it washes the soil away. The rainforest never fully recovers. Wildlife and plant life is reduced.
- Elimination of Indian groups and their way of life
- Estimates suggest that 80% of forest Indians have died since the arrival of Europeans in the sixteenth century. Most have died from western diseases such as malaria to which they have no immunity. Those remaining have been forced away by the construction of roads, ranches, mines and reservoirs
- When vegetation is removed soil is left exposed to the heavy equatorial rainfall. It is rapidly eroded. The removal of top soil means little vegetation will grow. Also, soil erosion leads to flooding as soil is deposited on river beds.
Deforestation can consume a country’s only natural resource. If deforestation is not managed in a sustainable manner a country’s only natural resource could be lost forever.
- Rainforest canopies absorb carbon dioxide which is a gas in the atmosphere. When the rainforests are burned and cleared, the carbon is released. Also, when trees are cut down they can no longer absorb carbon dioxide. This means more carbon dioxide is in the atmosphere. Carbon dioxide allows heat through the atmosphere (suns rays). However, it will not allow reflected energy to escape from the atmosphere. This is called the greenhouse effect and causes global warming.
What is the future for the tropical rainforest? – Sustainable Development
If development in the rainforest is to be sustainable (e.g. although the resources are used to aid development, it/they will still exist for future generations to use) a number of measures must be taken. These include:
- Afforestation – Trees should be replanted in areas of deforestation.
- Shifting Cultivation – Farmers should move on after 2-3 years to allow the rainforest to recover.
- Rubber tapping – More sustainable methods of exploiting the rainforest should be pursued e.g. rubber tapping
- Measuring trees – Trees should only be cut down when they reach a certain size. This will ensure younger trees survive longer and will encourage careful management of the rainforest.
It is a hot, moist biome found near Earth’s equator. The world’s largest tropical rainforests are in South America, Africa, and Southeast Asia. Tropical rainforests receive from 60 to 160 inches of precipitation that is fairly evenly distributed throughout the year. The combination of constant warmth and abundant moisture makes the tropical rainforest a suitable environment for many plants and animals. Tropical rainforests contain the greatest biodiversity in the world. Over 15 million species of plants and animals live within this biome.
The hot and humid conditions make tropical rainforests an ideal environment for bacteria and other microorganisms. Because these organisms remain active throughout the year, they quickly decompose matter on the forest floor. In other biomes, such as the deciduous forest, the decomposition of leaf litter adds nutrients to the soil. But in the tropical rainforest, plants grow so fast that they rapidly consume the nutrients from the decomposed leaf litter. As a result, most of the nutrients are contained in the trees and other plants rather than in the soil. Most nutrients that are absorbed into the soil are leached out by the abundant rainfall, which leaves the soil infertile and acidic.
Warm and wet describes the tropical rain forest climate. The average annual temperature is above 20C; there is never a frost. Rainfall varies widely from a low of about 250cm of rain per year to about 450 cm/year. That means a range from about 8 to 14 feet of rain per year.
As you can see from the map to the right, the tropical rainforests are, indeed, located in the tropics, a band around the equator from 23.5 N (the Tropic of Cancer) to 23.5 S (the Tropic of Capricorn) (red lines on map, right). Because the Earth tilts 23.5 degrees on its axis as it travels around the sun, at some point in the year (thesolstices, June 22nd in the north, December 22nd in the south) the sun will be directly overhead on one of these lines. At the equinoxes the sun is directly over the equator.
Within this band, solar radiation is most intense, and thus the surface of the planet warms the most. The warmth leads to a lot of evaporation, and as warm, moist air rises, it cools, the water condenses, and the water falls back to the earth as rain. Thus, the warmest areas of the planet also tend to be the wettest, and this sets the stage for the tropical rain forest.
Not all of the land in the tropics is tropical rainforest. Some areas are too cold (mountaintops), or are too dry (the far side of a mountain range from the ocean gets less rain). In some places there may be a lot of rain, but it falls seasonally and the long dry season prevents a tropical rainforest from developing.
Another biome similar to the tropical rain forest is the cloud forest. These forests form on mountaintops in the tropics; I have been to such forests in Jamaica and Costa Rica, and they exist in other mountainous areas as well. Because of their elevation, cloud forests are cooler than the tropical rain forests below them; much of the water there does not fall as rain but is instead wrested from the clouds by the plants living in the forest. These forests are critically endangered by global warming; as the planet warms tropical rainforest is able to move up the mountainsides and the cloud forests are displaced into smaller and smaller regions at the tips of the mountains – and if these mountaintops get too warm the entire cloud forest will be replaced by tropical rainforest. You can read more about cloud forests on this page from our trips to Costa Rica.
Tropical Rain Forest Distribution