The Amazonian rainforest is the largest in the world, covering most of the vast Amazon basin, chiefly in Brazil, but extending out to neighbouring countries. Its total area is approximately 4 million km². However, around 14% of the rainforest has already been deforested and this process continues at a rate of approximately 20,000km² a year. This Entry gives some of the characteristics of the Amazon rainforest, and adds details of some of the effects of deforestation.

Ecosystem

The rainforest climate is hot, wet and sticky - very humid. It rains every day, so regularly that you could set your watch by it. The rain comes down suddenly and stops just as suddenly. This is convectional rainfall, meaning that the Sun heats the ground, which heats the air nearest the ground causing it to expand and rise. When the air gets to a certain height it condenses to dew point and forms clouds, then it rains. Storms are common with convectional rainfall.

The plants in the rainforest have had to adapt to the unusual weather conditions in the forest. There are many different ways they have done this:

• Trees grow tall, up to 40m through the emergent layer, in order to get sunlight.

• Leaves have downward-curving tips so that rain drips off.

• The rainforest is deciduous, though it appears evergreen because the trees lose their leaves at different times.

• The trees are straight and only have branches at the top. They are supported by buttress roots.

• Rivers flood for a few months every year so the plants are adapted to handle the extra water without drowning.

• Undergrowth springs up wherever light can reach the forest floor.

• Fallen leaves and plant matter rot swiftly to provide nutrients for the rest of the plants.

• Lianas climb up trees to reach the light.

Millions of plants and animals coexist in the rainforest, such as leafcutter ants, shown in the picture. There are thousands of species as yet undiscovered by humans. Everything depends on all of the others. For example, here is one cycle:

• Trees and plants die.
• Dead organic material rots.
• The recovered nutrients help new trees and plants to grow.

Another example of interdependence is the weather: the rain provides water for all of the biotic community. The cycle of dependence is called an ecosystem.

Amazonian Indians

The native Amazonians live by a process called 'shifting cultivation': they live in one area and farm it, moving on when the land is no longer cultivable. This does not harm the forest, as it recovers. When the nutrients in the soil have depleted and growing the crops removes what little are left, that area will no longer grow enough food and the farmers have to move on. The rapid growth and rotting cycle of rainforest plants makes the situation more delicate.

The Indians build huge houses from wood and foliage. They cut down trees to extend the clearing and feed their fires. The ash provides nutrients for the soil. Then the women plant the crops (manioc, yams, beans and pumpkins). They do not just farm, they also fish and hunt. After four to five harvests, it is time to move on again. However, the increasing use of the Amazon by big business has reduced the size of land available for the Indians to farm. They therefore have to return to a previously used piece of land before it has fully recovered (which takes about 50 years). Indians are also in danger from Western diseases, against which they have no immunity.

Farming

Huge areas of Brazilian rainforest are being cleared to create agricultural land and animal pastures. In particular, cattle farming, typically done to make fast food products, is a very lucrative industry. To create enough pasture land for their cattle, ranch owners 'slash and burn' the forest: the trees and undergrowth are hacked down and burnt, after which the land is ready for use. However, when ranchers abandon this land, the forest takes a long time to grow back and when it does, it will be thick 'secondary jungle' rather than true rainforest.

Rainforest clearance is having a devastating effect on the environment: locally, because thousands of animals lose their habitats during this process; globally, because of its effect on climatic balance. During photosynthesis, trees take in carbon dioxide, a pollutant harmful to humans in large quantities. When there are fewer trees, there is more carbon dioxide. Much of the smoke produced in tree-burning escapes into the atmosphere where it adds to the carbon dioxide blanket over the Earth, stopping the heat from the Sun escaping the earth, adding to global warming. Rainforests, particularly the Amazon, have been described as the planet's lungs - it is small wonder there is now a Save the Rainforest movement.

A hamburger is cheap, quick food which is a enjoyed all over the world. However, is it worth it if it means running the risk of an irreversible change to the world's climate?

Mining

The mining industry is very important to the expanding Brazilian economy. Deposits of minerals known to exist in the Amazon Basin include diamonds, bauxite (aluminium ore), manganese, iron, tin, copper, lead and gold. The Brazilian Gold Rush began in 1980 when gold was discovered in Serra Palada in Palá state. Most of the incoming population (at least 250,000) worked for a low wage in very crowded, highly competitive gold mines.

The competition of mining for gold and other minerals has led to very lax environmental practices. Up to 9,000 tons of mercury, used in the mining process, has been washed into the region's rivers, along with huge quantities of sediment. The miners have also polluted the rivers with oil, litter and human sewage. All around the vicinity of the mines, vegetation, animals and settlements have been destroyed. While larger companies are beginning to take steps to protect the environment, such as landscaping and replanting, the impact on the area has already been severe.

Trans-Amazonian Highway

This is a vast road stretching for 5,300km across the Amazon region, construction of which began in the early 1970s. It stretches from Recife in the east to the Peruvian Andes in the west. It is the main east to west route across the rainforest and is crossed by north to south roads, some of which are made from gravel, though others are paved. There is also a railway and another one has been proposed. All of this is part of an ambitious Amazon development plan by the Brazilian government. Communications and power availability are being improved in addition to transport links, improving the local infrastructure. These developments facilitate logging, ranching and mining as transport of workers and materials becomes much easier and cheaper.

The disadvantages of this work are the environmental hazards. The road construction process, like mining, involves the use of many pollutants. Many trees have been cut down causing further loss of animal habitat. Also, as the rainforest is more and more 'opened up', its decimation increases further. At least one untouched rainforest tribe has been discovered every year of the project. Not only has their way of life been disrupted, but also their land has gone, not that they had any say in the matter.

HEP

As mentioned above, rainforest development requires power. The great rivers of the Amazon basin have a huge potential energy in the form of hydroelectric power, or HEP. Controversially, the Brazilian government plans to build 31 dams in the Amazon region by 2010. The biggest HEP project in the Amazon is the Tocantins River Basin Hydroelectric Project which plans to convert the Tocantins River into a series of lakes and hydroelectric dams, stretching for 1,200 miles and consisting of eight large dams and 19 smaller ones.

While these dams provide power and also irrigation, they do not create many jobs since it is expensive to employ workers to operate the site. Moreover, the amount of irreversible environmental damage they cause is huge. A typical dam site is a valley of primary rainforest, sometimes with an Indian village with farming land used for shifting cultivation (see above). The Indians depend on their land completely and use a river for washing, drinking and fishing. After the dam is built, the land slowly floods, driving the Indians away from the river¹ and eventually drowning their village and destroying the entire forest in the valley, endangering animal and plant species, and sometimes making them extinct.