The Amazon rainforest
The Amazon rainforest is a vast tropical rainforest that covers an area of 7 million km². About 60% of the Amazon forest is part of Brazil. The other 40% belongs to Colombia, Peru, Venezuela, Ecuador, Bolivia, Guiana, Suriname and French-Guiana. Most of the Amazon rainforest is found in the Amazon basin. This is the part of South America that is drained by the Amazon river and its more than 1000 tributaries.
Biodiversity
The Amazon rainforest has an extremely high biodiversity and many species are not yet known to science. Estimations of the number of plant and animal species vary widely. According to a recent publication by the WNF, the Amazon rainforest counts about 40.000 species, 427 mamal species, 1294 bird species, 378 species of reptile, 427 species of amphibians and 3000 species of fish. These are minimum figures as new species are discovered very often.
Vegetation types
The Amazon rainforest is characterised by high levels of precipitation. As a result of this, the landscape is green throughout the year. The Amazon rainforest can be subdivided in different vegetation types.
The largest part of the Amazon rainforest consists of terra firme forests. “Terra firme” means means “dry land”. These are forests that stay dry during the yearly flooding of the Amazon river. Most terra firme forests grow on soils that are that old that these are completely weathered. The red colour of these soils is caused by iron oxide, one of the stable minerals that stay behind long after other minerals leached away. These soils contain few plant nutrients. Because of the heat, organic litter is decomposed very rapidly and it is this process of decomposition that provides plants with the nutrients needed for growth.
A terra firme forest that is not yet disturbed by humans has a closed canopy at an altitude of 30-40 metres. Some trees are able to grow towards an altitude of 50 metres. Few light penetrates below the canopy. Most plants that grow on the forest floor are seedlings of trees and are waiting for the day that an opening in the canopy appears. Because of their adaptation to low light conditions, the young trees of some species differ that much from the adult trees that some of them where originally described as separate species. The few herbs that grow on the forest floor are adapted to low light conditions as well and have large, coloured leaves that capture the few light that is available. Because of the lack of light, the vegetation of the forest floor is open and accessible.
As the Amazon river has an extremely shallow gradient, the river is unable to transport sufficient water during the rain season. As a result of this, water levels rise several meters (up to 12 metres near Manaus). The Amazon basin has two types of forest that are seasonally inundated: the igapó forest and the várzea forest. The igapó forest grows along the black water rivers. The water of these rivers has a black colour that is caused by humic acid. This water is poor in nutrients. The várzea forests grows along the white water rivers that carry fertile sediment from the volcanic Andes mountains. The várzea forest has a higher species diversity than the igapó forest. Both forest types are adapted to annual flooding. The trees in these forests have thick, protective barks. If leaves are submerged, they stop their metabolism but the tree do not shed their leaves. The trees continue to flower and carry fruits above the waterline. Trees like the rubber tree even depend on the streaming water and on fruit eating fishes to spread the seeds.
Upstream, the lowland rainforest is replaced by the montane rainforest at an altitude of 1000 metres. The montane rainforest is more humid than the terra firme forest. Lights penetrates deeper into the forest because of its location on mountain slopes. Even higher are the cloud forest where the trees are surrounded by clouds.
Threats to the Amazon rainforest and wildlife conservation
Deforestation is the most important threat to the Amazon rainforest. The largest part of this deforestation happens illegally. The Brazilian government faces large difficulties in implementing the state of law in the Amazon basin because of the large distances. Except for illegal logging, there is also an illegal trade in animals.
Large parts of the Amazon are deforested in order to convert these into agricultural lands. Traditionally, farmers cleared small patches of forest for agriculture. After a few years, the soil fertility decreased and the farmer moved to another area. The former agricultural land was set aside and after a fallow of a few decades the land was once again fertile enough for agriculture. Due to the increased population, this system is no longer sustainable. Large scale, commercial cattle ranging also decreased the soil quality resulting in a need for new areas.
Contrary to what is often said and written, the cultivation of soya beans does not have a negative impact on the Amazon rainforest. At this moment, only a small part of the Brazilian soya bean production takes place on areas that where previously covered by Amazon rainforest. Most soya beans are grown outside the Amazon, especially in the Cerrado and the southern states of Paraná and Rio Grando do Sul. The cultivation of arable crops has expanded on former pastures, replacing unsustainable cattle ranging with sustainable arable agriculture. The sustainable use of land decreases the need to convert new areas into agriculture.
Although the Brazilian government has difficulties in protecting the Amazon rainforest, most Brazilians think that the rainforest should be protected. A growing number of wildlife reserves protects the Amazon rainforest. This includes a number of national parks that are protected by the Brazilian federal government, but also a large number of parks that are run by other organisations.
See also
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