The impact of human activity in tropical rainforests - examples from Madagascar.

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The impact of human activity in tropical rainforests

Impact of human activity: deforestation:

Destruction of the world’s tropical rainforests is a major environmental issue. Deforestation is the deliberate clearance of woodland by cutting, burning or the application of a defoliant, such as that used during the 1960s by American troops to clear the jungle in Vietnam.

In some developing countries and NICs, tropical rainforests, such as those in the Amazon basin in South America, and in Indonesia and Malaysia in the far east, are being destroyed at an alarming rate. There are claims that half of the world’s original rainforests have already been cleared, with an area the size of the UK being cleared every year. Climatic climax vegetation has been destroyed and this has resulted in both secondary succession and pagioclimax. The vegetation that eventually grows to replace the original rainforest tends to be smaller in height and less diverse, with a reduction in the overall biomass.

Causes of deforestation:

  • Demand for hardwood, such as teak, for building and furniture is increasing and many developing countries rely on export earnings from timber to help pay their debts and finance major development projects
  • Deforestation also occurs to provide land for rubber plantations, cattle ranches for beef farming, soya plantations, roads and railways
  • In the Brazilian rainforest, rivers have been dammed and large areas flooded to provide water for hydroelectric power stations- example of such a reservoir lies behind the Tucuruí dam on the Tocantins River in Amazonia.
  • Forest is also being cleared in Brazil for mining
  • There are vast resources of aluminium and iron ores in the ground beneath the rainforest and the Carajás mining project in Amazonia has resulted in the destruction of large areas of climax vegetation
  • Most countries with large areas of rainforest are still developing economically. During the 1960s and 70s, the population of southeast Asia and South America increased rapidly because birth rates exceeded death rates, and so population pressure led to increasing clearance of rainforest.
  • In Indonesia, the transmigration policy encouraged people to move from the overcrowded island of Java to less populated islands such as Sumatra, where rainforest was cleared away to make way for settlements and agriculture.
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Impacts of deforestation:

  • Impacts can be physical, economic, social and cultural, and mainly occur on a local scale, but some impacts can be global
  • As habitats shrink, plant species become endangered and the food chain within the forest is disrupted. Some animal species, for example orang-utans and tigers are threatened by extinction
  • The vegetation protects the latosol soils from the regular heavy tropical downpours. Once the trees are removed, the topsoil is open to erosion and to leaching of nutrients and minerals. Runoff causes sediment to block river channels and increases flooding
  • The microclimate of the forest is disturbed ...

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