Climat

[pic 1]

- The causes
 

* Deforestation is the removal of at least 90% of forest cover on a given surface.
 
* One of the first causes of deforestation is the logging. Heating the wood (or firewood) still constituted an important source of energy in developing countries, whose needs are amplified by population growth (60% of global wood consumption).
 
* Tropical forests are also rich in precious wood (teak, mahogany or balsa) overexploited in an intense trade with developed countries in relation to the economic difficulties many poor countries.
 
* Forest clearing for crops is another major cause of deforestation. It can be a slash and burn agriculture, still practiced in some areas: a parcel cleared by fire is cultivated for some years before being abandoned. In most cases, however, the clearing is to obtain farmland. Overgrazing (or overgrazing) is another factor in the disappearance of forests.
 
* Fires sometimes destroy large areas, like the fire that destroyed more than 37,000 sq km of forest in Borneo in 1982-83. 400,000 hectares have disappeared in 1988 in a fire striking Yellowstone Park in the United States, while in France forest fires destroy about 45,000 hectares per year.


B- Consequences
 
* Deforestation causes, first, the disappearance of many plant and animal species, reducing the biodiversity of environments. For example, the mountain gorillas of Rwanda or lemurs of Madagascar and have paid a heavy price to logging. 4 000-6 000 animal and plant species are lost every year as well.
 
* The exposure of bare soil to rainfall significantly increases erosion. This leads to loss of soil fertility, then unusable. Runoff increases, causing landslides and frequent floods, rapid and devastating downstream of deforested areas. Laden water clay particles leave their load in rivers, causing silting of river beds, especially at the dams. The action of water on bare ground often leads to the development of a lateritic as a hard surface layer.
 
* Finally, the destruction of large forest areas can locally modify the climate, with a soil warming and reduced precipitation. The large clearing by burning waste wood and one hand represent a major source of carbon dioxide released by humans.

...