Theory:

Earth is filled with many species of plants and animals. A variety of organisms are essential for the survival and well being of humanity.
Biological diversity is the variety of organisms existing on earth, the interdependence between them, and the relationship of an organism with the environment.
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Biodiversity
  
Biodiversity - "Bio" means life, and "diversity" means different or varieties. Forests have a wide variety of life forms that include different trees, flowers, birds, animals and other wildlife. Nowadays significant cut down of forests takes place through the phenomena called deforestation.
Deforestation:
Large scale cut down of forest trees to meet the demands of the increasing population is called deforestation
Deforestation is seen around the globe, which poses a big threat to the forests. Forests are destroyed continuously so that the forest land can be used for other purposes. Due to the rising population, forests are cleared as there is competition for space and food.
 
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Deforestation 
Causes of deforestation:
Deforestation can be caused by human activities or naturally.
 
Deforestation caused due to human activities:
  • Forests are cleared to obtain land area for cultivation of crops.
  • They are mainly cleared so that land can be used for construction of roads, dams, houses, industries etc.
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Deforestation due to building the larger dams
  • Due to urbanization and increase in population, the expansion of the city caused the clearing of forests.
  • Mining of coal and diamond caused large scale clearing of forests.
  • Forests are cut down for obtaining firewood for fuel needs.
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Cutting down the trees for firewood
  • Forests are also cut down to obtain timber (wood obtained to build houses, furniture)
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Timber extraction
  • For the products made from wood like paper, matchstick etc. forests are cleared
Deforestation is caused naturally through:
  • Forest fire that wipes out a large area of forest.
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Forest fire due to deforestation
  • Cyclone destroys the trees and the livelihood of people.
  • Drought causes the plant's parts to degrade into fragments.
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Drought due to deforestation
  • Flood also is one of the reasons for deforestation.
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Flood due to deforestation
Reference:
https://upload.wikimedia.org/wikipedia/commons/2/25/Mali_firewood.jpg
https://www.flickr.com/photos/planeta/15451998411
https://www.piqsels.com/en/public-domain-photo-jefbb/download
https://commons.wikimedia.org/wiki/File:Bandipur_fires_2019.jpg
https://www.pxfuel.com/en/free-photo-qfzgz/download
https://www.piqsels.com/en/public-domain-photo-oudio/download
https://www.piqsels.com/en/public-domain-photo-fxksc/downloadhttps://upload.wikimedia.org/wikipedia/commons/thumb/6/6c/Madagascar_Deforestation.jpg/1024px-Madagascar_Deforestation.jpg