Deforestation refers to the illegal cut down of trees.Deforestation has several disadvantages such as:
1]The pollution in the atmosphere increases. 
2]It will lead to less amount of rain,which will further lead droughts and famines.
3]It will also contribute to the global warming as the number of gases in the atmosphere increases. 
It ca be controlled by taking measures such as:
1]Encouraging afforestation.
2]Stopping illegal cut down of trees.
3]Government should implement policies to control deforestation and take stringent actions against those breaking the laws.etc....