Question

why did the colonial government decide to declare some parts of the forest as reserved forests.how did this benefit them..

Answer 1

they help wild to be safe in forest n ....Hunter not able to hunt.....

Answer 2

Colonial Government in India decided to reserve the forests for :
1] First, the colonial government wanted forests for timber productions for ship building in England and for sleepers to construct railway lines.

This reservation benefited them in many ways as they got a means for the cultivation of strong and durable timbre  for ship building in England and for sleeper production in India.