Answer from Praveen Bhargav, Trustee, Wildlife First:
Typically, most Sanctuaries or National Parks in India have been created by amalgamating two or more Reserved Forests. In the preamble of the notification it is stated that the area is being constituted as a National Park or Sanctuary based on its ecological, floral, faunal, zoological, geomorphological significance. Such forest areas are identified/recommended either by forest officers and/or scientists, expert committee members, conservation NGOs… with sufficient justification on conservation values. Since India has adopted a flagship species approach to conservation, the presence of an endangered species is considered as an important criterion. Lastly, RF(s) free of human presence and contiguous with some existing Sanctuaries or NPs fulfill a very important requirement for notification.