Let the trees flourish and tigers will save themselves.
We read somewhere in the news that an educational institution spent INR 100,000 (around US$ 2,275) to adopt a tiger in a zoo for an year. First of all, a zoo is a very wrong place for a tiger to be in. Secondly, a zoo has funds allocated already to take care of the national animal.
We would rather this amount was spent on adopting trees in the villages. Each student of that school could have adopted a tree. You could adopt a tree and then look after it like your own child. Form a group and go to villages and forest fringe areas to educate people about saving nature to save tigers. Motivate the village folks, especially children for adopting trees in partnership with your group. Your group could provide moral support and other incentives to that person or child on the spot, who will actually save the tree.
You know, if you or your group have sufficient resources, you could even buy a piece of land and setup a plantation in partnership with the local folks. Why we are stressing partnership with local folks is that they are the ones who will ensure protection to the trees. Saving the trees will in turn save tigers.