In this sentence "There are few rain forest left", I wonder if "which are" was omitted between "rain forest" and "left". So, may I understand that "left" could modify the "rain forest"?
Sentences beginning with there is / there are are called existential sentences. They have a particular syntax. As exemplified in the above sentence, you can use there + be + + noun + participle instead of using a structure with be as an auxiliary verb (Few rain forests are left.)