Fern Gully is a collective Hive Mind of super-intelligent trees that seeks to wipe out all humans and cover the Earth in itself, destroying all other kinds of ecosystems and species in the process. It is the only forest in the entire world that grows through fairy witchcraft. The fairies, the only beings that can speak to the trees, all blindly worship it as a god; and they use their magic to help it grow anywhere it wants to because Earth's diverse ecosystems, such as deserts, can't all support rainforests.