Given the minimal figurative attention paid to descriptions of the environment and nature, what makes Birnam Wood an eco-thriller?

Eleanor Catton stated that each character betrays either another person, themselves, or their ideals in some way. How does the novel depict the various types of betrayal?

The rifle described at the beginning is an example of foreshadowing, as it is used at the end to shoot the villain. What are other instances of foreshadowing in the novel? What does the foreshadowing do for the reader?