What is the importance of the forest in the novel, The Vegetarian?

A few sections in Part 3 - specifically, those describing Yeong-hye's escape attempt - take place in the forest surrounding the psychiatric hospital. The forest is the setting for Yeong-hye's encounters with trees and rain, both of which trigger the realization in her that the transformation she is heading for, and has perhaps been unconsciously desiring all along, is a transformation into a tree. For her, therefore, the forest is the setting for self-revelation and truth, a metaphoric sensibility that has its echo in the book's final moments, in which In-hye, riding in an ambulance with her sister, insistently looks into the trees that flash by the vehicle for answers to her questions about identity and independence.