Ecopsychology is a new and "diverse field committed to placing human psychology into an ecological context", that proposes that the mind is "tangled up with" the natural world. (Fisher, 2005: 557-558). Perhaps the best established theory of ecopsychology is the 'wilderness effect’ which Greenway claims is "increasingly accepted as a given" (Greenway, 1995: 128).
Robert Greenway's paper On Crossing and Not Crossing the Wilderness Boundary (circa 1997) is now quite out of date but still offers facinating insights into the wilderness effect.
From there, I hope you'll be inspired to explore more through my selection of suggested websites.
the green fuse - bringing philosophy to life