Aldo Leopold (2013). “Aldo Leopold: A Sand County Almanac & Other Writings on Conservation and Ecology: (Library of America #238)”, p.502, Library of America
Michael J. Cohen (2003). “The Web of Life Imperative: Regenerative Ecopsychology Techniques That Help People Think in Balance with Natural Systems”, p.83, Trafford Publishing
Michael J. Cohen (2003). “The Web of Life Imperative: Regenerative Ecopsychology Techniques That Help People Think in Balance with Natural Systems”, p.84, Trafford Publishing