"Father of the National Parks," the founder of the Sierra Club, and perhaps the United States' most famous conservationist, John Muir was a naturalist and an author. He was instrumental in the establishment of Yosemite as a national park, and in creating the foundation for how the US thinks about conservation, and the preservation of it's wilderness areas.
Deeply spiritual, and raised in religious household, Muir eventually came to see Nature as the a primary source for understanding God. Muir believed in the inherent tension between civilization and the natural world. His philosophical beliefs reflect this tension, and the belief that "wild is superior" and that the wilderness was to be preserved from "corruptions of civilization."
The above quote, "I never saw a discontented tree." is pulled from a longer section in John of the Mountains: The Unpublished Journals of John Muir that talks about the nature of trees, rebuffing the idea that trees are somehow worse off for being rooted to the earth.
"It has been said that trees are imperfect men, and seem to bemoan their imprisonment rooted in the ground. But they never seem so to me. I never saw a discontented tree. They grip the ground as though they liked it, and though fast rooted they travel about as far as we do. They go wandering forth in all directions with every wind, going and coming like ourselves, traveling with us around the sun two million miles a day, and through space heaven knows how fast and far!"
- John of the Mountains: The Unpublished Journals of John Muir, (1938), page 313.
Published posthumously, John of the Mountains: The Unpublished Journals of John Muir is one the many books written by John Muir, about six volumes of which were published during his lifetime, and four more after his death, along with a number of volumes that collect together his articles and essays.
John Muir's writings focus on nature and his natural surroundings, he wrote about his observations, his philosophies, and tried to translate the wilderness into the written word. On writing about nature, he once wrote in one of his journals,
"One day's exposure to mountains is better than cartloads of books. See how willingly Nature poses herself upon photographers' plates. No earthly chemicals are so sensitive as those of the human soul. "
- John of the Mountains: The Unpublished Journals of John Muir, (1938) page 95.