Thanks to Walden, Thoreau is known as one of the first environmentalists. How did he get this title? Well, he interpreted nature in a way that hadn't been done before. For Thoreau, nature isn't just a mirror to man's soul, as it was for the Romantics, nor is it celebrated within the confines of a well-ordered landscape or farm, as it is in the pastoral tradition. Thoreau wants wild nature, nature untouched by human hands. As is demonstrated simply through his presence as an observer, this untouched-by-human-hands thing may not be possible, but, hey, a guy wants what he wants.
Thoreau represents this wild vision of nature through various lenses – first, with a naturalist's eye for the differences between species, and for the changes in distinctive habitats as they evolve over the seasons. Second, he represents it as a historian, capturing the way that humans have altered the landscape. This includes his own attempts at farming, which is in tension with his respect for native plants. In the end, the nature Thoreau describes is only about a mile away from the center of town, and not in some far-off wilderness. But so what? Thoreau wants to remind us that nature is all around us, and there to inspire us to be better than we are.
In Walden, Thoreau successfully shows us why it is so important to conserve nature. He's good at converting us into tree-huggers.
Thoreau primarily appreciates nature as a way to get back in touch with what is most human in himself.