Final answer:
Ralph Waldo Emerson was the "Nature" author who served as a pallbearer at Nathaniel Hawthorne's funeral. Emerson was a key figure in the transcendentalist movement and a strong advocate for connecting with nature.
Step-by-step explanation:
The three-named "Nature" author who served as one of the pallbearers at Nathaniel Hawthorne's funeral in 1864 was Ralph Waldo Emerson. Emerson, a prominent American essayist, lecturer, poet, and leader of the transcendentalist movement, was indeed a close associate of Hawthorne. While Henry David Thoreau was also a leading transcendentalist and a passionate advocate for nature, he could not have served as a pallbearer for Hawthorne in 1864 due to his own death in 1862, eliminating him and the other provided options as correct answers. Emerson's contributions to the transcendentalist and ecological thinking of the time were significant, as well as his deep involvement in the social issues of his day.