In 1851 American author, naturalist, transcendentalist, tax resister, development critic, abolitionist, surveyor, and philosopher Henry David Thoreau delivered an address to the Concord, Massachusetts Lyceum declaring that "in Wildness is the preservation of the World." In 1863 this address was published posthumously in Boston as the essay "Walking" in Thoreau's Excursions.
Thoreau second major contribution to the environmental movement was an address he delivered to the Middlesex (Massachusetts) Agricultural Society in 1860 entitled "The Succession of Forest Trees." In this speech Thoreau analyzed aspects of what later came to be understood as forest ecology and urged farmers to plant trees in natural patterns of succession. The address was also published in Excursions, becoming perhaps Thoreau's most influential ecological contribution to conservationist thought.