Editing Henry David Thoreau (section)

===Later years, 1851–1862===
[[File:VII. Rowse.jpg|thumb|Thoreau in 1854]]
In 1851, Thoreau became increasingly fascinated with [[natural history]] and narratives of travel and expedition. He read avidly on [[botany]] and often wrote observations on this topic into his journal. He admired [[William Bartram]] and [[Charles Darwin]]'s ''[[The Voyage of the Beagle|Voyage of the Beagle]]''. He kept detailed observations on Concord's nature lore, recording everything from how the fruit ripened over time to the fluctuating depths of Walden Pond and the days certain birds migrated. The point of this task was to "anticipate" the seasons of nature, in his word.<ref>[http://www.walden.org/documents/file/Library/Thoreau/writings/correspondence/LettersBlake.pdf#page34 Letters to H.&nbsp;G.&nbsp;O. Blake] {{webarchive|url=https://web.archive.org/web/20110617003953/http://www.walden.org/documents/file/Library/Thoreau/writings/correspondence/LettersBlake.pdf |date=June 17, 2011 }}. Walden.org</ref><ref>Thoreau, Henry David (1862). "Autumnal Tints". ''The Atlantic Monthly'', October. pp. 385–402. [http://www.walden.org/Institute/thoreau/writings/essays/Thoreau_Autumnal%20Tints.pdf Reprint] {{webarchive|url=https://web.archive.org/web/20100307053611/http://www.walden.org/Institute/thoreau/writings/essays/Thoreau_Autumnal%20Tints.pdf |date=March 7, 2010 }}. Retrieved November 21, 2009.</ref>

He became a [[Surveying|land surveyor]] and continued to write increasingly detailed observations on the natural history of the town, covering an area of {{convert|26|sqmi|km2|abbr=off|sp=us}}, in his journal, a two-million-word document he kept for 24 years. He also kept a series of notebooks, and these observations became the source of his late writings on natural history, such as "Autumnal Tints", "The Succession of Trees", and "Wild Apples", an essay lamenting the destruction of the local [[wild apple]] species.

With the rise of [[environmental history]] and [[ecocriticism]] as academic disciplines, several new readings of Thoreau began to emerge, showing him to have been both a philosopher and an analyst of ecological patterns in fields and woodlots.<ref>{{cite book|last1=Thorson|first1=Robert M.|title=Walden's Shore: Henry David Thoreau and Nineteenth-Century Science|date=2013|publisher=Harvard University Press|location=Cambridge, Massachusetts|isbn=978-0674724785}}</ref><ref>{{cite news|last1=Primack|first1=Richard B.|title=Tracking Climate Change with the Help of Henry David Thoreau|url=http://www.elsevier.com/connect/tracking-climate-change-with-the-help-of-henry-david-thoreau|access-date=September 23, 2015|date=June 13, 2013|archive-date=September 23, 2015|archive-url=https://web.archive.org/web/20150923155958/http://www.elsevier.com/connect/tracking-climate-change-with-the-help-of-henry-david-thoreau|url-status=live}}</ref> For instance, "The Succession of Forest Trees", shows that he used experimentation and analysis to explain how forests regenerate after fire or human destruction, through the dispersal of seeds by winds or animals. In this lecture, first presented to a cattle show in Concord, and considered his greatest contribution to ecology, Thoreau explained why one species of tree can grow in a place where a  different tree did previously. He observed that [[squirrel]]s often carry nuts far from the tree from which they fell to create stashes. These seeds are likely to germinate and grow should the squirrel die or abandon the stash. He credited the squirrel for performing a "great service ... in the economy of the universe."<ref>{{cite book|last1=Worster|first1=Donald|title=Nature's Economy|date=1977|publisher=Cambridge University|location=New York|isbn=0-521-45273-2|pages=69–71}}</ref>
[[File:Walden Pond, 2010.jpg|thumb|left|[[Walden Pond]]]]

He traveled to [[Canada East]] once, [[Cape Cod]] four times, and Maine three times; these landscapes inspired his "excursion" books, ''[[A Yankee in Canada]]'', ''Cape Cod'', and ''The Maine Woods'', in which travel itineraries frame his thoughts about geography, history and philosophy. Other travels took him southwest to [[Philadelphia]] and New York City in 1854 and west across the [[Great Lakes region (North America)|Great Lakes region]] in 1861, when he visited [[Niagara Falls]], Detroit, Chicago, [[Milwaukee]], [[St. Paul, Minnesota|St. Paul]] and [[Mackinac Island]].<ref>Thoreau, Henry David (1970). ''The Annotated Walden''. Philip Van Doren Stern, ed. pp. 96, 132.</ref> He was provincial in his own travels, but he read widely about travel in other lands. He devoured all the first-hand travel accounts available in his day, at a time when the last unmapped regions of the earth were being explored. He read [[Ferdinand Magellan|Magellan]] and [[James Cook]]; the [[arctic explorer]]s [[John Franklin]], [[Alexander Mackenzie (explorer)|Alexander Mackenzie]] and [[William Parry (explorer)|William Parry]]; [[David Livingstone]] and [[Richard Francis Burton]] on Africa; [[Lewis and Clark]]; and hundreds of lesser-known works by explorers and literate travelers.<ref>Christie, John Aldrich (1965). ''Thoreau as World Traveler''. New York: Columbia University Press.</ref> Astonishing amounts of reading fed his endless curiosity about the peoples, cultures, religions and natural history of the world and left its traces as commentaries in his voluminous journals. He processed everything he read, in the local laboratory of his Concord experience. Among his famous aphorisms is his advice to "live at home like a traveler".<ref>[http://www.walden.org/Library/The_Writings_of_Henry_David_Thoreau:_The_Digital_Collection/Correspondence Letters of H.&nbsp;G.&nbsp;O. Blake] {{webarchive|url=https://web.archive.org/web/20110617003655/http://www.walden.org/Library/The_Writings_of_Henry_David_Thoreau%3A_The_Digital_Collection/Correspondence |date=June 17, 2011 }} in ''The Writings of Henry David Thoreau: The Digital Collection''.</ref>

After [[John Brown's raid on Harpers Ferry]], many prominent voices in the abolitionist movement distanced themselves from Brown or [[Damn with faint praise|damned him with faint praise]]. Thoreau was disgusted by this, and he composed a key speech, "[[A Plea for Captain John Brown]]", which was uncompromising in its defense of Brown and his actions. Thoreau's speech proved persuasive: the abolitionist movement began to accept Brown as a martyr, and by the time of the [[American Civil War]] entire armies of the North were [[John Brown's Body|literally singing Brown's praises]]. As a biographer of Brown put it, "If, as Alfred Kazin suggests, without John Brown there would have been no Civil War, we would add that without the Concord Transcendentalists, John Brown would have had little cultural impact."<ref>Reynolds, David S. (2005). ''John Brown, Abolitionist''. Knopf. p. 4.</ref>
[[File:Henry David Thoreau - Dunshee ambrotpe 1861.jpg|thumb|left|Thoreau in his second and final photographic sitting, August 1861.]]