"Witness Tree: Landscape and Dissent in the Nineteenth-Century United States" is a cultural and environmental history that draws on a range of primary source materials, both textual and visual, to trace how nineteenth-century Americans unsure about the costs of Progress reimagined and actively reshaped their landscapes. I do this by following one green thread in particular: the ways that Americans incorporated trees into their cultural productions. In a country popularly known in the nineteenth century as Nature's Nation, trees have historically borne a rich mantle of cultural allusion. For instance, land surveyors-often figured as the advanced guard of modern capitalism-used trees to denote the bounds of property and empire, which they called "witness trees." This dissertation begins by stepping back from the material world of the surveyor for a moment, and asking of his trees, what was it they witnessed: a crime, or divine revelation? Were they helpless observers, or active participants in what unfolded before their knotty eyes? If trees are witnesses, can they speak? Can what they say be heard? As it turns out, nineteenth-century Americans from quite different backgrounds-radical land surveyors, abolitionists, utopian socialists, anarchists, landscape photographers, wilderness tourists, artists, and popular writers-were asking similar questions; what's more, they consistently created varied landscapes highlighting the unnaturalness of capitalism, industrialization, scientific racism, and Manifest Destiny. "Witness Tree" is the story of these widely dispersed yet culturally cohesive dissidents, a story emphasizing a lost legacy of environmental humility, spatial sensitivity, and radical social justice.