"Environmentalist' is a touchy word within environmental history. Environmentalism, the late-twentieth century movement, is marked by advocacy for environmental preservation, anti-industrialization and anti-corporate capitalism -- none of which values would resonate with Progressive Era conservationists from the early twentieth century, or urban environment activists in the late nineteenth century, though both of these movements undeniably moved their society's relationship with the environment in a more positive, less destructive, and arguably more sustainable direction. (Everything is relative, including modern environmentalism.) Not all movements that improved the environment and/or our relationship with it before the twentieth century were necessarily oppositional or 'reactionary' as you put it either (this is one hallmark of twentieth century environmentalism). However, if we open up our parameters beyond standards established only recently for pro-environment action, we can see a long and storied past of progress, albeit in-between and often overshadowed by massive amounts of environmental destruction.

Even without the adversarial input of environmentalism, historians have documented instances within American history where the capitalist ethos of exploitation and degradation simply failed to dictate use of nature. Frank Uekötter's case study of smoke pollution in Germany and the U.S. shows how since the dawn of the industrial age, people have protested the 'smoke nuisance,' and companies had been slowly but surely (and actively) collaborating with pollution reduction efforts; “the regulatory approach was a strange mixture of cooperation and cooptation” In his telling, the anti-capitalism and anti-corporatism of environmentalism actually disrupted this progress; the trope of 'evil industrialists motivated purely by the capitalist ethos' became a self-fulfilling prophecy as environmentalist litigation fed antagonism in the twentieth century.

Another example is the horticultural-renovationist vision of some early 19th century Californians, the subject of Ian Tyrrell’s True Gardens of the Gods. The vision of diversified, sustainable and regionally self-sustaining garden economy existed within American industrial society, and was one version of it. Isolated on the periphery of American society, these Californians were determined to not be dependent on the national movement of commodities to self-sustain, and wanted to maintain the aesthetics and environmental advantages of their un-ravaged fields of plenty. (The more environmentally destructive course of monoculture cropping triumphed because, “Fundamentally, however, local and regional structures and sentiments succumbed to national ones.” )

Finally, there is the 19th century urban improvement campaigns. On both sides of the Atlantic, people started to think that dumping their excrement and other waste into the same water source they drank from wasn't such a hot idea. Think of Chicago, pouring their feces, animal carcasses, and industrial by-products into the same river that poured into Lake Michigan, where they drew their drinking water. [This eventually led to them REVERSING the flow of the Chicago river temporarily in 1871 and then with permanent success in 1900.] Likewise, "The Great Stink" (one of the best names for a historical event in all history, and one of the most descriptive), was the summer in 1858 where even the House of Commons disbanded their meeting because the smell was so overwhelming, even when hanging chlorine-soaked sheets over every window. Yeah, there was a lot of outcry, and a lot of disease, and the result was a renovated (still very imperfect) London Sewer System. After clean water and sewage, city residents (especially women) started to agitate for municipal garbage services, and rulings to prevent the dumping of garbage on the city streets. Activist Jane Addams reported to the authorities in Chicago that she only hit pavement after digging 16 inches through accumulated garbage in the 1880s!! The result was modern solid waste management services, which was a big environmental upgrade (for the time) from both people's and an ecological perspective! For proof of how commonly bad it was, check out any number of these historical photos through the Digital Public Library of America: http://dp.la/search?utf8=✓&q=street+garbage

SOURCES:

• Frank Uekötter, The Age of Smoke: Environmental Policy in Germany and the United States, 1880-1970 (Pittsburgh, Pa.: University of Pittsburgh Press, 2009), 114. To clarify, he is not arguing that such corporations were environmentalist, but that they were willing to make or even lead the way on environmental issues, to prevent more serious fines, regulations, or other consequences in the future.
• Ian R. Tyrrell, True Gardens of the Gods: Californian-Australian Environmental Reform, 1860-1930 (Berkeley, Calif.: University of California Press, 1999), 223. Steven Stoll confirms the crucial importance that scale of capitalist endeavors have on environmental impact in his own study of California: “the unity of North America as an agricultural economy demand that each region find a purpose to dedicate to the whole,” providing an impetus to specialization and intensification over the less-risky option of crop diversification, just as in Tyrrell. Steven Stoll, The Fruits of Natural Advantage: Making the Industrial Countryside in California (Berkeley: University of California Press, 1998), 155.
• Martin V. Melosi, The Sanitary City: Urban Infrastructure in America from Colonial Times to the Present (Baltimore: Johns Hopkins University Press, 2000). This is a HUGE book, containing these and so many more stories.

EDIT/CAVEAT: My specialty is twentieth century America, as you can see by my flair, so there are many many many many more examples that I am simply not well versed enough in to explain here, or may be completely ignorant of. However, there are few historians of 'environmentalism' in this subreddit, so I thought I'd contribute what I could. Other examples include the intensive management of the Black Forest in Germany going back way long ago, Italian efforts to stop mountaintop erosion in their lovely peninsula, and England's ongoing struggles to preserve woodlands and firewood supplies.