Much of Shelford's work was on terrestrial ecology, but he also did much aquatic research. Some of his publication in "Ecology" were studies from locations such as stream communities (1929), bottom communities in western Lake Erie (1942), analysis of tundra communities (1935), and of Mississippi floodplains (1954). He published a work in 1939 in "Bio-Ecology" in collaboration with Frederic E. Clements which attempted to integrate animal, plant, and aquatic ecologies as part of an ideal community. He left the University of Illinois in 1946, but the same year would found the Ecologist's Union, an organization which promoted the need to preserve entire ecological communities as part of nature conservation. The Union was founded in response to the ESA deciding it would be inappropriate for a scientific society to take a political stance. The Ecologist's Union is today known as The Nature Conservancy.