American botanist, a pioneer in the field of plant ecology.

During the 1890s, Cowles conducted a study of sand dune vegetation that resulted in his development of the concept of ecological succession. This idea assumed an inevitable sequence of biological communities, each rendering the habitat more favourable to its successors than to itself, until a climax community characteristic of the climatic conditions of the region is attained. Cowles's concept became a fundamental tenet of modern ecology and helped bring attention to the dynamic nature of biotic populations.

Cowles spent most of his career at the University of Chicago (1897–1934). His Vegetation of Sand Dunes of Lake Michigan (1899), outlining the concept of ecological succession, established the university as an early centre of ecological research in the United States.