Henry A. Gleason (botanist)

Henry Allan Gleason (1882–1975) was a noted American ecologist, botanist, and taxonomist, known for his endorsement of the individualistic or open community concept of ecological succession, and his opposition to Frederic Clements's concept of the climax state of an ecosystem. His ideas were largely dismissed during his working life, leading him to move into plant taxonomy, but found favour late in the twentieth century.

Gleason was born in Dalton City, Illinois, and after undergraduate and master's work at the University of Illinois earned a PhD from Columbia University in Biology in 1906. He held faculty positions at the University of Illinois, the University of Chicago and the University of Michigan, before returning to the East Coast, to the New York Botanical Garden in the Bronx, New York, where he remained for the rest of his career, until 1950.

In Gleason's early ecological research on the vegetation of Illinois, around 1909-1912, he worked largely within the theoretical structure endorsed by ecologist Frederic Clements, whose work on succession was the most influential during the first decades of the twentieth century. Building on Henry C. Cowles's landmark research at the Indiana Dunes and some of the ideas of his mentor Charles Bessey at the University of Nebraska, Clements had developed a theory of plant succession in which vegetation could be explained by reference to an ideal sequence of development called a sere. Clements sometimes compared the development of seres to the growth of individual organisms, and suggested that under the right circumstances, seres would culminate in the best adapted form of vegetation, which he called the climax state. In his early research, Gleason interpreted the vegetation of Illinois using Clementsian concepts like associations, climax states, pioneer species, and dominant species.

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