Gleason, Henry A. (1882 – 1975) American Ecologist

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Henry A. Gleason (1882 – 1975) American ecologist

Henry A. Gleason was a half generation after that small group of midwesterners who founded ecology as a discipline in the United States. He was a student of Stephen Forbes and his early work in ecology was influenced strongly by Cowles and Frederic E. Clements . He did later, however, in 1935, claim standing—bowing only to Cowles and Clements and for some reason not including Forbes—as "the only other original ecologist in the country." And he was original. His work built on that of the founders, but he quickly and actively questioned their ideas and concepts, especially those of Clements, in the process creating controversy and polarization in the ecological community. Gleason called himself an "ecological outlaw" and probably over-emphasized his early lack of acceptance in ecology, but in a resolution of respect from the Ecological Society of America after his death, he was described as a revolutionary and a heretic for his skepticism toward 'established' ideas in ecology. Stanley Cain said that Gleason was never "impressed nor fooled by the philosophical creations of other ecologists, for he has always tested their ideas concerning the association, succession , the climax, environmental controls, and biogeography against what he knew in nature ." Gleason was a critical rather than negative thinker and never fully rejected the utility of the idea of community, but the early marginalization of his ideas by mainstream ecologists, and the controversy they created, may have played a role in his later concentration on taxonomy over ecology.

He claimed that if plant associations did exist, they were individualistic and different from area to area, even where most of the same species were present. Gleason did clearly reject, however, Clements' idea of a monoclimax, proclaiming that "the Clementsian concept of succession, as an irreversible trend leading to the climax, was untenable." His field observations also led him to repudiate Clements' organismic concept of the plant community, asking "are we not justified in coming to the general conclusion, far removed from the prevailing opinion, that an association is not an organism?" He went on to say that it is "scarcely even a vegetation unit." He also pointed out the errors in 'Raunkiaer's Law,' on frequency distribution, which as Robert McIntosh noted, was "widely interpreted [in early ecology] as being a fundamental community characteristic indicating homogeneity," and questioned Jaccard's comparison of two communities through a coefficient of similarity that Gleason believed unduly gave as much weight to rare as to common species.

Gleason's own approach to the study of vegetation emerged from his skills as a floristic botanist, an approach rejected as "old botany" by the founders of ecology. As Nicolson suggests, "a floristic approach entailed giving primacy to the study of the individual plants and their species. This was the essence of [Gleason's] individualistic concept." In hindsight, somewhat ironically then, Gleason used old botany to create a new alternative to what had quickly become dogma in ecology, the centrality of the idea that units of vegetation were real, that the plant association was indispensable to an ecological approach.

Clements was more accepted in the early part of the twentieth century than Gleason, though many ecologists at the time considered both too extreme, just in opposite ways. Today, Clements' theories remain out of favor and some of Gleason's have been revived, though not all of them. Contrary to his own observations, he was persuaded that plants are distributed randomly, at least over small areas, which is seldom if ever the case, though he later backed away from this assertion. He could not accept the theory of continental drift, stating that "the theory requires a shifting of the location of the poles in a way which does considerable violence to botanical and geological facts," and therefore should have few adherents among botanists.

Despite Gleason's skepticism about some of Clements' major ideas, the older botanist was a major influence, especially early in Gleason's career. Especially influential was Clements' rudimentary development of the quadrat method of sampling vegetation, which shaped Gleason's approach to field work; Gleason took the method much further than Clements, and though not trained in mathematics, was the first ecologist to employ a number of quantitative approaches and methods. As McIntosh demonstrated, Gleason, following Forbes lead in aquatic ecology "was clearly one of the earliest and most insightful proponents of the use of quantitative methods in terrestrial ecology."

Gleason was born in the heart of the area where ecology first flourished in the United States. His interest in vegetation and his contributions to ecology were both stimulated by growing up in and doing research on the dynamics of the prairie-forest border. He won bachelor's and master's degrees from the University of Illinois and a Ph.D. from Columbia University. He returned to the University of Illinois as an instructor in botany (1901–1910), where he worked with Stephen Forbes at one of the major American centers of ecological research at the time. In 1910, he moved to the University of Michigan (1910) and while in Ann Arbor, married Eleanor Mattei. Then, in 1919, he moved to the New York Botanical Garden, where he spent the rest of his career, sometimes (reluctantly) as an administrator, always as a research taxonomist. He retired from the Garden in 1951.

Moving out of the Midwest, Gleason also moved out of ecology. Most of his work at the Botanic Garden was taxonomic. He did some ecological work, such as a three-month ecological survey of Puerto Rico in 1926, and a restatement of his "individualistic concept of the plant association, (also in 1926 and also in the Bulletin of the Torrey Botanical Club ), in which he posed what Nicolson described as "a radical challenge" to the basis of contemporary ecological practice. Gleason's challenge to his colleagues and critics in ecology was to "demolish our whole system of arrangement and classification and start anew with better hope of success." His reasoning was that ecologists had "attempted to arrange all our facts in accordance with older ideas, and have come as a result into a tangle of conflicting ideas and theories." He anticipated twenty-first century thinking that identification on the ground of community and ecosystem as ecological units is arbitrary, noting that vegetation was too continuously varied to identify recurrent associations. He claimed, for example, that "no ecologist would refer the alluvial forests of the upper and lower Mississippi to the same association, yet there is no place along their whole range where one can logically mark a boundary between them. As Mcintosh suggests, "one of Gleason's major contributions to ecology was that he strove to keep the conceptual mold from hardening prematurely."

In his work as a taxonomist for the Garden, Gleason traveled as a plant collector, becoming what he described as "hooked" on tropical American botany, specializing in the large family of melastomes, tropical plants ranging from black mouth fruits to handsome cultivated flowers, a group which engaged him for the rest of his career. His field work, on this family but especially many others, was reinforced by extensive study and identification on material collected by others and made available to him at the Garden.

A major assignment during his New York years, emblematic of his work as a taxonomist, was a revision of the Britton and Brown Illustrated Flora of the Northeastern United States (1952) which Maguire describes as a "heavy duty [that] intervened and essentially brought to a close Gleason's excellent studies of the South American floras and [his] detailed inquiry into the Melastomataceae...this great work...occupied some ten years of concentrated, self-disciplined attention." He did publish a few brief pieces on the melastomes after the Britton and Brown, and also two books with Arthur Cronquist, Manual of Vascular Plants of Northeastern United States and Adjacent Canada (1963) and the more general The Natural Geographyof Plants (1964). The latter, though coauthored, was an overt attempt by Gleason to summarize a life's work and make it accessible to a wider public.

Gleason's early ecological work on species-area relations, the problem of rare species, and his extensive taxonomic work all laid an initial base for contemporary concern among biologists (especially) about the threat to the earth's bio-diversity. Gleason wrote that analysis of "the various species in a single association would certainly show that their optimum environments are not precisely identical," a foreshadowing of later work on niche separation. McIntosh claimed in 1975 that Gleason's individualistic concept "must be seen not simply as one of historical interest but very likely as one of the key concepts of modern and, perhaps, future ecological thought." A revival of Glea son's emphasis on the individual at mid-twentieth century became one of the foundations for what some scientists in the second half of the twentieth century called a "new ecology," one that rejects imposed order and system and emphasizes the chaos, the randomness, the uncertainty and the unpredictability of natural systems. A call for 'adaptive' resource and environmental management policies flexible enough to respond to unpredictable change in individually variant natural systems is one outgrowth of such changes in thinking in ecology and the environmental sciences .

[Gerald L. Young ]