Clements, Frederic

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Clements, Frederic

American Botanist
1874-1945

More than any scientist of his time, Frederic Clements (1874-1945) developed the methods and ideas that helped ecologists unravel nature's complexity. Indeed, ecology is arguably the most complex of all the sciences. The natural world that ecologists seek to understand is in constant flux. The weather and hundreds of other variables in the environment change from day to day, month to month, and from year to year. In any given habitat thousands of species and millions of individual plants and animals interact in a bewildering array of intricate associations.

When Clements arrived at the University of Nebraska in 1892 to begin studies in botany, the science of ecology was just beginning to crystallize from its diverse origins in plant physiology , plant geography, and plant morphology . Clements had been influenced by several European botanists, especially the German plant geographer Oscar Drude. Drawing on the ideas of Alexander von Humboldt, Drude had stressed the holistic nature of the plant community and the need for general theories of plant distribution rather than static descriptions of where different species lived. While studying at Nebraska, Clements began to formulate his own theory of plant associations. He soon became the leading ecologist in America during the early part of the twentieth century.

Despite his stature, little has been written about Clements's life outside of his contributions to ecology and the plant sciences. We know that he received his doctoral degree from Nebraska in 1898 and married another Nebraska Ph.D. student, Edith Schwartz. The two collaborated on research and published numerous scientific books throughout their lives. After his studies at Nebraska, Clements joined the biology department at the University of Minnesota. In 1913, the Carnegie Institution of Washington helped Clements move his field studies to the Alpine Laboratory near Pikes Peak in Colorado. There Clements and his wife conducted detailed studies of environmental influences on plant associations, including the effects of temperature, humidity, light levels, and evaporation.

Early in his career, Clements set out to bring order to what was thought of as the chaotic and unsystematized state of ecology. Over a period of forty years, Clements developed a dynamic theory of plant communities that viewed plant associations as constantly changing rather than static, fixed entities. One of the major ideas that Clements used to understand ecological systems was the concept of vegetation as a super organism. To Clements, plant communities, like an animal's body, are comprised of interrelated parts, each vital to the functioning of the entire organism. Just like an individual organism, communities are born, grow, and mature, and then die.

Clements is best known for his theory of ecological succession. Building on the studies of Johannes Warming and Henry Chandler Cowles, Clements stated as a universal law that "all bare places give rise to new communities except those which present the most extreme conditions." Clements spent a lifetime studying vegetational changes in "bare places" such as ploughed fields or forests destroyed by fire. One of his major conclusions was that, in a given climatic area, all ecological successions lead to the same stable association of plant species. Clements called this final stage in a series of changes in plant communities the "climax state." While modern ecologists have rejected the theory of stable climax associations, Clements's pioneering ideas continue to influence our efforts to understand change and complexity in the natural world.

see also Humboldt, Alexander von; Warming, Johannes.

Bradford Carlton Lister