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Recent Evolution of Ecological Concepts in Relation to the Eastern Forests of North America

R. H. Whittaker
American Journal of Botany
Vol. 44, No. 2 (Feb., 1957), pp. 197-206
Stable URL: http://www.jstor.org/stable/2438311
Page Count: 10
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Recent Evolution of Ecological Concepts in Relation to the Eastern Forests of North America
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Abstract

1. Study of the eastern forests of North America has been the source of many ecological concepts, some of which became part of the widely influential system of Clements. Such concepts as formation and association, succession and climax, dominance, vegetational phylogeny, and the complex organism were synthesized by Clements into an orderly, coherent, deductive system of vegetation interpretation. 2. Further experiences in the eastern forests and elsewhere have led to changing views of these concepts: a) The formation and association seem no longer distinct, clearly bounded entities comparable to organisms or species. With recognition of the significance of vegetational continuity and the principle of species individuality, these have come to be regarded as man-made classes of natural communities. b) Succession seems a less orderly process than in Clements' view; only a part of the incessant flux of populations in natural communities can be understood in terms of succession. Relative stability of vegetation is not determined by climate alone, and varied approaches to the definition of "climax" are possible. c) Dominant species do not control the distribution of other species and characterize communities and their environments in the way assumed by Clements. d) Since plant species are free to change their distributional relations to one another through evolutionary time, evolutionary relations of communities are reticulate. Natural communities do not evolve by phylogenetic descent from past communities in the same sense as organisms. e) The concept of the community as a complex organism, central to Clements' system, has been largely abandoned as inappropriate or unproductive. Current interpretations emphasize the functional system formed by community and environment, the ecosystem. 3. These changes in individual concepts, taken together, amount to a fundamental re-orientation of the field. The deductive system of Clements has broken down into the more detailed, more complex, and less coherent understanding of an inductive science. Because of multiplicity of ecological factors, effects of chance, and individuality of species distributions, natural communities are not an area of orderly, clear-cut, exactly predictable phenomena to which the system of Clements might be appropriate. A fundamental characteristic of natural communities affecting all ecological concepts is the condition of loosely ordered complexity. Ecological concepts cannot be thought inherent in, or uniquely determined by, vegetation; they are the means of human abstraction by which some of the diverse information about natural communities can be brought into comprehensible forms.

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