17 



RECENT EVOLUTION OF ECOLOGICAL 



CONCEPTS IN RELATION TO THE 



EASTERN FORESTS OF 



NORTH AMERICA^ 



R. H. Whittaker 



Introduction: the system of Clements. The eastern forests have always 

 been the real homeland of American ecology. It is here that the largest num- 

 ber of American ecologists have lived and worked, the most extensive ecologi- 

 cal research has been carried out. From study of the eastern forests have 

 developed many of the concepts which ecologists have applied to interpreta- 

 tion of other areas. Results of ecological research in other areas have also 

 influenced interpretation of the eastern forests; but the commerce of ecologi- 

 cal ideas has been more one of export from than of import into the eastern 

 forests. Of all the exports from the ecology of the eastern United States, 

 the most widely influential was the system of vegetation interpretation de- 

 signed by Clements. Discussion of changing views of ecological concepts, espe- 

 cially in relation to the eastern forests and Clements' system of interpreta- 

 tion, is the object of this paper. 



The major unit of vegetation in Clements' system is the plant formation. 

 The formation is a great regional unit of vegetation characterized by its domi- 

 nant growth form, as the eastern forests are characterized by deciduous trees, 

 the prairie where Clements did his early work by grasses. Every formation is 

 a product of climate and is controlled and delimited by climate and climate 

 alone; the formation occurs in a natural area of essential climatic unity and 



^ Based on the conclusion to a symposium on "Approaches to Interpretation of the 

 Eastern Forests of North America," including also the cited papers of Braun (1956, 

 published in this volume), Wang (1956), Raup (1956), and Bray (1956b), at the 

 meetings of the American Institute of Biological Sciences, Storrs, Conn., August 28, 

 1956. 



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