January, 1923 ECOLOGICAL CLASSIFICATION OF PLANT COMMUNITIES I5 



in the way different ecologists have applied it. By some its use has been 

 restricted to the concrete individual pieces of vegetation which we study in 

 the field— the sense in which I have interpreted it in the preceding section. 

 By others these concrete individual communities have been viewed merely as 

 "examples" of an association— -i.e., the term has been applied in a purely 

 abstract sense to a concept which in itself has no material existence. By still 

 others the association has been regarded as a concrete aggregate comprising 

 all the individual pieces of vegetation of a given kind in existence, taken 

 collectively. The situation may be illustrated by a concrete example. We 

 have in central Connecticut any number of pitch pine (Pinus rigida) com- 

 munities, all of them essentially alike in their vegetation, but all (broadly 

 speaking) topographically separated from one another and therefore organi- 

 cally disconnected. Now, to some ecologists each one of these pitch pine 

 communities, by itself, is an association. To others the term "pitch pine 

 association " implies a sort of pigeonhole to which all the individual pitch pine 

 communities can be referred ; the individual community is merely a concrete 

 example of the abstract association. Still others would say that all the indi- 

 vidual pitch pine communities in existence, considered as a single aggregate 

 and concrete whole, constitute the "pitch pine association," and that the 

 individual pieces of vegetation themselves are but parts or fragments of this 

 association. 



Uniform Usage Desirable. Now, to some these differences in interpreta- 

 tion may appear to be of academic interest, but of little practical. importance. 

 As a matter of fact, if ecologists were content to confine themselves to the 

 study of plant associations alone, it might perhaps make no particular differ- 

 ence how they used the term, provided each one made clear just what he 

 meant by it. But just as soon as we carry our studies beyond the association, 

 as soon as we begin to arrange associations into units of a higher order than 

 the association, and as soon as we start to call these new units by special 

 names, then, if not before, our troubles begin. 



A Definite Proposal Generally Accepted. As a remedy for this some- 

 what confusing state of affairs, in October, 192 1, the following recommenda- 

 tion was submitted by circular letter to about 85 ecologists in the United 

 States and Canada, mostly botanists or foresters and mostly members of the 

 Ecological Society of America : " That the term Plant Association be recog- 

 nized as applicable both to the abstract vegetation concept and to the concrete 

 individual pieces of vegetation on which this concept is based." ( Of 76 who 

 replied, 67 were in favor of adopting the recommendation and only 6 were 

 opposed. 7 



■ This idea was suggested to the writer in replies to an earlier questionnaire on this 

 same topic (September, 1921), by four different ecologists: viz., Prof. W. S. Cooper, 

 Dr. W. A. Dayton, Dr. R. M. Harper, and Prof. C. A. Shull. 



^ This recommendation was also submitted to various European ecologists and was 

 considered favorably by about half of them. 



