April, 1923 ECOLOGICAL CLASSIFICATION OF PLANT COMMUNITIES 



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Characterized, as they tend to be, by more or less obvious peculiarities of 

 external appearance, it is chiefly the different association-types, rather than 

 the associations, which picture themselves before the eyes of most of us, as 

 we view the landscape from speeding train or auto — such types as evergreen 

 and deciduous forests, groves and thickets, meadows and marshes. It is the 

 association-types, rather than the associations, which first impress us when 

 we visit a floristically unfamiliar region. The associations reveal themselves 

 only when the vegetation is considered with reference to its floristic composi- 

 tion, whereas it is quite possible to describe the vegetative features of any 

 region in terms of physiognomy and ecological structure without knowing the 

 name of a single plant. In short, from the point of view of ecological plant 

 sociology the association-type is of much greater fundamental importance than 

 the association, in so far as the latter is regarded as an abstract vegetation 

 unit. It is from this point of view that Cooper ('22) describes the associ- 

 ation-type (he uses the term formation), rather than the association, as the 

 fundamental unit of vegetation. 30 



In naming association-types, they are appropriately designated in terms 

 of physiognomy and ecological structure. Thus, in a general way, the various 

 associations of lakes and swamps can be grouped under such heads as : sub- 

 merged leaf association-type, floating leaf type, reed swamp type, and decidu- 

 ous swamp-forest type. 



Association-type Compared until Association Abstract. — The concept of 

 the association-type is essentially an abstract one, corresponding in this respect 

 to the abstract concept of the association. Both of these abstract concepts 

 are represented in the concrete by the individual association. That is to say, 

 the association concrete is an example both of the association abstract and of 

 the association-type. As an example of the first it is considered more espe- 

 cially with reference to its floristic composition. As an example of the second 

 it is considered with reference to its physiognomy and ecological structure 

 alone. Thus an individual pitch pine forest (association concrete) is an 

 example of pitch pine forest (association abstract) ; it is also an example of 

 what might be termed xerophytic conifer forest (association-type). 31 



given the most diverse meanings. There are cover types and site types and management 

 types, none of which are comparable to the ecological association-type. The ecological 

 forest-type, however, is identical with the ecological association-type. Unfortunately 

 the term association is little used by the foresters. It seems hardly necessary to more 

 than suggest the desirability that, so far as their work is ecological in character, the 

 foresters should at least adopt the association as the basis of classification. 



• 30 To quote Pavillard ('20) in this connection : " L'association [= abstract associa- 

 tion] est l'unite fondamentale de la Sociologie vegetale. ... La formation [— asso- 

 ciation-type] est la notion fondamentale de la synecologie." 



31 It is from somewhat this point of view that Pavillard in 1912 (see '22, p. 20) 

 wrote " La formation [= association-type] est a l'association ce que la forme biologique 

 est a l'espece. On pourrait dire encore: la formation est la ' forme biologique' de l'as- 

 sociation." Negri ('14) has expressed the same idea as follows: "Alia formasione 



