.Reprinted from Ecology, Vol. IV, No. i, January, 1923.] 



LIBRARY 



NEW YOKK 

 BOTANIC ^l 



A WORKING BASIS FOR THE ECOLOGICAL CLASSIFICATION 

 OF PLANT COMMUNITIES 1 



George E. Nichols 

 Yale University 



CONTENTS, PART I 



I. Introduction 11 



II. The plant association as the fundamental unit of vegetation 12 



A. The essential characteristics of the association 12 



B. Interpretation and application of the term Plant Association 14 



III. The plant association in its relation to the habitat 17 



A . The general situation 17 



B. The habitat factors 19 



1. Climatic habitat factors 20 



2. Physiographic habitat factors 21 



3. Biotic habitat factors 22 



4. Anthropeic habitat factors 23 



5. Pyric habitat factors 23 



I. Introduction 



Object and Plan of Paper. During recent years various schemes have 

 been suggested for the ecological classification of plant communities and many 

 divergent views have been brought forward. So much has been written, 

 indeed, that one feels somewhat hesitant about adding anything further to the 

 already voluminous literature on the subject. The present contribution is 

 more or less in the nature of a revision and amplification of an earlier one 

 (Nichols, '17) along this same general line, and it owes its existence primarily 

 to the favorable reception which that paper was accorded. My chief aim here 

 will be to present in as clear and simple a manner as the nature of the material 

 will permit the essential facts and principles which underlie the ecological 

 classification of plant communities, and to suggest a generalized scheme which 

 may be used as a working basis in undertaking an ecological survey of the 

 vegetation in any particular tract of country. Various of the more important 

 recent works dealing with classification are referred to in the text, but it is 

 not my intention either to review these or to enter into any general discussion 

 of controversial points. 



The study of plant communities in their relation to environment comprises 

 the field of what might be termed ecological plant sociology; 2 more commonly 

 it has been called plant synecology. Various kinds of plant communities may 



1 Contribution from the Osborn Botanical Laboratory. 



2 Plant sociology may be described simply as the study of plant communities. The 

 term ecological plant sociology is used by Pavillard ('18) in a somewhat more restricted 

 sense than that in which it is here employed. 



1 1 



