.Reprinted from Ecology, Vol. IV, N'o. 2, April, 1923.] 



A WORKING BASIS FOR THE ECOLOGICAL CLASSIFICATION 

 OF PLANT COMMUNITIES 



George E. Nichols 

 Yale University 



Contents, Part II 



IV. The ecological classification of plant associations 1 54 



V. Classification based on physiognomy and ecological structure 156 



VI. ification based on geographic relations ,. . . . 160 



A. Introductory 160 



B. Climatic unit-areas and climatic plant formations 162 



C. Physiographic unit-areas and physiographic plant formations 163 



D. Interrelations of the various geographical vegetation units 165 



VII. Classification based on successional relations 167 



A. Introductory 167 



B. Types of succession in relation to cause 169 



C. Types of succession in relation to trend 17° 



D. Types of succession in relation to origin 1 7 l 



E. Types of succession in relation to climax 1 7 2 



VIII. Summary and conclusions 1 74 



IX. The method in practise 1 75 



IV. The Ecological Classification of Plant Associations 



Classification, generally speaking, may be described as the arrangement 

 into groups of objects or phenomena which are related to one another by the 

 possession of certain characters in common. The principle of classification, in 

 the words of Hugh Miller, 26 is one which is " inherent in the human mind " ; 

 it is a principle " which we find pervading all science, which gives to each of 

 the many cells of recollection its appropriate facts, and without which all 

 knowledge would exist as a disorderly and shapeless mass, too huge for the 

 memory to grasp and too heterogeneous for the understanding to employ." 

 The phase of ecological plant sociology which deals with the classification of 

 plant associations might be called systematic plant sociology. 21 



Any attempt to classify natural phenomena presents obvious difficulties. 

 Especially is this true in a field such as ecology, where authorities disagree 

 so strongly on many points, not only in the interpretation of facts, but con- 

 cerning the nature of principles. To fulfill scientific requirements a scheme 

 of classification must be logical in its concepts, clear-cut in its definitions, and 



36 The old red sandstone, p. 106. Edinburgh, 1882. 



* I would employ this term in a somewhat more comprehensive sense than that in 

 which it is used by various European authorities. 



i. r J 



