THE CLIMAX AS A BASIS. 177 



produce essentially the same area, as is frequently true of wind erosion and 

 deposit, and not altogether rare in the case of water. While the value of the 

 initial area for purposes of classification rests upon its water-content, it must 

 not be forgotten that the nature of the latter may be more significant than its 

 amount. In other words, an alkaline or acid holard determines the nature of 

 the sere, more or less irrespective of the amount of water present. 



The initial causes of bare areas are largely or predominantly physiographic. 

 Their r61e in succession is not due to their nature as physiographic processes, 

 but to their effect upon water-content. As indicated above, this effect is due 

 in some degree, and often a controlling one, to the nature of the agent. This 

 relation is not so definite, however, that the process can be substituted for 

 water-content as a basis of classification. Thus, while it is clear that a com- 

 plete study of succession must include the causes which initiate seres, it assigns 

 to physiography a subordinate r61e in classification as in development. 



Relative importance of bases. — ^The basic division of the developmental 

 classification of seres here proposed is the climax or formation. Every climax 

 is subdivided into priseres and subseres, each with a larger or smaller number 

 of adseres. Priseres and subseres are further grouped with reference to the 

 initial water-content of the bare area, in the manner indicated by Cooper's 

 distinction into hydrach and xerarch seres. Finally, these may be further 

 divided into groups based upon the causes which produce a partictilar bare 

 area. Such a classification is developmental throughout, since even the minor 

 divisions based upon initial causes have this value, if the causes are grouped 

 in accordance with their action rather than their nature. 



The climax as a basis. — ^The nature of the cUmax as the final condition of 

 the vegetation of a climatic region through a climatic period makes unavoid- 

 able its use as the primary basis for the classification of existing seres. The 

 use of the climax necessarily depends upon its recognition, and this is a matter 

 of some difficulty in the present state of our knowledge. Neither climatology 

 nor ecology has reached a point at which climatic climaxes can be delimited 

 accurately. In fact, climatology is obviously of secondary importance in 

 this connection. While it is perhaps easier to study climate than vegetation, 

 it is the latter alone which makes possible the recognition of a particular 

 climate so far as plants are concerned. In other words, a climax must be 

 determined by its developmental and structural character, as is true of any 

 biological unit. This is true in spite of the fact that cUmate is the cause of a 

 chmax, or at least the force in control of it. 



In the United States and Europe the developmental study of vegetation has 

 gone far enough to disclose a large number of seres. This has had the effect 

 of delimiting in a general way the majority of climaxes on the two continents, 

 first by determining the successional termini of the various regions, and 

 secondly, by making it possible to distinguish between serai stages, associes 

 and consocies on the one hand, and ultimate communities, associations and 

 consociations on the other. The result has been to confirm the general 

 floristic evidence as to the existence and extent of cUmaxes, though the limits 

 and relations of these are still to be determined with precision (plates 48, a, b; 

 49, A, b). 



Recognition of climax areas. — ^All the attempts to divide the surface of the 

 earth into vegetation zones or climatic regions have some bearing upon the 



