176 CLASSIFICATION OF SERES. 



and the greisit advances in these fields are regarded as necessarily consequent 

 upon an increased knowledge of development. What is true of the individual 

 and the species seems equally true of the community. Studies of physiognomy, 

 floristic, and habitat all have their importance, but their chief value lies 

 in their correlation into the basic process by which communities arise and 

 grow, namely, development. It is evident that our knowledge of develop- 

 ment will advance more slowly than it will in the three fields just mentioned, 

 but it is also clear that the final importance of any advance will depend upon 

 its developmental significance. 



The natural classification of seres rests upon the fact that each sere leads to 

 a climax or formation. Hence, the fundamental grouping of seres is deter- 

 mined by their relationship to a particular formation. As a consequence, all 

 the seres of one formation constitute a natural group, strictly homologous 

 with all the seres of another formation. Thus, all the existing seres of the 

 world fall into as many coordinate groups as there are climatic climaxes in 

 vegetation. In short, the primary division in a natural classification of seres 

 is that into climaxes or formations. As previously indicated, the latter fall 

 into the major developmental groups of clisere and cosere. While formations 

 may also be arranged in formation groups, classes, or types, for convenience of 

 reference, such groupings seem unfortunate in that they tend to postpone a 

 natural classification (plate 47, a, b). 



The grouping of seres within each formation should also be based upon 

 development. The reasons for the distinction of primary and secondary seres 

 have been discussed at length (pp; 60, 169), and it is only necessary to empha- 

 size the fact that these represent the basic developmental differences within 

 the formation. The actual recognition of priseres and subseres is a simple 

 matter, except occasionally in the final stages which are converging into the 

 climax. The distinction between primary and secondary bare areas is readily 

 made as a result of experience in successional investigation, though it should 

 always be checked by instrumental study. The only possible diflSculty with 

 the division into prisere and subsere arises when the secondary disturbance 

 is so profound as to cause the resulting area to approach the condition of 

 a primary one. The difficulty here, however, is not one of distinguishing 

 prisere and subsere, since the distinction between them is clear-cut. The 

 prisere repeats the whole course of normal development, the subsere retraces 

 only a part of it. The subsere regularly comprises the later half or less of the 

 succession. While it may exceptionally begin at an earlier point, its initial 

 stage is always subsequent to the pioneer associes of the prisere. In short, a 

 subsere can never begin on an initial bare area of rock, water, or sand unless 

 the effects of plant reaction are already manifest in it. 



Initial areas and causes. — It has already been shown that the significance 

 of initial areas for succession lies in the conditions as to water-content, and not 

 in their causes. Since the initial water-content is determined in some degree 

 by the initial cause, the latter may be used as the basis for subdivisions. In 

 this connection, however, it is necessary that the causes themselves be con- 

 sidered and grouped from the standpoint of their effect upon water-content, 

 and not from that of their nature. Such a classification would regularly sepa- 

 rate erosion and deposit by water, since the one produces relatively dry and 

 the other relatively wet initial areas. It would bring them together when they 



