X. CLIMAX FORMATIONS OF NORTH AMERICA. 



Classification. — In attempting to give a summary of all the studies of suc- 

 cession in North American vegetation, a number of difficulties have been 

 encountered. The chief of these has been in determining what articles should 

 be included. Besides those that deal directly with succession, which consti- 

 tute a minority, there are a large number which deal only with structure or 

 floristic, as well as with single processes or factors in development. In addi- 

 tion, there are many papers which have to do with historical problems in 

 vegetation, but are based only upon general observations. A striking example 

 of these is found in the literatuse dealing with the origin of the prairies. It 

 has been impossible to follow any rule consistently, beyond that of including 

 all articles which deal directly with the course of development, whether suc- 

 cession was the real objective or not. In this connection, two groups of 

 papers have proved particularly troublesome. Since the extent of climaxes 

 has necessarily made them the chief subject of floristic and formational study, 

 one encoimters a great nimiber of such articles which have at least a slight 

 connection with succession. These have been abstracted, however, only 

 when the developmental relation is intentional or at least primary. In other 

 cases, their titles are cited in the bibliography, but in general they have been 

 ignored. This has been the practice also in regard to articles which deal with 

 the effect of fire or lumbering on vegetation, but only in general terms. 



As to the abstracts themselves, it has proved impossible to make them aU 

 with the same thoroughness or detail. The earUer studies in one region are 

 often more important than later ones, which are necessarily repetitions in 

 some degree. In many the whole treatment is local and concrete, while in 

 others the scope is broader and permits the drawing of general conclusions. 

 In a few cases, moreover, abstracts or quotations have already been given in 

 earlier chapters. Finally, the limitations of space have often made it neces- 

 sary to treat a book of several hundred pages with relatively much greater 

 brcArity than an article of a score or more of pages. A usable abstract of a 

 paper may be given in less than a page, but for a book such an account can do 

 little more than indicate its scope. 



The abstracts are grouped in accordance with the classification of seres 

 proposed in Chapter IX. The first division is into climaxes, which are sub- 

 divided into prisere and subsere. The former is fiu-ther divided into hydrosere 

 and xerosere. In each of the groups the arrangement is chronological, in 

 order to give some idea of the historical development of successional investi- 

 gation in each region. The deciduous forest, prairie-plains, and Cordilleran 

 climaxes, however, are the only ones in which there has been a sufficiently 

 large number of studies to warrant the grouping indicated above. 



THE DECIDUOUS FOREST CLIMAX.' 

 PRISERE: HYDROSERE. 



The first studies of succession proper in lakes and swamps were made by 

 MacMillan (1894, 1896, 1897), as indicated in Chapter II. Shaler (1886, 

 1890) had proposed a classffication of swamps, which has much interest his- 



^The few articles on the northeastern climax are included here for the sake of convenience. 

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