PLANT SUCCESSION 225 



climate. Thus the major climax regions are easily recognized : 

 grassland, desert, and semidesert with shrubs predominating; and 

 forest climaxes that are boreal, deciduous if temperate, or broad- 

 leaved evergreen if tropical. In addition to life form there is uni- 

 formity of genera among the dominants of a climax. Variations of 

 the dominant species, as well as dependent ones, are a product of 

 the environmental variations discussed above. 



The major climaxes are distinguishable on the basis of physi- 

 ognomy or life form of the dominants alone. Such climaxes are 

 termed formations.™ Floristic variation within a formation is usu- 

 ally sufficient to produce two or more recognizably distinct cli- 

 max communities, which, following Clements, would be called 

 associations. Although distinct, the associations of a formation are 

 at the same time bound together by one or more species present in 

 all associations and by the constant presence of some dominant 

 genera throughout. Thus the associations of a formation are quite 

 obviously similar and related. 



Just as associations are recognizable subdivisions of formations, 

 there are distinguishable variations within associations. These geo- 

 graphical variants that make up the association are called facia- 

 tions. 60 They are recognizable by differences in the abundance or 

 relationships of the dominants. Faciations may be further subdi- 

 vided into local variations, called lociations. Further subdivision is, 

 of course, possible and often desirable. The various systems of 

 classification and the terminologies that have been used make for 

 more detail and controversy than can be presented here. 



Because, unfortunately, the term, association, is constantly used 

 in more than one sense, it deserves further mention. The systems 

 of classifying communities, as supported by the various schools 

 of thought, almost invariably include the term. Although not 

 always in agreement among themselves, European ecologists con- 

 sistently consider associations as basic units of classification that 

 can be grouped into categories of successively higher rank. Thus 

 lociations, as mentioned above, might be given associational rank 

 in such a system. The use of the term here is in an absolutely 

 contrasting sense in that it makes it a community of the highest 

 rank, inclusive of, and divisible into, numerous lesser categories. 

 It has been suggested that, to avoid conflict, the use of the term 



