The floristic criterion is the most basic one in segregating units 

 of vegetation because it deals more intensively and adequately 

 with the inherent nature of each unit, including data on the 

 other criteria. It is often more convenient to use one of the others, 

 but a complete, scientific classification requires consideration of 

 species composition, in addition to the other analytic and syn- 

 thetic characteristics, of the various kinds of stands occurring in 

 each group distinguished by any of the last four major criteria 

 listed above. In America classification based on the first criterion 

 is less common because of the lack of sufficient plant sociological 

 analysis, the use of one of the others being more prevalent than 

 in Europe. Progress in America in the classification of vegetation 

 on the basis of inherent characters requires more detailed analyses 

 of the communities making up the large heterogeneous units. 



Floristic or Species Composition 



Classification on the basis of floristic characteristics or species 

 composition is based strictly on intrinsic properties of the commu- 

 nity, as shown especially in plant sociological tables (see Tables 

 3-1 and 4-1). Some stands have more characteristic species in 

 common than others, so they are placed in one community-type, 

 and similar community-types are placed in one group. Such 

 grouping of similar entities is essential for more complete com- 

 prehension and orderly presentation of isolated data developed 

 by analytic methods. 



In sociological analysis a number of inherent qualities are 

 used, and since in classification the number of criteria is limited, 

 emphasis is placed upon those qualities that are considered the 

 most significant. Ecological characterization of the units is also 

 included. In some countries, chiefly Norway and Sweden, the 

 dominant species (those with greatest numerical abundance or 

 cover and frequency) and constant species are employed for 

 arranging stands into sociations and associations, and character- 

 istic species (see p. 127) have been used for placing associations into 

 higher categories: alliance, order, and class. ^^^'^' In many other 



178 • ClassiCicatiosm of Coxnmimzmities 



