74 THE STUDY OF PLANT COMMUNITIES * Chapter IV 



would be desirable if we had both values available for all com- 

 munities. 



Coefficient of Community.— When comparing two communi- 

 ties or the vegetation of two regions, a mathematical expression of 

 the similarity of lists of species may be useful. If community X 

 is compared to Y, the number of species common to both, ex- 

 pressed as a percentage of the number for Y has been termed the 

 coefficient of community. The same principle can be used for 

 evaluating variation or similarity among several stands of an ab- 

 stract community. Then, however, each must be compared with a 

 standard or list of the characteristic species of the community as a 



whole. 130 



OBJECTIVES DETERMINE PROCEDURE 



If these several sociological concepts are grouped systematically 

 in tabular form, their relationships become clearer (Table 5). Such 

 a grouping has the further usefulness of presenting tabulation of 

 values obtained in the field in compact and logical order for in- 

 terpretation. 



When the objective is merely to describe a community as com- 

 pletely as possible, it might well be desirable to have such a table 

 completely filled out. In studies involving the application of phy- 

 tosociological methods to special problems it is frequently onlv 

 necessary to use a few of the values. This does not mean that not 

 all are of significance, or that some can be ignored entirely. Rather, 

 it suggests that each has its uses and that some are applicable where 

 others are not. 



The limitations and possibilities of usefulness of the several con- 

 cepts become increasingly understandable after one has had some 

 experience with them. Nevertheless, selection of the most useful 

 values for study and application to a particular problem always 

 remains a matter for serious consideration. The concepts to be 

 used must be selected in terms of their contribution to the object 

 of the study, the time available, and the labor involved. 



GENERAL REFERENCES 



J. Braun-Blanquet. Plant Sociology : The Study of Plant Communities. 

 S. A. CAIN. Concerning Certain Phytosociological Concepts. 

 C. RAUNKIAER. The Life Forms of Plants and Statistical Plant Geography; 

 Being the collected papers of C. Raunkiaer. 



