72 BASES AND CRITERIA. 



due to a lack of both factors, though in different degree. As a consequence, 

 competition-forms can at present be used directly only as indicators of the 

 general degree of competition. In connection with the habitat-forms or ecad, 

 they have an indirect value in making it possible to distinguish in indicators 

 the direct effect of the habitat as contrasted with the added effect of com- 

 petition. 



COMMUNITIES AS INDICATORS. 



Value. — The community as an indicator is a complex of all the preceding 

 values. It derives its primary significance from the dominants, chiefly 

 through their life-forms and ecological requirements. It includes the mean- 

 ings of the less significant subdominants, and those of the much less important 

 secondary species. In short, it is a complete scale upon which all the indica- 

 tions of the habitat are written. These values can be obtained only by 

 analysis, however, and the latter leads at once to the study of dominants and 

 subdominants, both climax and serai. The general principles of the latter 

 have already been outlined under the sections on associational and succes- 

 sional bases. This leaves for consideration the various types of communities 

 and the functions and structures they exhibit. 



Kinds of communities. — With reference to association alone, three kinds o*f 

 communities may be distinguished, viz, consocial, 1 associal, and mixed. The 

 first consists of a single dominant, the second of two or more belonging to the 

 same association or serai stage, and the third of dominants from different 

 associations or associes. The basic indicator value of these is determined by 

 whether they are climax or serai. The consocial community affords the most 

 definite indication, while the associal type has the advantage of checking the 

 indications of one dominant by those of the related ones. This is even truer 

 in the case of mictia, but the indications are necessarily somewhat confused 

 here, since one set of dominants is disappearing and the other increasing in 

 number and importance. In this connection it is desirable to emphasize the 

 fact that serai and climax communities furnish not only indications of existing 

 factors and possibilities, but also of past and future ones. Each serai stage 

 indicates the preceding stage and its habitat. The climax forecasts the con- 

 sequences of any primary or secondary disturbance in it, and foreshadows the 

 effects of climatic changes. As a result, both serve as invaluable indicators 

 of the course and outcome of all possible human practices in them, and lend 

 themselves to methods of scientific prophecy which can hardly be surpassed. 

 A similar relation exists between consocial and associal communities. Wherever 

 a consocies or consociation is found, the related dominants have occurred or 

 can occur, at least with the slightest modification of the habitat. Thus, the 

 indicator analysis of a community involves not only the measurement of 

 existing conditions, but especially also a study of the linkage with the other 

 communities of the sere or the climax. For indicator research, as in all 

 serious ecological studies, any investigation which fails to take full account of 

 successional and climax relations is inadequate, and at best can only lead to 

 half-truths. 



1 This term is here used to refer to the community marked by a single dominant, whether con- 

 socies or consociation, and associal in a similar sense. Both terms are also used to refer definitely 

 to consocies and associes respectively, but the context is usually decisive. 



