348 FOREST INDICATORS. 



Edaphic indicators.— These are either climax or serai dominants and sub- 

 dominants. Serai dominants are typical edaphic indicators, since they mark 

 the changing conditions of the habitat in its progressive development to the 

 final climax condition. Climax dominants differ in their requirements and 

 necessarily show indicator responses to local edaphic as well as general cli- 

 matic conditions. Subdominants, whether serai or climax, mark minor differ- 

 ences in the habitat, and serve also to indicate the dominants in many cases 

 where these have been destroyed or removed. The most striking edaphic 

 indicators are the seres which arise in bare or denuded areas. Each prisere 

 not only marks a particular type of initially bare area, such as water, rock, or 

 dune-sand, but it also indicates the changes of the habitat complex, as well as 

 the final climax. As already mentioned, each serai stage or community 

 indicates a certain set of factors, and at the same time the stages which are to 

 come in the development of the climax. This is likewise true of subseres, 

 which differ from priseres chiefly in arising in areas denuded by fire or other 

 accident, or by the agency of man. They are much more numerous than 

 priseres, the successional movement is much more rapid, and the stages fewer. 

 Each subsere is an indicator of the disturbance process that originated it, and 

 its stages mark the different degrees of development of community and habitat 

 on the way to the climax. Such stages, or associes, occur in both subsere and 

 prisere. Each marks a particular stage of the habitat which controls it, and 

 in turn reacts upon the habitat to produce the next stage. It consists of two 

 or more consocies, or serai dominants, which indicate minor changes in the 

 stage and hence perhaps different areas of habitat. In addition, each serai 

 community contains a varying number of subdominants which constitute 

 socies, corresponding to the societies of climax communities. The socies 

 mark the more minute differences of the habitat, and perhaps also the minor 

 movements within the associes. 



The most important edaphic indicators are those which denote differences 

 in water-content, light, or soil, or mark the effect of disturbing agencies, such 

 as fire, grazing, etc. In addition to the presence or composition of a com- 

 munity, its growth or the growth of one of its dominants serves as an indi- 

 cator of variations in the habitat complex or of site quality. 



Water-content indicators.— In the several forest climaxes, the physical pro- 

 perties of the soil in relation to water-content are so much more important 

 than the chemical that the latter require little attention. As a consequence, 

 the indicators of water-content serve as indicators of soil texture, aeration, and 

 temperature as well. The water relations of the climax and subclimax 

 dominants have been considered briefly under each forest association. The 

 climatic relations of the dominants of a community are reflected in the edaphic 

 ones, and this may even be true of the dominants of different formations. 

 The dominants of drier climates or subclimates take the drier slopes and ridges 

 of the local area, and those of moister climates grow on northerly slopes and 

 in canyons or valleys. Picea engelmanni frequently reaches the lower limit 

 of the montane forest along the moist canyons of north slopes, while Pinus 

 ponderosa extends to the middle of the subalpine forest zone or even higher on 

 dry and warm south slopes. In short, dominants indicate the total water 

 relation, and hence their climatic indications may be completely subordinated 

 to local conditions. 



