CLIMATIC AND EDAPHIC INDICATORS. 345 



The greatest importance of the successional basis for the classification of 

 forest types lies in its indicator values. The climax communities of different 

 degree are the indicators of the climates and subclimates, while the serai com- 

 munities indicate soil and other local or edaphic conditions. At the basis of 

 succession he competition and reaction, and within the control of the climate, 

 these are the forces which largely determine the density and growth of stands. 

 But even greater indicator values inhere in the sequence typical of succession. 

 Each stage indicates not only its particular habitat, while its variations in 

 composition or structure indicate similar variations in the controlling factors. 

 In addition, it serves to indicate communities and habitats which have pre- 

 ceded it, and those which will follow it. Seen in its successional relation, each 

 community or cover type is an indicator not only of physical conditions, but 

 also of the past history and future possibilities of the area concerned, and hence 

 of the system of management or of planting. 



Significance. — The primary value of forest indicators lies in denoting the 

 physical factors in control. The climax communities of different degree indi- 

 cate the corresponding climates and their subdivisions. The serai communi- 

 ties indicate local or edaphic conditions, usually of water-content, and at the 

 same time mark the presence of progressive changes due to reaction. The 

 dominants of both climax and serai communities serve to measure the light 

 relations, and this is especially true of tree seedlings and of the subdominants 

 that form the societies of the forest floor. Processes, such as fire, lumbering, 

 grazing, etc., that produce disturbance, are either marked by relicts of the 

 original vegetation, or by subseres more or less typical of the particular pro- 

 cess. Growth is one of the most sensitive and hence one of the most important 

 of indicators in the detailed study of communities and stands. Furthermore, 

 the climax and the serai stages of a region taken together determine the 

 general type of management possible or desirable. The composition and 

 successional position of the community in any particular spot furnish a clear 

 indication of the type of management necessary to the utilization of a certain 

 species or stage as the preferred crop. Since succession is essentially progres- 

 sive in nature, the maintenance of a particular crop or rotation depends upon 

 a knowledge of the competition and reaction of the dominants, and the relation 

 of these to the successional movement. In any climax, there will be seres in 

 all possible stages of development. Some of these will need to be held in the 

 present stage, while in other cases the progressive movement must be favored 

 or hastened, and in still others it will need to be retarded. Whatever the 

 desired method, when the dominants in possession are used as indicators of 

 the forces which initiate and maintain the succession, it becomes possible 

 to adjust the system of management to all the differences in composition and 

 development. 



CLIMATIC AND EDAPHIC INDICATORS. 



Climatic indicators. — It is axiomatic that all forest climaxes are indicators 

 of forest climates. The four climax formations, woodland, montane forest, 

 Coast forest, and subalpine forest, indicate as many corresponding forest 

 climates, while the scrub formations and especially the chaparral indicate 

 climates in which water conservation is important. It is well understood 

 that the three mountain climaxes indicate climates with a progressive in- 



