344 FOREST INDICATORS. 



not always represent physical conditions of growth, as the same site classes 

 may be found in stands which have entirely different physical conditions of 

 growth; in other words, belong to two distinct forest types. Site class, there- 

 fore, while it indicates the actual character of the timber found on the ground, 

 is not a silvicultural unit which can be used in management. The average 

 height of the stand or site class may be the result of the interference of man, 

 fire, animals, etc., and for this reason can not always be taken as the true 

 measure of the productive capacity of the soil, even within the same type. 

 The classification of stands on the basis of their average height is still further 

 deceptive, because it does not take into effect the taper or the soundness of 

 the timber, two qualities closely connected with the physical conditions of 

 growth of the stand. The use of quality classes alone as indicators of the phys- 

 ical conditions of growth is as misleading as to use the composition of the 

 stand for determining forest types. Both at best show only the actual 

 condition of the stand, but are entirely mute as to the physical factors that 

 are the cause of it." 



The question of sites and their recognition has received much attention at 

 the hands of foresters. It is essentially a matter of indicator values, in which 

 growth, or its consequences, furnishes the indications desired. For this 

 reason it is discussed briefly in a later section on growth as an indicator. 



Succession as a basis. — A complete and satisfactory solution of the forester's 

 difficulties in the recognition and use of types and sites is possible only on the 

 basis of successional studies. Succession at once removes the confusion be- 

 tween sites and types, since it emphasizes the basic relation of the two as cause 

 and effect. The site or habitat is the controlling cause and hence the explana- 

 tion of the type or community, but is itself reacted on by the latter in such a 

 way that it passes through a number of developmental stages to the final 

 climax condition, each stage marked by its characteristic community. An 

 adequate study of the community can no more neglect the habitat as cause 

 than it can the community as effect, and also as the cause of modifications in 

 the habitat. Moreover, it leads to confusion in the minds of others to use 

 such terms as physical type and cover type, which appear to ignore one or the 

 other. This is abundantly shown by the opinions cited above, in which essen- 

 tial uniformity is often completely hidden by superficial disagreement. 



But succession does not merely put type and site in this proper relation to 

 each other. It is even more important in furnishing the only basis for the 

 natural classification of types, and hence of sites also. Other bases may be 

 natural in some degree, depending upon the criteria used, but development is 

 the only one which takes into account all the factors and processes concerned 

 and in their proper relation (Plant Succession, 111). Its essential feature 

 is the recognition of the forest as a complex organism with a characteristic 

 structure and development. The mature or adult stage is the climax forest 

 while its development is represented by a series of typical stages or com- 

 munities arising in bare or denuded areas. The climax communities corre- 

 spond with permanent types, and the developmental or serai ones with tem- 

 porary types, while both are cover types where they actually occur on the 

 ground. The management type, whatever its name may be, is peculiarly 

 successional in nature, since it depends not only upon the climax and its 

 succession, but also upon the degree to which the latter can be controlled in 

 the interests of optimum production. 



