350 FOREST INDICATORS. 



various degree, so is it desirable to recognize several categories of site. Climax 

 and serai habitats or sites are fundamentally different, though they are often 

 found side by side. The habitat of one consociation differs from that of 

 another of the same association, and mixed areas of the two show subordinate 

 differences. Finally, the same consociation exhibits marked variations in 

 growth and density, each corresponding to smaller differences of the factor- 

 complex. 



In practice, the forester has emphasized two of the several categories of 

 sites. The first is the consociation habitat or the site occupied by a dominant, 

 and the second the minor sites marked by significant differences in the growth 

 or density of a particular dominant. The more specialized use of the word 

 has been in the latter connection (Roth, 1916: 3; 1918: 749; Watson, 1917: 552; 

 Bates, 1918:383). As a matter of fact, the two types are developmentally 

 connected, the growth sites, commonly designated as I, II, III, and IV, repre- 

 senting a sequence of minor habitats within that of the dominant consociation, 

 such as Pinus ponderosa, Pseudotsuga, etc. The recognition of growth sites 

 is chiefly important in connection with yield tables and working plans. In 

 planting operations, consociation sites must first be determined, and then 

 growth sites may be employed to ascertain the most promising areas. 



Growth as an indicator. As stated in a previous chapter, the presence of a 

 dominant furnishes one set of indications, and its growth, another. The 

 latter naturally affords a more sensitive scale of measurement, and hence 

 indicates the effective differences of the habitat in terms of timber production. 

 It is obvious that total growth is the most complete indicator, as Bates has 

 insisted (1918 : 383), though it is equally clear that height-growth or even width- 

 growth may be used with much success. Since readiness and convenience 

 are essential in the practical use of indicators, height-growth has received the 

 most attention at the hands of those interested in the classification of sites. 

 The whole question of site indicators as well as the advantages of height-growth 

 in this coimection has been well stated by Frothingham (1918 : 755) : 



"Any method of determining forest sites must employ an indicator, whether 

 this be the probable ultimate forest ('climax type'), the height-growth of one 

 or more species present, the current annual volume increment of a fully 

 stocked pure stand, some herb or shrub typical of a locaHty, or merely the 

 composition of the existing stand. Similar sites are then to be recognized 

 either by the identification of similar indicators or by determining the simi- 

 larity of the physical-site factors. These may be measured in precise terms 

 or simply estimated. Precise measurements appeal to the investigator. 

 Accepting the permanent type as an indicator, for example, it would only 

 remain to learn quantitatively the physical factors determining it. These 

 physical factors wherever found interacting in precisely the same amounts 

 will always produce, in time, barring accident or design, precisely the same 

 form of forest. The plan of classification based on physical factors appeals 

 to the investigator because it is truly fundamental. The apparent difficulties 

 in deciding what is the permanent type in the isolation and measurement of the 

 several physical factors, etc., may not be so formidable, after all, and the work 

 may be simphfied by the discovery that only one or two of the factors are of 

 particular significance. In many large regions, the permanent forest type is 

 strikingly apparent. In other places it remains exceedingly obscure. Even 

 where plainly evident, subdivisions with reference to yield are a necessity 



