3:g journal of forestry 



ber — which is the center of interest in forestry, as bushels of potatoes 

 or barrels of corn are in agriculture — is the direct and reasonable 

 measure of the site when it is available. The truth is that it is rarely 

 available. We have yield tables for a number of species, which are in 

 all or nearly all cases based upon and only intended to be applied to 

 even-aged, well-stocked stands. Thus our yield tables, w^hich are 

 themselves site class tables, cannot be used directly in the identification 

 of sites except when the stand is even-aged and well-stocked. In these 

 tables, however, a relation between yield per acre of regular stands 

 and height grow^th of dominant trees is shown to exist, permitting 

 the use of the latter as a guide to the former. This relation is true 

 of board foot as well as cubic foot yields. There are other factors — 

 total basal area, number of trees per acre, and average diameter — 

 which vary with the yield, but none of these compares with height 

 growth in degree of freedom from the effect of influences v.hich are 

 not inherent in the site. Of all the factors of yield, height growth is 

 the best expression of the physical components of the site. It is the 

 most convenient since it makes possible the identification of sites by 

 the simple determination of the age and height of dominant trees. In 

 the case of forest lands not well stocked it is tJie only possible factor 

 which could be employed without laborious and as yet doubtfully prac- 

 tical studies of the physical factors themselves. 



The American yield tables have been criticized for their failure to 

 describe sufficiently, if at all, the physical factors of the sites. This 

 failure to tie up the causes with the efifects produced w^as unfortunate 

 but apparently unavoidable, since we yet have n.o simple way of 

 measuring and expressing the significant physical factors, suitable 

 for use in every day field work. Meanwhile there is much work to do. 

 Large areas, often of complex topographic and soil character, must 

 be classified in some way reflecting the growth potentialities. With 

 some easily observed precautions, the rate of height growth (summed 

 up by Roth, for classification purposes, as the height at a commonly 

 agreed upon age), furnishes a means of accomplishing this. 



There is nothhig new in the use of height as an indicator of site 

 quality : witness the yield tables above referred to. The novelty con- 

 sists in the proposal to standardi::c its use and extend it beyond the 

 yield tables to which it has hitherto been restricted. 



