Current Literature. 441 



obtained when Douglas fir is placed under a definite system of 

 management. For that reason, the yield shown, in the tables is 

 higher than is attained now in the average run of Douglas fir in 

 its present state of growth. 



The yield tables in this report indicate the average yield for 

 each quality and not the maximum yield which can be obtained 

 under very favorable conditions. Therefore these tables are 

 very conservative on the whole and can be safely used after the 

 conditions and quality of the site have been determined. In ap- 

 plying the tables, it is very important that the quality of site be 

 known, and in many cases this is a difficult matter to decide 

 easily. Therefore, in study No. 7 there is a discussion concern- 

 ing the question as to the determining factors. 



The data for these tables was secured by the method of stand 

 measurements, consisting of ascertaining the size and number of 

 trees per acre in even-aged stands of various ages. About sixty- 

 one tracts', ranging in age from 24 to 137 years, were measured, 

 in each of which from five to thirty-three sample plots, in size 

 from one-sixteenth to one acre, aggregating 598 in all, were ex- 

 amined. The diameter of each tree on the plot and the heights 

 of a few of them were measured and the data systematically 

 tallied. 



The tables were derived by applying volume tables found in 

 Forest Service Circular 175 "The Growth and Management of 

 Douglas Fir in the Pacific Northwest" by T. T. Munger, to the 

 actual sample plots measured in stands of various ages, and the 

 results read from evened-off curves. The yield in cubic feet in- 

 cludes the contents of the whole stem of all trees ; that in board 

 feet includes only the merchantable contents of the trees which 

 are 12 inches or more in diameter breast high. 



