Current Literature. 447 



nual growth is at the age of 55 years, at which period the growth 

 is 147 cubic feet a year. After this age, the decline is very 

 gradual, allowing a rotation of from 50 to 60 or 70 years, ac- 

 cording to the quality of the products desired. 



On Quality III sites, the mean annual growth in board feet 

 culminates at the age of 115 years, giving a growth of 505 board 

 feet per year, making a stand per acre of 58,000 feet B. M. 

 This period may be considered as the silvicultural rotation of 

 Douglas fir stands on the poorest quality of soils. 



Taking the cubic volume, the mean annual growth culminates 

 at the age of 50 years, with a rate of growth of 113 cubic feet a 

 year. The decrease is gradual from this period, making a rota- 

 tion of from 50 to 60 or 70 years possible. 



In the following table (No. 6) is given the length of rotation, 

 the mean annual growth, the stand per acre, for the different 

 soil qualities. 



TABLE No. 6. 



Table showing the silvicultural rotation for cubic volume and board vol- 

 ume production for three qualities. 



CUBIC VOLUME BOARD VOLUME 



Quality Mean An. Mean An. 



Rotation Yield Growth Rotation Yield Growth 



Years Cu. Ft.. Cu. Ft. Years ft. B. M. ft. B. M. 



I 52 9,050 181 no looM 1,000 



II 55 8,110 147 no 74M 673 



III 52 5,650 113 115 58M 50s 



3. A Study of the Site Qualities of Washington and Oregon. 

 In this discussion an attempt is made to classify the soils of 

 Oregon and Washington into different site qualities on the basis 

 of the cubic volume of Douglas fir stands. 



In summing up the question of sites, the following conclusions 

 are reached: 



1. In the State of Washington about one-half the Quality I 

 sites will be placed under cultivation for agricultural crops ; in 

 Oregon much of this quality is absolute forest land. 



2. The Quality III sites in both states will always remain as 

 true forest land. 



3. The Quality II sites both in Washington and Oregon will 

 only in part be turned over to the raising of agricultural crops. 



