446 Forestry Quarterly. 



The following table (No. 5) gives the approximate time in 

 years required to produce different wood crops according to the 

 different qualities of site in western Washington and Oregon. 



Note — In the saw timber column the average diameter is taken as the 

 diameter of the average tree of all the trees 12 inches or more in D. B. H. 



2. The Mean Annual Groivih and the Rotation. The mean 

 annual growth of Douglas fir varies considerably for each quality. 



On the Quality I sites, the mean annual growth ranges from 

 413 feet B. M. per acre at 40 years of age to 1,013 feet B. M. at 

 no years of age. At this latter period the growth culminates, 

 decreasing therefrom to 965 feet at 140 years. 



In cubic volume, the maximum volume production is attained 

 at the age of 50 years, at the rate of 181 cubic feet per year. 

 The decline in the mean annual growth is very slow, decreasing 

 only a few feet each year, so that at 100 years the rate of growth 

 is only 6 cubic feet a year less than at 50 years. Therefore for 

 a stand which is to be managed on a cubic volume rotation, such 

 as for cordwood, pulp wood, etc., it is seen that a rotation of from 

 50 to 70 years might be best, depending much upon the quality of 

 the product desired. 



For Quality II soils, the mean annual growth in board measure 

 varies from 300 feet per acre at 40 years to 673 feet at no and 

 120 years. After this period the growth decreases gradually to 

 653 feet at 140 years. For this quality, it is recommended that, 

 silviculturally, a rotation of no years be used, with a mean an- 

 nual growth of 673 board feet per acre, making a total stand per 

 acre of 74,000 board feet. 



For a cubic volume rotation, the culmination of the mean an- 



