THE PACIFIC NORTHWEST 75 



necessary if the cutting amounts only to selection of the mer- 

 chantable trees and leaves a fair stand of smaller ones. In 

 the latter ease, yield tables based on average acreage produc- 

 tion are of little use because so much depends upon the char- 

 acter of the stand which remains on the tract in question. 

 Here the basis must be the rate of growth of the average indi- 

 vidual tree. An estimate by the number in each present 

 diameter class may be made of the trees which will escape 

 logging, showing, let us say for example, about five trees of 

 each diameter from 6 to 12 inches, or thirty-five in all which 

 are over 6 inches. If the growth study indicates that in 20 

 years there will have been added 6 inches in diameter we can 

 estimate a crop of five trees each of classes extending from 12 

 to 18 inches. Actually the process will not be so simple, for 

 the different aged trees will not grow with equal rapidity, 

 and several other factors must be reckoned with, but the gen- 

 eral principle is to apply rate of growth knowledge to the 

 material on hand, and study of this material is essential. 



For predicting even-aged crops resulting from entire re- 

 stocking, the acquisition of necessary basic information is as 

 difficult, or more so, but its application is far simpler. That 

 the ground will be fully stocked by natural or artificial means 

 must be assumed, but we can also assume that the result will 

 be influenced only by normal locality conditions and not by 

 accidental condition of the present forest. Therefore we use 

 a yield table and not a growth table. This can be made by 

 actual measurement of existing second growth stands of dif- 

 ferent ages, which proves not only the growth rate but also 

 the number of trees which the natural shade-thinning process 

 results in at different periods of the forest life. The chief 

 danger of inaccuracy in such information lies in basing it on 

 insufficient measurements or in applying it where soil or 

 moisture conditions are greatly different. The latter error 

 can be guarded against, however, by use of growth figures 

 taken in conjunction with it. For example, if a yield table 

 showing 25,000 feet to the acre at 50 years from seed is ac- 

 companied by one showing that the average stand it repre- 



