LAWS OF DIAMETER GROWTH IN EVEN-AGED STANDS 355 



the greater the age with which the resulting growth curve will coincide as an expres- 

 sion of yield per acre and average tree; e.g., for predicting the growth to 35 years of 

 stands now 20 years old, the group of trees, A to H, whose average tree is D, must be 

 included, omitting classes J to L which would lower the average tree at 20 years 

 to F. 



Fig. 71. — Number of trees in each diameter class in normal stands at four successive 

 ages, and resulting curves, when averaged respectively on basis of age and of 

 diameter. 



The composite curve of average growth in which each successive decade is based 

 on a lesser number of trees than the preceding period, is a useful tabulation to show 

 the average diameter of surviving trees at given ages, but as shown does not correctly 

 indicate the progress of growth for any of the trees on which it is based, unless it is 

 confined to a given number of trees throughout. 



