50 



According to Pressler this formula gives the percentage of 

 increase in volume not only for the stem alone, but also for the 

 entire tree inclusive of the branches ; and experiment has proved 

 this assumption of Pressler's to be very nearly true. 



In order to simplify the calculation, Pressler employs the relative 



diameter A = - , in which D = the actual diameter exclusive 



8 



of bark, and 8 = the increment of the diameter during n years. 

 Now since 



D = SA, and d = 8A 8 = 8 (A 1), we have 



and also p = . _J2 x approximately. 



For the calculation of the future increment per cent., the pro- 

 bable diameter after n years may be assumed to be D + 8, and 



. , ! (A + l) 2 A 2 200. 



increment per cent, to be approximately 1 J- -x -- - 



Pressler has published tables showing the values of this percentage 

 for different values of A from '2 to 300. 



In the case of standing trees, of which only the increment of 

 diameter at the base can be measured, and rarely, if ever, the 

 height, the percentage of increase in volume cannot be determined 

 with any very jjreat accuracy. For such trees Pressler has drawn 

 up a set of tables for determining, with the aid of the relative 

 diameter, the rate of increase per cent, for five grades of height- 

 growth. In order to determine the percentage with sufficient 

 approximation without the aid of such tables, we must first find 

 1) and d = D 8 by measurement, and, then the rate per centi 



. ,. Ttli 200 , 



of increase m diameter = p d - ^ x - (f or a single year p d 



*.JJ -J- d .11 



100A\ 



- I, and the minimum increase per cent, or volume p v = 



2 p d . In most instances varies from fc p A to 3 p d , and in the 

 cape of trees enjoying t ;11 height-increment and forming a 

 canopied crop, p v = 8|[ p* v 



In calculating the increment per cent, for a single year, we may 

 employ BREYMANN'S formula. On page 48 it has been shown that 

 tho increment on volume is approximately equal to 



