444 ESTIMATION OF INCREMENT 



applied for the percentage increment for the past year, the 

 past diameter increment for the single year equals twice the 

 breadth of the last annual ring; equals D d, if 



D = present diameter, 



d = diameter one year ago ; 



and D + d may be taken as equal to twice the breadth of the 

 present diameter, although this is really somewhat too great, 

 and therefore gives too small a percentage ; but, except with 

 trees of small diameter, it will not materially alter the result. 



Hence : 



, Breadth of last ring in inches x 2 400 



Present diameter x 2 i 



. __ Breadth of last ring 400 

 Diameter i 



Now, in order to obtain a true average ring, the number 

 of rings forming the last inch of radius should be counted, 

 and the above formula divided by this number. 



Thus, if 



n number of rings in last inch of radius 

 D = diameter (at breast high), 



Then p = 



Dxn 



. . 



Dxn 



This is Schneider's formula, and it gives the percentage l 

 increment for the coming year that will take place on the 

 basal area at breast high. 



This formula may be represented in terms of quarter girth 

 measurement thus : 



315 



Quarter girth x n (years in i in. radius)' 



Now, as already mentioned, the percentage as indicated 

 by applying the above formulae to data obtained from 

 measurements made at breast high on standing timber, is 

 not, generally speaking, correct. 



It assumes that the height and form factor remain the 



1 This percentage is slightly too high ; and in the case of trees with 

 small diameters the discrepancy is increased. Though for the past year, 

 the percentage will be slightly too little. 



