VON MANTEL'S METHOD. 



101 



(c) We can now put the problem iu general terms, where 

 trees and wood are enumerated and measured down to a diameter 

 corresponding to an age X 



b' 



ox r 



The real growing stock V is now represented by A b x r, and 

 as before, it is easy to see that in r X years, the total yield = 

 figure rbb' X = 2V 



r x 



r x 



This formula is approximately true for all values of X, provided 

 that the crop is both enumerated and measured down to the 

 diameter corresponding to age X. (This diameter is in the United 

 Provinces generally 8".) To apply Von Mantel's formula to this 

 limited growing stock is wrong, and the extent of the error 

 introduced is evidently 



2V 



a v 



r 



a v 



The adoption of this formula pre-supposes the existence of 

 normal crop below age X. If these are in deficit, after r X years 

 we shall have less growing stock over age X than at present, and 

 hence the formula would then give too large a yield. 



Blanford and Simmons have worked out a very useful formula 

 (being a modification of Von Mantel's formula, and a generalised 

 modification of Howard's formula), to calculate the yield where 

 V=the growing stock enumerated to X years of age, but the 

 volume of the individual trees measured to include both timber and 

 smallwood. The formula is 



