100 



PRACTICAL FOREST MANAGEMENT. 



and the yield in r years = figure oraa' = 2 A aor = 2V. and 

 meanwhile the areas felled over will have grown up to give the 

 same growing stock = A aor. 



. . annual yield Y= -7- 



This is Von Mantel's formula unaltered. 



(6) 



Howard has examined this problem (vide Indian Forester 

 August, 1920), and has modified Von Mantel's formula to read 



* = TT 



This is based on the statement that by ignoring all trees 

 under ^ years 'old, V = the figure a. b. | r. 



This is true if the volume of total wood per tree down to 0" 

 diameter is included, but not otherwise. For it is obvious that 

 the volume of a crop -|- years old is proportional to the line b. g-if 

 all wood is included, but is zero if only wood exceeding a diameter 

 Y is included. In this latter case, the growing stock V is repre- 

 sented by a A on -JT as base, and if, as yield tables for sal indi- 

 cate, the volume of small wood (i.e., below 8") in a crop remains 

 approximately coristant after years old, this V will be the A V r * 



To apply Von Mantel's formula to this V will introduce a 

 very large error, to apply Howard's modification will introduce 

 smaller but still appreciable error, From the diagram it is obvious 

 that the total yield in r - years = figure r. c. b.-|-=2V 



2V 



and . ' . annual yield Y = - 



