PERIODICAL LITERATURE 761 



sented by a triangle, permits of assuming that the vohime of the age 

 classes composing the last half of the total series is three-fonrths of 

 the total. 



Then if V = volume in last Vz R series, and I = annual increment, 

 which equals annual cut desired, or Y, then V = M (^^^) = ?^ I x R. 



Since Y = I, Y = ^. 



In applying this formula to selection forests, the girth which is 

 equivalent to the age of an average tree of !/> R years is taken as the 

 limit of size for enumeration of growing stock. The growth data 

 required are, the age required for the rotation, and the average age 

 of trees of different girths. 



The author claims that this formula, which can be applied univer- 

 sally, is superior to existing methods of determining the rate of growth 

 of girth classes, the number of trees which will mature in a given 

 period, and the attempt to predict loss of numbers and possibility on 

 the basis of numbers. 



The weakness in this method is its assumption of normality for 

 the younger age classes. The French Method of 1883, which has been 

 successfully applied to selection forests, is based on the principle pro- 

 posed in this formula, except that 1/3 R is the period adopted, and 

 the crop is enumerated for 2/3 R or two periods, which permits of a 

 comparison to determine whether the older age class is deficient or 

 has a surplus. By this plan the normal proportion is 3/9 to 5/9 leaving 

 ]/9 to represent the first 1/3 R in the triangle. 



Then the exploitable volume of the last ^? R is V = f (^^) = y^ 



(I x R), and Y = 



1 8 



R 



Comparing Von Mantel's formula with these adaptations we have 

 Von Mantel Y = j^\ = y^ V = V 



Indian method Y = ^ = ~^- Vi = M V 



V2 



T'^ ** .27SR ^ 2 1) 



As a short cut to the solution of the problem of increment and 

 regulation of selection forests in India it is i)rol)ablc that the proposed 

 ada])tation of Von Mantel's forniula may i^rovc distinctly useful. 



H. H. C. 

 Indian Forester. Vol. 4(5, pp. 417-421, .August 1, 1020. 



French method Y = _?' ^ = — ^- \j = ^5. v 



"H ** .27SR ^ i ') '' • 



