434 JOURNAL OF FORESTRY 



the (1) weighted yield table method, (2) "middle of period" and (3) 

 half the growth method follow : 



(1) By Weighted Yield Table Formula: 



f 5,400+5,930X4 1 , r 5,930+6,320X3 l . f 6,320+6,590X2 1 , f 6,590+6,840X1 1 



1 2 -J+l 2 j + l 2 J + i 2 J 



4+3+2+1 



^^^ = 6^066 X 10,000 = 60,660,000 cubic feet 



to be cut in a period of 40 years or 1,516,500 cubic Jeet per year. 



(2) By Middle of Period Method: 



6,320X10,000 = 63,200,000 cubic feet 

 to be cut in a period of 40 years or 1,580,000 cubic feet per year. 



(3) By Half the Growth Method: 



(5,400X 10,000) + [ ^'^^^~^'^^^ X 10,000] =61,200 cubic feet 



to be cut in a period of 40 years or 1,530,000 cubic feet per year. 



Assuming that (1) is correct then (2) is 63,500 cubic feet too high 

 and (3) only 13,500 in excess. The variations between the methods, 

 however, will have no constant ratio, but must depend on the trend of 

 the yield curve. 



It may frequently happen that (2) and (3) will be identical, namely, 

 where the average of the yield (at the initial year of the period and the 

 last year) is identical with the yield at the middle. As a whole the 

 tendency in American forest mathematics is to split hairs, whereas it is 

 essential to realize that the final cut predicted is only an approximation 

 at best. Frequently the computed yield will not be used because reasons 

 of policy or market conditions dictate cutting less or more than the 

 formula or estimated yield. For this reason the writer is cautious 

 about urging 'the weighted yield table method for computing volumes, 

 except under circumstances where exactness with long periods may be a 

 necessity. 



