THE THEORY AND PRACTICE OF WORKING PLANS 97 



The resulting surplus will be 1,100,000 — 220,000 = 880,000 M. 

 This surplus is to be removed during the first third of the 

 rotation. The cut for the first third of the rotation will there- 

 fore be the 880,000 M., surplus and the 700,000 M. normal 

 volume of old trees, plus the increment on their sum. This 

 increment will be 12,000 M. per annum, or 12,000X30 = 360,000 

 for the sixty-year period.* Therefore the annual cut for the 

 first third of the rotation will be: 



,, 880,000+700,0004- S60,000 T,*- r . 



Y = '—^ ^ = 32,333 M. feet. 



This amounts to 1.61 per cent of the total volume. Not 

 counting the surplus or increment on the surplus, there will be 

 a cut of only 853,000 M. feet for the sixty-year period, or an 

 annual cut of only 14,216 M. feet. This is but .71 per cent of 

 the total volume, or approximately the increment on the group 

 of old trees. 



In carrying out this method, site qualities producing very 

 marked differences in growth must be distinguished in the field 

 work and kept separate in the computation. For instance, in 

 some of the very dry limestone soils of the Western yellow-pine 

 belt of the Southwest the trees are small and stunted, and even 

 when mature hardly reach the diameter of poles on ordinary 

 sites. Such areas if small and unimportant may be thrown 

 out and ignored; but if of some extent they should generally 

 receive a separate calculation and proper consideration in the 

 final allotment of the cut. 



(c) Value and Application. — A disadvantage of the French 

 method is that it requires the tallying of trees down to one- 

 third of exploitable diameter. This means that if the ex- 

 ploitable diameter is 24 inches, everything above 8 inches must 

 be tallied. It is, therefore, best adapted to a high diameter 

 limit and long rotations, which is, however, generally the case 

 in many of our selection forests. The advantages of the method 



* The increment is taken for only half of the period because cutting is 

 going on. 



