THE THEORY AND PRACTICE OF WORKING PLANS 123 



possibility of heavy cutting. The total cut for the period will 

 be the volume of the decadent class plus half the growth (or 

 minus half the loss) for the period as found in step 4. The 

 annual cut equals the cut for the period divided by the number 

 of years. 



Step 6. — Plan to remove the volume of the mature class in a 

 period (II) beginning in the year when the volume of decadent 

 timber is exhausted and stretching over a number of years 

 according to its acreage and volume. The total cut for Period 

 II equals present volume of the mature class plus the growth 

 during Period I plus one half the growth (or perhaps minus 

 one half the loss) during Period II. 



Step 7. — Treat group 3 the same way, remembering that 

 the calculation becomes increasingly uncertain the more remote 

 the period. 



Step 8. — Determine for groups 4, 5 and 6 the per cent of 

 total area occupied and assign to it a period at the end of the 

 rotation equaling this per cent of the total rotation. 



Step p. — The sum of the periods should equal the number of 

 years in the rotation, since before the expiration of the full 

 rotation all timber now growing, from seedlings up, will pass the 

 exploitable age. 



Step lo.^Should the first arbitrary assignment of periods 

 give very irregular yields, alter the lengths of the periods and 

 recompute the yields, until the desired equalization of yield is 

 approximated. 



(b) Example. — The complete figures of an example are too 

 extended to be given here; however, as worked out by the 

 author for Western yellow pine on the Coconino National 

 Forest in Arizona in 19 13, this method gives, for an area of 

 100,000 acres, an annual cut of 12,160 M. feet b.m. or, on a 

 basis comparable with the data used in figuring the cut by 

 ether methods, of 4,053,333 feet b.m., as against 6202 M. feet 

 b.m. by Heyer's formula (No. 9), and 5457 M. feet b.m. by 

 Hufnagl's method (No. 12, Var. II). This bespeaks a thor- 

 ough conservativeness of regulation by the American method. 



