122 THE THEORY AND PRACTICE OF WORKING PLANS 



such it has been termed by him for convenience the " American " 

 method of regulation. 



Step I.— The forest is grouped into four or five rough age 

 classes such as: 



1. Decadent (overmature) O 



2. Mature (mature) M 



3. Young merchantable (young) Y 



4. Immature poles (poles) P 



5. Immature saplings (saplings) S 



6. Seedlings (reproduction) R 



The rotation age may coincide with the upper limit of 

 class 3. 



Step 2. — Find the average age of each age class either by 

 area or by volume (as described under method 8) or by draw- 

 ing a curve of height on diameter for the t\pe, and thus secur- 

 ing a t}'pe volume table based on diameter alone. The aver- 

 age volume of the trees in the age class is found from knowing 

 the total volume and total number of trees. The diameter, 

 which corresponds to this average volume, is taken direct from 

 the volume table, but interpolated to one-tenth of an inch. 

 The age of a tree of this diameter is found from the growth 

 curve of diameter based on age, prepared on a similar site 

 by analyzing the growth on stumps. This age is accepted as 

 the average age of the class. 



Step 3. — The volume in each group, or age class, is com- 

 puted from reconnaissance. 



Step 4. — From the yield table (which may be constructed 

 by any of the accepted methods) read the current annual in- 

 crement per cent for stands of each age class. The increment 

 in decadent stands (overmature) may be a minus quantity. 



Step 5. — Plan to remove the volume of the decadent class 

 within a given period (I) corresponding to the quantity and con- 

 dition thereof, the distribution of the age classes * and the 



* The presence of large areas of immature timber of good size should permit 

 the more rapid cutting of the older stands. 



