THE THEORY AND PRACTICE OF WORKING PLANS 175 



period to the rotation which is usually ^ = ^- An annual 



sustained yield is not required, but, under regular conditions, the 

 periodic yield must be sustained even for the individual blocks; 

 under irregular conditions more than the normal area can be 

 cut if there is an excess growing stock, and vice versa. With 

 species requiring a long period of reproduction (e.g., natural 

 reproduction by shelterwood-selection method often requires 

 forty years) the areas are allotted in detail for the I and II 

 periods, but not the volumes. 



The cutting is virtually restricted to the stands indicated 

 for the I period. The manifest impossibility of selecting such 

 stands twenty years in advance and then barring all the others 

 has led to a universal demand for the ''Opening of the II 

 Period." This is met by providing for an intermediate revision 

 in the eleventh year which may lead to the preparation of a 

 new cutting plan. 



The choice of stands for the I period, i.e., the stands to be 

 cut during the next twenty years, is prescribed as follows: 

 Mature stands and defective stands are chosen first. Without 

 undue sacrifices the object to attain is the equalization of the 

 age-class distribution by smoothing out the age differences 

 between subcompartments (unless they are extreme), but not 

 having too large adjacent areas of the same age class, because 

 of the increased danger from fire, insects, windbreak, etc., in 

 coniferous stands especially. Cutting series are, therefore, 

 advised and so many points of attack that each cutting area 

 will have become stocked with young, thrifty growth before 

 the adjacent area is cut. This usually means a wait of twenty 

 years. 



The rotation for the chief species is determined for all Prus- 

 sia, hence only departures therefrom need detailed explanation 

 and justification. 



The yield or allowed cut for the twenty-year period is the 

 growing stock on the cutting areas of the I period plus the 

 increment thereon during ten years (half the period). This 



