188 THE THEORY AND PRACTICE OF WORKING PLANS 



by means of prompt reproduction, care of soil and growth, the 

 increment in volume and in value is furthered, then the demands 

 of a sustained yield are fully met. 



In the normal forest the periodic cutting area is constantly 



equal to — : X 20. Where the age-class distribution is 



Rotation 



abnormal this figure can serve only as a means of comparison. 



In such a case the periodic cutting area is the sum of the stands 



requiring cutting for silvicultural reasons {" hiebsbediirftig "), 



stands now mature (" hiebsreif ") or becoming mature in the 



next twenty years. 



Where the distribution of the age classes shows 'a marked 

 departure from the normal, the progress of the cuttings must 

 be gauged for several decades in advance, so as to foretell the 

 progress which the cutting of the present working period will 

 make toward a normal distribution of the age classes. This 

 is to be done schematically according to the following form: 



Premise. — Rotation = ioo years. Area = 982.2 acres. 



-KT 1 • !• • 082.2 , 



JNlormal periodic cutting area = ^ — -X 20 = 190.4 



100 



acres; for silvicultural reasons (overmaturity and poor growth) 

 this has to be increased to 258 acres. This overcutting is 

 then equalized in ensuing periods. (See p. 189.) 



The distribution of cutting areas for the ensuing working 

 period is not confined to assigning half the periodic area to the 

 ten years elapsing before the intermediate revision. The admin- 

 istrative officer in charge of the forest requires leeway in the 

 choice of where to cut; for he must vary his points of attack, 

 use to the full each seed year, secure a mixture of species by 

 advance reproduction of certain ones (e.g., of fir in spruce-fir 

 type; of beech in pine-beech t^pe), take thought of the fluctua- 

 tions in the demand for timber, aim to secure each year an 

 approximately equal revenue, etc. This is possible only if 

 the field of operations is larger than the mere ten-year cutting 

 area. This is secured by allowing the administrative officer 

 in charge of the forest to pick from the periodic (twenty-year) 



