THE THEORY AND PRACTICE OF WORKING PLANS 225 



is increased or diminished according to the distribution of the 

 age classes. The volume on the periodic cutting area consti- 

 tutes the allowed periodic cut and affords, by volume regula- 

 tion, a check on the sustained character of the >ield. 



The consequent progress of forest organization is also very 



similar. In the formula - or a — , which represents the annual 



r r 



or the periodic cutting area, respectively, r, the rotation, is 

 set as a definite figure, as indeed is necessary for the execution 

 of a w^orking plan during a definite working period. As a 

 matter of fact, however, the rotation age is not a fixed quantity, 

 when considered for a longer period of time, but a varying 

 quantity influenced by the changing conditions of management. 

 To recognize these conditions and to set forth clearly their 

 influence is the common task of all methods of forest organiza- 

 tion, a task more important than the form of the working- 

 plan document and the method of determining the cut. The 

 rotation age, i.e., the age of technical, economic, financial, 

 or other maturity, whichever may be chosen, is dependent on 

 all the conditions of site, silviculture, utiHzation, and economics, 

 w^hich influence the increment of the stands and the value of the 

 timber. 



