THE THEORY AND~ PRACTICE OF WORKING PLANS 187 



produces the maximum amount of timber of medium size, 

 provided the site quahty permits. On poorer sites the growth 

 is slower, and there the management must be satisfied with the 

 production of smaller sized timber if the rotation is not to be 

 unduly prolonged. 



Some sacrifices, however, of mere income to the production 

 of larger tunbers is proper, smce it is the duty of the state to 

 provide for these. But where this can be secured only at the 

 sacrifice of a satisfactory income per cent the prolongation of 

 the rotation is unwarranted. 



Besides the mathematical calculations of timber and money 

 yield certain other factors come into play, i.e., the influence 

 of the rotation age on the condition of the soil and on the capacity 

 of the stand for natural reproduction, the increased danger of 

 windfall, the decreased vigor with increasing years, the possi- 

 bihty of intensive thinnings, and other partly economic, partly 

 silvicultural, partly administrative considerations. 



Where there are several species with considerable variance 

 in their rotation age, but the working unit is not subdivided 

 into working groups, the rotation age is taken as the average of 

 the respective areas and rotations. 



In selection forest a rotation age is difficult of determination 

 because of the widely varying conditions of growth. Diameter 

 is a better guide, i.e., the diameter of greatest productivity 

 determined by measurements of sample trees. Trees which 

 have reached the diameter so determined are merchantable. 



For every working unit the area must be determined which 

 is to be cut over in the ensuing twenty-year working period. 

 The fundamental consideration is to gauge the cutting areas 

 so that overmature stands and cutting of immature stands are 

 both avoided, but at the same time so that undue vacillations 

 of area cut over do not occur with their bad eft'ect on local 

 market for and needs of timber^ employment for men in the 

 woods, and also delayed normality in the distribution of the age 

 classes. 



If the cutting areas are gauged properly and if, in addition, 



