THE THEORY AND PRACTICE OF WORKING PLANS 61 



From this, a rotation of fifty to fifty-five years could safely 

 be chosen for maximum production in cubic contents and 

 of no to 115 years for maximum production in board-foot 

 contents. 



Unlike the technical rotation, this rotation finds but little 

 application to-day, since it usually takes quantity of material 

 as the goal. It is satisfactory from the silvicultural stand- 

 point hence it is sometimes spoken of as a " silvicultural 

 rotation." 



Financial Rotations. — These introduce considerations of cost 

 and attempt to secure either the maximum forest rent or max- 

 imum soil rent. 



The doctrine of forest rent considers the soil and forest 

 jointly as capital and chooses that rotation which, in the form 

 of a normal forest, would produce the maximum net annual 

 income after subtracting the annual cash expenses. The rota- 

 tion age which yields this maximum income for the entire forest 

 coincides with the year of maximum mean annual net income 

 from an even-aged crop of timber, found by dividing total gross 

 income, minus actual cash expenses, by number of years in the 

 rotation. 



In other words it is " a mere bookkeeper's balance of income 

 and outgo, under annual management, without consideration 

 of time of income or outgo, forest and soil representing the capital 

 producing the rent as an annual receipt, like a house and lot 

 producing the annual rent." * 



The Norway spruce will serve as an example of financial 

 rotation based on forest rent. According to European tables 

 (Endres, after Schwappach) the gross income, expenses and net 

 income per acre for different decades is as follows for medium 

 sites, t 



* From letter by Dr. B. E. Fernow to the author under date of February 23, 

 1914. 



t Taken from " Forest Valuation," Roth, Ann Arbor, Mich., 1916. 



