Forest Management 25 



backward into later periods and vice versa. After shifting, each col- 

 umn contains in toto, approximately, an equal number of acres. 



By valuation surveys or yield tables, the volume contents of the 

 compartments allotted to the first period are ascertained; and the con- 

 tents are increased by the probable volume increment of these com- 

 partments expected during half a period. The total contents are then 

 divided by the number of years comprised by the period. The result 

 is the annual "sustained yield." Obviously, the sustained yield is apt 

 to change at the end of each period. 



The installation period comprises a whole rotation. At the end of 

 a rotation the forest is sure to exhibit a more normal age gradation. 



This method is in use in Prussia, Bavaria, etc., and has been working 

 in almost all European forests since 1780. The method is not applica- 

 ble to selection forests. It might be improved by replacing the 

 "Statement of Ages" by a "Statement of Indicating Percentages." 



PARAGRAPH XX. 



VOLUME METHOD. 



A statement of ages is prepared, each compartment being allotted 

 to a periodical column according to the number of years which separ- 

 ates it from maturity. The compartmental entries made in the state- 

 ment of ages are, in' this case, however, the final volumes expected at 

 maturity, and not the compartmental acreages. 



The totals for each period are drawn and compared with the average 

 volume expected from each periodical column. Again, by shifting com- 

 partments onward and backward, surpluses are shifted into columns 

 showing a deficit, under adequate allowance for changed yields. The 

 possibility is obtained by dividing the total of the first column, as it 

 stands after shifting, by the length of a period. 



The method does not work towards 1 normal age gradation. The 

 shifting of volumes is times taking, and the method is not in use 

 nowadays. 



PARAGRAPH XXI. 



CHARLES HEYER METHOD. 



By cutting the actual annual increment, the growing stock is left 

 undisturbed. In order to convert the actual growing stock into a 

 normal growing stock, it is necessary to decrease the annual cut if 

 the normal growing stock is larger than the actual growing stock; and 

 to increase the cut if the normal growing stock is smaller than the ac- 

 tual growing stock. Heyer expresses this idea by the formula: The 

 annual possibility (P) is equal to the sum (S) of the expected average 

 increments diminished by the n'th part of the difference existing be- 



