14 THE NORMAL AGE CLASSES. 



however, that the cleared coupes lie fallow for one or more, 

 say s years ; in that case : 



c- A 



~~ 



so that the forest consists, immediately before cutting, of a 

 series of age gradations from 1 to r years old, and s blanks, 

 or altogether r + s coupes. 



c. The ShelUr-ivood Compartment System. 



Under this system the regeneration of each coupe extends 

 over a number of years, say m ; hence it is necessary to throw 

 m annual coupes together into a periodic coupe, the crop on 

 which is, by gradual cuttings, led over, in the course of m 

 years, into a young wood. The size of the periodic coupe is, 



therefore = X m. 

 r 



In this case the first of the successive cuttings towards 

 regeneration may be made : 



Either in the year r, so that the trees removed at the end 

 of the regeneration period would be r + m years old, and the 



M| 



mean age r + years ; in other words the procedure would 



lead to a raising of the rotation from r to r + years ; 



2 



Or, the first cutting may be made in the year r - and 



2 



the last in the year r + , so that the mean final age comes 



to r years. 



In the present chapter the latter is assumed. 



d. The Selection System. 



Strictly speaking, the annual coupe is equal to the total 

 area of the forest. For convenience sake, however, the cuttings 

 of each year are restricted to a portion of the area, so that it 

 takes a number of years to go round the forest, and before 

 cuttings are again made on the same area. If that number 

 is I, then 



