THE USE OF THE FOREST. 



275 



saw-mill, (see Handwork in Word, Chapter II,) so one object of 

 forestry is to carry this economy back into the woods. 



One of the underlying ideas in conservative lumbering is that the 

 "yield," i. e., the amount of wood taken out of a healthy forest in a 

 given time, shall be equal to the amount grown during the same 

 period. If less is taken out than grows, some trees will overmature 



Fig-. 142. Conservative Lumbering-. Black Hills National Forest, South Dakota. Note 

 the brush, cord-wood, and logs piled separately, a fine clean up. Nothing- 

 cut below 12" diameter. U. S. Forest Service. 



and decay; if more is taken out than grows, the forest will ulti- 

 mately be exhausted. 



This principle may be carried out in a number of ways; but in 

 any case it is necessary to know how fast the forest is reproducing 

 itself, and this is one of the functions of the forester. The United 

 States Forest Service makes a definite offer of cooperation with 

 farmers and lumbermen and owners of forests to provide them with 

 skilled foresters for direction in this matter. 



In the United States, the most practicable way of determining the 

 yield is by area, i. e., a certain fraction of a forest is to be cut over 



