WHAT FORESTRY IS AND WHAT IT DOES 197 



trees infested are removed as soon as observed and in 

 advance of all others, whenever a lumbering operation is 

 undertaken. 



How forests are harvested: Forestry and forest pres- 



FiG. 135. — A Typical Montana Sawmill. 



ervation require that a forest should be cut and not merely 

 held untouched. But it also demands that the cutting 

 shall be done on scientific principles, and that only as much 

 timber shall be removed in a given time as the forest can 

 produce in a corresponding period. After the cutting, the 

 forest must be left in a condition to produce another crop 



