IMPROVEMENT OF THE FOREST 215 



be disposed of. During the first half of the rotation the 

 aim is to improve the form of the good trees, and to pre- 

 vent a too great reduction of the crown. Trees of poor 

 form, with spreading crowns, and those of poor species 

 which are crowding better ones, are therefore cut. If no 

 thinning is made until after middle life, the spreading 

 trees will have done their principal damage. Such trees 

 are cut only when the trees crowded by them are capable 

 of prompt recovery and rapid growth. 



During the first half of the rotation the aim should be 

 to thin to about a C grade, and then to increase to a D 

 grade, or sometimes even a heavier cutting. Thinnings 

 ire repeated when the crowns close together over the 

 openings. 



There are frequently overcrowded groups among the 

 dominant trees. These are usually thinned by cutting the 

 co-dominant trees, or such of the dominant trees as have 

 the shortest crowns. Sometimes, however, the removal 

 of one dominant tree will stimulate the growth of several 

 co-dominant trees which, in the long run, would be over- 

 topped and crowded out by the former. If these trees 

 are released, their aggregate value will ultimately be 

 greater than that of the single dominant tree. This 

 principle is used in thinnings at all ages. 



In a great deal of work in this country the thin- 

 nings will tend toward the French principle, and leave 

 the subordinate classes standing. This will usually be 

 because the small material is not merchantable, rather 

 than because it is desirable to leave it for silvicultural 



