36 



155. The classes into which trees become separated in 

 the course of their struggle with one another help to deter- 

 mine the trees to be removed. A moderate thinning in- 

 volves the removal of the intermediate trees that are in- 

 terfering with the development of the dominant trees. 

 The stand should not be opened up too much. If it is opened 

 too much and too much light is admitted, an undesirable un- 

 dergrowth of grass, weeds, briers, and shrubs may result, 

 or it may bring on reproduction before it is wanted. Kinds 

 that are liable to windfall, like the pine, should not be heav- 

 ily thinned, or windfall may occur. But while care should 

 be taken not to thin too heavily, the stand must be opened 

 up enough to influence its growth. The cover should be 

 broken, but it should not be broken to such an extent that it 

 will take more than 2 or 3 years for it to close again. 



156. Whether the suppressed and dead trees should be 

 i-emoved depends principally on whether they contain enough 

 wood to make their removal worth while. Some stimulation 

 may result from the removal of the suppressed trees; but 

 most of them are so far behind the dominant trees that their 

 presence or absence has little effect one way or another on 

 the development of the final stand. Yet it often pays to re- 

 move some of the suppressed and dead trees while the thin- 

 ning is in progress, although it would not pay to go into the 

 stand for the suppressed and dead trees alone, except in ex- 

 traordinary cases. And, on the general, principle of cleaning 

 a stand of all the useless material which might invite disease or 

 increase the risk from fire, it is sometimes expedient to remove 

 dead and suppressed trees while thinning is going on and it 

 can be done without extra cost. If, on the other hand, the 

 cover composed of dominant and intermediate trees is not 



