108 FARM FORESTRY 



trees which are grown too closely together will show scarcely 

 any growth for many years. This is because the crowns being 

 crowded are unable to manufacture sufficient food and the 

 roots are unable to absorb sufficient food and moisture for 

 rapid growth. A thinning is made to lessen this competition 

 or struggle between the trees. The trees to remove are those 

 with the smallest crowns or those that have fallen behind in 

 the struggle for existence. Not all trees have equal vigor or 

 grow at the same rate. Some will in time forge ahead of 

 their fellows, while others will lag behind. It is those that are 

 falling behind, the suppressed trees or badly crowded trees, 

 that should be removed in making thinnings, leaving the more 

 vigorous trees or dominant trees to grow. Where all the 

 trees seem to be growing equally well in a dense stand some 

 of them must be removed to give the crowns of those left 

 more room to develop. The tendency will be to remove too 

 many trees. Only enough trees should be taken out to liberate 

 a little the crowns of the trees left. In general the openings 

 should not be so large but that they will close again in from 

 3 to 5 years by the growth of the crowns remaining. The 

 struggle for existence must not be stopped entirely, for it is 

 this struggle that produces the long, slender boles of trees 

 in the woodlot. The size of the opening that can be made 

 will depend largely upon the rapidity of the growth of the 

 trees. Rapidly growing trees such as cottonwood or silver 

 maple should have their canopy opened up to a much greater 

 extent than slower-growing trees such as ash, oak and walnut. 

 In young stands the trees to be removed can be selected from 

 those that should remain by shaking the trees, so as the better 

 to see the crowns. By thinning out the trees lightly in this 

 way there can be accomplished in a short time what it would 

 take the trees themselves years to bring about, that is, the 

 death of the trees that gradually fall behind or the natural 

 thinning of the stand. 



Subsequent Thinnings. The trees left after the first thin- 



