THINNING THE WOOD CROP. 295 



must either be cut out or cut back and topped, if that is practicable, so that the crown of the 

 superiors can develop freely. Those that are only narrowing in the superiors from the side, with- 

 out preventing their free top development, need not be interfeied with, especially while they are 

 still useful in preventing the formation and spreading of side branches on the superiors. As 

 soon as the latter have fully cleared their shafts, these crowding inferiors must be removed. Care 

 must be taken, however, not to remove too many at a time, thus opening the crown cover too 

 severely and thereby exposing the soil to the drying influence of the sun. Gradually, as the 

 crowns of inferiors standing farther away begin to interfere with those of the superiors, the 

 inferiors are removed, and thus the full effect of the light is secured in the accretion of the main 

 harvest crop; at the same time the branch growth has been prevented and the soil has been kept 

 shaded. Meanwhile thinnings may also be made in the subordinate crop, in order to secure also 

 the most material from this part of the crop. This is done by cutting out all trees that threaten 

 to be killed by their neighbors. In this way many a useful stick is saved and the dead material, 

 only good for firewood, lessened. It is evident that trees which in the struggle for existence have 

 fallen behind, so as to be overtopped by their neighbors, can not, either by their presence or by 

 their removal, influence the remaining growth. They are removed only in order to utilize their 

 wood before it decays. 



It may be well to remark again that an undergrowth of woody plants interferes in no way 

 with the devolopment of the mam crop; on the contrary, aids by its shade in preserving favorable 

 moisture conditions. Its existence, however, shows in most cases that the crown cover is not 

 as dense as it should be, and hence that thinning is not required. Grass and weed growth, on the 

 other hand, is emphatically disadvantageous and shows that the crown cover is dangerously open. 

 The answer to the three questions, when to begin the thinnings, how severely to thin, and 

 how often to repeat the operation, must always depend upon the varying appearance of the growth 

 and the necessities in each case. The first necessity for interference may arise with light-needing 

 species as early as the twelfth or fifteenth year; with shade-enduring, not before the twentieth or 

 twenty-fifth year. The necessary severity of the thinning and the repetition are somewhat inter- 

 dependent. It is better to thin carefully and iej)eat the operation oftener than to open up so 

 severely at once as to jeopardize the soil conditions. Especially in younger growths and on poorer 

 soil, it is best never to open a continuous crown cover so that it could not close up again within 

 three to five years; rather repeat the operation oftener. Later, when the trees have attained 

 heights of 50 to 00 feet and clear boles (which may be in forty to fifty years, according to soil and 

 kind) the thinning may be more severe, so as to require repetition only every six to ten years* 



The condition of the crown cover, then, is the criterion which directs the ax. As soon as the 

 crowns again touch or interlace the time has arrived to thin again. In mixed growths it must not 

 be overlooked that light-needing species must be specially protected against shadier neighbors. 

 Shade-enduring trees, such as the spruces, beech, sugar maple, and hickoiies, bear overtopping 

 for a time and will then grow vigorously when more light is given, while light-needing species, 

 like the pines, larch, oaks, and ash, when once suppressed, may never be able to recover. 



Particular attention is called to the necessity of leaving a rather denser "wind mantle" all 

 around small groves. In this part of the grove the thinning must be less severe, unless coniferous 

 trees on the outside can be encouraged by severe thinning to hold their branches low down, thus 

 increasing their value as windbreaks. 



The thinnings, then, while giving to the "final-harvest" crop all the advantage of light for 

 promoting its rapid development into serviceable timber size, furnish also better material from 

 the subordinate crop. At CO to 70 years of age the latter may have been entirely removed and 

 only the originally selected "superiors" remain on the ground, or as many of them as have not 

 died and been removed; 250 to 400 of these per acre will make a perfect stand of most valuable 

 form and size, ready for the final harvest, which should be made as indicated in the x^receding 

 chapter. 



The Relation op Forests to Faems. 



That all things in nature are related to each other and interdependent is a common saying, a 

 fact doubted by nobody, yet often forgotten *or neglected in practical life. The reason is partly 

 indifference and partly ignorance as to the actual nature of the relation ship; hence we suffer, 

 deservedly or not. 



