28 



sides of whose crowns are shaded by neighboring trees; and (3) 

 dominant trees, those which have been the most successful in the 

 struggle for existence and whose crowns are fully exposed to sunlight. 



Left to themselves the dominant trees are the only ones capable of 

 good future development. The intermediate trees will gradually 

 become suppressed, and the suppressed trees will eventually die. 

 This method of nature, however, is wasteful. It produces good tim- 

 ber with part of the trees, but allows the others to decay and die. 

 Thinning at the proper time produces better trees with a larger per 

 cent of the stand, and, in addition, utilizes the timber which is 

 removed. 



The frequency and extent of thinnings should depend upon the kind 

 of soil, the age of the plantation, and the class of material desired. 

 Theoretically, frequent but light thinnings will give the best results. 

 In practice, however, it is best to thin only at stated periods, when 

 enough material may be taken out to compensate for the cost. 



With regard to the manner of removal, thinnings may be designated 

 as regular and irregular. In regular thinnings a certain definite pro- 

 portion of the stand is removed, as one-half, one- third, etc., without 

 regard to the condition of the individual trees. In irregular thin- 

 nings the number of trees to be removed is determined by inspection 

 and consideration of the needs of the plantation. To make an irregu- 

 lar thinning requires a much better knowledge of the laws of tree 

 growth than is necessary for a regular thinning, but if well executed 

 it will result in the production of better material. 



Regular thinnings are best adapted to regularly spaced plantations, 

 in which conditions are uniform throughout. For example, if a plan- 

 tation is spaced 5 by 5 feet by the square system, one-half of the trees 

 can be removed and the remaining stand will be spaced practically 

 7 by 7 feet, with the new rows running diagonally to the original ones. 

 A thinning of this kind is shown in the accompanying diagram, in 

 which the trees to be removed are underscored: 



rp rp m rp rp rr\ 

 rr\ m rp rr\ rp rp 

 rp rp rp rp rp rp 



Irregular thinnings are especially adapted to plantations which 

 have grown unevenly or which are irregularly spaced. The manner 

 of executing an irregular thinning is shown in the following diagram, 

 in which the dominant trees are indicated by D, the intermediate 

 trees by I, and the suppressed trees by S. The trees to be removed 



are underscored. 



J_ D I ^ D D £ 



S_ D J_ D _S_ S_ D 

 I £ I D S_ D I_ 



[Cir. 81] 



