LOBLOLLY OR NORTH CAROLINA PINE. 159 



THINNINGS. 



Thinnings are made in crowded even-aged stands in order to concen- 

 trate the productive power of the soil in a few best trees, accelerate their 

 growth, and in this way shorten the time necessary for them to reach 

 maturity. Since only the smaller or defective large trees are removed, 

 the mature stand eventually consists of large well-developed trees. In 

 the natural process of thinning the elimination of the weaker specimens 

 takes place too slowly for the best development of the stand. (Plates 

 IV; XVII; XXVII.) In the struggle for light and food both the sup- 

 pressed and dominant trees suffer. A certain amount of crowding, how- 

 ever, is necessary, particularly during the period of rapid height growth, 

 to develop long straight stems reasonably free from knots in the lower 

 logs. (Plate XVII.) Thinnings, therefore, should be light during 

 the period of rapid growth in height, and should be largely limited to 

 removing the knottiest trees. After the clear length of stem, however, 

 has been developed (see Table 15) thinnings should be heavy in order to 

 favor the rapid development in diameter of individual stems, the diame- 

 ter of the tree has an important influence ; not only on the amount of 

 material in it but also on the high value of the lumber which is ob- 

 tained from it. (See page 120, and Tables 59 to 64, and 71.) It is 

 commonly held that when the larger trees are removed as they come to 

 merchantable size, the smaller trees left will begin to grow fast. Such 

 a thinning may be of benefit to the stand, but not to the same extent 

 as thinnings of the small trees; by thinning the small trees not only a 

 larger amount, but a higher quality is secured. 



It has already been noted (page 42) that loblolly pine exhibits with 

 age a progressive increase in its light requirements and a corresponding 

 decline in its capacity to endure crown compression. (Plates IV; XL) 

 This decline is especially marked on the dryer sites. (Plates III, and 

 XXV.) On good sites one effect of this pharacteristic is that in middle- 

 aged stands, 50 to 75 years, the suppressed and intermediate trees and 

 even such codominant trees as have endured prolonged crown compres- 

 sion lose their capacity to recover rapidly or even at all after their 

 crowns are freed ; on dry sites this inertness of the dominated classes 

 extends to much younger trees. The relative tolerance which the domi- 

 nant trees of different diameters and on different quality sites exhibit 

 as expressed by the demands of the crown for light, is shown numeri- 

 cally by the index of tolerance (Table 78) which is the ratio of the sur- 

 face of the crown space to the area of the surface of the stem of the tree 

 inside the bark. (Plates XXIV; XXV; XXVI; XXVII.) 



On account of its comparative intolerance of shade the natural thin- 



