160 LOBLOLLY OK NORTH CAROLINA PINE. 



ning which takes place in stands is rapid as is shown by the decrease in 

 the number of trees per acre (Table 42). (Plates IV; XI; XV.) 

 Stands of loblolly pine consequently are less benefited by artificial thiii- 

 nirig than those of such species as endure more crowding and in which 

 the struggle of the individual trees for supremacy is more prolonged. 

 Stands of this species on good sites (moist soil) are most responsive to 

 thinning (Plate IV) ; those on dry sites are less responsive (Plate III). 

 On very wet scils thinnings increase but little the growth of the remain- 

 ing trees and for this reason are hardly justifiable. 



Since the power of recuperation of the intermediate and suppressed 

 trees decreases with the age of the stands and with the length of the 

 period of overcrowding, thinnings in old .stands which have never been 

 previously thinned, must be entirely limited to the subordinate classes. 

 In young stands which are thinned when not more than 25 or 30 years 

 old, many dominant trees can be removed, since the codoininant and 

 intermediate trees of these ages still retain great recuperative power 

 (Plate 1 IX, A), have approximately the same height as dominant trees, 

 and straighter, clearer, and better formed stems (Plate XVII). Such 

 a thinning constitutes a combined thinning and improvement cutting. 

 A thinning of the dominant trees at this age will remove stems with 

 coarse knots which would saw out a large amount of low grade lumber, 

 even after they attained large diameters. (Plate XVI.) It also has 

 the advantage of yielding some sawlog timber, thus making cutting at an 

 early age remunerative. On the poorer, and particularly, on the drier, 

 sites, subsequent thinnings should be made only with the object of forc- 

 ing the development in diameter of the largest and choicest of the trees 

 in the stand. The smaller trees which are crowding the better trees, 

 which are to form the final stand, should be removed. Thinnings should 

 be repeated, dependent upon their severity, at intervals of from 5 to 15 

 years. Frequent and light thinnings are preferable to heavy ones made 

 at long intervals. The number of trees per acre on the different quality 

 sites decreases in natural stands at different rates in accordance with 

 the age of the stand (Table 42). This rate may serve as a guide in 

 making thinnings at any age. Thinnings are less effective when the 

 first one is deferred until the stand is 40 or more years old. 



Artificial thinnings should be heavier than natural thinnings, but never 

 so heavy as to leave large openings on all sides of the best trees selected 

 for the final stand. The trees which are removed in older stands should 

 be in the intermediate and codominant crown classes. The openings 

 which are made by removals should be closed before the time of the next 

 thinning in order to secure some lateral crowding and the clearing of the 

 stems of branches before they become too stout and horizontal. Since the 

 development of knots l^ inches in diameter causes a reduction in grade, 



