SHORTLEAF PINE IN VIRGINIA ) 5 



THINNINGS 



The objects of thinnings are, first, to accelerate the growth and 

 shorten the time necessary to bring the stand to maturity, and, 

 second, by removing defective trees to produce a mature stand 

 formed of perfect specimens and so increase the yield of lumber. 

 The elimination of the weaker specimens by natural process takes 

 place too slowly for the best development, because the growth of 

 the trees which are ultimately to survive is retarded by the pro- 

 longation of the struggle for light and food. Yet limited crowd- 

 ing is necessary at certain periods to force height growth and to 

 develop long, straight stems, reasonably free from limbs. More- 

 over, the number of trees to the acre largely determines the volume 

 of the yield and has an important bearing on the value of the 

 trees. Usually the crowded stands produce the greatest volume of 

 wood at all ages; but when the size or diameter of the individual 

 trees is of primary importance, as in the production of saw logs, 

 less crowding is desirable. By means of judicious periodic thin- 

 nings, it is possible both to favor competition and to relieve over- 

 crowding and in this way greatly to accelerate the growth of the 

 remaining trees. Such thinnings reduce the number of trees, but 

 they produce equally tall trees of much larger diameter, with 

 straight, clean stems and but little taper. It is commonly held 

 that if the larger trees are removed as they come to merchantable 

 size the smaller trees will make accelerated growth. This is un- 

 questionably true of many species and it is true also of short- 

 leaf pine under thirty years old, but in pure old stands of short- 

 leaf pine in Virginia the crowded and suppressed trees recuperate 

 so slowly that it is not profitable to thin the stands in this way 

 after they have passed the age of thirty-five years. 



CLASSES OF TREES 



Before thinnings can be intelligently made, the classes of 

 trees in a stand must be known and their relation to the growth 

 of the stand understood. The live trees in a second-growth pine 

 stand can be separated easily into three classes: 



Dominant Trees. These are the tallest and thriftiest speci- 

 mens with the largest crowns. Their growth is rapid, both in 

 height and in diameter. 



Intermediate Trees. These are the slender, clean-bodied trees, 

 with narrow, compressed crowns which are nearly as tall as the 



