lt$ SHORTLEAF PINE IN VIRGINIA 



dominant trees. Their height growth is rapid, but, on account 

 of their small crowns, their diameter growth is slow. Besides be- 

 ing unable to make good volume growth themselves, they retard 

 the growth of the dominant trees. 



Suppressed Trees. These have fallen behind in height and 

 are so much lower than the other trees that direct sunlight is 

 largely excluded from them. They interfere very little with the 

 growth of the larger trees. 



When overshadowing and suppression pass a certain point 

 the trees die. Three-fourths of the dead trees are in the sup- 

 pressed class, but intermediate trees also die from overcrowding. 

 Dead trees exert no influence upon the growth of the stand. When 

 .possible, however, they should be removed, since they contribute 

 to the clanger of disease, insects, and fire. 



HOW HEAVILY TO THIN 



Thinnings must be heavy enough to provide more light and 

 crown space, and more root space and soil moisture for the trees 

 that are left, yet they must never be heavy enough at one time to 

 admit too much sunlight and cause the crowns to spread unduly, 

 with a sacrifice in the rate of height growth. Too heavy a thin- 

 ning results in temporary understocking and produces the oppo- 

 site of the result desired. 



To be most effective, thinnings should begin when a stand is 

 twenty years old, and should be light and frequent. Early thin- 

 nings prevent the crowns from crowding before their symmetry 

 is destroyed, and yet" maintain sufficient crown rivalry to secure 

 continuous height growth and promote the rapid shedding of the 

 lower limbs. Before removing any tree, it is necessary to con- 

 sider how its removal will affect the remaining trees, not only un- 

 til the next thinning, but until the stand is mature and the trees 

 are merchantable. 



Thinnings should be made not less often than once every ten 

 years. Even with ten-year intervals cuttings have to be too 

 heavy for the best interest of the stand and excessive crowding 

 takes place before a thinning is repeated. An interval of five 

 years is recommended as the most desirable. This develops the 

 full value of the stand, and also allows the cutting of enough 

 cordwood from the thinnings to pay for the work. A careful 

 observer will be able to lengthen the interval if the cost of thin- 

 nings requires it. 



