128 LOBLOLLY OK NORTH CAROLINA PINE. 



The increase in the proportion of the higher grades in the tree with 

 increased diameter is influenced by several conditions, the most impor- 

 tant of which are (1) the density of the stand, (2) the quality site, and 

 (3) the rate of growth and the age of stand. 



Influence of Density of Stand. 



The proportion of different grades in trees of different diameters as 

 given in Tables 55, 56 and 57 applies only to fully stocked stands on 

 forest soils or at least not to upland old fields. As the stands be- 

 come more open, more limbs and larger knots develop on the trees with 

 consequent increase in the proportion of lower grades in them. (Plates 

 III and IV.) 



Influence of Quality Site. 



The wood of trees of loblolly pine grown on poorer quality sites gen- 

 erally is worth more per 1,000 board feet than that from younger domi- 

 nant trees of the same diameter and height on a good quality site. This 

 is due to the more thorough cleaning of the stem, the smaller size of the 

 knots, and less taper; knots, however, are more numerous in the upper 

 logs and there are fewer clear logs in the tree, since the length of mer- 

 chantable stem is shorter. This is shown by Table 65, which gives the 

 value per 1,000 board feet of the stumpage of trees growing on different 

 quality sites at different ages. By referring to Table 16 it is seen that 

 at the age of the same average diameter the stumpage of the stand on the 

 poorer quality site is more valuable. With a marked difference in the 

 heights of the trees of the same diameter, however, the shorter bodied 

 tree will have a larger proportion of crown and consequently a higher 

 proportion of the common grades and a lower average value for the 

 lumber. (Plates X, A and X, B.) 



The clean bodied and slow growing intermediate and suppressed trees 

 of a given diameter in an old stand yield a larger proportion of the 

 higher grades of lumber than dominant trees of the same diameter and 

 height in younger stands on this same site. (Plates IX, A, and IX, B, 

 also Plates XYI and XVII.) Tables 59 to 64 show the value of 

 lumber sawed from trees of the same diameter and approximately the 

 same height on an average in 45 and 65-year old stands. The trees 

 above 14 inches in diameter in the 45-year old age stand (Quality I) 

 are dominant. Trees from 14 to 18 inches in diameter in the 65-year 

 old age stand (Quality I) are intermediate. There is a difference of 

 about $2 per 1,000 board feet in the value of the lumber at Norfolk. 

 Since the cost of operation is the same for producing lumber from trees 

 of the same size, this difference results in a higher stumpage for the older 



