THE FOREST TREES. 39 

_ The average increase in height for each diameter class does not vary 
_ greatly for the different pines. At first rapid, it falls off regularly as 
the diameter increases. The average increase for Longleaf Pine under 
5 inches in diameter is a little over 7 feet. It then gradually falls off; 
at a diameter of 13 inches it is but 3 feet, and at 23 inches it has fallen 
to 1 foot. 
Clear length is the distance from the ground to the first large branch 
or large visible knot forming a serious timber defect. [or all the > 
pines the average increase in clear length equals approximately one- 
half the average increase in total height for the lower diameters, but 
is inconsiderable after they have reached a diameter of 14 to 16 inches. 
A Longleaf Pine 14 inches in diameter has more than four-fifths of the 
clear length of the largest trees. By the time the tree is 20 inches in 
diameter it has almost reached the maximum clear length. 
The actual merchantable length is the length of merchantable logs 
actually cut. The possible merchantable length is the length of logs 
which under identical conditions of market and transportation might 
have been cut had there been less waste in sawing. The waste is due 
fp to failure to vary the length of logs so as to include all of the tree 
_ which is not too rough to make timber under the required specifica- 
tions, and also to carelessness in cutting logs longer than is necessary 
for the required log lengths. Three or 4 inches on the length of 
each log is allowed in order to insure full-length boards after sawing 
at the mill; but the allowance is permitted from carelessness greatly 
to exceed this amount, with the result that what would otherwise have 
made another log is often left in the top. 
The proportion of merchantable length, either actual or possible, to 
the total height does not follow the proportion of clear length to total 
height. It is much smaller for small trees, and increases much more 
‘apidly as the tree grows. Longleaf Pine 12 inches in diameter will 
not average two i2-foot logs cutting to a top diameter of 8 inches. 
In this locality trees smaller than 14 to 15 inches in diameter at breast- 
height are not often logged. <A 15-inch tree yields on the average 
three 12-foot logs. In practice, however, only one, or at most two, 
loge are taken. At this diameter the merchantable length is increasing 
apidly. This continues until the tree reaches a diameter of 22 inches, 
after which the increase in merchantable length is slight. 
MERCHANTABLE VOLUME ON A BASIS OF DIAMETER BREASTHIGH. 
Tables showing the total merchantable volume and the volume of 
merchantable heartwood and sapwood of Longleaf, Loblolly, Cuban, 
and Pond Pine for diameters from 12 to 36 inches are given on pages 
20 and 21. Diagrams 2, 4, 6, and 8 are graphic representations of 
these tables. 
