for loblolly shows that only 70 per cent of these trees are 9.6 
inches diameter breast high or larger; a 10-inch tree being the 
smallest likely to contain at least a 16-foot log 8 inches inside 
the bark at the small end. (No tree without a 16-foot log, 5 
inches inside the bark at the small end, contributes to the 
tabular yields in board feet by the international rule.) Whether 
10 inches is the correct minimum diameter on the site in question 
must be determined from a field study of felled trees on this site; 
it is assumed as correct in the present example. Then the 
volume of all 7, 8, and 9 inch trees included in the yields given 
in the board-foot table to a 5-inch top must be subtracted from 
the yield at 50 years on the 90-foot site. The stand table shows 
that about 5 per cent of the trees in this stand are 7 inches, 8 
per cent are 8 inches, and 10 per cent are 9 inches, 11, 18, and 
22 being the absolute numbers. At least an approximation of 
the number of logs to a 5-inch top in such trees will have been 
obtained in the course of the field study just referred to or may 
be estimated from the total-height tables. Their total volume 
may be ealculated from the volume tables. If the number of 
logs were two in each case, the total volume for the 3-inch 
classes would be 1,844 board feet. ‘This, then, would be the 
deduction necessary for trees which, under the actual limit of 
utilization, contain no merchantable logs. 
The lessened volume per tree of the remaining 169 trees may 
be calculated roughly by assuming an average deduction, based 
on the tree of median diameter among them. From the stand 
table it will appear that about half of the 169 trees 10 inches and 
over are above 13 inches in diameter, and half are below that 
size. Assuming that investigation has shown that a 13-inch 
tree has, by the international] rule, 10 board feet less to an 
8-inch top than to a 5-inch top, the deduction for 169 trees would 
then be 1,690 feet, which added to the 1,844 board feet in the 
trees below 10 inches gives a total deduction of 3,534 board 
feet. The yield of 37,500 board feet for a 50-year stand on a 
90-foot site then becomes 34,000 board feet (rounded), when an 
8-inch top limit is used in place of a 5-inch. 
DETERMINATION OF NORMALITY AND PREDICTION OF FUTURE 
YIELDS. 
The yield tables should never be used as a substitute for an 
actual cruise of an existing stand. That a stand is of a certain 
age and occupies a certain site by no means proves that its yield 
per acre will be the same as that shown in the tables for that age 
and site. This is of course because the stands vary widely in 
stocking from the 100 per cent stocking represented by the tables. 
| By actual measurement of a sample plot or strip it will be 
possible to establish a percentage relationship between the 
actual values and the tabular values. The two most satis- . 
12 
