is called the site index. Thus a site with an index of 70 feet 
produces dominant trees averaging 70 feet in height at 50 years. 
The average site for each species encountered by the field crews 
in the course of the present study had the following site index: 
Loblolly, 92 feet; long leaf, 71; short leaf, 70; and slash, 81. 
Yields—The yields in any unit are based on the same limits 
of utilization as shown in the volume tables for that unit. By 
all trees 2 inches diameter breast high and over is meant all those 
1.6 inches and over; by all trees 4 inches diameter breast high 
and over, those 3.6 inches and over; and similarly for all diame- 
ters named. 
LOG RULES. 
Doyle rule-—The Doyle rule, which even in virgin timber gives 
an overrun of 10 to 25 per cent, does not begin to give the actual 
contents of most second-growth trees and stands. Volumes and 
yields by the Doyle rule are included in the present publication 
purely because this rule is the only one familiar to many southern 
lumbermen. 
Scribner rule.—The Scribner rule, while not widely used in the 
South, is employed widely in other sections of the country, and 
at present is used by the Forest Service in its timber sales in 
modified form (decimal C). Although fairly satisfactory for 
virgin timber, it fails to indicate the true contents of small 
second-growth timber by a considerable margin. An overrun of 
10 to 20 per cent in second-growth timber is common, but this 
varies with size of log; the overrun for 8 and 10 inch logs may be 
as high as 40 per cent. 
International rule-——The international rule is given in Table 
173; its derivation is described in Graves’ Forest Mensuration.’ 
The rule is believed to approximate the actual quantities of lum- 
ber, without overrun, which may be sawed out with good equip- 
ment, proper care, and market conditions prevailing at least in 
those portions of the South where virgin timber is small or not 
sufficient in quantity to compete substartially with second growth. 
TYPE OF STAND. 
Pure stand.—A pure stand is one in which 80 per cent or more 
of the trees are of a single species. 
Even-aged stand.—An even-aged stand is one in which the 
oldest and youngest trees do not differ in age by more than 10 
years. 
Normal or fully stocked stand.—A normal stand is one which is 
producing wood at the fullest capacity, in terms of cubic feet, for 
that species, age, climate, and soil. The number of trees per 
10 GRAVES, H. 8. FOREST MENSURATION. 458 p., illus.) New York and London. 
6. 
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