They are predicated also upon ultimate utilization 
of the full area classified as commercial by the 
Forest Survey, utilization up to Forest Survey 
standards, and salvage of such losses as may be 
caused by large fires, insect and disease epidemics, 
etc. 
The allowable annual drain calculations were 
- derived for each forest type by the following 
formula: 
( 7A + 5A: + 3A2 + As ) M 
A 
4R 
The coefficients 7, 5, 3, and 1 (implied) are 
growing stock weights for the respective stand-size 
classes based on the familiar triangular diagram 
used to depict the growing stock of a normal forest. 
A=area of saw-timber stands. 
A,=area of pole-timber stands. 
A.—area of seedling and sapling stands. 
A.—=nonstocked area. 
A+ A, + A. + A,=total commercial forest land area. 
4=number of stand-size classes. 
R=rotation in years. 
M =average volume per acre (by species) of current saw- 
timber stands—the “A” stratum. 
The rotations assumed were as follows: 
Rotation in years 
Western Eastern 
Forest type:* Montana Montana 
White: pine {o2ls5.-ceerem steer ie 120 as 
Ponderosa pine .......------.-++++ee++: 150 160 
Tsarchts 205 5 ic sincere eerie Sees ne ree 150 aoe 
Douglas-fir =. tice cote aren 150 200 
Lodgepole pine .......-.... ee cena eee AU!) 140 
Whitebark and limber pine ............ Fen 140 
Spruce <5...5.0.10). Na+ se elesisisse ee ee ciara 120 120 
Hemlock-grand fir .......-..-.-+++-+++: 120 ae 
Alpine fir’ .....0. 060.222 cece teed eee BBS 140 
Western redcedar’.....2-.22 225225 cee 120 ee 
Cottonwood) yi... 22th ece esac einer 100 100 
Aspen and other hardwoods ........---- ie 80 
1 No allowable drain was calculated for the coniferous woodland type. 
The allowable annual drain as derived includes 
only the final harvest yield, i. e., no allowance is 
made for normal losses of which, under intensive 
management practices, considerable portions may 
be salvaged, nor the possibilities of additional yields 
from intermediate cuttings. 
Definitions 
Forest Land Classes 
Forrest Lanp.—Includes (a) lands at least 10- 
percent stocked by trees of any size and capable of 
producing timber or other wood products, or of ex- 
erting an influence on the climate or on the water 
regime; (b) land from which the trees described 
in (a) have been removed to less than 10-percent 
stocking and which have not been developed for 
other use; and (c) afforested areas. The minimum 
area for forest-land classification was 10 acres with 
a minimum width of 120 feet. 
COMMERCIAL FOREST LAND.—Forest land which is 
(a) producing, or is physically capable of pro- 
ducing, usable crops of wood (usually saw timber) , 
(b) economically available now or prospectively, 
and (c) not withdrawn from timber utilization. 
NONCOMMERCIAL FOREST LAND.—Forest land in- 
capable of yielding usable wood products (usually 
saw timber) because of adverse site conditions, or 
so physically inaccessible as to be permanently un- 
available economically and not withdrawn for 
special purposes. 
RESERVED FOREST LAND.—Forest land that has been 
withdrawn from timber utilization through statute, 
ordinance, or administrative order. 
Reserved commercial forest land.—Re- 
served forest land that otherwise qualifies 
as commercial forest land. 
Reserved noncommercial forest land.— 
Reserved forest land that otherwise qualifies 
as noncommercial forest land. 
Forest Stand-Size Classes 
SAW-TIMBER STANDS.—AII stands with saw-timber 
trees of softwoods and/or hardwoods having a 
minimum volume of 1,500 board feet per acre, 
International 14-inch rule. 
POLE-TIMBER STANDS.—Stands failing to meet the 
saw-timber stands specification, but at least 10- 
percent stocked with pole-timber and larger (5.0 
inches d. b. h. and larger) trees, and with at least 
half the minimum stocking in pole-timber trees. 
SEEDLINGS AND SAPLING STANDS.—Forest stands not 
qualifying as either saw-timber or pole-timber 
stands, but having at least 10-percent stocking of 
trees and with at least half the minimum stocking 
in seedlings and saplings. 
NONSTOCKED AND OTHER AREAS NOT ELSEWHERE 
CLASSIFIED.—Areas not qualifying as saw-timber, 
pole-timber, or seedling-sapling stands. 
Forest Type Classes 
WHITE PINE GROUP: 
White pine.—Forests in which 20 percent 
60 Forest Resource Report No. 5 U. S. Department of Agriculture 
