rent cubic-foot growth is greater in every unit than 
realizable cubic-foot growth for the first decade 
and that realizable growth in cubic feet gradually 
increases, exceeding current growth in the second 
decade in all but four units and in the third decade 
in all but three units. In the Rogue River unit, 
realizable growth in board feet is approximately 
the same in the third decade as in the second. It 
was assumed that in this unit greater depletion of 
stands increasing. rapidly in board-foot volume 
would occur in the third decade. 
Interpretation of Results 
Where extensive areas of very young growing 
stands and nongrowing virgin stands are involved, 
as in the Douglas-fir region, this type of growth 
computation clearly demonstrates that even with- 
out any marked increase in the intensiveness of for- 
estry practice, future forest growth may be expected 
to exceed current growth as of 1933 by a consider- 
able margin. 
The next logical question is, What value can 
realizable growth be expected to approach? The 
detailed computation was carried forward only 
three decades because to have carried it further 
would have involved great additional labor and 
highly speculative assumptions regarding deple- 
tion and standards of forest practice and utilization, 
but an appraisal was made of the end result of simi- 
lar computations for decades succeeding 1963. 
The computation of realizable mean annual 
growth, if carried forward, would lead to estimates 
of growth for approximately 100-year rotation on 
80 percent of the commercial forest sites at a stock- 
ing of 55 percent of normal. Hence an approxima- 
tion of its end result may be extrapolated by apply- 
ing normal yield table rates for the commercial 
conifer forest sites under the stated assumption re- 
garding stocking. This operation indicates an ulti- 
mate value of 4.5 billion board feet at the current 
standard of measurement and one of 7.4 billion 
board feet at the more intensive standard used in 
these growth calculations. 
Potential Annual Growth 
Potential annual growth is the average annual 
increment that could be obtained on the whole of 
60 
the region’s commercial forest land through inten- 
sive forestry practice. It could be achieved only 
after years of careful and effective forest-land man- 
agement. As here computed potential growth does 
not represent the maximum increment obtainable; 
the theoretical ultimate value of increment has 
been substantially reduced (25 percent) to allow 
for a certain amount of understocking and nonuse 
of forest land believed inevitable. In computing it 
all the commercial conifer forest land was assumed 
to be occupied by immature stands, averaging 75 
percent of normal stocking, with all age classes up 
to technical rotation age, approximate age of maxi- 
mum mean annual growth, equally represented. 
Stocking in excess of this adjusted standard can be 
found throughout the region’s natural forests, uni- 
formly over areas of several thousand acres. The 
mean annual growth rate for each site-quality class 
was multiplied by the corresponding acreage, and 
the sum of the resulting products is the estimated 
potential annual growth ? (table 25). 
Lands in the region capable of producing com- 
mercial conifer forests total about 26.1 million 
acres. These lands have the capacity to produce 
annually, under intensive sustained-yield forest 
management, 2.8 billion cubic feet of wood. Ex- 
pressed in board-measure content of sawlogs from 
trees 15.1 inches d. b. h. or larger, the potential 
annual growth totals 8.2 billion board feet, log 
scale, Scribner rule; in board-measure content of 
all trees 11.1 inches d. b. h. or larger, it comes to 
12.6 billion board feet, log scale, Scribner rule. 
Of the region’s total potential growth, 28 percent 
is contained in the three Puget Sound units and 16 
percent in the two Columbia River units. 
Areas of site-quality classes I and II include less 
than one-third of the region’s commercial conifer 
forest land, but nearly one-half of its potential for- 
est productivity (fig. 17). Less than one-tenth of 
the region’s growth capacity is in site-quality 
classes [Vand V, even though lands of these classes 
compose more than one-quarter of the commercial 
conifer forest land area. 
Almost one-third of the commercial forest land 
in the region is within national torests; but because 
of relatively low site quality, these national-forest 
lz [he rates used in making these calculations, and the 
corresponding approximate rotation ages, are shown in 
table 55. 
