lands have little more than one-fifth of the region’s 
potential forest productivity. 
Forest lands reserved from cutting have about 3 
percent of the timber-growth capacity of the region. 
Additional withdrawal of forest lands from com- 
mercial use may be anticipated, and all such clos- 
ure will correspondingly decrease the effective 
growth capacity of the region. The extent of this 
decrease is of course dependent upon the area and 
character of the lands withdrawn. 
The species-group distribution of current annual 
growth as shown in table 23 is some indication of 
that of potential growth. Under prevailing meth- 
ods of forest management and for the region as a 
whole, probably about three-fourths of the poten- 
tial growth can be assigned to Douglas-fir and one- 
fifth to the pulpwood species. These proportions 
could of course be materially altered by changes in 
forest management. Clear-cutting favors Douglas- 
fir, while partial cutting tends to increase the per- 
cent of western hemlock, western redcedar, the 
balsam firs, and other tolerant species in the stand. 
Comparison of Current, Realizable, and 
Potential Growth 
Comparison of the growth calculations described 
is facilitated by table 26. 
In 1933, growing stands occupied 38 percent of 
the total commercial conifer land. The increment 
in such stands, however, was but 32 percent of the 
potential growth in cubic measure and 28 percent 
of that in board measure. This discrepancy be- 
tween increment and area involved is due partly to 
differences in age-class distribution, but principally 
to the lower average stocking of current immature 
stands (62 percent of normal) compared with that 
assumed for the potential growth calculation (75 
percent of normal). Differences in site on the 
areas involved are slight; the average site on the 
area that supported growing stands in 1933 is 
virtually equivalent to that of the entire commer- 
cial conifer area. 
Although the end result of realizable growth is 
based on 80 percent of the commercial conifer land, 
the calculated end increments are but 55 to 59 
percent of corresponding potential increments. 
This is due principally to the lower average stock- 
Tas ie 26.—Comparison of current annual, realizable mean annuai, 
and potential annual conifer growth in the Douglas-fir region 
Increment on trees— 
Kind of annual growth cal- | Area in- | 
culation and period volved 5.1+ 111+ 15.1+ 
inches inches inches 
| d.b.h. | d.b. h.!] d.b. h.2 
Thousand) Million | Million | Million 
acres | cubic feet | board feet | board fect 
Current1933 "==> ee 9, 917 8863) eee 2, 310 
Realizable: | 
1933-4952 ee 12, 132 | 733 4, 675 3, 306 
1943-52-22 eee 13, 195 953 5, 713 3, 869 
1963=6222 Se ee ee eee 14, 193 1, 060 6, 166 4, 066 
Rndgvalueseess ss eee 20, 907 | 1, 575 7, 400 4, 500 
‘Potentials eae se ene 26, 134 | 2, 759 12, 575 8, 244 
Summary in terms of poten- | 
tial values: | Percent | Percent | Percent | Percent 
Current, 1933____________ 38 | S21 | os eee 28 
Realizable (end values) __ 80 | 57 59 55 
1 Calculated by estimating volume in 16-foot logs to 8-inch top, by 
Scribner rule. 
2 Calculated by estimating volume in 32-foot logs to 12-inch top, by 
Seribner rule. ; 
ing, 55 percent of normal, assumed for the realiza- 
ble increment in contrast with the 75 percent of 
normal stocking on which the potential growth 
calculation is based. Slight differences are also 
due to the rotations assumed. For the realizable 
calculation a constant 100-year rotation was as- 
sumed, while the potential-growth calculation is 
based on technical rotations (table 55). 
Under ideal forestry practice all the forest land in 
the region should be supporting either virgin or 
growing stands. However, of the area not now 
occupied by virgin stands, only 70 percent is sup- 
porting growing stands of one sort or another, and 
for this area as a whole current growth is but 58 
percent of the potential in cubic measure and 51 
percent in board measure. Opportunity for in- 
creasing forest growth in the region is therefore 
obvious. 
Trends in Future Forest Increment 
If Present Forest Practice Continues 
If forest practice neither improves nor declines, 
annual growth may be expected to increase gradu- 
ally from 2.3 billion board feet as of 1933 toward a 
maximum of 4.5 billion board feet. The rate of 
this increase and the date at which the maximum 
