low. Taking into account this indicated bias, and 
the sampling errors of volume estimates on the 
sampled area, the true volumes for the State as a 
whole are estimated to lie within the following 
limits: primary growing stock, 16 to 17 billion 
cubic feet; live saw timber, 55 to 58 billion board 
| feet. 
Growth 
In estimating timber growth, the possible sources 
/of error, in addition to those cited under “Area” 
and “Volume,” include: errors in measuring in- 
crement cores, in reconstructing tree volumes, and 
in dating mortality. All practical efforts were made 
to eliminate errors from these sources. Growth esti- 
mates for the area covered by complete survey are 
believed to be somewhat low. As mentioned under 
“Methods,” the original growth calculation for 
that part of the State excluded approximately one- 
third of the commercial area where stand volume 
was in a more or less static condition. It appears 
now that there may actually have been some net 
_ growth in these stands in recent years. 
For the area sampled, standards errors of net 
growth are +8.4 percent, or +11 million cubic 
feet for primary growing stock, and +15 percent, 
or +36 million board feet for saw-timber trees. 
Actual growth for the State as a _ whole, 
“including judgment estimates of growth on stands 
previously considered nonproductive, is estimated 
to lie between the following limits: 
Primary growing Live saw-timber 
stock trees 
(million (million 
| cubic feet) board feet) 
| Gross annual growth............. 290-320 840-930 
Net annual growth. 2.000... 240-280 600—700 
Commodity Drain 
Estimates of commodity drain are based chiefly 
on a complete tabulation of production and con- 
sumption statistics, adjusted for waste on the basis 
of woods and mill studies. Only 18 percent of the 
cubic-foot and 12 percent of the board-foot drain 
is based on sampling. However, the translation of 
production statistics into drain introduces an in- 
determinable error. The commodity drain estimates 
for the State as a whole during the period 1939— 
48 are judged to be between 90 and 100 million 
cubic feet of primary growing stock and between 
520 and 550 million board feet of saw-timber vol- 
ume. 
Forest Resources of Montana 
Comparison of 1949 and Earlier Estimates 
“At least six different estimates of Montana’s 
timber resources have been published in the past 
(table 19). Differences between the 1949 and 
earlier estimates are accounted for by sampling er- 
rors in the statistics derived by sampling;” tech- 
nique errors; variations in definitions, inclusive- 
ness, and standards of measurement; and actual 
change. 
The apparent increase in total forest and com- 
mercial forest land can be at least partially ac- 
counted for by changes in definition and inclusive- 
ness. Prior to the completion of the systematic 
survey in 1949, only extensive estimates were avail- 
able for the area east of the Continental Divide. 
Hardwood areas and volumes were desregarded en- 
tirely prior to 1938. Furthermore, the present 
estimate of the commercial forest area includes a 
considerable area formerly classed as noncommer- 
cial. Volume estimates of 1918 and 1925 include 
all forest land as indicated in table 19, whereas 
later estimates are for commercial forests only. Part, 
and perhaps all, of the apparent differences may be 
accounted for by differences in definition of what 
constitutes. a saw-timber tree. 
For the foregoing reasons, a comparison of the 
1949 and previous estimates provides no definite 
indication of quantitative changes or trends. There 
have, of course, been changes in the character and 
distribution of the timber volume. It is particu- 
larly evident that the proportion of the volume in 
prized species such as ponderosa and western white 
pine is diminishing, and that the volume of these 
and other species is becoming less concentrated in 
large blocks. 
Conditional Allowable Annual Cut 
The estimates of allowable annual cut presented 
in this report are based on allowable annual drain 
calculations, discounted approximately 25 percent 
to allow for abnormal mortality and other factors 
that may prevent utilization of total yields. They 
rest on the assumption that forest-management 
practices and protection will be improved to the 
point where the stands of the future will be 
as productive as the ones being 
cut now. 
** Approximately one-third of the forest area was derived 
by sampling, the remaining two-thirds from complete surveys 
(p. 56). ‘ 
BY) 
