2 BULLETIN 1163, U. S. DEPARTMENT OF AGRICULTURE. 
METHOD OF COLLECTING DATA. 
The trees selected for study were part of a defective, overmature 
stand of pure Douglas fir on the west slope of the Cascade Mountains 
at McCredie Hot Springs, above Oakridge, Lane County, Oreg. 
The area was at an elevation of about 2,000 feet above sea level, and 
the local topography was characterized by moderate slopes and almost 
level benches. The stand was quite typical of the bulk of the Douglas 
fir type on the west slope of the Cascade Mountains. 
Each tree was felled with a stump height of lb feet measured at a 
point halfway on the slope. The hole was then cut into 16-foot logs 
to an 8-inch top-diameter limit inside the bark. Complete measure¬ 
ments were then taken. Next, the logs were split open and any 
further data available recorded. In this way it was possible to study 
each tree very completely, particularly with reference to the character 
and distribution of decay. Volumes of the trees were worked up in 
both board and cubic feet. The board-foot volume included the 
merchantable portion of each tree from the stump height of 1^ feet 
to a diameter limit of 8 inches inside bark. The 16-foot logs were 
scaled with the Scribner Decimal C scale and the volume of decay 
determined in accordance with the standard scaling practice of the 
Forest Service (5). 
The cubic-foot volume included the contents of the entire stem 
from the ground level to the tip. In computing volumes the stump 
was considered as a cylinder, each 16-foot log as the frustum of a 
paraboloid, applying the Smalian formula (2, p. 161), the top (that 
is, the section from the 8-inch diameter inside bark to the tip) as a 
cone, and a broken section of the top which did not include the tip 
as the frustrum of a cone. The actual cubic-foot volume of decay 
was computed by the same formulas. 
A general idea of the size and age of the trees analyzed is given 
in Table 1. 
Table 1— Size and age of Douglas fir trees studied. 
Age class. 
Average 
age 
(years). 
Average 
diameter 
breast 
high 
(inches). 
Percentage of 
total volume. 
Number 
of trees, 
basis. 
Cubic 
feet. 
Board 
feet. 
41 to 60 years. 
59 
9.5 
0.04 
0 
1 
61 to 80 years. 
68 
12.1 
.91 
0.62 
8 
81 to 100 years. 
95 
14.0 
.53 
.42 
3 
101 to 120 years. 
103 
16.3 
.75 
.62 
3 
121 to 140 years. 
129 
■ 16.0 
.15 
.11 
1 
141 to 160 years. 
(i) 
161 to 180 years. 
o 
181 to 200 years. 
195 
18.7 
1.36 
1.11 
5 
201 to 220 years. 
214 
25.3 
15.49 
14.89 
29 
221 to 240 years. 
230 
27.5 
32.69 
33.91 
47 
241 to 260 years. 
246 
27.9 
10.81 
11.20 
15 
261 to 280 years. 
271 
28.1 
15.81 
15.74 
25 
281 to 300 years. 
284 
29.2 
1.52 
1.63 
2 
301 to 320 years. 
309 
29.7 
6.07 
5.97 
9 
321 to 340 years. 
333 
29.8 
10.38 
10.22 
16 
341 to 360 years. 
348 
28.9 
2. 48 
2.46 
4 
361 to 380 years. 
362 
39.6 
1.00 
1.10 
1 
Combined. 
238 
26.1 
169 
i One tree, too small to consider. 
