2 BULLETIN 1163, U. S. DEPARTMENT OF AGRICULTURE. 
METHOD OF COLLECTING DATA. 
The trees selected for stucty 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 vest slope of the Cascade Mountains. 
Each tree was felled with a stump height of H feet measured at a 
point halfwa}^ on the slope. The bole was then cut into 16-foot logs 
to an 8-inch top-diameter limit inside the bark. Complete measure- 
ments were then taken. Xext, 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). 
1 
A- erage 1 
diameter j 
breast - 
high | 
(inches), j 
Percentage of 
total volume. 
Number 
of trees, 
basis. 
Cubic 
feet. 
Board 
feet. 
41 to 60 years 
59 
68 
95 
103 
129 
9.5 
12.1 j 
14.0 
16.3 
16.0 
0.04 
.91 
.53 
.75 
.15 

0.62 
.42 
.62 
.11 
1 
61 to SO vears 
• .> 8 
81 to 100" years 
3 
101 to 120 vears 
3 
121 to 140 vears 
1 
141 to 160 years 
(') 
161 to ISO vears. 

181 to 200 vear< 
195 
214 
230 
246 
271 
284 
309 
333 
348 
302 
IS. 7 
25.3 
27.5 
27.9 ; 
28.1 , 
29.2 
29.7 
29.8 : 
28.9 
39.6 . 
1.36 
15.49 
32.69 
10.81 
15.81 
1.52 
6.07 
10. 38 
2. 48 
1.00 
1.11 
14.89 
33.91 
11.20 
15.74 
1.63 
5.97 
10.22 
2.46 
1.10 
5 
201 to 220 vears 
29 
221 to 240 vears 
47 
241 to 260 years 
15 
261 to 280 vears 
25 
281 to 300 vears 
9 
301 to 320 vears 
9 
321 to 340 vears 
16 
341 to 360 years 
4 
301 to 3S0 vears 
1 
238 
26.1 
1 69 
i One tree, too small to consider. 
