22 
BULLETIN 234, U. S. DEPARTMENT OF AGRICULTURE. 
ROTATION. 
The length, of the rotation, which is the period represented by the 
age of the stand at the time it is to be cut, is determined by the rate 
of growth of the species under consideration and the purpose for which 
it is to be used. In the case of lodgepole pine, the tree's slow growth 
and the need for producing as large size material as possible neces- 
sitate a comparatively long rotation. Table 11 shows that the mean 
annual growth in cubic feet of normal stands in Montana, measured 
to about 2 -J- inches in the top, culminates at from 70 to 90 years. A 
rotation of this length, however, gives few trees 9 inches or more in 
diameter, and is therefore too short. For material scaled to a 6- 
inch top diameter limit the mean annual growth in board feet culmi- 
nates at 130 years, and for material scaled to 8 inches in the top, at 
from 200 to 210 years. At 130 years only about two-fifths of the 
scale material is 8 inches or more in diameter at the top end, which 
is too small a proportion, while at 200 years nearly nine-tenths of the 
material is of large size, which is more than is needed. The mean 
annual growth in board feet to .a 6-inch top is nearly at its maximum 
at 140 years, when 53 per cent of the scale material is 8 inches or more 
in top diameter. This is about as small a proportion of large ma- 
terial as a mature stand ought to produce; at the same time a rotation 
of 140 years is not unreasonably long. It would appear, therefore, 
that such a rotation is the best for normally stocked lodgepole stands 
on average sites in Montana. While yield figures for normal stands 
in Wyoming and Colorado are not available, it is probable that a 
rotation of approximately the same length would be satisfactory in 
these States for the production of mine timbers and ties. 
Table 12. l — Mean annual growth per acre of normal stands of lodgepole pine on average 
sites (quality II), at various ages, Deerlodge National Forest, Mont. 
Mean annual growth. 
Amount of 
Age. 
Entire tree, 
top 
diameter 
2h inches. 
Scale material. 
scale 
material 
8 inches 
and over in 
top 
diameter. 
Top 
diameter 
6 inches. 
Top 
diameter 
S inches. 
Years. 
60 
Cubic feet. 
40 
42 
42 
42 
41 
39 
37 
35 
33 
Board feet. 
81 
92 
100 
105 
109 
112 
113 
114 
113 
Board feet. 




15 
27 
38 
49 
60 
Per cent. 

70 

80 

90 

100 
14 
110 
24 
120 
34 
130 
43 
140 
53 
140 to 200 2 
200 
24 
23 
22 
103 
102 
100 
90 
90 
89 
87 
210 
220 
88 
89 
i Based on Table 9, Department of Agriculture Bulletin 154, "The Life History of Lodgepole Pine in the 
Rocky Mountains." While the board feet figures are not strictly accurate, they are sufficiently so to serve 
as a guide in determining the length of rotation. 
2 Between 140 and 200 years there is a constant decrease in the mean annual growth in cubic feet and in 
board feet to a top diameter of 6 inches, and a constant increase in the mean annual growth in board feet 
to a top diameter of S inches. 
