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\ 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. x — 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 

 scale 



material 



Age. 



Entire tree, 



top 

 diameter 

 2.V inches. 



Scale material. 



Top 

 diameter 

 6 inches. 



Top 



diameter 

 8 inches. 



and over in 



top 

 diameter. 



Years. 

 60 



Cubic feet. 

 40 

 42 

 42 

 42 

 41 

 39 

 37 

 35 

 33 



Board feet. 

 81 

 92 

 100 

 105 

 109 

 112 

 113 

 111 

 113 



Board feet. 



















15 



27 



38 



49 



60 



Pt r a nt. 

 



70 







80 







90 







100 



14 



110 



24 



120 



31 



130 



43 



140 



53 



140 to 200 2 





200 



21 

 23 

 22 



103 

 102 

 100 



90 

 90 

 89 



87 



210 



88 



220 



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 8 inches. 



