MANAGEMENT. 31 



the rotation of the greatest volume production is out of the question 

 if the financial aspect is considered. Since there is a difference in 

 the rate of growth for yellow pine, Douglas fir, and blue spruce the 

 rotation for each species must be considered separately. 



WESTERN YELLOW PINE. 



In yellow pine the minimum diameter from which a good grade of 

 saw timber can be obtained is about 20 inches, though the value of 

 timber from a 25-inch tree is considerably greater. Table 5, page 22, 

 shows that the average pine 25 inches in diameter is 202 years old and 

 contains 4.6 logs scaling 710 board feet. Eighteen years later, at a 

 diameter of 27 inches, there are &ve logs scaling 920 board feet. 

 From Table 8 it is seen that at the age of 200 years the periodic 

 annual growth is 1.5112 cubic feet — only slightly less than at the time 

 of culmination 60 years later. The periodic annual growth is 1.26 

 per cent, but rapidly decreasing. In view of these facts and since the 

 decay after 220 years would probably to a large extent offset the 

 growth, a rotation between 200 and 220 years seems advisable. 



DOUGLAS FIR. 



Douglas fir of a given diameter does not contain as many board feet 

 as yellow pine of the same size. This is due to its lower form factor 

 and to the greater thickness of its bark. However, volume growth 

 as compared to age is practically the same for the two species. From 

 Table 5 it may be seen that the average Douglas fir 28 inches in diam- 

 eter contains 720 board feet, and one 29 inches, 800 board feet. These 

 diameters are reached at the age of 202 and 210 years, respectively. 

 Table 8 shows the mean annual growth at 210 years to be 0.6751 and 

 the periodic annual growth to be 1.5123 cubic feet. The latter at 

 this point is increasing, which shows that it is near the point of cul- 

 mination. The annual growth at this time is 1.12 per cent. Taking 

 into consideration decay, which after this period no doubt largely 

 offsets the growth, it appears that the rotation for Douglas fir should 

 be set at about 210 years, or approximately the same as that for 

 yellow pine. 



BLUE SPRUCE. 



Since blue spruce should be used principally for poles and stulls, 

 and in view of the fact that large trees are invariably affected with 

 butt rot, the rotation will be comparatively short. While growth 

 figures are not available for trees older than 150 years, it is plain that 

 the maximum rate of growth occurs before this age is reached. At 

 130 years of age the average spruce is 22 inches in diameter and 98 

 feet tall. At 140 years it is almost 23 inches in diameter and has a 

 total height of 104 feet. While its board foot content at this size is 

 less than 400 feet, it will yield several stulls, or from one to two stulls 

 and a pole. Since spruce will be less valuable for saw timber than for 

 other purposes, it would not be profitable to allow this species to grow 



