MANAGEMENT PLANS THE NATIONAL EOEESTS 65 



of age classes. The number of trees passing into any age class depends on the 

 number in the next lower age class, which is in turn dependent on the extent 

 of competition by larger trees in the upper age classes. Thus there are no 

 more mature trees than every age class below can produce in mature trees. 

 If the balance is overthrown by some agency, such as fire or insects, and a 

 larger number of mature trees is produced by any one age class, then the lower 

 classes will suffer by competition and produce a smaller number. In time 

 the balance will be restored. 



2. The timber-survey stand tables given above show that 21 trees 10 inches 

 and over are left in the first cutting. It is estimated that in 40 years they 

 will be ready for cutting. Assuming that their net volume per tree will be 

 equal to that of the present veterans, or 102 board feet, the stand ready to 

 cut in 40 years will be 2,142 board feet. From the 50 poles, 6 to 10 inches 

 d. b. h., now present, 21 should have moved into the next class. 



Thus the mean annual increment is about 54 board feet per acre. 



3. The summary of the Fremont growth experiments shows that the average 

 total increment in heavy Douglas fir and Engelmann spruce on a good site is 

 about 175 board feet per acre. Half of this figure, or 87 board feet, would 

 closely approach the total increment on the average acre of timber type for 

 the whole forest. Much of this total is lost through decay, death, and incom- 

 plete utilization. Thus the available increment is in the neighborhood of from 

 40 to 50 board feet. As markets become better, with consequent closer utiliza- 

 tion and thinnings, the total increment will be approached more nearly by 

 the volume removed. 



In other words, about every 3.3 years an old veteran dies, and of the number 

 of seedlings taking its place only -one will reach 300 years. In each of the 

 six 50-year classes of the virgin forests there are 15 mature or eventually 

 mature trees, totaling 90 on an acre at any one time. 



Under forest management the forest will not run the full gamut of 300 years. 

 When the timber reaches 160 years of age (or as soon after that as logging 

 is practicable) it will be cut. Thus there will be four ^O-year age classes 

 instead of six 50-year classes. 



A mature tree of 160 years is about the equal of a veteran of 300 years in 

 net volume (gross minus rot and defect), crown space, and root space. Con- 

 sequently the number of mature or eventually mature trees in the 300-year 

 stand (90) will be the same as in the 160-year stand. This number will be 

 distributed over four age classes, since every mature tree needs one in each 

 age class that will supplant it. Thus there will be 22.5 trees reaching maturity 

 each 40 years, providing a cut is made each cycle. At 102 board feet per 

 tree the increment per acre would be 2,300 board feet in 40 years. The mean 

 annual increment is 57.5 board feet. 



CONCLUSIONS 



The above calculations, while at best only approximations, point to an aver- 

 age annual increment of 55 board feet per acre. Notestein (Naturita manage- 

 ment plan, 1912) found that the mean annual increment in western yellow 

 pine on the Naturita division of the Montezuma National Forest was 38 board 

 feet per acre. Considering all types, growth on the Woodland circle is better 

 than this, but it must be remembered that the 93,520 acres over which the 55 

 board feet would be applied contain many acres of very low productive 

 capacity. 



Accepting 45 board feet as a conservative minimum, the present annual incre- 

 ment for the circle is about 2,200,000 board feet accruing on 48,720 acres of 

 immature stands, eliminating 34,190 acres of virgin timber on which the net 

 increment is negligible and 10,610 acres of unstocked land. After these virgin 

 mature stands are cut over and the burns are planted, the total acreage of 

 timber type, 93,520 acres, will be putting on its full increment, or approximately 

 4,208,000 board feet. 



Extracts from the Marking Policy Statement for the Pike National Forest 

 Especially Applicable to the Woodland Working Circle 



General Msis of management. — Generally speaking, trees should be marked 

 for cutting as nearly as possible at the time when the mean annual growth 

 begins to fall off. This does not coincide with diameter growth ; for even when 



