MAXAGEMEIirT PLANS THE NATIONAL, FORESTS 35 



ume will be obtained from trees less than 15 inches that are defective, sup- 

 pressed, or otherwise in need of cutting, to more than make up this difference.* 

 The marking rules now followed in the Black Hills forests call for the 

 removal of 70 per cent of the stand by volume, on the average. An inspection 

 of cut-over areas in this circle leaves no doubt in the observer's mind that a 

 second cut can be made in 35 years which (barring insects, fire, etc.) will 

 yield all of the volume expected. 



CALCULATION OF ALLOWABLE CUT 



A good Stand of poles or reproduction, or of both, is generally found under 

 the mature stand. It is estimated that 75 per cent of the area bearing mer- 

 chantable timber carries an understory of both reproduction and poles. Hence, 

 age classes 3a and 3b will not have to be carried in the stand any longer than 

 70 years to prevent a hiatus in the supply of timber ready for cutting. This is 

 brought out more clearly by the following calculations; 



Table 1 shows that there is now an area of 109,838 acres bearing merchant- 

 able timber. On this area there is a volume in trees 10 inches and over d. b. h. 

 of 468,969,000 feet board measure. In the first cutting cycle, approximately 

 70 per cent by volume of this stand will be removed. This volume will come 

 from the mature, decadent, and defective trees. The calculation included 

 under "Growth and yield" indicates that at the beginning of the second cut- 

 ting cycle more volume can be cut than was removed during the first cutting 

 cycle. This second cut will be obtained from the almost mature trees left 

 at the time of first cut, and from the most mature of what are now thrifty 

 intermediates. 



By the end of the second cutting cycle 70 years will have elapsed. During 

 this period the poles that were on the area at the time of the first cut will 

 have increased in d. b. h. at an average rate of 1 inch every 10 years (refer 

 to Table 3) and there should be at least 16 averaging 15 inches or over, 

 d. ^. h. Such a stand vsdll be found on 75 per cent of 109,838 acres, or on 

 82,378 acres. In addition there is an area of 28,008 acres of pole stands, with 

 reproduction underneath, that will contain mature timber at the time of 

 starting the third cutting cycle. There will then be a total area of 110,386 

 acres from which to obtain the third cut of the rotation. 



The fourth cut of the rotation will be obtained from the area of 29,412 acres 

 now bearing reproduction, and from 75 per cent of the area now bearing mer- 

 chantable timber, or 82,378 acres. Thus the total area that can be cut over 

 during the last cutting cycle will be 111,790 acres, with a strong probability of 

 an additional area from the 28,008 acres of present pole stands. 



CALCULATION AND CHECK ON VOLUMES TO BE CUT 



First cutting cycle. — At the present time (1923) 109,838 acres in this circle 

 bears a stand of timber in trees the majority of which are 10 inches or over 

 in diameter. Owing to the large amount of mature and decadent timber on this 

 area, it is imperative that it be cut over in the first 35-year cutting cycle. This 

 will necessitate cutting an area of 3,138 acres annually. The total volume in 

 trees over 10 inches d. b. h. on this area is 468,969,000 feet b. m. Seventy per 

 cent, or 328,278,000 feet will be cut. This is equivalent to 2,988 feet b. m. 

 per acre. Rounding this figure off to 3,000 feet, the indicated annual allowable 

 cut for the first cutting cycle is 9,414,000 feet b. m. annually. 



Using Von Mantel's formula for a check on this figure, the following result 

 is obtained: 



Total volume of stand (468,969,000 feet) divided by one-half the rotation 

 (70 years) equals 6.699,000 feet b. m. — the indicated annual cut allowable 

 according to this formula. 



In view of the discrepancy between these two calculations the figure obtained 

 by Von Mantel's formula is rounded off to 7,000,000 feet b. m., and this figtire 

 is fixed as the maximum allowable annual cut for the first cutting cycle, sub- 

 ject to change at such time as additional data may show that a change is 

 justified. 



* It is not intended here to convey the idea that all trees over 15 inches d. b. h. will 

 necessarily be cut. Marking in all cases will be guided by the standard marking rules. 

 It happens, however, that most trees over 15 Inches d. b. h. are ready for cutting, and 

 this gives a basis on which to check the next cut. 



