MANAGEMENT PLANS THE NATIONAL FORESTS 35 



ume will be obtained from trees less than 1". inches that are defective, sup- 

 pressed, or otherwise in need of cutting, to more than make up this diffen-nce.'* 

 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 Hi) years whidi (barring in.sects, lire, etc.) will 

 yield all of the volume expected. 



CALCULATION OF ALLOW.VllU': CUT 



A good stand of poles or reproduction, or of l)Oth, is generally found under 

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

 chantable timber carries an understory of >M)th reproduction and i)ole,s. 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 468,909.000 feet board measure. In the lirst cutting cycle, approximately 

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

 from the mature, decadeiil. and defeclive 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. b. h. Such a siaiid will be found on 75 i)er cent of 109,838 acres, or on 

 S2,378 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 110,380 

 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. 



C.:VLCUL.\TI0N AND CHECK ON VOLUMES TO BE CUT 



First cutting ryclc. — At the present time (1923) 109,838 acres in this <'lrcle 

 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 :>5-year cutting cycle. This 

 will necessitate cutting an area of 3,i:58 acres annually. Tlie total volume In 

 trees over 10 inches d. b. h. on this area is 408,900,000 feet b. m. Seventy per 

 cent, or 328.278.(H>0 feet will be cut. This is equivalent to 2,988 feet b. m. 

 per acre. Uouixling tliis ligure off to 3.000 feet, the indicated annual allowable 

 cut for the first cutting cycle is 9,414,(100 feet b. m. annually. 



T'sim,' Von Manlil's formula for a check on this ligure, the following result 

 is obtained : 



Total volume of st.'ind (408,909.0(M) feet) divided by one-lialf the rotation 

 (70 years) equals (;.(;9i),(K)0 feet b. m.— the indicate*! annual cut allowable 

 according to this formula. 



In \ jew of the discreiinncy betW(>en these two cal<nlatl(»ns the figun> ol>laine.l 

 by Von M.-intel's formula is rovnided ofT to 7.0(M).(KH> feet l>. m.. and this (Itaire 

 is fixed as the maximum allowable jinnnnl cut for the first cutting cy<'le. sub- 

 ject to change at such time as additional data niav show that a change Is 

 justified. 



* It Is not intended lirro to convey the Idcn thnt nil trc«s over 15 Inrhea d. b. h. will 

 necessarily be cat. MnrkinK In all rnsi'S will be Kiildod by tho Btnndnrd marking nilen. 

 It happens, however, thnt most trees over 15 Inches d. b. h. nrc rendv for cuftlnR, nnd 

 this pives n bnsls on which to check the next cut. 



