34 



MISC. PUBLICATION 11, U. S. DEPT. OF AGRICULTURE 



Assuming that for the remaining 15 years of the 35-year cutting cycle the 

 growth continues at the same rate as between the tenth and twentieth years, 

 the total volume increase on the average acre for the 35 years following the 

 first cut will be 254.78 per cent.^ (See Table 4.) The volume on the area at the 

 time the second cut begins will then be as follows (rounding off the increment 

 per cent to 254 per cent) : 



Volume per acre, feet 6. m. 



Cutting 

 cycle 



Average 

 original 

 stand 



Amount 

 cut.1 70 

 per cent 



Amount 

 left, 30 

 per cent 



Increment 

 on stand 

 left, 254 

 per cent 



Stand 70 per cent 

 next to 1 cut 

 cut next cycle 



35 years.. 



5,623 



3,936 



1,687 



4,285 



5,972 4,180 



1 Based on 8,619 acres containing merchantable timber, where 33,921,200 feet b. m. were cut. 

 ROTATION AND CUTTING CYCLES 



Studies made by Notestein in uncut stands of Black Hills western yellow 

 pine show that the average sUvicultural rotation is 160 years in virgin stands. 

 Notestein's studies have been recently supplemented by those of Johnson. The 

 latter studied cut-over areas. 



Johnson's figures show that after the first cut in the virgin stand there is a 

 substantial increase in the rate of growth of the trees left on the area. This 

 increase is so marked that we are apparently justified in setting the length 

 of rotation at 140 years, with four cutting cycles of 35 years each. At any 

 rate, we are safe in using a period of 35 years for the first cutting cycle, as 

 is shown by the following : 



It seems safe to assume that the rate of diameter growth attained between 

 the tenth and twentieth years after cutting will continue for at least 15 years 

 more. Then, at the beginning of the second 35-year period, trees which were 

 10 inches d. b. h. at the time of the first cut will have attained a diameter of 

 13.5 inches, and trees which were 12 inches will have increased to 15.5 inches 

 d. b. h. There will be at least 16 trees whose diameter will be 15 inches or 

 more (see Table 3). On the assumption that these trees average the usual 

 three logs per tree, they will produce a volume of 4,019 feet when cut, as is 

 shown in the following tabulation : 



Volume at beginning of second 35-year period 





Diameter class 



3-log 

 volume 

 per tree 



i 



Trees 

 per acre 



Indicated 

 volume 

 per acre 



15-inch 





1 Feet 6. m. 

 i 200 



Number 

 7.21 

 4.41 

 3.37 

 1.22 

 .19 



Feet b. m. 

 1,442.00 



16-inch 





225 



992.25 



18-inch 





300 



1,011.00 



20-inch 





395 



481. 90 



22-inch 





485 



92.15 











Total 



[■ 



16.40 



4,019.30 







i 





This is 161 feet less than the estimated cut for the next cycle, as given in 

 calculation of " Volume per acre " under " Growth and yield." Sufficient vol- 



s There is a divergence of opinion on the reaction that is obtained in the form of 

 increased growth after the first cut. However, it has been proved that there is a marked 

 increase in growth, and further data will be obtained. If it is shown by future studies 

 that the increased growth does not continue to the end of the 35-year cutting cycle It 

 may be found necessary to cut the increment per cent figure down, since it is desired to 

 obtain maximum growth at all times. Growth in young stands can be increased many 

 times over that now being obtained when economic conditions make it possible to thin 

 such stands properly. It is thought that such thinnings can be started within 10 years. 



