34 



MISC. rUBLICATIOX 11, U. S. I»KPT. OF AGRICULTURE 



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

 growth continups nt tho same rate as Itotwoon the tenth and twentieth years, 

 the totJil Vdlunu' iiuroase on tho avcriigo acre fur the 35 years following the 

 lirst fut will be 254.78 per cent.' (Si-c 'Pablo 4.) Tho volunio on tho area at the 

 tiiuo tho seoniul cut l)ogins will then bo as follows (rouiidinir off the increment 

 IMM- oent to 254 por <ent) : 



\'oluine per acre, feet h. >n. 



1 Hasc<l on 8,(519 acres containing merchantable timber, where 33,921,200 feet b. m. were cut. 

 ROTATION AND CUTTING CYCI.KS 



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

 pine show that the average silvicultural rotation is IGO years in virgin stands. 

 Notostoin's studies liavo been recently supplomonted by those of Johnson. The 

 latter studied cut-over areas. 



.lolinson's tiguros show lliat after the first cut in the virgin stand there is a 

 substantial iiicroaso in the rate of growth of the tro<\v; i(.ft, on tho area. This 

 increase is so marked that we are apparently justillod in sotting tho 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 tho time of the first cut will have attained a diameter of 

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

 d. b. h. There will bo at least 10 trees whose diameter will be 15 inches or 

 more (see Table ."'>)• f>n tho assumption that these trees average (he usual 

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

 shown in the following tabulation: 



Vohime at 'beginnbiu of second .l.j-yenr period 



Diameter cla.ss 



l.=i-inch. 

 10-lnch. 

 18-lnch. 

 20-inch. 

 22-inch. 



Total. 



16.40 



4,010.30 



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

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



• There is n dlverfcence of opinion on the reaction that Is obtained In the form of 

 liicrf.isfd jfrowth after tho first cut. Ilowcver, It has been proved that thoro I.s a marked 

 increaHo In growth, and further data will be obtained. If It is shown by future studies 

 that the Incron.^ed Rrowtli does not continue to the end of the 35-ycar cutting cycle It 

 may ho fouTid nocossary to cut the Increment nor cent llgure down, sinco It Is desired to 

 obtain maximum growth nt all times. Growth in younp 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. 



