on the area, or by 10 1 1 20.^ Therefore if the saw-timber stands of a 

 unit are sufficient to last 50 years on a sustained-yield basis, it is assumed 

 that the loeged area should be reduced by 95/120 of an acre for every saw- 

 timber acre burned (average of 70 and 120). Likewise, if the 60-year- 

 old pole stands are not to be cut for 65 years, owing to an excess of older 

 age classes, the cut need only be reduced by 55, 120 for damage in these 

 stands. Therefore, the effective area-loss figure for all commercial 

 forest area in northern Idaho may be translated into reduced cut in the 

 following fashion: 



Area annually 



burned Effective annual 



1931-37 Conversion area loss 



Acres factor Acres 



Saw-timber stands 9,300 X 95 120 = 7,400 



Pole stands 6,5(K) X 55/120 = 3,000 



Seedling and sapling 



stands I I.KKJ X 20, 120 = 1,800 



Total area deduction for lire losses 12,200 



Volumes 



.After the logging has proceeded for a number of years, theoretically 

 each acre of timber cut will be 120 years of ai;e at the time of logging. At 

 that time the sustainable volume cut will be the allowable acreage times 

 volume per acre at 120 years. The bulk of the present virgin timber 

 is now older than 1211 years. On much of the area supporting this saw 

 timber the volume is greater than it was at 120 years, but on some of it 

 the reverse is true. Inasmuch as the only volume which will be logged 

 for a considerable period is that which is already there, the volumes per 

 acre used in this calculation are those of the present saw-timber stands, 

 regardless of age. The critical reader may take exception to this on the 

 grounds that many of the saw-timber stands will make additional 

 growth before their cutting date. This is especially true in the Clear- 

 water district, where a large area of saw timber is less than 120 years old. 

 However, fire losses which will occur in this additional growth have not 

 been adjusted for. Furthermore, several other compensating factors 

 such as increased insect losses make this a more reasonable calculation 

 than it might appear at first glance. 



Calculatiotis of Allotxable Cut 



With the assumptions and methods just described, the following 

 calculations were made to arrive at the estimates of allowable cut used 

 in the chapter on forest-management possibilities: 



THE ALLOWABLE AN'NLAL CUT OK ALL .S1"EC1E> IN NORTHERN" 

 IDAHO 



Area of stocked commercial forest land, excluding Cot- 

 tonwood (fig. 43) acres . . . 5,869,4«Hi 



Annual area cut belore deducting for t;rc loss 



(1, 1201 acres. . . 48,9(Xi 



.Area reduction for fire loss. do. . . 12,200 



Net area cut do . . . 36,700 



Volume per acre in saw-timber stands. . board feet 14,100 



Allowable- annual cut, all species do 518,000,000 



IHE ALLOWABLE ANXLAL CI T OK WESTERN WHITE IMNE 

 I.\ NORTHERN IDVHO 



Area of stocked western white pine land ^fig. 44) 



acres ... 2,34S,8(KI 



" The greater actual volume loss (equal to the difference between the 

 volume which the present saw-timber stand would have in 50 years and 

 the volume the 70-year-old stand would reach by that time) is not so 

 important as the ages might indicate, since many of the present saw- 

 timber stands are slowing up in gn»wth, remaining stationary, or de- 

 clining. 



RGE 



(Yeors) 



101 + 



81 + 



61 4- 



4! 4- 



21 4- 



I 4- 



PLL COmmERCIfiL 

 UJMITE PinE STonos 





ACTUAL 



IDEAL 



0.5 



1.0 1.5 



MILLION ACRES 



2.0 



2.5 



Figure 44. — Present age distribution 'cumulative) of all commercial 

 western white pine stands compared with ideal pattern for a f 20-year 

 rotation on a one-cut basis. 



.Annual area cut allowing for age deficiency (stands 



older than 20 years spread over KKl years), acres 17,900 



.Area reduction for fire loss. A" 2,9<ii) 



Net area cut lio 15,l«'<i 



Volume of western white pine per acre in saw-timber 



stands board feet . 9,3«K» 



.Allowable annual cut of western white pine do. . . . 140,000,000 



RGC 



(Yeors) 



COmmERCIflL UUHITE PinE STRHDS 

 in nflTlODFIL FORESTS 



101 + 

 81 + 

 61 + 

 41 -»- 

 21 + 

 1 -t- 





1 



' 1 







/y^ACTUAL 











J 







^ 



A=P.^^.». 



1 



1 



1 L 





~M 





















































1 



1 



( 



D .\.' 4 6 8 10 

 MILLION ACRES 



n 



FiGi'RE 45. — Present nge JittrHution (cmrnulatht) if nmmrrti^ mi M fu 



white pine stands on natioMal JtrtsU (ompartJ trith a¥ iJn- 



a /2l)-\ear rotntiaH on a o»,--cHt Kuis. 



63 



