APPENDIX — ADEQUACY OF DATA 



667 



assumptions, play an important role in the 

 procedure. 



The needed growth estimates are no more than 

 the projections of timber cut from Future Demand 

 for Timber plus an allowance for possible under- 

 estimation, catastrophic losses, and reduction in 

 commercial forest area. The needed inventory 

 estimates are capitalized values calculated from 

 the needed growth figures. The capitalization 

 rates used represent the weighted average mean 

 annual growth (including growth harvested in 

 thinnings or intermediate cuttings) of well-stocked 

 stands of each region's important timber types at 

 appropriate rotation ages. The rotations selected 

 were those deemed necessar}^ on the average to 

 provide timber of the size and quality implicit in 

 the future demand estimates under the intensity 

 of protection and management which might pre- 

 vail in the year 2000." When the results from all 

 regions are brought together, the capitalization 

 rates applied to needed sawtimber growth were 

 found to average 5.4 percent for eastern softwoods, 

 4.4 percent for eastern hardwoods, 3.7 percent for 

 all species in the Douglas-fir subregion, and 2.8 

 percent for all species in the remainder of the West. 

 Corresponding rates in terms of growing stock 

 averaged 4.6, 4.0, 3.3, and 2.0 percent, respec- 

 tively. All of the capitalization rates and rotation 

 ages chosen are considered practicable and feasible, 

 but they may be subject to errors. 



Projected growth and inventory estimates also 

 are dependent upon the estimates of future demand 

 plus an allowance. In addition, they involve the 

 assumptions that (1) forestry" progress will con- 

 tinue at the rate shown by recent trends, and (2) 

 timber will be cut each year from 1952 to the 

 projection dates as demand steadily rises from 

 1952 consumption to the projected levels. The 

 former assumption is based partly on resurveys 

 and other plot remeasurement data and partly on 



" Calculations of needed inventory were made inde- 

 pendently in each region. E.xamples of rotations used 

 include: 60 years for southern yellow pine, 80 years for 

 eastern hardwoods, 100 years for Douglas-fir, and 120-150 

 years for ponderosa pine. In such calculations, the longer 

 the rotation needed to produce a desired range of size 

 classes, the greater the ratio of timber volume to annual 

 yield and the smaller the capitalization rate to convert 

 needed growth to needed inventory. 



judgment. It takes into account intensified pro- 

 tection with consequent substantial reductions in 

 mortality, rapid expansion in tree planting, in- 

 creased growth rates in the West resulting from 

 liquidation of old-growth timber and improvement 

 in forestry, and decreased growtli rates in the 

 East as understocked stands fill in. If more 

 adequate information had been available, it would 

 have been desirable to calculate these and other 

 items of forestry progress independently instead of 

 selecting rates of gi'owth and rates of mortality 

 that purport to include tliem all, as was actually 

 done. The procedures used varied from region to 

 region depending upon differences in the nature of 

 the forest itself and in the statistical data avail- 

 able. Some formulas provided for separate calcu- 

 lation of ingrowth, for example, while others used 

 a gross growth rate wliich included ingrowth.'^ 

 The details of procedure are fully described in the 

 working plans which may be consulted in Forest 

 Service regional offices, as mentioned previously. 

 Finally, the estimates of realizable growth 

 should be mentioned. Tliey were prepared by 

 groups of local foresters in each region who were 

 acquainted with the growth achieved on the best 

 managed properties in their regions. Records of 

 growth and yield were used where available, along 

 with information on areas of types and sites. 

 However, in the last analysis, the results are based 

 mainly on professional judgment. They should 

 be used only as indicators of the levels of growth 

 that might be considered reasonably attainable. 



'2 The following formulas, or variations of them, were 

 used in most cases for projecting inventory and growth for 



/ 



specified years 



A = liGS-y2C-M) 



.Os- (C+M)] 



l.ai;''-l 

 .Ox 



where .4 = Addition to the growing stock during the period 

 GjS= Growing stock at the beginning of the period 

 C= Average annual cut during the period 

 M= Mortality in first year of the period 

 .Os = Average annual gross growth rate during the 



period 

 .Oa;= Gross growth rate minus the mortality rate. 

 NG=(GS-y2C-M) .Os-M 

 where NG=Net growth during an individual year 



G*S= Growing stock at the beginning of the year 

 C= Timber cut during the year 

 M= Mortality during the year 

 .Os= Annual gross growth rate. 



