Diameter Change Model 



The data for estimating the change in d.b.h. are derived from three sources: The 

 levels-of-growing-stock studies established in 1957 by David Tackle, formerly of Inter- 

 mountain Station; the permanent sample plots established for management planning 

 inventory on the Helena, Beaverhead, and Bitterroot National Forests; and the levels 

 of growing stock studies established by the Pacific Northwest Station in the vicinity 

 of Bend, Oregon. The steps followed in developing this model aire described elsewhere.^ 

 The model is given by the following expression: 



DG = ^DBH^ + DDS - DBH 



where: 



DDS = BKR' FINT- exj)(-1.669S5 + 0.4143 ln(5J) - 0.004388 EL - 0.3781 1t\(CCF) 



+ 0.4879 ln(C7?) + 0.9948 iTi(DBH) + 0.006141 (PCT) 

 SI = Site index (Alexander, Tackle, and Dahms 1967) 

 EL = Elevation in 100 's of feet 

 CCF = Crown competition factor 

 CR = Crown ratio CO.O <CR < 1.0) 

 DBH = Diameter at 4.5 feet, in inches (o.b.) 

 PCT = Percentile in basal area distribution (see Appendix I) 

 BKB = Bark ratio = ^ 

 FINT = Projection interval in years 

 exp(i4) = Exponential function of A 

 IniA) = Natural logarithm of A. 



Equation for Predicting Height Increment 



The data necessary to predict height increment from stand density, crown ratio, 

 diameter increment, etc., were derived from data collected by destructive sampling in 

 the course of management planning inventories. Trees to be felled were selected by 

 first drawing a random sample of the inventory locations that have been measured. At 

 each location a subsample of the trees was then drawn so that ultimately the trees were 

 selected with probability proportional to their basal area. In addition to the stand 

 characteristics described by the standard management planning inventory location data, 

 the radial increment is measured on two radii of a trunk section at breast height. 



^Dennis M. Cole and Albert R. Stage. Intermt. For. and Range Exp. Stn., 

 Moscow, Idaho. (Ms. in preparation.) 



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