Yield Capability 



Yield capability of western white pine can be estimated by the equation: 

 YC = bQ + bjS, where 



YC = yield capability in cubic feet per acre of mean annual 

 increment on all trees at the age of culmination of 

 increment 



S = site index at a 50-year base age 

 bQ = 14.849891 

 bj = 1.7311563. 



This equation was derived from table 7 of Haig's (4) yield tables which show average 

 mean annual increment of all trees in so-called normal stands for various ages and 

 levels of site index. For western white pine, cubic mean annual increment culminates 

 at a stand age of about 105 years, regardless of site quality, according to Haig's 

 table. Consequently, this equation expresses the relationship between site index and 

 cubic volume mean annual increment at a stand age of 105 years, as shown in figure 1. 



PONDEROSA PINE 



Site Index 



The estimating procedure for even-aged stands of ponderosa pine is based on the 

 curves developed by Lynch (7) . The index base age was changed from 100 years to 50 

 years and the base of logarithms in the equation was changed so as to use natural 

 rather than common logarithms.-^ The surface of dominant stand height over age and site 

 index remains unchanged, because the conversion of the curves resulted only in a 

 rescaling of the independent variables. Lynch 's system of site index curves takes into 

 account the reduction in height growth due to overdense stocking on lower quality 

 sites. Because one or the other of two equations is to be used, depending on whether 

 or not stocking and site conditions have reduced height growth, the estimation pro- 

 cedure has been put into a computer program subroutine, shown in figure 2. 



SLDKCLTlNh PP'j.LJti ,h,ii ibloO fSC) 

 U=l. + C.2''+32*( lOC./A-l.) 



Fi = ( H*1C ( O.o^jsT* I IGC ./ A- i . ) ) )**( i ./U ) 

 SD=E*(0..i9i.d + 0.Ci'M3*H-C.o^fa7'l'h/A + 29.752/M) 



IF(SC-10l. 0)3,3,1 



1 iF( PI-75.D)2,3,3 



2 Z= ( SC-ICO. ) *( 75 .-Pi ) 

 RZ = EXP(-0.3 3 12 3t:-U3*Z + 0.2 7 63CfcE-G6*Z*Z) 



GC TO 4 



3 HZ=1. 



A PA = tXP(-l . 19222* ( lOt ./A-2 .) ) 

 uA = C. 19i62J*(10C./A-2.) 

 SI5C^(H/(PA*FU) )**(!./( 1.<-UA)) 



RETURN 

 END 



■^Natural or Naperian logarithms are to the base e, where e = 2.71828. Common loga- 

 rithms are to the base 10. In conventional notation, which will be used in this report. 

 In X means the natural logarithm of X, while log X means the common logarithm of X. 



Figure 2. — Site index 



estimating subroutine 

 for ponderosa pine. 



5 



