On any particular site, the maximum mean annual increment is reached at the age when 

 3 m.a,i./9 A = 0. 



Evaluating the indicated derivative and solving the equation for age, we find that 

 mean annual increment is a maximum when 



by S-l + "^by^S"^ + 8 b2 



so the age at which mean annual increment is maximized can be expressed as a function 

 of site index. Then, 



YC = Co S^l • exp (C2S - b2A-2 - byA'^S'^) • A'l, 



where 



A = the age of mean annual increment culmination expressed 

 as a function of site index, as shown above. 



These equations have been put into a computer subroutine, which is shown in figure 3, 

 and the relationship between site index and yield capability is shown in figure 4. 



SLBRGUTINE PPYC^iP (S.YCAPHJ 



A=(18^i.67/S + S0RT( . 339V 1 1 E + 7 / ( S* S ) + . 3 7407 6E +4 ) )/2. 



YCAPP=( 13 100. 2dl*S**(-C.'^»930327J*EXP(C. 267829 E-01 *S-4 67.b9 5 / (A 

 1*A)-1843.67 /(A*sn)/A 

 RETURN 

 ENC 



Figure S. — The ponderosa pine yield aapability subroutine. 



Figure 4. — Relationship between site index and yield capability. 



7 



