Cubic-Foot Growth 



The periodic gross annual cubic-foot volume growth per acre equa- 

 tion was based on functions of three variables: mean age (breast- 

 height ) , site index, and basal area per acre ( for trees 3.0 inches d.b.h. 

 and larger). The model for this growth rate is as follows: 



Yl = bo + bi (— -) + bo ( r-rr ) + bs (— T-nrr ) + e Model 3 



A 100 1000 



where: Yl = periodic gross annual cubic foot 



volume growth per acre 

 A = mean age (breast-height) 

 SI = site index 

 BA = basal area per acre (for trees 3.0 inches d.b.h. and 

 larger) 

 e = error 



The regression solution to Model 3 was: 



Yl = 48.9 — 949.739 i-^) + 1.595 (-^L^rM-) _ .027 ,_SIjL^A2_ 



A ^ 100 1000 



where: Coefficient of determination (R-) = .354 

 Standard error = 20.49% 



All variables in this equation were significant or approached sig- 

 nificance. The solution to the periodic gross annual cubic-foot volume 

 growth per acre equation is shown in Table 6 and is shown graphically 

 in Figure 1. Table 6 indicates that gross growth increases at ages 20 

 to 60 years. After 60 years age has a negligible effect on growth. 



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