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

 tion was based on functions of four variables: mean age (breast-height), 

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

 and total stems per acre. Total stems per acre was used in this equa- 

 tion because it accounted for the fairly high mortality of trees in the 

 smaller size classes. The model for this growth rate is as follows: 



Y2 = bo + bi (TS) + bo (BA) + bs (-y^) + ^4 (^— ) + e Model 4 



where: Y2 = periodic net annual cubic-foot volume growth per acre 



TS = total live stems per acre 



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

 SI = site index 

 A = mean age (breast-height) 

 e = error 



The regression solution to Model 4 was: 



Y2 = —56:0 — .132 (TS) + 2.135 (BA) — .501 ( ^^^" ) + 7.444 {-^—) 



100 A 



where: Coefficient of determination (R-) = .674 

 Standard error = 48.05% 



Although the site index and age interaction (SI/A) variable was 

 not significant, it was retained because it does not appear biologically 

 sound to develop a model for predicting growth without site index and 

 age. All other variables in this equation were significant (5-percent 

 level). The high standard error results from volume loss due to mor- 

 tality which is only partially influenced by age, site, and density. The 

 solution to the periodic net annual cubic-foot volume growth per acre 

 equation is shown in Table 7 and is shown graphically in Figure 2. 



Board-Foot Growth 



The periodic gross and net annual board-foot volume growth per 

 acre equations were based on functions of four variables: mean age 

 (breast-height), site index, basal area per acre for trees 3.0 inches 

 d.b.h. and larger, and basal area per acre for trees 9.0 inches d.b.h. 

 and larger. The model for these growth rates is as follows: 



Model 5 



Y3 or Y4 = bo + bx (P) + ho i-j-) +bs ( ^^ ^^^^ ) + b, ( ^^ ^''J^' ) +e 



where: Y3 = periodic gross annual board-foot volume growth per acre 

 Y4 = periodic net annual board-foot volume growth per acre 



(basal area per acre for trees 9.0 inches d.b.h. and larger) 



P = _ , — X 100 



(basal area per acre for trees 3.0 inches d.b.h. and larger) 



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 



Data were analyzed only for the 50 plots with an average tree age 

 of 35 years or older. Plots younger than 35 years contain few trees 9.0 

 inches d.b.h. and larger that qualify for board-foot growth analysis. 



13 



