The regression solution to Model 1 was: 

 Logio Height = 2.083 — 12.775 xi — .008 X2 — .'024 xs + .018 X4 + .024 X5 



where: xi = 

 X2 = 



/age 

 if excessively drained; if not 

 X3 = 1 if somewhat excessively drained; if not 

 X4 ^ 1 if well drained; if not 

 xr, ^ 1 if moderately well drained; if not 

 Coefficient of determination (R-)t ^ .85 

 Standard error in percent = 2.2 



The solution to the equation is given in Table 3. (Soil drainage 

 classes are described in Appendix 1.) Dominant-codoniinant stand 

 height is given for a breast-height age of 50 years, and thus is defined 

 as site index. The poorest growth occurs on the somewhat excessively 

 drained soils where site index averages about 64 feet. It is important 

 to note that soils classified as somewhat excessively drained were shal- 

 low and might retain less moisture for tree roots than excessively 

 drained soils where site index averages 66 feet. Site index increases to 

 70 feet for well drained soils and to 71 for moderately well-drained 

 soils. Then site index drops to 67 feet for poorly drained soils. Under 

 the present scheme of drainage classification it is difficult to point the 

 optimum moisture condition for growth, for it is likely included some- 

 where within the broad category of "poorly drained". Had a finer de- 

 lineation of moisture conditions within this category been used, it is 

 probable that a somewhat poorly drained site would be well suited for 

 white pine growth as indicated by Husch and Lyford (1956). Note that 

 site index ranges from only 64 to 71 feet — a narrow range when com- 

 pared to soil-site studies for species in other regions. 



Table 3. Predicted Site Index in Terms of Drainage Classification 



Summarizing Stand Plot Data 



Plot volvmies were computed using volume equations for individ- 

 ual trees, site-index curves, and methods described by Leak et al. (1970) . 

 Cubic-foot volume was computed for trees 3.0 inches d.b.h. and larger 

 to a 3.0-inch inside-bark top. Board-foot volume (International l^-inch 

 rule) was computed for trees 9.0 inches d.b.h. and larger to a 6.0-inch 



t Coefficient of determination and standard error (expressed as a percent of the mean) 

 are described by Draper and Smith (1966). 



