58 



between regions (F = 4.02, p = 0.019), reflecting the fact that impor- 

 tance values of trees were greater in the Mississippi Valley, averaging 

 49.1 + 47.6, than the Gulf Coast (37.5 + 37.2) and Atlantic Coast 

 (39.3 + 34.4) regions. A number of factors may contribute to this phe- 

 nomenon, including stand maturity and localized disturbances. 



Another two-factor ANOVA also was used to determine whether the 

 predicted zone values generated were more accurate in one region or 

 another. The absolute value of the difference between the predicted and 

 actual zones was used as the dependent variable. There was neither an 

 interaction (F = 1.44, p - 0.18), nor a main effect (F = 1.54, p = 0.22) 

 involving region, which indicates that the hydrologic zones can be pre- 

 dicted with equal accuracy among the specified regions. 



