To evaluate the relative importance of each predictor,
regression coef®cients were recalculated on the
standardized values of predictors and SI. The weight
of each predictor was expressed as percent of the sum
of the absolute values of regression coef®cients. The
variable having the greatest effect on site index estimation
was annual rainfall (37.2%), followed by water
surplus (32.9%), clay content in the horizon 25±50 cm
below ground (11.8%), calcium-carbonate content in
the horizon 25±50 cm below ground (10.6%) and
east±west component of aspect (7.6%).