Agreement of included predictors, and the signs of
their coef®cients, with the expectations based on other
studies (Section 4.2) corroborates model Eq. (1). As
expected, increased rainfall is associated with
increased site index; calcium and clay contents has
a negative relation to site index; and surplus water has
a negative coef®cient in accordance with well known
problems of Douglas-®r planted in excessively wet
soil conditions.