et al., 1990; Carmean, 1996; Tyler et al., 1996).
Quantitative analysis of the in¯uence of environmental
factors on forest stand productivity is a recognized
study ®eld. Reviews of principles and
investigations have been presented, inter alia, byCarmean (1975); Spurr and Barnes (1980); HaÈgglund
(1981) and Monserud (1987). Experimental works are
based on the identi®cation of speci®c site features that
are quantitatively related to site quality. By far the
most common indicator of site quality in even-aged
stands, such as plantations, is site index, i.e. stand top
height (mean height of the 100 dominant thickest trees
per hectare) at a given reference age.