Summary:

A site quality index is the main factor determining the tree stand growth dy-namics. Furthermore, in natural afforested stands (a felling-less forest system) it is possible to observed high variability of tree heights, especially during the first-years of their life. It mainly results from overshadowing the regenerated trees with the upper storey or dominant trees and the growth process is suppressed then. Col-lected empirical data show that even the long lasting period of growth in suppres-sion does not prevent such a stand from reaching a rapid growth ratio in the later age. The paper presents a method of estimating a forest site quality and a roughly approximated period of the slow growth in suppression. The algorithm was based on the tree stand growth model proposed by Suliński [2007], which takes into con-sideration only parameters with direct ecological interpretation. The postulated procedure was verified on empirical spruce stand growth benchmarks from expe-rimental sites in the Białowieża forest and Witów in the Western Tatras.