Above-ground phytomass acid light regime in Norway spruce stands, planted with different initial density (from 0.8 to 200,000 trees ha(-1)) have been investigated. Two phases of needle mass increment (open-growth and after crown closure, i.e. ecosystem formation) have been singled out. The greater the initial density of stand, the earlier culmination of phytomass increment-from 8-10 years at the initial density of 100,000 trees ha(-1), and 24-26 years at the initial density of 3200 trees ha(-1). Stand radiation regime follows the dynamics of the above-ground phytomass. At the moment of canopy closure only 40-50% of PAR penetrates through the canopy as compared to open area. The denser the stands, the quicker T-PAR decreases. After crown closure, the PAR under the canopy makes up 1% of that in an open area. Copyright (C) 1996 Elsevier Science Ltd.