Potential influence of air elevated [CO₂] on aboveground biomass was investigated on young (17-19 year old) Norway spruce (Picea abies [L.] Karst.) trees cultivated inside glass domes (GD) with ambient (A, 370 mmol (CO₂) mol^-1) and elevated (E, 700 mmol (CO₂) mol^-1) atmospheric CO₂ concentrations ([CO₂]) established in 1997. GDs were working as a semi-open system (Urban et al. 2001). The trees were growing in two different stand densities (S, 5,000 tree ha^-1 and D, 10,000 tree ha^-1) until 2002. Then the first analysis of harvested trees from schematic thinning was done. Two years later the second analysis was performed.

 Amount of branches with secondary shoots (SS), total amount of SS on branches were higher within the crowns of E- trees comparing to A- ones, particularly in S stand. After thinning, number of branches with SS and stem SS decreased and it was found to be even lower in ES than in AS. However, leaf (LB), branch (BB), stem (SB) and total aboveground (TBA) biomass of tree were found to be unaffected by elevated [CO₂], stem dendrometric parameters and the aboveground tree organs’ biomass increments were stimulated by thinning, especially in S stand. Then the number and length of whorl branches increased on average by 13 % and 8 %, and by 3 % and 10 % (insignificantly) in E- sparse and dense sub-treatments, respectively. Tree height, stem thickness, number of whorl branches, length of whorl branches and angle of their inclination were found to be unaffected by elevated [CO₂]. The percentage differences between treatments were within ±10 % interval and they showed slightly higher stimulation of initial growth for trees in D- spacing. The thinning stimulated growth of the stems and branches of primary structure.

Key words: biomass allocation, dendrometry, long-term experiment, secondary shoots, thinning