The effect of elevated air CO2 concentration on dendrometric parameters and biomass of European beech and Norway spruce in their monocultures and intermixtures

An increased CO₂ concentration should have a positive effect on tree growth, but in different species mixtures, due to mutual interaction between species, this effect may be insignificant or even negative. Therefore, our research focused on the influence of elevated CO₂ concentration on the height, stem diameter and biomass production of beech and spruce planted in the following arrangements: Pure (one species), Single (an individual of one species surrounded by trees of another) and Group (groups of three trees of one species surrounded by trees of another). In autumn 2005, these saplings were planted inside two glass-domes under ambient and elevated CO₂ concentration in the Beskydy Mts. (Czech Republic). Fumigation of CO₂ took place each vegetation period from 2006 to 2013. From 2006 to 2012, the height and stem diameter of each plant were measured. In autumn 2013, the plants were harvested (together with their roots) and their biomass was determined. The beech trees were mostly statistically significant larger under elevated CO₂ concentration (the greatest difference being between trees growing in Single). Under elevated CO₂ concentration, Spruce growing in Single was larger and that growing in Pure was smaller than Spruce growing under ambient CO₂ concentration. Although trees are affected not only by increased CO₂ concentration but also by other phenomena (i.e. nutrient, water etc.), we assume that, in the future (with all current factors being maintained, except for the CO₂ concentration), it can be more suitable to grow beech almost as a monoculture or singly and spruce only singly.