THE EFFECT OF LIGHT AND COMPETITION ON HEIGHT GROWTH AND CROWN MORPHOLOGY OF NORWAY SPRUCE (PICEA ABIES [L.] KARST.) AND SILVER FIR (ABIES ALBA MILL.) REGENERATION IN SPRUCE STAND IN CONVERSION

The present study analyses light environment and the influence of radiation and competition on height growth and crown morphology of Norway spruce and silver fir regeneration in a spruce forest stand under conversion (Orayska Magura Mts., Slovak Republic). In 10 circular sample plots we selected 40 spruce individuals from natural regeneration and 40 fir individuals from artificial regeneration, growing under different light and competition conditions. For each individual we assessed the values of relative height growth (RHG), apical dominance ratio (ADR), relative crown length (RCL), and level of competition expressed by competition index. To quantify the light conditions, hemispherical photographs were taken in the centre of each sample plot in the height of 3.5 m as well as directly above the terminal shoot of every sampled individual. The results showed that the stem density of mature stand significantly affected the level of relative radiation in the lower layer. Under similar light conditions, underplanted firs reached significantly higher height increments than the spruce natural regeneration. Increased diffuse light intensity had a positive impact on height growth of spruce, but only a minor impact on that of fir. The influence of competition between the regeneration individuals on their height growth and morphological parameters of crowns was not significant, both for spruce and fir. The results of this study imply that the adequate canopy in initial phases of conversion significantly favours the fir underplantings in the competition with natural regeneration of spruce.