Tempo wzrostu wysokości i pierśnicy jodły pospolitej (Abies alba Mill.) w Beskidzie Niskim

Silver fir is one of the main tree species of mountain and foothill forests in Poland that in optimal conditions forms pure stands with multi−layer structure. The study objective is to present differences in height and diameter growth rates of firs growing in upper stand layers and in the undergrowth. The research was conducted in 12 fir stands located in the Beskid Niski Mts. (southern Poland). In each stand height and diameter at breast height (dbh) were measured for 25 fir trees in order to develop a height curve. The first canopy layer included trees that were higher than ⅔ Hmax established from the height curve of the tree with the largest dbh. Height and diameter were measured on eight trees selected from the first canopy layer. An increment core was extracted at breast height in order to estimate the tree age. From the third canopy layer, which included trees higher than 2 m with dbh below 7 cm, five trees were selected. After cutting those trees, the length of the last ten branch whorls was measured. Five−year ring width measurements starting from the bark towards the pith were done at the stem cross−sections obtained at breast height. The number of rings was counted on remaining stumps. Height growth rate was defined as the height at the base age of 100 years (eq. 1). For the first canopy layer, the height growth rate was on average 31.8 m, while for the undergrowth it was 12.1 m. There was also large difference between diameter growth rate of the first stand canopy layer (55.7 cm) and undergrowth (18.3 cm). Both differences were significant at p=0.05. These discrepancies could result from low amount of light reaching the forest floor. The correlation between height and diameter growth rates and undergrowth tree age was negative in both cases. Long periods of shading result in smaller number of firs reaching the first canopy layer. Assuming that uneven−aged stand structure is optimal for that species, it should be characterized by a spatial variability (mosaic) of various canopy layers including even−aged patches with sparse canopy closure as well as gaps where fir regeneration will be initiated having favorable growth conditions.