LAUSR

In mixed-species forests, species composition of the overstorey affects regeneration processes through its influence on seed rain intensity and micro-site characteristics. Based on extensive inventory data (1583 sample plots), this study investigated relationships between the percentages of silver fir (Abies alba Mill.), European beech (Fagus sylvatica L.), and Norway spruce (Picea abies (L.) H. Karst.) in the overstorey and in naturally established regeneration (seedlings of a height below 0.5 m). A useful framework for this analysis was the assumption that for a given stand density level expected seedling density increases approximately linearly with the increasing percentage of conspecific trees because of increasing seed supply. The analysis partly disproved this assumption and indicated that the species’ proportions in the overstorey and regeneration change in a nonlinear manner. In the beech–fir and beech–spruce mixtures, a strong tendency for beech regeneration to increase its proportion was found in the stands with similar percentages of the species. Fir regeneration positively responded to the presence of beech and spruce in the overstorey; an over-proportional increase in fir percentage was found in stands with more than 60% of beech and, depending on stand density, in a wide range of mixture variants with spruce. These effects may be viewed as increase-when-rare mechanisms that limit superior competitors and counteract the transformation of mixed-species stands into monocultures of spruce or beech. The analysis indicated that reduced stand density considerably facilitates establishment of spruce regeneration in the mixtures with fir and beech, but decreases the percentage of fir regeneration in the mixtures with beech.