Regeneration growth in different light environments of mixed species, multiaged, mountainous forests of Romania

Growth of regenerating trees in different light environments was studied for the mountainous, mixed-species forests in the Carpathian Mountains of Romania. The primary species in these mixtures were silver fir (Abies alba Mill.), European beech (Fagus sylvatica L.) and Norway spruce (Picea abies (L.) Karst). Seedlings/saplings of these species were selected and measured in different stands from two different geographical locations. Regenerating trees were measured for height and diameter growth during the summer of 2002. For each seedling/sapling, percentage of above canopy light (PACL) and stand basal area (BA) were used to assess available and occupied growing space respectively. Regeneration growth was compared against these two variables and regression relationships were developed. Using these models, we predicted the dynamics of regeneration as both growth and species composition. Our results showed that in low-light environments (PACL < 20-35%; BA > 30 m(2)/ha), shade tolerant fir and beech clearly outcompeted the spruce. Therefore, in dense stands, spruce could be eliminated by the shade tolerant species. For intermediate levels of cover (PACL=35-70%; BA=15-35 m(2)/ha) the spruce grew at comparable rates as the beech and fir. All three species showed similar growth rates in open conditions (PACL > 80-90%; BA < 15-20 m(2)/ha) with the spruce having a tendency to outgrow the others. However, in terms of establishment, such conditions favor spruce and inhibit fir and beech.