Leaf area and growth efficiency of regeneration in mixed species, multiaged forests of the Romanian Carpathians

Dynamics in volume growth efficiency of regenerating trees in different light environments were studied for the mountainous, mixed species multiaged 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). Leaf area–sapwood area relationships were developed for seedlings/saplings of each species. Height and diameter growth were measured and used to compute average annual stem volume growth of each tree. Percentage of above canopy light (PACL) and stand basal area were used as surrogates for the available growing space of each seedling/sapling. For all three species, volume growth of regenerating trees increased exponentially with leaf area. Conversely, growth efficiency followed a saturating increasing trend along the range in tree leaf area. Generally, growth efficiency increased with light and decreased with basal area. The fir was the most efficient in dense stands, while beech and spruce were less efficient and followed similar trends with basal area. In open, conifers showed similar efficiency rates while beech was less efficient. For beech, the lower rates in open compared to conifers and the similar rates in dense stands compared to spruce may be an artifact of using only stem volume to compute growth efficiency.