Lichtverfügbarkeit, Baumwachstum und Nachhaltigkeit im Dauerwald auf Buchenstandorten

The availability of light plays a major role in shaping the regeneration dynamics in oligotrophic and mesic forests. In selection silviculture, regeneration is initiated below canopy and usually remains shaded for a certain period. To better quantify growth patterns under these conditions on beech site types, beech (Fagus sylvatica L.) and sycamore maple (Acer pseudoplatanus L.) of the thicket and pole stage classes were subjected to an extensive stem disc analysis. The results were then used to explore the possibilities of species mixtures in uneven-aged forests. While height and diameter development of both tree species depended strongly on the availability of light, it was shown that height growth of beech was larger in dense stands. Sycamore maple benefited from a longer crown and should therefore be released from competing neighbors by active management interventions. But already at small diameters, height growth was reduced the older the sycamore trees were. Therefore, at the demographic equilibrium in beech selection forests (basal area of 21– 25 m²), growth of sycamore into the crown layer is strongly questioned, especially in small gaps (<270 m²) with less than 10% light availability. Under these conditions, its share in the regeneration is less than 25%, and the time to outgrow from the first two diameter-at-breast-height (DBH) classes (1–8 cm DBH) is on average 51 years. To maintain a demographic equilibrium, 90–120 trees per hectare should be present in DBH class 3 (8–12 cm DBH). However, to ensure a substantial proportion of sycamore maple in the mixture, it should be regenerated in gaps of at least 400 m². By spatially heterogeneous removals and group cuttings a diverse mosaic of regeneration niches can be created to initiate and maintain a mixture of tree species.