Morphological plasticity of six tree species with different light demands growing in multi-layered deciduous forests in Central Europe

Tree allometry is a plastic feature and scaling parameters may considerably vary depending on phylogeny, life strategies, growth conditions and ontogeny. We hypothesized that in multilayered forests growing on rich sites and driven by stand dynamics without stand-replacing disturbances, light is a primary driver of allometric relationships and thatthe morphological plasticity of tree species is closely associated with their shadetolerance. We quantified and compared the morphological properties of six species forming a shade tolerance gradient: Alnus glutinosa (L.) Gaertner, Quercus robur L., Fraxinus excelsior L., Ulmuslaevis Pall., Tilia cordata Miller, and Carpinus betulus L.The relationships between tree height and local stand density as predictors and dbh, crown width, crown length and crown volume as response variables were characterized. We found thatin the lower stand layer the values of crown parameters increased with tree height at a lower ratein light adapted than in shade tolerant species. In contrast, the response of morphological traits on competition was stronger in light adapted than in shade tolerant species.The crown widthtocrown length ratio was not associated with light demand. Except for the different allocation pattern of ash, between-species differences in the slenderness ratio were insignificant. Allometry and sensitivity to competition was different in trees growing in the upper and lower stand layer. Our results show that the dichotomy of basic growth strategies of stress tolerance or stress avoidance is too simplistic and does not encompass social status and species-specific features such asapical control.