Competitive disadvantage of Quercus petraea seedlings in mixtures with Fagus sylvatica and Carpinus betulus can be explained by different biomass allocation patterns

Natural regeneration of Quercus petraea is often inferior in height growth compared to shade-tolerant companion species. As a result, frequent removal of competing vegetation is typically required to promote Q. petraea for successful regeneration. Here we examined whether differences in species’ biomass allocation, biomass density, and total leaf area are responsible for inferior competitiveness of Q. petraea. For this purpose, 37 four-year-old Q. petraea seedlings and 15 and 17 seedlings of the shade-tolerant Fagus sylvatica and Carpinus betulus, respectively, were excavated along a radiation gradient within a mixed Q. petraea forest. Solar radiation above each seedling ranged from 1 to 70% of open field conditions. Annual shoot lengths and total heights of F. sylvatica and C. betulus were higher than in Q. petraea across the radiation gradient. Total biomass was comparable among the species at any level of radiation, but aboveground woody mass fraction in Q. petraea (34%) was always significantly lower than in F. sylvatica (47%) and C. betulus (52%), while its root mass fraction was significantly higher at 47% compared to 34% and 26%, respectively. At the same time, Q. petraea had a significantly lower average height-to-root collar diameter ratio (56) than F. sylvatica (71) and C. betulus (105). In contrast, biomass density of Q. petraea roots and shoots was significantly higher than in F. sylvatica and C. betulus. Owing to different biomass allocation patterns between Q. petraea and companion species, there are no light levels at which Q. petraea regeneration does not require control of competition to survive.