Morphological and physiological responses of beech and oak seedlings to canopy conditions: why does beech dominate the understory of unmanaged oak fuelwood stands?

Secondary forest succession after abandonment of traditional agricultural and silvicultural lands is occurring in many parts of the world. Quercus crispula Blume-Quercus serrata Murray fuelwood stands have so far been artificially maintained in natural Fagus crenata Blume forests, central Japan, by resprouting after cutting. It is known that unmanaged fuelwood stands return to F. crenata dominated stands. This study aimed to examine why the two Quercus species are replaced by F. crenata by investigating seedling morphological and physiological responses of the three species to canopy conditions (forest edge and understory). The two Quercus species allocated more carbon to roots and stored more total nonstructural carbohydrates in roots as compared with F. crenata. Therefore, the two Quercus species allocate more photosynthetic production to roots than aboveground growth to maintain sprouting ability. On the contrary, F. crenata increased the light-harvesting efficiency (i.e., low leaf mass per area and high chlorophyll concentration) in the understory and increased height growth at the forest edge by greater allocation to stem. These traits would be beneficial for an increase in survival in the understory and height growth at the forest edge. Therefore, it is suggested that Quercus species in unmanaged stands will be replaced by F. crenata, a competitively superior species.