Dependence of flower-bearing on trunk size and trunk origin in four tree species of the subgenus Quercus

ABSTRACT We investigated the flower-bearing properties of four sympatric oak species in the subgenus Quercus commonly grown in semi-natural forests in western Honshu Island, Japan. Quercus variabilis and Quercus acutissima belong to the section Cerris and Quercus serrata and Quercus aliena belong to the section Quercus. The timing and pattern of flower-bearing varied among the four oaks, but were synchronized between the male and female inflorescences within each species. Trunk size was the primary factor affecting the flower-bearing properties; more flowers were borne on thicker trunks. Threshold trunk sizes for flower-bearing, below which no flowers were borne, were identified in the two Cerris section oak species; in contrast, the two Quercus section oak species bore flowers even on the smallest trunks. The smallest flower-bearing trunk sizes of the Quercus section oaks were extremely small compared with the other tall tree species distributed in the temperate zone of Honshu Island. The flowering probability was not clearly influenced by whether the stem originated from a seedling or a sprout, except for the male inflorescences of Q. aliena, which rather showed a positive relationship between sprout-origin and flower-bearing. Thus, no trade-off relationship between sprouting and flowering was observed.