Growth characteristics of standing individual Japanese oak (Quercus crispula) qualifying for barrel timber in a secondary forest

The demand for Japanese oak (Mizunara; Quercus crispula) as barrel timber has been increasing. To prevent liquid leakage, small grain angles and abundant tyloses are essential. This study examined the grain angles and tylose filling ratios in Q. crispula and their relationships with individual tree growth characteristics. A total of 237 disks were collected at 3 m tree height at a 7.1 ha secondary forest dominated by Q. crispula. The grain angles were measured via the splitting method to calculate the absolute average (AGAab). The proportion of earlywood vessels filled with tyloses in the sapwood−heartwood transition zone (2 cm²) was also assessed (TFRtr). Relationships between AGAab, TFRtr, and various factors were analyzed via structural equation modeling. The most influential factor for AGAab was wood ec centricity (the estimated standardized path coefficient = 0.33, p < 0.01), followed by annual ring width (coefficient = 0.29, p < 0.05). This suggests that uneven and fast radial growth increases the grain angle. The strongest factor for TFRtr was annual ring width (coefficient = −0.21, p < 0.05), indicating that slow-growing trees allocate more resources to maintaining existing structures than to form new cells. These findings suggest that promoting rapid growth does not necessarily enhance wood quality. For barrel wood production, long-rotation forestry is recommended to ensure moderate competition.