Correlation between Height: Diameter ratio and shoot growth in containerised and bare-root seedlings of Cryptomeria japonica

Previous studies revealed that in terms of the stem height growth, containerised seedlings with an average height: diameter ratio (HDR) of ca. 60 are superior to conventional bare-root seedlings and containerised seedlings with an average HDR of ca. 100 are inferior to conventional bare-root seedlings. In this study, we focused on the correlation between the stem growth and HDR in individual seedlings. We measured the stem growth of 2-year-old containerised seedlings and 3-year-old conventional bare-root seedlings for four growth seasons. In each of the growth seasons, HDR showed a negative correlation with stem height growth rate and a positive correlation with the stem radial growth rate of an individual seedling; the strongest correlation was observed in the first and second growth seasons. Therefore, the seedling with a high HDR allocated resources to stem radial growth rather than to height growth. Regarding the stem height growth, we analysed the sequential data for four growth seasons using a linear mixed effects model. HDR showed a negative correlation with the stem height growth. In conclusion, high HDR had negative effects on not only the relative height growth rate but also on the actual height growth.