Effects of Seedling Size, Stock Type, and Mechanical Site Preparation Method on Initial Survival and Growth of Japanese Larch (Larix kaempferi) Seedlings

It is important to understand the characteristics of Japanese larch (Larix kaempferi) seedlings that allow them to grow vigorously after planting and quickly exceed the height of surrounding vegetation, resulting in lower weeding costs. Seven stock types, including bareroot and container-grown seedlings, were planted in two plots with different mechanical-site-preparation (MSP) methods and evaluated for survival, height, and root collar diameter (RCD) for four consecutive years. Three-year-old bareroot seedlings, which were one year older and larger than normal, had low survival rates in the mulcher MSP. Initial seedling height significantly differed among the seven stock types, while almost no significant differences were observed after four growing seasons. Model analyses showed that initial seedling height and RCD had a significant effect on seedling height after planting until the second growing season, while the effect of planted seedling age and plot became increasingly significant after the third growing season. The difference in seedling type, bareroot versus container-grown seedlings, had no effect on the seedling height during the four growing seasons after planting. A decision tree analysis suggests that the seedlings with sufficiently large RCD and young age, regardless of seedling type, can grow taller than surrounding vegetation more quickly.