Growth and survival of hybrid larch F1 (Larix gmelinii var. japonica x L. kaempferi) and Japanese larch under various intensities of competition

Competition between planted seedlings and vegetation is a critical constraint affecting the survival and growth of seedlings at the initial stages of forestation. Quantitatively assessing the impact of competitive vegetation on the growth of planted seedling is vital for reduction of weeding cost. This study compared the survival and growth of potentially fast-growing hybrid larch F-1 seedling (Larix gmelinii var. japonica x L. kaempferi) with Japanese larch (L. kaempferi) at three competitive levels, which were 0-50%, 50-75% and 75-100% of the seedling surface covered by vegetation after planting. When more than three-quarters of the seedling surface was covered by vegetation, the survival rate of Japanese larch dropped substantially. In contrast, hybrid larch F-1 sustained a high survival of 95% despite the high covering. Annual height growth significantly decreased with increasing coverage for both species. In addition, the height growth of hybrid larch F-1 was significantly higher than that of Japanese larch, whereas the difference became insignificant when more than three-quarters of the surface was covered. If the requirement for weeding is whether three-quarters of the seedling surface is covered or not with vegetation, it was determined that hybrid larch F-1 did not require weeding if the seedling height attained about 170 cm in the previous fall; whereas Japanese larch needed about 200 cm. The findings imply that weeding is needed to unlock the hybrid larch F-1's high growth potential, and that weeding can be accomplished more than a year earlier than with Japanese larch.