Effects of Weed Competition on the Survival and Initial Growth of Planted Seedlings of Japanese Larch (Larix kaempferi)

Abstract

We investigated how competition with weeds affects survival and height growth of Japanese larch （Larix kaempferi） seedlings in three consecutive years after planting. We planted three types of nursery stock, two-years and three-years-old bareroot and one-year-old containerized seedlings, with different height to examine the effect of initial seedling height on the competition with weeds. The tallest three-year-old bare-root seedlings showed less suppression by weeds in all three years, whereas the shortest containerized seedlings experienced much suppression. In the first year, when weeding was conducted, the degree of competition had no effect on survival rate; height growth was decreased only when weeds covered the entire seedling crown. In the second and third years, when weeding was not conducted, survival rate and height growth were significantly decreased when at least 75 and 50％ of the seedling crown was covered by weeds, respectively. It was estimated that the seedling height will be 91-100 cm shorter three years after planting if more than 75％ of the crown is covered by weeds. These results suggest that Japanese larch seedlings are susceptible to suppression by weeds, and, thus, weeding should be conducted to hold the crown cover by weeds below 75％. Planting taller seedlings would be effective for reducing weeding cost in Japanese larch.