Abstract
To predict the yield of sugi (Cryptomeria japonica) plantations on a long rotation in private forests in Kagoshima Prefecture, the stand-density control diagram, site quality curve, and yield table were improved. The curvilinear equations required for the stand-density control diagram, including the full density curve equation, were also improved. Consequently, the new diagram may be more accurate than the existing diagram. The Mitscherlich function was applied as the site quality curve. Using the function, site quality was divided into three ranks. Using the average height of the dominant trees to decide site quality and the functions in the stand-density control diagram, the numerical values for the stand composition factor in the yield table were computed. Consequently, the stand-density control diagram, site quality curve, and yield table were shown to be correlated. The estimated numerical values of the stand composition factor in the yield table in this study were better than the values derived using the existing method. During long-rotation management of sugi plantations in our prefecture, improvement of the yield prediction information has been an important problem. The stand-density control diagram and yield table produced in this study should improve the efficiency with which the forestry engineers of our prefecture manage forest stands on long rotation.
