Density control of coastal Larix dahurica var. japonica stands in Hokkaido, northern Japan

Abstract

Density control diagram for the coastal Larix dahurica var. japonica (Dahurian larch) stands in Hokkaido was developed in this study. Intercept of the full density curve of Dahurian larch stands (23921.95) was larger than that of Pinus thunbergii stands (20399.15). If the data of the thinning experiment in Teuri was plotted on the density control diagram, relative yield (Ry) of intensively thinned plot changed from ca. 0.6 (moderate density) to 0.4 (low density), and it reached ca. 0.7 about 12 years after thinning procedure. However, Ry’s of weakly thinned- and control plots reached ca. 0.9 (crowded condition) within 12 years after thinning procedure. Distribution of the site index (SI; stand height at 20 years old) of each study site aggregated in the 4-6 and 6-8 SI classes, and SI of the stands in the Pacific region tended to be larger than that of the stands in the Okhotsk- and the Japan Sea regions. We proposed the management practice system with reference to the thinning experiment in Teuri, that is, the stand is thinned to satisfy Ry = 0.4, if the stand height reaches at 4 m. Second, the stand is thinned to satisfy Ry = 0.6, if the stand height reaches at 8 m. However, development of understory vegetation could not be expected even in the intensively thinned plot in Teuri. It implies that the stand density should be always maintained in lower density.