A spacing experiment for Japanese oak (Quercus mongolica var. grosseserrata) with Nelder's design have been studied at the Kyushu University Forest in Hokkaido, since 1975. The oak seedlings were planted according to systematic spacings which were 20 levels varying gradually from 40,816 to 1,086 seedlings per hectare with concentric circular arcs (22 in number) and spokes (41 in number). In 1992 when the planted oak seedlings were 18-year-old, DBH, crown diameter, total height and clear length of the survival trees were measured. Based on the results obtained from analyzing the relationships between planting density and the mean values of each block, the optimum planting density should be 7,241 seedlings per hectare.Key words: Japanese oak, optimum planting density, planting system, spacing with systematic design An experimental management system for Japanese oak (Quercus mongolica var. grosseserrata) forest has been studied since 1972, in a natural Japanese oak forest, approximately 200 ha in area, in the Kyushu University Forest in Hokkaido, the northernmost main island of Japan (Imada, 1974). This natural oak forest was created by clear-cutting in tongue-form blocks surrounded by shelter belts system (Imada, 1973) on a 150-year rotation, and hence 150 annual tongueform cutting blocks were set up. The natural stands of these blocks have been managed by a silvicultural process designed for producing high-quality Japanese oak timber (Imada, !972, 1974(Imada, !972, , 1996.This silvicultural process was designed by applying a natural seeding system with seeds that had fallen from the finalcut (clear-cut) trees. However, in the case of poor seed years, such natural seeding system has been converted to a planting system under which the standard planting density of 20,000 seedlings per hectare (hereafter, we say the term of "planting density" to "density") has been applied (Imada, 1974). Because of the lack of scientific knowledge of the optimum density for Japanese oak planting, we started a spacing experiment for Japanese oak with the systematic spacing design of Nelder's wheel (Nelder, 1962) at the Kyushu University Forest in Hokkaido, in 1975 when three years had passed after setring up the preceding experiment for the silvicultural process.The objectives of this paper are to report on the suitability of the standard density that has been applied and to deal with the optimum density for producing the high-quality timber from Japanese oak.In 1992 when oak seedlings planted for this spacing experiment were 18-year-old, we measured DBH, crown diameter, total height and clear length of the survival trees. Based on the results obtained from measurements, we determined that the standard density of 20,000 seedlings per hectare is excessive and that 7,241 seedlings per hectare is optimum density to be applied in the future.
MethodsThe experimental area of 0.21 ha in area is a part of the Kyushu University Forest in Hokkaido and is located in eastern Hokkaido. For the above area, we selected a gentle slope (approximatel...
