Growth Analysis of 88 Year-Old Japanese Larch (Larix kaempferi) Plantations in Akito Prefecture, North-eastern Japan

1991

S. 1-15

12 Abb., 1 Tab.

Unselbständiges Werk

200062329

Japanese larch (Larix kaempferi) is one of important silvicultural species in northern Japan, because of its fast growth and resistance to cold. In the Tohoku district, in north eastern Honshu, Japan, its plantation area has been increasing rapidly since the 1950's. And now, there are about 84 000 ha of national forest alone planted with Japanese larch. The rotation of Japanese larch plantations is usually about 40-50 years in this district. It tends to be prolonged for several purposes, such as, improvement of timber quality, production of larger timber, and stand protection. However, there is little informatin available about the growth of old plantations of Japanese larch. In this study, the growth patterns and wood production of old plantations of Japanese larch stands, where the growth and working histor had been recorded for 70 years from 18 to 88 year-old, were analyzed. The study area is located at the foot (350 m altitude) of the west side of Mount Mahiru-dake (1 060 m above the sea level), Akita prefecture. This area is in the cool temperate zone, and its climate is characterized by deep snow in winter. In the period 1979-1988, the annual precipitation was 1 911mm and annal mean temperature was 10.4C at the nearest weather bureau. Four plots of 0.1ha each (B1, B2, C and D) were established on an 18 year-old Japanese larch plantation in 1916, and each plot was subjected to a different thinning method, respectively. Since then, the DBH (diameter at breast height) and the tree height of individuals had been measured at about ten year intervals. At the final measurement in 1988, each plot showed 37.3-44.2 cm in mean DBH, 29.5-31.7 m in mean trunk height, 240-430 stems/ha in stand density, 498-689 m3/ha in total stem volume and 9.13-10.63 m3/ha/year in mean annual increment. Values of mean DBH, mean height and total trunk volume of each plot had been increasing constantly till final measurement. These changes of the values seem to be different from those of the current yield table applied to this district whose values had been diminishing their increment gradually as stand age increased. The values of mean annual increment of each plot has been stable or shown a gradual increase for trees of over 40 to 50 year-old. The tendency of these changes of the values were also dissimilar to that of the yield table whose values decrease after then. Distribution ratios of total increment to trees whose DBH were over 38 cm had increased from 0-3% in 51 year-old trees to 46-63% in 88 year-old trees. These results show that 88 year-old stands were superior than younger stands in terms of both the mean annual increment and the production of high quality wood.