GROWING BEHAVIOR IN INITIAL STAGE OF MACHILUS THUNBERGII POTTED SAPLINGS PLANTED AROUND THE NORTHERN LIMIT OF THE PACIFIC SIDE OF JAPAN

Abstract

We investigated the initial growth behavior of Machilus thunbergii（Kosterm） potted saplings planted around the northern limit of the Pacific side of Japan for five years to study reforestation of coastal forest degraded by a tsunami. Measurement of tree height, basal diameter, and air temperature at the planting site were recorded from October 2012 to October 2017. Numerous M. thunbergii potted saplings were affected by low temperature and low humidity in the winter season. Further, sprouting regeneration, after the main stems withered, was observed in more than 40% of the potted saplings. There was a difference in height and survival between the regenerated potted saplings and the undamaged ones. The average height of undamaged saplings was 324 cm, with nearly the same growth as other sites on the southern and western sides of Japan, and showed a 92.8% survival rate. However, the regenerated saplings exhibited a height of 210 cm, and a 48.4% survival rate, which decreased annually. This suggests, that low-temperature damage in the initial growth stage causes the shorter regenerated potted saplings to decline in survival rate for several years, due to the lack of sunlight caused by the closed crown that formed on the undamaged saplings.