The species distribution of Fagus crenata, has shifted northward during phytogeographical changes that occurred during the Pleistocene and Holocene epochs. The present distribution of the northernmost geographical margin is Kuromatsunai Depression in Oshima Peninsula, where continuous populations of F. crenata can be seen and only isolated populations exist further north. Genetic diversity parameters were clearly declining toward northernmost populations. The results of the STRUCTURE analysis revealed that southwestern continuous populations consisted of homogeneous ancestral clusters. Northeastern marginal populations consisted of highly differentiated clusters with higher levels of genetic drift than found in the continuous populations. Approximate Bayesian Computation (ABC) indicated that the northern F. crenata populations have experienced several distributional shifts, which resulted in genetic admixture within the northernmost marginal populations.

Eight hypotheses on the cause of northern distribution limit of buna (Fagus crenata) can be classified into two types, the climate determining one and the northward migrating one. According to two distribution models for buna forests and individuals, northern and upper limits of distribution, southern and lower limits, and its dominance were respectively controlled by winter coldness, heat in the growing season, and snow accumulation. Northern and eastern regions of Hokkaido were predicted to be non-habitats both for buna forests due to winter coldness and a little snow, and for buna individuals due to winter coldness. Since the distribution models were developed using distribution data of whole Japan including Hokkaido, the models seem to underestimate potential habitats (PHs) in Hokkaido. However, PHs covered coastal areas along the Sea of Japan in Hokkaido, reaching the northernmost region. These results support the northern migration hypothesis. The models predicted the expansion of PHs in Hokkaido under the future climate scenarios. Buna populations near the northern distribution front (NDF), which had increased in the past, were estimated to reproduce and expand in future, according to previous studies. The buna population found in Niseko Mountains in 2013 is located 12 km apart from NDF. This new northernmost population also showed reproduction since it consisted of individuals of various size with the oldest one of 131 years and many small ones. Because of this population established such many years ago and no other buna populations found by the survey in extensive areas, buna populations are very rare in the areas beyond NDF. The migration speed was estimated to be 12 m/yr, based on this population.

The aim of the present study was to investigate the effects of Japanese cedar and Japanese cypress needles in the soil on nitrogen accumulation in forest soil according to stand age in the Kanto region of Japan. We determined nitrogen content of litterfall, forest floor, needle leaves in the soil, and soil in cedar and cypress forests. The study sites were located in forests planted with Japanese cedar and Japanese cypress trees that were adjacent to each other on the same slope with different stand ages (13, 21, 34, 48, 66, and 93 years). In cypress forests, the C/N ratio of needle leaves in the soil was intermediate between that of forest floor and soil nitrogen content at a depth of 0-10 cm. The contribution of nitrogen by needle in the soil to the soil nitrogen content at a depth of 0-10 cm in the cypress forests was larger than that in the cedar forests. The easily decomposed cypress litter entered the soil at a depth of 0-10 cm, and increased soil nitrogen content in the cypress forest. On the other hand, the nitrogen content of litterfall decreased more than 21 years old in the cedar forests. However, litterfall of decomposed with difficulty was increasing with stand age in the cedar forest. This suggest that the soil nitrogen content at a depth of 0-10 cm remains unchanged with stand age in the cedar forests.

Root system of a containerized seedling is restrained from natural development due to the limited volume of the cavity. The form of the root system can be a limiting factor for water supply from roots to leaves because of low connection between root and soil. In the present study, we ran a planting trial of the containerized Cryptomeria japonica seedlings in late August. We selected the planting season in order to allow the planted seedlings to grow the roots to prepare for the next growing season. The seedlings were planted in late August. The transpiration and net photosynthetic rates were measured five times during two months after planting. We also measured the growth of shoot and root-collar diameter until the next November. The transpiration rates of the containerized seedlings just after planting were significantly higher than those of the bare root seedlings which were planted at the same time. This result suggested that the roots of the containerized seedlings maintained the water absorption ability even just after planting. The H/D ratio of the containerized seedlings decreased by next April and showed significant height growth from May. The height of the containerized seedlings increased from 29 ± 4 cm at planting to 85 ± 20 cm during the growing season until the next November.