This research was conducted in radiologically contaminated forests at Fukushima Prefecture from 2011 to 2014 to reveal the contribution for air dose rate at a height of 1 m in the forests from the various forest compartments, by calculating air dose rates from radiocesium inventories in leaves and branches, the litter layer, the mineral soil layers, and natural radiation. In 2011, air dose rates in forests comprised gamma rays emitted from the canopy layer, litter layer, the surface mineral soil layer (0–5 cm), and natural radiation. However, in 2014, >88% of the total air dose rate in the forest originated from the litter layer, the surface mineral soil layer (0–5 cm), and natural radiation, and emissions from the canopy layer were <3%. These results suggest that after 2014, air dose rate could be calculated from radiocesium inventories of the litter layer, the surface mineral soil layer (0–5 cm), and natural radiation in the forest. In addition, air dose rates calculated at a height of 1 m before and after the removal of the litter layer demonstrated that the removal of the litter layer caused a decrease in the air dose rate in forest, even 4 years after the Fukushima Dai-ichi Nuclear Power Plant (FDNPP) accident. It is of interest that the reduction effect of the air dose rate by the removal of the contaminated litter was larger than that when increasing the air dose rate by decreasing the shielding effects caused by the forest litter.
Beechnuts (Fagus crenata seeds) were evaluated as a local specialty in a snowy semi-mountainous area in Japan. After monitoring the production of beechnuts in climax (C), satoyama (S), and isolated (I) stands for 11–17 years, a good or medium crop was observed biennially, every 2–4 years, and once in 17 years, respectively. The beechnut embryos had higher protein and lower lipid contents than those of commercial walnut. The oxidative stability of embryonic oil from beechnut was greater than that from walnut. The estimated potential quantity of beechnuts in a good crop was ca. 8 ton (equivalent to ca. 8 million yen) in the largest satoyama beech forests (ca. 5.5 ha) in the study area. To use beechnuts sustainably, various strategies should be adopted for different types of stand: in C, fallen beechnuts should be collected from managed open sites; in S, beechnuts should be collected actively to promote the re-use of satoyama sites; and in I, beechnuts should not be collected, to conserve the beech population. Therefore, although beechnuts will be available with appropriate resource management, it is necessary to find a way to increase their added-value to sustain them as a local specialty.
In recent years, wood log boilers have been introduced to hot water bathing facilities or spas in Japan, particularly in mountainous areas. Producing wood logs is relatively easy, on the other hand, input of wood logs into the boilers has to be done manually, and it is pointed out that wood log boilers are not efficient if they are used as facilities generating over 100 kW. In this context, the cases discussed in academic papers are limited to small scale ones. In this paper, the analysis of two cases of boilers generating over 100 kW are examined to verify potentials of the large scale facilities with wood logs. It reveals that (1) operating costs are reduced compared with the system using kerosene, and substitution rates are over 70％ (2) manual input of wood logs was a certain load on the boiler users; (3) impacts on the managements, such as rise of labor costs caused by the manual input of wood log, were not seen and (4) wood log systems can potentially reduce the loads on the facilities depending on heat supply systems.
Future Tree Mangement (FTM) is a method based on the Qualification-Dimensioning strategy, which has been recently introduced from Germany. In this study, to clarify the effects of the FTM practice on surface soil movements, we measured the transport of materials on a range of sloping forest stands over a three year period, comparing our findings with those of related studies using transport rates (in g m-1 mm-1) as the indicator of soil erosion. We placed sediment traps at two sites, a Cryptomeria japonica (Sugi) and a Chamaecyparis obtusa (Hinoki) to analyze four factors; tree species, openness of canopy, slope gradient, and terrain, with material type and time period as additional factors. Statistical testing with ANOVA showed time period to be highly significant, most likely due to variation in rainfall intensity between periods. In the year following thinning, when ground disturbance was still pronounced, large surface soil transport rates were observed, leading to small collapses where factors that positively affected sediment discharge rates combined. The Hinoki site had higher levels of ground vegetation cover, a lower rate of litter accumulation and higher sediment transport rates than the Sugi site. Transport rates were also greater than those observed in other similar studies. More extensive thinning, especially in Hinoki plantations, is recommended to enhance early vegetation recovery to address better application of the FTM practice.
In this study, we evaluated the spatial distribution of radiocesium in a forest and explored its causal factors. We set 61 litter traps and collected the fallen leaves of a dominant tree species, Quercus serrata, in a deciduous broad-leaved forest in 2011 and 2012. Then we examined relationships between the radiocesium of fallen leaves and the aspect, gradient of slope, leaf mass. The spatial distribution of radiocesium in the fallen leaves was not uniform in 2011: radiocesium concentrations in fallen leaves were higher at the east-facing slope compared to those at the west-facing one, and were higher at sites with higher leaf mass. Although the spatial bias was smaller in 2012, the same tendency was observed. Eastward wind direction at the study site when massive radiocesium was emitted from the Fukushima Daiichi Nuclear Power Plant was considered as one of the reasons for the phenomenon.
To clarify the effects of reduced planting density on stand structure and growth of sugi (Cryptomeria japonica) plantation, we examined stands planted 11 years ago at densities of 1,000, 2,000, and 2,500 trees ha-1 in Akita, Japan. Sugi trees in a 1,000 trees ha-1 stand had significantly larger diameter and diameter growth than those planted at other densities. Nevertheless, the larger tree height in this stand, along with the comparable height: diameter ratio and height to the lowest branch among the three planting densities, suggested a limited effect of competition among planted sugi trees. The proportion of sugi trees with defects, such as bent or forked stems, was higher in the stands planted at a lower planting density. Naturally regenerated trees other than sugi exceeded 40% of the total tree density in 1,000 and 2,000 trees ha-1 stands. Stem density above median sugi height in these trees was higher in these stands than in the 2,500 trees ha-1 stand, suggesting that trees in these stands suppress sugi trees and cause large variations in sugi heights.
The basic information about the discs of Yaku-sugi, old Cryptomeria japonica more than 1,000 years old on Yakushima Island in Japan, has been collected and 88 discs (54 individual trees) are displayed as Yaku-sugi discs in Japan. By checking the tree rings on the discs, 54 discs (23 individual trees) are identified as the Yaku-sugi disc on which the tree rings are recognized to total more than 1,000. The highest number of the tree rings on the disc is about 2,000.
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Edited and published by : The Japanese Forest Society Produced and listed by : Center for Academic Publications Japan/Shobi printing Co., Ltd. (Vol.96 No.2-) Center for Academic Publications Japan/Fukasawa Ltd. (Vol.91 No.3-Vol.96 No.1) Center for Academic Publications Japan/Daishowa Printing Co., Ltd(Vol.88 No.1-Vol.91 No.2)