Following the Tokyo Electric Power Company’s Fukushima Daiichi Nuclear Power Station accident in March 2011, shipping restrictions were imposed on more than 10 Japanese edible wild-plant species (July 31, 2017) in which high levels of radiocesium (^134+137Cs) were detected. However, few studies have examined radiocesium transfer from the environment to edible wild plants or the factors that affect this transfer; therefore, it is difficult to assess current criteria for determining whether shipping restrictions should remain in place. In this study, we sampled leaves of wild zenmai (Osmunda japonica), an edible fern, from 131 habitats in Koriyama, Fukushima Prefecture, Japan, in July and August 2015. We also collected data for environmental factors that could affect ¹³⁷Cs transfer to wild plants. Multiple regression analysis showed that zenmai leaf ¹³⁷Cs concentrations had significant relationships with several environmental factors including litter ¹³⁷Cs amounts, air dose rates, canopy coverage, and litter coverage. Using the latter three environmental factors as parameters, models to predict ¹³⁷Cs concentrations in zenmai leaves were constructed using 100 samples and verified with the remaining 31 samples. The results showed low systematic error and high accuracy. However, model precision was low, with predicted values distributed between about 1/5 and 5 times observed values. Because the residual sums of squares between the measured and predicted values were large, we concluded that information about these three environmental factors could not reduce the number of samples required to cancel shipping restrictions on wild zenmai from the current standard (60) without also reducing prediction accuracy. Differences in phenology may have contributed to the variation in ¹³⁷Cs concentrations observed in this study. Future studies should clarify the mechanism that causes this large variation.

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Downturns in Japanese timber prices are currently discouraging the participation of Japan’s forest owners in management practices, to the extent that timberlands are being sold and reforestation and renewal projects are being abandoned. In contrast, some corporate entities that actively require a timber supply are engaging in, and even expanding, forest management investment; long-term forest management are also being established. Thus, Japan’s approach to forest management is undergoing reorganization. In 2008, we had an opportunity to discuss with two major financial institutions about the possibility of the forest trust in Japan. This study aims to clarify the factors regarding main difficulties of the forestry business through the forest trust indicated by major financial institutions. The obstacles that these institutions faced included uncertainty in securing cash flow for forestry projects, a potential shortage of cooperating experts and financial institutions, and instability in the physical status of and rights to the forest properties. In the context of these issues, we describe the conditions affecting the commodification of the forest industry, which has allowed the formation of forestry business active in Japan today.

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Following the Tokyo Electric Power Company’s Fukushima Daiichi Nuclear Power Station accident in March 2011, shipping restrictions were imposed on more than 10 Japanese edible wild-plant species (July 31, 2017) in which high levels of radiocesium (^134+137Cs) were detected. However, few studies have examined radiocesium transfer from the environment to edible wild plants and the factors that affect this transfer. We sampled the petioles of fuki, (wild butterbur: Petasites japonicus), an edible deciduous perennial, from 100 habitats in four municipalities in Fukushima Prefecture, Japan, in June 2016. The amounts of ¹³⁷Cs in litter and soil to a depth of 5 cm were each significantly associated with fuki petiole ¹³⁷Cs concentrations (P < 0.001) and with air dose rates (ADRs, P < 0.01). Regression analysis between ADRs and fuki petiole ¹³⁷Cs concentrations was performed and verified using a petiole dataset that was obtained in April 2016 from 28 habitats with a wide range of ADR values. The slopes of the regression equations for June and April were not significantly different (P = 0.494). However, their Y-intercepts were significantly different (P = 0.0002) and the June ¹³⁷Cs concentration was approximately five times that for April at the same ADR, suggesting an increase in ¹³⁷Cs concentrations between April and June. We determined the 95% prediction interval of ^134+137Cs concentration per fresh petiole weight for June 2016, based on petiole water content and ¹³⁴Cs/¹³⁷Cs concentration ratio. The prediction interval of fuki petiole ^134+137Cs concentrations were distributed between about 1/8 and 8 times the predicted values. This dramatic seasonal variation in ¹³⁷Cs concentrations suggests that further examination of temporal shifts in fuki ¹³⁷Cs concentrations is required.

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This study aimed to investigate the effect of forest fire on radiocesium (RCs: ¹³⁴Cs and ¹³⁷Cs) status in forest ecosystem, in Japanese red pine forest on the ridge area and Japanese cedar forest on the riparian zone in Mt. Juman, where a forest fire occurred on 29^th April to 10^th May in 2017. In both the forests, we sampled bark on the burned side as well as from the non-burned side of the same tree trunk, along with samples from organic layer and mineral surface soil in burned areas and those from adjacent non-burned areas. We analyzed RCs concentrations in each specimen. Lower value for the concentration and the inventory of RCs was observed for the biomass in burned bark in Japanese red pine. The RCs concentration of organic layer was also lower in burned area than in adjacent non-burned area in all specimens from Japanese red pine forest and Japanese cedar forest.

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In 1954, the 15th typhoon (also known as the Tôyamaru typhoon) caused catastrophic windthrow to trees in the headwater region of the Ishikari River, Hokkaido, Japan. To monitor forest regeneration, the Hokkaido Research Center of the Forestry and Forest Products Research Institute began periodic surveys of vegetation and tree stem at six study sites in stands that had, prior to the typhoon, been near-climax conifer forest. To date, surveys have been conducted in the following years: 1957–1968, 1972, 1976, 1980, 1984, 1988, 2002, 2009, and 2017. For the surveys, belts 2 m wide and 30–50 m long were chosen in each plot, each divided into 2 × 2 m quadrats. In each quadrat, every plant species present was recorded and its coverage ranked (0–1%: +, 1–10%: 1, 10–25%: 2, 25–50%: 3, 50–75%: 4, 75–100%: 5) in each layer (canopy, subcanopy, shrub, herb, vine, and moss). Surveys of tree stems were conducted in 1993, 1998, 2002, 2009, and 2017, with plot widths enlarged to 10 m. In each belt, height and diameter at breast height were measured for all stems whose heights were ≥ 1.3 m. All the survey data have been organized in machine-readable format and published under a Creative Commons Attribution 4.0 International license.

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The Kamabuchi experimental watershed, which is located alongside the sea of Japan in the Tohoku district, northern Japan, receives considerable amount of snowfall in winter. We reported the mean annual solute concentrations of the rainwater and streamwater obtained between 2000 and 2014 in a small, forested watershed of this experimental watershed. The area of this watershed was 3.06 ha, and the vegetation was a mixed forest of deciduous and evergreen species. The mean annual NO₃⁻ and SO₄²⁻ concentrations in rainwater showed no trend. The mean annual dissolved inorganic nitrogen input through rainwater was 12.4 kg ha⁻¹ yr⁻¹, about 60% of which was in the form of NO₃⁻-N. SO₄²⁻ input was 63.0 kg ha⁻¹ yr⁻¹, and about two third of that was the non-sea salt SO₄²⁻ input. Annual NO₃⁻-N and SO₄²⁻ input had a positive correlation with the annual precipitation, suggesting that the loads of these inputs were mostly dependent on the amount of precipitation rather than the concentrations. There was a fluctuation in the mean annual NO₃⁻ concentration in streamwater, but an obvious annual change was not recognized. A change was not observed in the mean annual SO₄²⁻ concentrations in streamwater.

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