Forestry and Forest Products Research Institute

Forest contamination by radiocesium (137Cs) has hindered the resumption of forestry activities after the Fukushima nuclear accident, particularly the production of coppiced konara oak (Quercus serrata) bed logs for shiitake mushroom (Lentinula edodes) cultivation. Methods are being developed to estimate stem 137Cs activity concentrations using current-year branches as an indirect indicator that can be used to identify available bed logs efficiently. However, the behavior of 137Cs in current-year branches—especially in the juvenile stage—is insufficiently understood, limiting efforts to improve the accuracy of stem concentration estimates. In this study, current-year branches were collected in the winters of 2020–2021 and 2025 from the same konara oak trees in 20 survey plots in Miyakoji, Tamura City, Fukushima Prefecture, where coppice regeneration occurred between 2011 and 2016. Temporal changes were examined using the abovementioned sampling data, along with the previous monitoring data from the winter of 2016–2017. Results showed that in konara oaks aged 1–3 years at the beginning of each 4-year interval, 137Cs activity concentrations in current-year branches decreased over four years by more than that expected from physical decay alone. By contrast, for trees aged 4–9 years at the start of the interval, the 4-year decline in concentrations was approximately consistent with physical decay. Thus, for konara oaks with a stand age of 4–9 years, the influence of stand age can be ignored when applying the developing relationship between current-year branch and stem 137Cs activity concentrations.

ABSTRACT To clarify the characteristics of montane riparian forests in extreme snowfall areas, the community composition, forest structure, and growth of dominant tree species in dwarf montane riparian forests, established in extreme snowfall environments (maximum snow depth of 5 m), were compared with those of tall‐tree montane riparian forests in heavy snowfall environments (maximum snow depth of 2 m) in the Tadami region of Japan. The dominant species in both forests were high‐sprouting Pterocarya rhoifolia and low‐sprouting Aesculus turbinata , which are representative of Japan's cool‐temperate montane riparian forests. In the tall‐tree montane riparian forest, both species exhibited single‐trunk forms with a maximum height of about 30 m, whereas in the dwarf montane riparian forest, P. rhoifolia had a maximum bent trunk length of about 18 m and a height of 10 m, and produced more and smaller sprout trunks, which appeared to contribute to stool persistence, whereas A. turbinata produced a single trunk in creeping form, with a maximum trunk length of 30 m and a height of about 5 m. Thus, although P. rhoifolia and A. turbinata were dominant in forests with both heavy and extreme snowfall, they had different survival strategies in terms of sprouting, dwarfing, and layering in response to extreme snowfall. In dwarf riparian forests, Acer nipponicum , which is common in heavier snow environments, dominated after P. rhoifolia and A. turbinata . These findings suggest that montane riparian forests under extreme snow conditions are maintained by tree species that are adapted to severe snow accumulation.

本研究では，森林レンタルサービスForenta利用者の森林に対する感情反応に関する特徴を把握するため，東京都民を比較軸とした自然に対する感情反応に関する調査を実施した。Forenta利用者は森林空間の自由な利用に動機づけられており，一般市民と比較して「自然に対する感情反応」は特有に高いと予想される。東京都民を比較対象とした「自然に対する感情反応」の潜在ランク分析を実施し，Forenta利用者の自然に対する感情反応の相対的な位置づけを検討した。本研究で得られた潜在ランク構造はランク7以降については森林への関心と対応を，ランク8以上では森林への関心と森林の観察的体験を中心とした利用実態と対応した感情反応の多寡を示しており，一定の妥当性を有していた。その構造を踏まえてForenta利用者の位置づけを確認すると，ランク8以上の高い感情反応得点を示すことが特徴として挙げられた。ただし，ランク6・7にも一定のForenta利用者が含まれており，森林レンタルサービスを利用する動機をもちつつも森林を高い頻度で， 積極的に利用するには至らない別の動機をもつ利用者の存在が示唆された。

熱赤外動画を用いた現地踏査により，湧水の空間分布と水質を把握する独自手法を，堆積岩流域と火山岩流域に適用し，その結果を比較した論文で論文奨励賞を頂きました．受賞にあたり，お世話になった方々へのお礼と，本研究の実施に至った経緯を書きました．

Fine-scale spatial genetic structure (fine-scale SGS) refers to the pattern of spatial distribution of genetic variation at the local scale, which can indirectly estimate gene flow among individuals and reveal microevolutionary processes in plant populations. Although fine-scale SGS is important in explaining dispersal patterns and adaptive variation in plants, few studies have explored its potential application in species conservation strategies. In addition, phenotypic traits, particularly leaf shape, may also exhibit specific spatial variation patterns at fine scales. In this study, we investigated the genetic and leaf shape variation of two genus Quercus species (Quercus glauca Thunb. and Q. multinervis J. Q. Li) and three genus Castanopsis species (Castanopsis tibetana Hance, C. faberi Hance, and C. fargesii Franch.) in Wuyishan National Park in southeastern China. Using genetic markers, we found that Quercus species exhibited stronger fine-scale SGS and more limited gene flow than Castanopsis species, suggesting greater habitat fragmentation affecting local Quercus species. Leaf morphological analysis revealed inter-generic differences and partial overlap in leaf shape between Quercus and Castanopsis species, with the greatest variation observed in leaf area (LA) and leaf mass (LM). In addition, all five Fagaceae species exhibited significant diminishing returns, with C. fargesii showing the most pronounced effect and possessing the smallest leaves, which may enhance its adaptability to the harsh environments. Despite the leaf shape overlaps blurring species boundaries between Quercus and Castanopsis species, their genetic structure is remained clearly distinct. The observed differences in the intensity of fine-scale SGS and leaf shape variation between the two genera reflect their different environmental adaptability, offering new insights into the integration of genetic and phenotypic data for conservation planning.

Understanding the long-term dynamics of radiocesium (137Cs) in forests contaminated by the Fukushima nuclear accident requires determining when these dynamics reach a quasi-equilibrium state, in which the flux of 137Cs between soil and trees becomes approximately balanced. In this study, we analyzed time-series variations from 2011 to 2020 in the total 137Cs inventory and 137Cs distribution in aboveground compartments (needles/leaves, branches, bark, sapwood, and heartwood). Time-series analysis using a dynamic linear model indicated that the decay-corrected total 137Cs inventory (as of September 1, 2020) and its distribution in the aboveground compartments remained stable from 2017 onward, suggesting that a quasi-equilibrium state had been reached. Given this stability in both inventory and distribution, the aggregated transfer factor (Tag)—defined as the 137Cs activity concentration in aboveground tree tissues divided by the total 137Cs inventory in soil—measured approximately 6 years after the Fukushima nuclear accident can be considered representative of the long-term transfer of 137Cs from forest soil to trees. These findings on the stability of 137Cs in forests provide valuable insights for validating the accuracy of models that predict long-term 137Cs activity concentration in stem wood.Supplementary InformationThe online version contains supplementary material available at 10.1038/s41598-025-34898-0.

In this study, we investigated the differences in efficient vibrational pollination related to flower characteristics among 10 commercially available Japanese tomato cultivars, focusing on their shapes, weights, and natural frequencies. Although the acceleration thresholds for pollen dispersion varied depending on the excitation frequency and tomato cultivar, they were significantly higher at 100 Hz compared to 15, 30, and 50 Hz. For cherry tomato cultivars, the acceleration thresholds were lower at 50 Hz, while for large and medium tomato cultivars, those were lower at 15–50 Hz than those at 100Hz. No correlation was found between the acceleration threshold for pollen dispersal and the amount of pollen per flower. The natural frequencies of the flowers were examined by applying vibrations ranging from 5 to 100 Hz to the flowers using a non-contact shaker and measuring the displacement with a high-speed camera. Although the natural frequencies varied among individual flowers, differences were also observed among different varieties. Furthermore, the optimal period for vibrational pollination of ‘Momotaro Hope’ was determined to be from 1 day before to 4 days after flowering, in terms of the acceleration threshold for pollen dispersion, which closely aligns the optimal period identified in previous studies.