The transition pattern of radiocesium released from the 2011 TEPCO Fukushima Daiichi Nuclear Power Station accident from the environment to edible wild plants varies across species. We investigated the relationship between radiocesium in bracken (Pteridium aquilinum subsp. japonicum) and habitat conditions of bracken, such as the radiocesium mass and slope position, in four bracken communities at Iwaki (IO), Iitate (IM and IU), and Katsurao (KM) in 2017. In the bracken communities on land that was formerly pasture (IO, IM, and IU), there was no significant (P = 0.499) difference in ¹³⁷Cs concentrations between the young leaves, adult leaves, and belowground organs of bracken, while there was a difference among the research sites (P = 0.049). The exchangeable potassium (K) concentrations in soil were 0.42–1.11 cmol_c kg^-1, and there was no relationship between exchangeable K concentrations and the ¹³⁷Cs aggregated transfer factor (T_ag) from litter layer and soil to bracken leaves. Young-leaf ¹³⁷Cs concentrations were more closely related to ¹³⁷Cs mass values in soil (R² = 0.7844) than to those in the litter layer (R² = 0.4669). A strong indirect correlation (r = 0.757) was found between air dose rates (ADRs) and the concentrations of young-leaf ¹³⁷Cs via the ¹³⁷Cs mass in soil. At KM, which did not have a grazing history, the concentrations of young-leaf ¹³⁷Cs were lower than those estimated from ADRs, implying the influence of other conditions, such as more roots in deeper soil with lower ¹³⁷Cs values.

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Bracken (Pteridium aquilinum subsp. japonicum) is a fern with edible young leaves. To clarify the growth of bracken and temporal changes in the levels of radiocesium released from the 2011 TEPCO Fukushima Daiichi Nuclear Power Station accident in bracken, we have investigated bracken communities in former pasture since 2017. We also tested the effect of potassium (K) application on reducing radiocesium concentrations. From spring to autumn, when the leaves are green, about 40% of bracken’s biomass is comprised of leaves while the other 60% consists of belowground organs (rhizomes and roots). There is little seasonal difference in the total plant biomass. The cesium-137 (¹³⁷Cs) concentrations in bracken varied among organs such as young leaves, adult leaves, and belowground organs, reflecting seasonality, but the total concentrations in plants decreased gradually (P = 0.023). The decline, as approximated by an exponential function, was 27% per year. After application of K in June 2017, total potassium-40 concentrations of treated bracken plants were higher than those of control plants from about August to March of the following year. Consequently, the ¹³⁷Cs concentrations of the treated bracken were suppressed to about 70% of those of the control plants (P < 0.001).

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In this study, the spatial distribution of stream water chemistry was investigated in headwater areas within the Shimanto River basin to evaluate the effect of forested headwater on the quality of downstream waters under ordinary flow condition. The study area was mainly underlain by Paleozoic/Mesozoic sandstone and shale, with partially exposed limestone and granite. The difference in the bedrock geology of the catchments strongly affected the solute composition of the stream water. The catchments underlain by limestone were characterized by high pH, EC, and Ca²⁺ and HCO₃^- concentrations, and the ones underlain by granite were characterized by low pH, EC, and concentrations of major ions as compared to the catchments underlain by sandstone and shale. The concentrations of Na⁺ and Cl^- negatively corresponded to a distance from the coastline of the Pacific Ocean, thereby suggesting the difference in the deposition of sea salt during storm events that frequently occur from June to October. High runoff rate during rainy season affected the decreasing Na⁺, Mg²⁺, Ca²⁺, and SO₄^2- concentrations in the stream water by dilution with the rainwater. Warm and humid summer climate may further accelerate the dissolution of silicate minerals in the bedrock and soils, resulting in an increase in the Si concentrations. The mean concentration of dissolved total nitrogen in the headwater was 0.17 mg L^-1 in summer and 0.26 mg L^-1 in winter. These results satisfy one of clear stream standards of the Shimanto River (i.e., 0.3 mg L^-1 for dissolved total nitrogen) established by Kochi Prefecture Government and indicate that the forested headwaters would contribute to the clear downstream water environment.

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We collected aculeate wasps in ten naturally regenerating broad-leaved stands (1–178 years old) and eight Cryptomeria japonica conifer plantations (3–76 years old) using Malaise traps through the wasp flight season (April–November) in Ibaraki Prefecture, Japan. There were 167, 12, and 3605 species, families, and individuals collected, respectively, in the broad-leaved stands and 136, 11, and 2645 in the conifer plantation stands. The most speciose family was Crabronidae, followed by Pompilidae, while in terms of the number of individuals, Pompilidae dominated in every stand. Species richness and abundance were the highest in young stands, decreasing as the stands grew older. Although most collected wasp species preferred young stands, some species characteristically occurred in older stands.

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Five species of Mecoptera (three species of Panorpidae and two species of Bittacidae) were recorded in the Tama Forest Science Garden, the Forestry and Forest Products Research Institute, Hachioji City, Tokyo Metropolis, Japan. Seasonal abundance parterns of these species were studied by examining the collection dates for specimens preserved and also by conducting a series of transect counts from April through October in 2017. Univoltine species varied in their phenology: Panorpa fulvicaudaria Miyake and P. wormaldi MacLachlan appeared from April to May, Bittacus takaoensis Miyake almost only in early May, whereas B. nipponicus Navás appeared from June to July. Bivoltine Panorpa japonica Thunberg appeared in May and June in a first brood and from late August to October in a second brood. The very short appearance period of B. takaoensis could be the reason why the species has never been found in or around its type locality, Mt. Takao, since the original description in 1913. The first brood of P. japonica was the most abundant on the basis of counts per generation made by the transect census, B. takaoensis was the next, whereas P. wormaldi was the least abundant. Tama Forest Science Garden has a relatively rich mecopteran fauna as a low elevation area in the Tokyo Metropolis, reflecting its stable forest environment.

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To efficiently measure the radioactivity of radiocesium (¹³⁷Cs) in samples from a forest ecosystem, we examined whether the following two measuring methods are acceptable by comparing them to a normal method that uses an U-8 container and a coaxial Ge detector for a powdered sample: 1) filling a Marinelli container sparsely with an unpowdered sample and 2) using a #737 container and a well Ge detector. The ¹³⁷Cs activity determined by both methods showed no systematic errors. Additional random errors caused by the former method were estimated to be less than 7% and those caused by the latter method less than 6%. The measurements using a #737 container (well Ge) tended to produce smaller values when self-absorption of the gamma rays was corrected in the same way as for the U-8 container (coaxial Ge) but showed reasonable values when the self-absorption was corrected using the bulk density of a reference material or when the self-absorption was not corrected. In addition, we found that measuring only a part of the sample with a smaller-volume container than the sample volume itself resulted in relatively large errors even though the samples were powdered. Thus, it is important to select a measurement container matching the sample volume to achieve measurements that are efficient and have small errors.

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