There has been leakage of radioactive materials from the Fukushima Daiichi Nuclear Power Plant. A heavily contaminated area (≥ 134, 137Cs 1000 kBq m−2) has been identified in the area northwest of the plant. The majority of the land in the contaminated area is forest. Here we report the amounts of biomass, litter (small organic matter on the surface of the soil), coarse woody litter, and soil in the contaminated forest area. The estimated overall volume and weight were 33 Mm3 (branches, leaves, litter, and coarse woody litter are not included) and 21 Tg (dry matter), respectively. Our results suggest that removing litter is an efficient method of decontamination. However, litter is being continuously decomposed, and contaminated leaves will continue to fall on the soil surface for several years; hence, the litter should be removed promptly but continuously before more radioactive elements are transferred into the soil.

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This data paper provides some biogeochemical nitrogen (N) properties and related chemical properties of forest soils from 39 sites throughout the Japanese archipelago. The data set was collected and analyzed under the GRENE (Green Network of Excellence) environmental information project and the ReSIN (Regional and comparative Soil Incubation study on Nitrogen dynamics in forest ecosystems) project. The sites cover 44°20¢N to 26°50¢N and the climate ranges from cool-temperate zone to subtropical zone. At each site, litter on forest floor and soil samples (three or four layers to 50 cm depth) were collected between August and November in 2010-2013 from five soil profiles. From the litter layer samples, the stocks and concentrations of total carbon (C) and N were measured. From the mineral soil samples, bulk density, pH (H 2 O), total C and N concentrations, net and gross rates of N mineralization, nitrification and concentrations of water-soluble substances were measured. The measurements are relevant for other biogeochemical N studies in forest ecosystems and the data set provides basic information on the N pool and fluxes with related chemical properties of forest soils across the Japanese archipelago. The average rates of net and gross N transformation at 20°C across the sites were 0.26 ± 0.47 mgN kg À1 soil d À1 for net N mineralization, 0.25 ± 0.45 mgN kg À1 soil d À1 for net nitrification, 4.06 ± 0.47 mgN kg À1 soil d À1 for

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Estimation of carbon sequestration in the forest sector should take into consideration changes in carbon stock in all carbon pools, including above‐ground and below‐ground biomass, litter, deadwood and soil. In this review, we discuss current knowledge of carbon stocks in litter, deadwood and soil in Japan’s forest sector. According to data from published reports and nationwide surveys, the carbon stock in forest litter is less than that indicated in the Intergovernmental Panel on Climate Change (IPCC) guidelines for temperate and cool temperate forests; for example, coniferous species showed 4.4 Mg C ha−1 for Cryptomeria japonica and 3.1 Mg C ha−1 for Chamaecyparis obtusa, and broad‐leaved species ranged from 3.5 Mg C ha−1 for Castanopsis spp. to 7.3 Mg C ha−1 for Fagus spp. For deadwood carbon stock, coniferous plantations with a record of non‐commercial thinning showed 17.1 Mg C ha−1 and semi‐natural broad‐leaved forests showed 5.3 Mg C ha−1 on average, although only limited data were available. The black soil group (comparable to Andosols and Andisols) showed large carbon stocks in soil layers 0–30 cm deep (130 Mg C ha−1). The brown forest soil group (Cambisols and Inceptisols), occupying the most dominant area, showed a carbon stock of 87.0 Mg C ha−1 on average, which was similar to the data shown in the IPCC guidelines. In a comparison of land use between the forest sector and the agricultural sector for the same soil group, the carbon stock in the agricultural soil was 21% lower and in the grassland soil it was 18% higher than the stock in the forest soil. In this review, we also discuss issues for improving the estimation method and inventory of carbon stock in litter, deadwood and soil in Japan.

To clarify the mechanisms underlying the coexistence of Abies mariesii Masters and Abies veitchii Lindl. in a fir-wave forest, we surveyed the population dynamics of the two Abies species throughout stand development on Mount Shimagare, central Japan. We established three belt transects and found that, overall, A. veitchii dominated this fir-wave forest. However, A. mariesii dominated the canopy initially, whereas A. veitchii increased as stand development progressed; thus, dominant A. mariesii was eventually replaced by A. veitchii. This replacement was explained by the presence of an A. mariesii sapling bank that formed under the canopy of a mature stand and by the large A. veitchii seedling bank resulting from greater seed production. For ordinary canopy individuals, which are taller than midcanopy individuals, the increase in height suggested that taller individuals grow faster vertically regardless of species; moreover, height growth did not differ significantly between the two Abies species, which facilitated the growth of A. mariesii into the canopy and the production of seeds for the next generation. We concluded that the persistence of A. mariesii in this fir-wave forest is supported by its shade tolerance.

To clarify the nutrient acquisition strategies for below-ground resources in a subalpine Abies forest with shallow soils, we examined the vertical patterns of fine root biomass, morphology, nitrogen concentration of fine root tissue and soil chemical characteristics in nine quadrats of sapling, young and mature stands in a subalpine fir-wave forest, central Japan. The community characteristics changed with stand development, but stand development did not influence the vertical pattern of fine root characteristics. Fine root biomass decreased with soil depth. Specific root length did not differ among soil depths, and neither average diameter nor tissue density of fine roots changed vertically. The nitrogen concentration of fine roots differed significantly among soil depths, and was higher in surface soils than in deeper soils. Moreover, soil pH, soil electrical conductivity and soil nitrogen concentration were higher in surface layers than deeper layers. Therefore, we suggest that the subalpine Abies community has a nutrient acquisition strategy that allows uptake of more nutrients near the surface in shallow soils due to the larger investment in biomass and more active metabolism, but not due to phenotypic plasticity in fine root morphology. In addition, we observed that fine root biomass changed with stand development, where specific root length was greater in sapling stands than in older stands.

Estimating carbon (C) and nitrogen (N) stocks in deadwood in forests nationwide is required for understanding large-scale C and N cycling. To do so requires estimated values of wood density and C and N concentrations. Additionally, parameters that show variation should be examined. In this study, we clarified the estimated values and the variation in three parameters in each decay class of each of two tree species and examined whether dead log diameter and region contribute to variation in the parameters. Data were collected from 73 Chamaecyparis obtusa (Sieb. et Zucc.) Endl. plantations and 66 Cryptomeria japonica D. Don plantations throughout Japan. Wood densities decreased from 386 to 188 kg m À3 for C. obtusa and from 334 to 188 kg m À3 for C. japonica in decay classes 1-4. The variation in wood density increased with decay class, and the coefficient of variance increased from 13.9% to 46.4% for C. obtusa and from 15.2% to 48.1% for C. japonica. The N concentrations increased from 1.04 to 4.40 g kg À1 for C. obtusa and from 1.11 to 2.97 g kg À1for C. japonica in decay classes 1-4. The variation in N concentration increased with decay class, and the coefficient of variance increased from 51.9% to 76.7% for C. obtusa and from 50.3% to 70.4% for C. japonica. Log diameter and region contributed to variations in wood density and N concentration in decay classes 1 and 2 for C. obtusa and C. japonica. However, no relationship was observed between regional climates and the two parameters. In contrast, C concentrations ranged from 507 to 535 g kg À1 and were stable with much lower coefficients of variance throughout the decay classes for both tree species. Thus, we recommend that the same C concentration can be adapted for all decay classes of both tree species.