Characteristics of initial deposition and behavior of radiocesium in forest ecosystems of different locations and species affected by the Fukushima Daiichi Nuclear Power Plant accident.

After the Fukushima Daiichi Nuclear Power Plant (FDNPP) accident, information about stand-level spatial patterns of radiocesium initially deposited in the surrounding forests was essential for predicting the future dynamics of radiocesium and suggesting a management plan for contaminated forests. In the first summer (approximately 6 months after the accident), we separately estimated the amounts of radiocesium ((134)Cs and (137)Cs; Bq m(-2)) in the major components (trees, organic layers, and soils) in forests of three sites with different contamination levels. For a Japanese cedar (Cryptomeria japonica) forest studied at each of the three sites, the radiocesium concentration greatly differed among the components, with the needle and organic layer having the highest concentrations. For these cedar forests, the proportion of the (137)Cs stock in the aboveground tree biomass varied from 22% to 44% of the total (137)Cs stock; it was 44% in highly contaminated sites (7.0 × 10(5) Bq m(-2)) but reduced to 22% in less contaminated sites (1.1 × 10(4) Bq m(-2)). In the intermediate contaminated site (5.0-5.8 × 10(4) Bq m(-2)), 34% of radiocesium was observed in the aboveground tree biomass of the Japanese cedar stand. However, this proportion was considerably smaller (18-19%) in the nearby mixed forests of the Japanese red pine (Pinus densiflora) and deciduous broad-leaved trees. Non-negligible amounts of (134)Cs and (137)Cs were detected in both the sapwood and heartwood of all the studied tree species. This finding suggested that the uptake or translocation of radiocesium had already started within 6 months after the accident. The belowground compartments were mostly present in the organic layer and the uppermost (0-5 cm deep) mineral soil layer at all the study sites. We discussed the initial transfer process of radiocesium deposited in the forest and inferred that the type of initial deposition (i.e., dry versus wet radiocesium deposition), the amount of rainfall after the accident, and the leaf biomass by the tree species may influence differences in the spatial pattern of radiocesium by study plots. The results of the present study and further studies of the spatial pattern of radiocesium are important for modeling future radiocesium distribution in contaminated forest ecosystems.

Climate change mitigation effect of harvested wood products in regions of Japan.

BACKGROUND: Harvested wood products (HWPs) mitigate climate change through carbon storage, material substitution, and energy substitution. We construct a model to assess the overall climate change mitigation effect (comprising the carbon storage, material substitution, and energy substitution effects) resulting from HWPs in regions of Japan. The model allows for projections to 2050 based on future scenarios relating to the domestic forestry industry, HWP use, and energy use. RESULTS: Using the production approach, a nationwide maximum figure of 2.9 MtC year-1 for the HWP carbon storage effect is determined for 2030. The maximum nationwide material substitution effect is 2.9 MtC year-1 in 2050. For the energy substitution effect, a nationwide maximum projection of 4.3 MtC year-1 in 2050 is established, with at least 50 % of this figure derived from east and west Japan, where a large volume of logging residue is generated. For the overall climate change mitigation effect, a nationwide maximum projection of 8.4 MtC year-1 in 2050 is established, equivalent to 2.4 % of Japan's current carbon dioxide emissions. CONCLUSIONS: When domestic roundwood production and HWP usage is promoted, an overall climate change mitigation effect is consistently expected to be attributable to HWPs until 2050. A significant factor in obtaining the material substitution effect will be substituting non-wooden buildings with wooden ones. The policy of promoting the use of logging residue will have a significant impact on the energy substitution effect. An important future study is an integrated investigation of the climate change mitigation effect for both HWPs and forests.

Radiocesium concentrations in the bark, sapwood and heartwood of three tree species collected at Fukushima forests half a year after the Fukushima Dai-ichi nuclear accident.

Radiocesium ((134)Cs and (137)Cs) distribution in tree stems of Japanese cedar (aged 40-56 y), red pine (42 y), and oak (42 y) grown in Fukushima Prefecture were investigated approximately half a year after the Fukushima Dai-ichi nuclear accident. Japanese cedar, red pine, and oak were selected from five sites, one site, and one site, respectively. Three trees at each site were felled, and bark, sapwood (the outer layer of wood in the stem), and heartwood (the inner layer of wood in the stem) separately collected to study radiocesium concentrations measured by gamma-ray spectrometry. The radiocesium deposition densities at the five sites were within the range of 16-1020 kBq m(-2). The radiocesium was distributed in bark, sapwood, and heartwood in three tree species, indicating that very rapid translocation of radiocesium into the wood. The concentration of radiocesium in oak (deciduous angiosperm) bark was higher than that in the bark of Japanese cedar and red pine (evergreen gymnosperms). Both sapwood and heartwood contained radiocesium, and the values were much lower than that in the bark samples. The results suggest that radiocesium contamination half a year after the accident was mainly attributable to the direct radioactive deposition. The radiocesium concentrations in the Japanese cedar samples taken from five sites rose with the density of radiocesium accumulation on the ground surface. To predict the future dynamics of radiocesium in tree stems, the present results taken half a year after the accident are important, and continuous study of radiocesium in tree stems is necessary.