The accident at the Fukushima Dai-Ichi Nuclear Power Plant (FDNPP) in Japan on 11 March 2011, caused by an earthquake-induced tsunami, was classified as one of the world’s largest nuclear accidents, comparable to the accident at the Chernobyl Nuclear Power Plant (ChNPP) in Ukraine on 26 April 1986 (IAEA Citation2015). The FDNPP accident resulted in massive emissions of radioactive substances into the atmosphere and, subsequently, over a wide area, not only in the vicinity of the FDNPP but also across a vast area in northeast Japan.
Forests are the dominant component of the terrestrial landscape in northeast Japan, and they were contaminated to varying degrees by radiocesium fallout from the accident (Hashimoto et al. Citation2012). During the initial stages of radiocesium contamination after the accident, forests acted as a barrier against direct radiocesium fallout in urban areas and neighborhoods, and radiocesium was subsequently retained in forest ecosystems.
Extensive decontamination measures were undertaken to enable residents to return to evacuated areas after the accident. However, some severely contaminated areas were designated as “areas where returning is difficult.” In this regard, in April 2017, 6 years after the accident, evacuation orders were lifted for the areas surrounding difficult-to-return areas, which are dominated by forests. Decontamination was mostly conducted in residential and agricultural areas and was limited in nearby forest areas, indicating that most of the forests in these zones will remain contaminated.
The Ministry of Agriculture, Forestry and Fisheries formulated regulations after April 2012 for the use of forest products, setting permissible levels at 40 Bq kg−1 in firewood, 50 Bq kg−1 in logs for mushroom cultivation, 280 Bq kg−1 in charcoal for cooking, and 400 Bq kg−1 in biochar and leaf litter origin compost (MAFF Citation2011a, Citation2011b, Citation2012); however, no regulations were established for timber for construction use. These regulations differ from those implemented after the ChNPP accident.
Although limited information was gathered during the initial period of the ChNPP accident in April 1986, many studies of radiocesium contamination and dynamics in forest ecosystems and forest products commenced soon after the FDNPP accident (e.g. Kato et al. Citation2012, Citation2017; Komatsu et al. Citation2016; Ogawa et al. Citation2016). Recently, Gonze and Calmon (Citation2017) compiled the results of many early studies to clarify the generic trends of the radiocesium dynamics in 2011–2013. Therefore, the findings from the initial stages of the impact of the FDNPP accident on forest ecosystems are important to complete this information.
The first symposium on the FDNPP and the ChNPP accidents, at the annual meeting of the Japanese Forest Society (JFS), was held at Utsunomiya University in March 2012 (Ohkubo et al. Citation2012). Special sessions on the issues of radioactive contamination and countermeasures in forests and forestry after the accidents were coordinated in the subsequent annual meeting of the JFS (Kaneko and Ohkubo Citation2013, Citation2014; Ohkubo and Kaneko Citation2016). About 40 papers, consisting of approximately 15 oral presentations and 25 posters, were presented and discussed each year over 3 years. The topics covered the distribution and dynamics of radiocesium in forests, transfer factors of radiocesium in various forest products, various types of countermeasures, influence of radiation contamination on forestry, local communities, etc.
From this perspective, the Editorial Board of the Journal of Forest Research (JFR) is creating the special feature titled, “Radiocesium dynamics in forest ecosystems after the Fukushima Nuclear Power Plant accident: experiences during the initial five years.” The aim was to collect reviews and articles concerning various aspects of forest ecosystem contamination and the decontamination measures undertaken in the 5 years after the FDNPP accident. The original review and articles belonging to this special feature are included in this issue (vol. 23, issue no. 1) and subsequent issues. This special feature includes a review paper and five original articles, and covers topics such as a comparison of radioactive contamination between Fukushima and Chernobyl forests (Yoschenko et al. in this issue), forest edge effects in radioactivity-contaminated forests (Imamura et al. in this issue), the effects of inoculation with ectomycorrhizal fungi on the accumulation and distribution of radiocesium in konara oak (Quercus serrata) seedlings (Choi et al. in this issue), the mass of the organic layer in the soil affecting downward migration of radiocesium (Ito et al. in this issue), a demonstration of radiocesium absorption through bark into sapwood in Konara oak by stable cesium experiments (Wang et al. in this issue), and differences in shoot positions affecting radiocesium contamination of needles in Japanese fir (Oba et al. in this issue).
Over time, radiocesium contamination levels are decreasing and the area of low contamination is expanding after natural decay and weathering of radiocesium. Long-term monitoring of radiocesium in forest ecosystems and the adjacent landscapes, absorption of radiocesium by forest products, especially related to timber trees, mushroom logs, wild vegetables, and mushrooms, is indispensable. Further studies to clarify the mechanism of radiocesium dynamics in ecosystems should be explored under low contamination levels to determine the outcomes of countermeasures for the reconstruction of the forestry and forest products industries in Fukushima and other areas.
We hope that this special feature becomes a milestone of the outcomes of radiocesium dynamic studies in forest ecosystems. A number of field studies are currently ongoing; therefore, this special feature will promote the expansion of a wide range of related studies to be compiled as future virtual issues of JFR.
Acknowledgments
We wish to express our gratitude to all of the contributors who participated in the special sessions during the JFS annual meetings and the compilation of the current special issue, including those who served as anonymous reviewers.
Disclosure statement
No potential conflict of interest was reported by the author.
References
- Gonze MA, Calmon P. 2017. Meta-analysis of radiocesium contamination data in Japanese forest trees over the period 2011–2013. Sci Total Environ. 601–602:301–316.
- Hashimoto S, Ugawa S, Nanko K, Shichi K. 2012. The total amounts of radioactively contaminated materials in forests in Fukushima, Japan. Sci Rep. 2:416.
- IAEA. 2015. The Fukushima Daiichi accident. Vienna: IAEA. Technical volume 5. Post-accident recovery.
- Kaneko S, Ohkubo T. 2013. Report of special session of 124th annual meeting of Japan Forest Society (Morioka), “Present status of radioactive contamination in forest ecosystems”. For Technol. 854(5):34–35. (in Japanese).
- Kaneko S, Ohkubo T. 2014. Report of special session of 125th annual meeting of Japan Forest Society (Omiya), “Towards clarifying facts of radioactive contamination in forest ecosystems”. For Technol. 866(5):24–25. (in Japanese).
- Kato H, Onda Y, Gomi T. 2012. Interception of the Fukushima reactor-accident derived 137Cs, 134Cs and 131I by coniferous forest canopies. Geophys Res Lett. 39:L20403.
- Kato H, Onda Y, Hisadome K, Loffredo N, Kawamori A. 2017. Temporal changes in radiocesium deposition in various forest stands following the Fukushima Dai-ichi Nuclear Power Plant accident. J Environ Radioact. 166:449–457.
- Komatsu M, Kaneko S, Ohashi S, Kuroda K, Sano T, Ikeda S, Saito S, Kiyono Y, Tonosaki M, Miura S, et al. 2016. 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. J Environ Radioact. 161:2–10.
- MAFF. 2011a. About setting of provisional tolerance of radioactive cesium-containing fertilizer/soil improvement material/soil supplement and feed. [Internet]. [accessed 2017 Jun 26]. http://www.maff.go.jp/j/syouan/soumu/saigai/shizai.html.
- MAFF. 2011b. Q & A on setting immediate indicator values for firewood and charcoal for cooking and heating. [Internet]. [accessed 2017 Jun 26]. http://www.rinya.maff.go.jp/j/tokuyou/shintan4.html.
- MAFF. 2012. On the revision of immediate index value of mushroom logs and medium for bacterial bed. [Internet]. [accessed 2017 Jun 26]. http://www.rinya.maff.go.jp/j/press/tokuyou/120328_2.html.
- Ogawa H, Hirano Y, Igei S, Yokota K, Arai S, Ito H, Kumata A, Yoshida H. 2016. Changes in the distribution of radiocesium in the wood of Japanese cedar trees from 2011 to 2013. J Environ Radioact. 161:51–57.
- Ohkubo T, Kaneko S. 2016. Report of special session of 127th annual meeting of Japan Forest Society (Fujisawa), “Clarifying facts and the countermeasures of radioactive contamination in forest ecosystems toward reconstruction of forestry”. For Technol. 890(5):28–29. (in Japanese).
- Ohkubo T, Kaneko S, Kaneko N, Tanaka H, Zibtsev S, Kashparov V, Yoschenko V, Yoshida S, Onda Y. 2012. Special feature, Report of special session of 123th annual meeting of Japan Forest Society (Utsunomiya), “Radioactive effects on forest ecosystems after the Fukushima Nuclear Power Plant accident”. For Sci. 65:26–44. (in Japanese).