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Seed soundness is of paramount importance for all plants. Seed soundness of forest trees might have been negatively affected after the Fukushima Daiichi Nuclear Power Plant (FDNPP) accident in March 2011, when a massive amount of artificial radionuclides deposited on forest areas. However, information on seeds of forest tree species contaminated with radionuclides is limited because they are rarely encountered in forest ecosystems. Japanese fir (Abies firma Sieb. et Zucc.) is a predominant tree in natural secondary forests in the Abukuma Mountains in Fukushima, and this species shows masting; cone production occurs every 2 or 3 years, meaning that the contamination levels of A. firma seeds remain unknown. We investigated the contamination levels of 137Cs in cone components (seeds, wings and cone scales) of A. firma approximately 4.5 years after the FDNPP accident. The 137Cs concentration in seeds showed the lowest contamination level of the three cone components. In addition, there was a differenc...

Japanese fir (Abies firma Sieb. et Zucc.) usually shows a trifurcated branching form, differentiated into main and lateral shoots. We compared the radiocesium (137Cs) concentration in needles betwe...

We estimated the sample size (the number of samples) required to evaluate the concentration of radiocesium (137Cs) in Japanese fir (Abies firma Sieb. & Zucc.), 5 years after the outbreak of the Fukushima Daiichi Nuclear Power Plant accident. We investigated the spatial structure of the contamination levels in this species growing in a mixed deciduous broadleaf and evergreen coniferous forest stand. We sampled 40 saplings with a tree height of 150 cm–250 cm in a Fukushima forest community. The results showed that: (1) there was no correlation between the 137Cs concentration in needles and soil, and (2) the difference in the spatial distribution pattern of 137Cs concentration between needles and soil suggest that the contribution of root uptake to 137Cs in new needles of this species may be minor in the 5 years after the radionuclides were released into the atmosphere. The concentration of 137Cs in needles showed a strong positive spatial autocorrelation in the distance class from 0 to 2.5 m, suggesting that the statistical analysis of data should consider spatial autocorrelation in the case of an assessment of the radioactive contamination of forest trees. According to our sample size analysis, a sample size of seven trees was required to determine the mean contamination level within an error in the means of no more than 10%. This required sample size may be feasible for most sites.

Amphibians are key components in forest food webs. When examining radioactive contamination in anurans, it is important to understand how radiocesium transfer occurs from lower to higher trophic levels in forest ecosystems. We investigated the activity concentration of radiocesium ( 134 Cs and 137 Cs) in Tago's brown frog ( Rana tagoi tagoi ) captured on the forest floor approximately 2.5 years after the Fukushima Nuclear Power Plant (FNPP) accident. We collected 66 R. tagoi tagoi at different distances from the FNPP. Radiocesium accumulation showed positive correlations with the air radiation dose rate and litter contamination but not with distance from the FNPP. Whole-body radioactivity showed no correlation with body mass or length. Our results suggest that differences in the available food items result in large variability in individual contamination. Contamination level monitoring in terrestrial and aquatic amphibian is necessary for clarifying the processes and mechanisms of radiocesium transfer through forest food webs.