Kyodo News, Dec 16, 2013: Radioactive cesium levels in Miyagi forest soil up since 2011 […] The government of Miyagi Prefecture […] is worried about the impact on forestry and related industries if the trend persists, an official said. In a forest in the town of Marumori [60 km from Fukushima Daiichi], the average cesium level of 10 samples of fallen quills was 26,684 becquerels per kilogram in June 2012, but rose to 42,759 becquerels a year later. And the level in soil up to 10 cm deep increased from 721 becquerels to 3,225 becquerels [rising 4.5-fold], according to the study. In a forest in Ishinomaki, [120 km] from the damaged nuclear plant, the level climbed about 50 percent to 3,611 becquerels among fallen quills and by 2.5-fold to 620 becquerels in soil. […] The results differ from a study the Forestry Agency conducted in 2011 and 2012 in three municipalities in Fukushima Prefecture, which found levels of cesium increasing in soil but declining in fallen foliage.
Radioactive Cesium in Forests is Limited to the Soil’s Surface Layer (pdf), Nov. 29, 2013: For more than two years starting in May 2011, [Takahiro Nakanishi of the Japan Atomic Energy Agency] and his colleagues conducted observations of the broad-leaved deciduous forests in northern Ibaraki Prefecture, to determine how radioactive cesium which fell on fallen leaves of deciduous trees and other material migrated to the soil, and behaved after that. […] the research group believes it will be necessary to watch how the radioactive cesium which has accumulated in the surface layer of the soil is incorporated into the internal cycles of forest ecosystems. […] The total cumulative amount of 137Cs from the fallen leaf layer to a soil depth of 10cm was about 20kBq/m2 [20,000 becquerels per square meter] throughout the observation period […]