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was discharged into the atmosphere during the nuclear accident at Chernobyl on April 26, 1986. The deposition of radionuclides on the tree canopies is the most important contaminating form of 137Cs in forest ecosystems (Skoko et al. 2011). Given that the tree canopies are a major part of the biomass in the management of low aerodynamic resistance, they are effective “interceptor” of the radionuclide (Yamagata et al. 1969, Bunzl and Kracke 1988, Desmet and Myttenaere 1988, Sokolov et al. 1990). Generally, such “interception” in the trees (seen in the same unit volume of crown) is more effective for dry than wet deposition, especially for small particles and gases (Pröhl 2008). As the amount of 137Cs over time decreases exponentially, adoption root becomes the dominant source of intake of 137Cs in the trees long term (Ohashi et al. 2020). Accumulation of 137Cs in the trees is one of the most important problems in the wood use and forest pollution (Shinta et al. 2014). Wood as a raw material is permanently present in the environment of people, contributing to their radioactive exposure by increasing doses of radiation. However, compared to the annual equivalent dose per capita from various sources, the calculated annual equivalent doses do not pose a risk in beech, oak and silver fir wood panel samples tested from the territory of the Republic of Croatia (Hus et al. 2004). The objective of the research was to determine the incidence and intensity of the dynamics of the 137Cs in the silver fir tissues (Abies alba Mill.), including their by-products entering the human and animal food chain, as well as in samples of soil directly under the selected trees. At study sites, on a longer time scale (2003 - 2017), measured variability of 137Cs in the tissue of silver fir trees depend on seasonal dynamics of 137Cs followed the level of physiological activity and decay of 137Cs during time. The highest activity of 137Cs was determined in the bark and the physiologically most active parts of the silver fir (shoots and needles) during the growing season. Activities of 40K were of approximately equal values throughout the observed period. This research will contribute to the understanding of the biogeochemical cycle of 137Cs within the forest ecosystem, and will also contribute to the monitoring of 137Cs wood raw material pollution on wood products. This research also tends to contribute to the study review discussion of the consequences of human activity has on the forest ecosystem. MATERIAL AND METHODS MATERIJAL I METODE Research area – Područje istraživanja The research was conducted on the tissues of fir trees (Abies alba Mill.) in Lika (near Vrhovine), and the soils next to the trees. The chosen location is considered to be among the most contaminated during the Chernobyl disaster in Croatia (Barišić and Lulić 1990), and the sampling schedule is shown in Table 1. Sample collection method – Metoda prikupljanja uzoraka In the forest ecosystem at the site GJ Komarnica, subdivision 12a, studied the trees of silver fir (1, 2, 3) and recorded the coordinates of trees and soils samples. The measured trees were knocked down in the field by licensed workers of the company Hrvatske šume Ltd. after which the cut rings were used for further sectioning. Pits were dug next to fir trees in which root samples were collected for testing. The soil samples were collected along with the tree samples. The first sampling on a silver fir tree, 25 m high and 56 cm in (DBH) diameter at breast height, was performed during the vegetation dormancy on December 4, 2003. On a felled |