Lichens are considered by researchers as bioindicators of environmental pollution by artificial radionuclides, including 137 Cs. One of these bioindicator species is epiphytic lichen Hypogymnia physodes (L.) Nyl, the use of which for radioecological monitoring can be modified by several factors: tree species, placement on the tree (branches -trunk), height of sampling, etc. The purpose of this study was to investigate the specific activity of 137 Cs in thalli of hypogymnia in pine stands: on trunks of Pinus sylvestris L. and Betula pendula Roth at different heights of sampling in 3 height ranges: 0-65, 65-130, and 130-195 cm, and to analyse the intensity of radionuclide accumulation in the "lichen thallus -tree bark" link for both tree species in all height ranges. The study was conducted in August 2021 in the Korosten district of the Zhytomyr Oblast, Zhytomyr Polissia, on 4 test plots, in the Drevlianskyi nature reserve, mainly in middle-aged pine stands with an admixture of birch, where 130 samples of soil, tree bark, and lichen were taken. Specific activity of 137 Cs in the samples was measured using a SEG-001 "AKP-s"-150 gamma-ray spectrometer with a BDEG-20R2 scintillation detector (NaI(Tl). It was demonstrated that the content of 137 Сs in the thalli of Hypogymnia physodes at different altitude ranges did not differ statistically significantly at the 95% confidence level in all test plots on pine. A preliminary conclusion was made on the possibility of sampling Hypogymnia physodes thalli on pine trunks in the height range of 0-195 cm; however, for the convenience of sampling, it is recommended to perform sampling within 130-195 cm. It has been proven that both the specific activity of 137 Сs in Hypogymnia physodes thalli and the intensity of 137 Сs accumulation in the chain "Hypogymnia physodes ─ tree bark" are approximately 2 times higher on pine compared to birch. It was found that on a birch, the content of 137 Сs in lichen between the height ranges of 0-65 and 65-130 cm, and 0-65 and 130-195 cm differs significantly at the 95% confidence level; therefore, it is recommended to sample Hypogymnia physodes on a birch in the range of 65-130 cm