Indicators of caesium 137 concentration in forest litter and health status of pines (Pinus sylvestris L.) in the Chernobyl zone

We analyse the concentration of caesium-137 (¹³⁷Cs) in forest litter in relation to forest site conditions. The research was carried out in 2004–2019 in the Krasnogorsk district of the Bryansk region (the Russian Federation). It covered three areas corresponding to the exclusion zone, compulsory resettlement zone, and the zone of residence of the population with the right to resettlement. In all these areas, the concentration of ¹³⁷Cs in forest litter and the condition of pine stands was studied. We revealed that the forest litter contains more than 90% of ¹³⁷Cs in all combustible materials. The content of ¹³⁷Cs in fallen branches, bark, cones, and needles varies from 10 to 15%. More than 50% of the specific activity, which is an indicator of ¹³⁷Cs content, accounts for needles of pine phytocenoses. In 2019, the best state of pines was recorded for older trees. At the age of 60–80 years, 13% of the studied forest stands were classified as weakened, 87% – as very weakened, and 0% as dying. In the 40–56 age group, dying out and very weakened stands accounted for 50% each, whereas weakened ones were not revealed at all. The interaction between ¹³⁷Cs and tree age was not identified.