The study included a comparative analysis of two Pinus sylvestris L. trees growing next to each other, but in a different health condition, and the reference trees growing in the same area in Poland. The declining tree, although it was a more difficult research material, was subjected to the same analyses as healthy trees, including: creating a ring width index (RWI) record, a δ13C record, an intrinsic water use efficiency (iWUE) record and checking for the following correlations: δ13C-temperature, δ13C-precipitation, δ13C-SO2, and iWUE-SO2. Our study found that trees with different health conditions may have comparable growth patterns, but different carbon isotopic compositions and iWUE. Differences between individual trees were also observed in sensitivity to changes in temperature and SO2 emissions. The declining tree showed more significant correlations with summer temperatures, than the healthy tree and the reference trees, where significant correlations occurred in single months. Only in the instance of the declining tree, correlations were found between δ13C and SO2. iWUE of all trees did not show sensitivity to SO2 emitted in high concentrations; however, we observed the sensitivity of iWUE from the reference trees to low SO2 concentrations.
