Forest Site Conditions Shape Long-Term Tree Carbon Accumulation and Hydroclimatic Sensitivity in Scots Pine (Pinus sylvestris L.) of the Eastern European Forest-Steppe

Forest site conditions may influence both carbon accumulation and the hydroclimatic sensitivity of tree growth in mature Scots pine forests. We examined three 100–130-year-old Pinus sylvestris L. stands in the Eastern European forest-steppe representing fresh pine forest (A2), fresh mixed pine forest (B2), and moist mixed pine forest (B3). Stand inventories, biomass allometry, and tree-ring reconstruction were combined to estimate biomass carbon stocks and annual tree biomass carbon stock increment (ΔC), which was related to current- and previous-year hydroclimatic conditions and to selected dry events. Biomass carbon stocks were 99.4, 126.3, and 129.0 Mg C ha−1 in A2, B2, and B3, respectively. Mean ΔC for 1961–2025 was 3.74, 3.17, and 4.49 kg C tree−1 year−1. Hydroclimatic sensitivity differed among site types: B2 showed the strongest response to moisture-related variables, A2 an intermediate response, and B3 the weakest average linear sensitivity. Antecedent moisture conditions were also associated with subsequent ΔC. Responses to the 1972, 2010, and 2018 dry events differed among stands and did not consistently correspond to average climate–growth relationships. Overall, forest site conditions were associated with both long-term tree carbon accumulation and its sensitivity to hydroclimatic variability.