Pedunculate oak mortality as a long-term process shaped by climatic memory

Drought-related tree mortality is often interpreted in relation to individual extreme events, although decline may develop over many years before becoming visible at the stand or landscape scale. This temporal mismatch is particularly important for long-lived broadleaved species, such as pedunculate oak (Quercus robur L.), in which drought effects may persist through hydraulic impairment, reduced carbon reserves and increased vulnerability to secondary biotic agents. Here, we quantified the time scale of drought legacy in oak decline on the Krotoszyn Plateau, one of the most important lowland oak regions in Central Europe. Annual records of drought-related sanitary fellings from 2004 to 2025 were used as an operational indicator of severe oak decline and mortality in managed forests. Climatic water balance (CWB) was calculated for the main growing season, and antecedent CWB was accumulated over windows ranging from 1 to 20 years before each felling year. Oak sanitary-felling volume was most strongly associated with the cumulative CWB summed over the preceding eight years (r S = −0.89, p < 0.001), with neighboring windows performing almost equally well across a broad 7–10-year band, whereas short accumulation windows carried little explanatory signal. An exponential model described the mortality–cumulative CWB relationship better than a linear model and retained moderate predictive skill under leave-one-out cross-validation. These results suggest that oak decline is better interpreted as an accumulation-based process than as a direct response to the most recent drought. The approximately eight-year (7–10-year) CWB accumulation band provides a landscape-specific estimate of the climatic memory preceding oak decline and a useful basis for testing whether similar drought-accumulation periods occur in other oak regions.