Drought Response of Scots Pine Provenances in a Long-Term Common Garden Experiment: Associations with Climate of Origin and Tree Size

Abstract

One adaptive silvicultural strategy to address the increasing frequency and severity of climate extremes is the promotion of genetic material best suited to a changing environment. Using a long-term provenance trial established in 1966 in central Poland, we evaluated how climate humidity at the parental site (provenance origin) influences individual-tree growth–drought resilience trade-offs in Scots pine (Pinus sylvestris L.). Stem discs from 240 trees representing 16 provenances were initially assessed, of which 202 trees were retained following cross-dating and quality control. Drought responses were quantified using complementary growth resilience indices for major drought events identified using the Standardized Precipitation–Evapotranspiration Index. Mixed-effects models followed by Type III Wald chi-square tests and Sidák-adjusted pairwise comparisons revealed significant provenance-level differences in drought responses. Structural equation modeling showed that parental-site climate directly and indirectly affected drought resistance through its influence on relative tree size. Trees from provenances originating in more water-rich environments tended to be smaller but exhibited higher resistance, indicating a potential trade-off between growth and drought tolerance. Relative tree size was also negatively associated with resilience, whereas recovery and relative resilience were not significantly associated with provenance climate or relative tree size. These findings indicate that provenance climate is associated with drought resistance in Scots pine, with tree size emerging as an important mediator of this relationship.