Topo-climatic control on earlywood and latewood growth of Pinus sylvestris L. across the Eastern Black Sea (Türkiye) climatic barrier

This study investigates the growth dynamics of Pinus sylvestris across the Zigana and Tersun Mountains in the Eastern Black Sea transition zone (Türkiye), elucidating the role of topography in modulating climate–growth relationships. By utilizing 476 increment cores from 239 trees across 12 sites, we developed tree-ring width (TRW), earlywood (EW), and latewood (LW) chronologies to evaluate growth responses along elevation and aspect gradients using moving correlation analysis and Generalized Additive Mixed Models (GAMM). Results reveal a pronounced topo-climatic differentiation: northern slopes of Zigana operate under cold-limited regimes, where growth is primarily governed by early-season temperatures (March–April). Conversely, southern slopes and the inland Tersun Mountains exhibit a shift toward moisture-limited regimes, with growth showing high sensitivity to May–June precipitation. Moving correlation analyses demonstrate a significant temporal transition since the late 1960s, where temperature-driven growth stimulation has been progressively replaced by an intensifying sensitivity to early-season moisture availability. GAMM results revealed non-linear growth responses to seasonal temperature and precipitation variability. The response curves indicated reduced growth under colder March–April conditions, with relative growth increasing markedly when March–April mean temperatures exceeded a model-estimated threshold of approximately 2.0–2.2 °C. May temperature showed a narrow statistical optimum around 7.5–9.7 °C, above which the estimated growth response declined. May–June precipitation promoted growth up to a model-dependent saturation threshold of approximately 300 mm, followed by a tendency toward saturation or decrease. Ultimately, the Eastern Black Sea climatic barrier generates high local-scale variability, rendering inland populations increasingly vulnerable to drought stress under ongoing climate warming. These findings underscore the necessity of topographic context in climate-growth studies and emphasize the urgent need for site-specific, climate-adaptive forest management strategies.