Key message <p>During drought conditions, <i>Austrocedrus chilensis</i> closes its stomata in order to use water more efficiently and survive, even though this results in reduced growth.</p> Abstract <p>Climate change and its associated events, such as droughts, are exerting increasing pressure on ecosystems. Forests provide essential ecological, economic, and social functions, making their resilience a key concern. In South America, the temperate Andean forests are home to <i>Austrocedrus chilensis,</i> one of the longest-lived conifers in the region, which is highly sensitive to variations in climate conditions. Although it is among the most drought-resistant species in Patagonia, several studies have reported forest decline associated with drought events in recent decades. With projections indicating increasingly frequent and severe droughts in this region, understanding the adaptive strategies of this species is essential for developing&#xa0;effective management and conservation strategies to maintain ecosystem functioning. To investigate these strategies, we developed the first stable carbon isotope (δ¹³C) chronologies from <i>A. chilensis</i> cellulose. Using samples from two sites located&#xa0;at the drier margin of its distribution in Argentina, we developed annual resolution records spanning the period from 1818 to 2018. From δ¹³C, we derived estimates of carbon isotopic discrimination (Δ¹³C), intrinsic water-use efficiency (iWUE), and internal CO₂ concentration (C_i). Basal area increment (BAI) chronologies were also developed from tree-ring width data. The resulting chronologies reflect both environmental conditions and site-specific disturbance histories. Our results indicate increasing iWUE and C_i, accompanied by reduced growth, especially from the second half of the twentieth century onward. These trends suggest that <i>Austrocedrus chilensis</i> copes with drought primarily through stomatal regulation, enhancing iWUE at the expense of carbon assimilation and growth.</p>