Future suitability of sweet chestnut (Castanea sativa Mill.) is limited by susceptibility to drought

Global warming and associated droughts have revealed the vulnerability of many tree species throughout the world. The introduction of climate-resilient tree species is therefore a recurring topic in adaptive forest management. In this context, sweet chestnut (Castanea sativa Mill.) is receiving renewed attention due to its native distribution in the Mediterranean, which climatically corresponds to future climate projections for Central Europe. Despite its long history of cultivation throughout Europe and its significant potential in forestry, studies on the climate sensitivity of sweet chestnut remain scarce, particularly in its northern distribution area. By comparing growth responses based on tree-ring data along a gradient of soil water availability in southwestern Germany, this study contributes to the evaluation of the climate resilience of sweet chestnut. More specifically, sweet chestnut stands of low, medium and high water availability were compared regarding long-term growth trends, climate sensitivity of tree growth and growth responses in pointer years. While trends were weak along the studied gradient, sweet chestnut was generally found to be sensitive to spring and early summer drought. At four out of six sites long-term growth decline also indicate stress. Splitting the observation period into an early (1976-1999) and late (2000-2022) period revealed a decrease in climate sensitivity, demonstrating nonstationarity of climate-growth relationships. Growth responses in drought-related pointer years were similar along the soil water availability gradient, and revealed low resistance and high resilience. Our findings indicate that sweet chestnut is not per se a climate-resilient species. Given the importance of early summer water availability for chestnut growth, we recommend a careful site selection. Nevertheless, sweet chestnut seems a promising option for future forest management on better water-supplied sites.