A process-based spring phenology framework for projecting climate-change constraints on Chinese hickory cultivation areas

Climate warming is reshaping spring phenology and cultivation potential of extratropical tree species, yet most future suitability assessments rely on simplified climatic indices that overlook key phenological constraints. Here, we developed a process-based spring phenology framework for assessing cultivation suitability of subtropical tree species under climate change and applied it to Carya cathayensis Sarg. in south-eastern China. A process-based tree phenology model was developed using controlled-environment and warming experiments, independently validated with field data, and driven by six climate datasets to project leafout during 2025–2100 under RCP4.5 and RCP8.5. Suitability was evaluated using three constraints: leafout failure, excessively delayed leafout, and cold damage based on the experimentally estimated cold-hardiness threshold (LT 10 ) of young shoots. Leafout failure was projected mainly in the south, where warm winters provided insufficient chilling. Excessively delayed leafout occurred mainly in the north because of insufficient spring forcing and in a limited southern area where insufficient chilling reduced ontogenetic competence. Cold damage was most important in inland areas at intermediate-to-northern latitudes, where relatively early leafout increased exposure to subsequent low-temperature events. Suitable areas accounted for 66.6% and 65.4% of the study region under RCP4.5 and RCP8.5, respectively. Stronger warming reduced cold damage but increased leafout failure, resulting in a slight net reduction in suitable area. This framework provides a physiology-based tool for projecting cultivation suitability under climate change.