Provenance-specific responses to climatic mismatch in Betula ermanii Cham. and implications for climate adaptation

Climate change is expected to alter the growth and survival of forest trees, but the magnitude and direction of these effects remain uncertain at the intraspecific level, particularly across provenances adapted to contrasting climatic conditions. For Betula ermanii Cham., a dominant deciduous tree in cool-temperate and subalpine forests of Japan, it remains unclear how climatic mismatches between provenance origin and planting environment influence early-life performance. Here, we quantified the effects of climatic transfer distances on seedling performance using data from 11 provenance trials distributed across Japan. Performance was defined as a composite index integrating survival and growth (mean height × survival rate) at the provenance × site level. Generalized linear mixed models were used to evaluate the effects of temperature and precipitation mismatches, and the fitted models were applied to future climate scenarios based on Shared Socioeconomic Pathways (SSPs), specifically SSP2-4.5 and SSP5-8.5, to project changes in performance. Seedling performance showed a weak decline with increasing precipitation at the planting site relative to the provenance origin, while temperature responses varied substantially among provenances. This heterogeneity indicates strong genotype-by-environment interactions, with high-elevation central provenances showing greater sensitivity to warming, whereas northern provenances were comparatively less responsive. Under future climate scenarios, northern provenances generally maintained higher predicted performance in situ, while central provenances showed reduced performance at their origins but improved performance when projected into northern regions, suggesting potential for assisted migration. In contrast, the southern rear-edge provenance exhibited consistently low performance across scenarios, indicating limited adaptive potential under climatic change. Overall, our results demonstrate that responses to climatic mismatch vary among provenances, and that incorporating provenance-specific climatic sensitivity improves predictions of future performance. These findings emphasize the importance of provenance-based strategies for forest management, including the identification of climate-resilient source provenances, evaluation of assisted migration options, and conservation of genetically distinct but vulnerable provenances.