Simulation of potential suitable area and exploration of dominant environmental factor of Cercidiphyllum japonicum Siebold & Zucc. in Sichuan Province based on MaxEnt model

To support the scientific conservation and sustainable utilization of the germplasm resources of Cercidiphyllum japonicum Siebold & Zucc., a nationally protected and rare relict species, in Sichuan Province, this study employed MaxEnt modeling based on field population distribution data, 19 bioclimatic variables, and three topographic factors to simulate its potential suitable habitat and identify the key environmental drivers of its distribution. The results showed that: (1) the model exhibited high predictive accuracy, with AUC values of 0.940 and 0.964 for the training and test datasets, respectively; (2) after evaluating contribution rates and multicollinearity, seven variables were identified as key environmental factors: elevation (dem), mean monthly diurnal temperature range (bio2), mean temperature of the driest quarter (bio9), isothermality (bio3), precipitation seasonality (bio15), precipitation of the warmest quarter (bio18), and slope (Slope), with elevation being the dominant factor, and the suitable elevation range approximately 1300-3000 m; (3) the total suitable area in Sichuan Province was 124,513 km², accounting for 25.62% of the provincial area, with high, medium, and low suitability zones covering 1.77%, 6.02%, and 17.83%, respectively. Overall, the suitable habitats formed a northeast-southwest oriented arc-shaped corridor, mainly distributed in the “Sichuan Western Rain Shield” mountains along the transition from the Sichuan Basin to the western plateau; (4) over 90% of the highly suitable area was concentrated in the 1500-2500 m mid-mountain belt, exhibiting three distinct distribution patterns: the core concentrated area in the southern Sichuan mountains, interrupted by the Dadu River (4100 km²); the belt-like extension area along the Min Mountains and northern section of the Longmen Mountains in northern Sichuan, divided by the Fujiang River (2800 km²); and the patchy transitional area along the western edge of the central Sichuan Basin, from the southern Longmen Mountains to the eastern edge of the central section of the Daxue Mountains (1600 km²). Overall, the species exhibits a “refugial” ecological niche dependence on specific montane monsoon climates. These findings provide a comprehensive understanding of the potential distribution patterns and ecological requirements of C. japonicum in Sichuan Province and offer important scientific guidance and spatial reference for field germplasm surveys, priority conservation unit delineation, and population restoration.