Prediction of potential suitable areas and dominant environmental factors of Cercidiphyllum japonicum in Sichuan Province using a MaxEnt model

To scientifically protect and sustainably utilize of the germplasm resources of Cercidiphyllum japonicum, a nationally protected and rare relict species, in Sichuan Province, based on field population distribution data, combined with 19 bioclimatic variables and three topographic factors, the potential suitable areas were simulated by MaxEnt model, and the dominant environmental factors affecting its distribution were analyzed. The results showed that: (1) The prediction accuracy of the model was extremely high, and the AUC values of the training set and the test set were 0.940 and 0.964, respectively. (2) After evaluating contribution rates and multicollinearity, seven variables were identified as key environmental factors: elevation, 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), among which altitude was the dominant environmental factor and the suitable elevation range was about 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) More than 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 exhibit a "refuge" ecological niche dependence on specific montane monsoon climate. These findings effectively revealed the potential distribution patterns and ecological requirements of C. japonicum in Sichuan Province, offering important scientific evidence and foundation reference for field germplasm surveys fo genetic resources, idenfication of priority conservation areas, and population restoration efforts.