3.2 Importance of Environmental Variables Affecting T. sinense Distribution
The influence of 16 environmental factors on distribution was evaluated through a jackknife test (Fig. 2). Notably, the contribution rates (PC) of Bio6 (44.60%), T_CACO3 (10.29%), and Bio9 (8.90%) ranked highest, with a cumulative PC of 63.79%. Similarly, the permutation importance (PI) of Bio6 (34.18%), Bio4 (25.70%), and elevation (21.18%) were among the top three, with a cumulative PI of 81.06%. This analysis revealed that the primary environmental factors shaping the current geographical distribution of T. sinense include bioclimatic variables (Bio4 and Bio6), soil variables (T_CACO3), and topography (Elevation) (Table 3).
Environmental factor response curves further elucidated the relationship between the probability of T. sinense occurrence and environmental variables (Fig. 3). Generally, when the probability exceeded 0.5, corresponding environmental factor values favored T. sinense growth. Based on these curves, suitable environmental factor ranges for T. sinense growth were determined as follows: 407.4 to 731.3 (Bio4), -8 to 0.61°C (Bio6), 0% to 0.17% (T_CACO3), and 1355.8 to 3508 m (Elevation).