TABLE 1 Environmental variables selected in the MaxEnt model
It is necessary to analyze environmental variables before they can be used for niche simulation calculations to prevent the multicollinearity of the variables from causing overfitting of the model, because many bioclimatic variables are spatially related (Graham, 2003). ArcGIS10.2 was employed to examine the relationships among all the environmental variables. If the correlation coefficient of both variables was greater than or equal to 0.8, we removed the relevant environment variables with a lower contribution rate (Pan et al., 2020). A total of 10, 10, and 9 environmental variables based on the MaxEnt model analysis and the Spearman coefficient method were used to predict S. ciliatum ,S. nepalense , and S. yunnanense distributions in China, respectively (Table 1).