4 DISCUSS
The Satyrium plant species are important resources, but they are endangered and rare (Mishra & Saklani, 2012). MaxEnt models were applied to predict current and future potential distribution areas ofS. ciliatum , S. nepalense , and S. yunnanense.Generally, the evaluation index of prediction model accuracy is the ROC curve, which has the following advantage: the AUC value is not affected by the threshold and can be used for the comparison of various models (Fielding et al., 1997). However, further research shows that it is inaccurate to evaluate accuracy only by AUC value because it cannot reflect wrong spatial distribution information, and calculate the omission rate and error rate by a single method (Lobo et al., 2008; Peterson et al., 2008). Nowadays, the information measurement index AUC is used to select the ideal setting parameters of MaxEnt (Muscarella et al., 2014); the method of combining omission rate and AUC value is used to obtain the best parameters (Radosavljevic & Anderson., 2014); TSS value is used to evaluate accuracy (Bedia et al., 2011); and multiple parameters are set to select the optimal result (Elith et al., 2010; Warren et al., 2011). TSS can accurately correct the overall accuracy of the model without being affected by the size of the species validation data set and without depending on the model threshold, therefore, AUC and TSS values are used as evaluation indexes in this prediction (Bedia et al., 2011).
According to the four different future scenarios, the suitable habitat area for Satyrium in China will be extended in the 2050s and 2070s, moving slowly to higher altitude areas in the northwest side of China, where the humidity and habitat are suitable for the growth of theSatyrium species. These scenarios are consistent with the results of a study on the Houttuynia cordata Thunb (Ceercao) habitat suitability. In the study, the suitable distribution area in the high emission scenario was greater than that in the low emission scenario (Liu et al., 2021). The increased precipitation in China in the SSP5 - 8.5 emission scenario was higher than in the low concentration emission scenario (Yue et al., 2021). This shows the increased precipitation in the high concentration emission scenario can solve the limitations of precipitation on distribution of species, and the increased precipitation in the low concentration emission scenario cannot reduce or solve the limitations of precipitation on the distribution of species. This may also be the reason the most suitable habitat area and the increasing area of the Satyrium species are the largest in the high concentration emission scenario, particularly the SSP5-8.5 scenario. The prediction shows that the upcoming future will be the most suitable for the growth of the Satyrium species. It shows that, generally, the suitable habitat is stable and the species will not face extinction due to climate change. This study shows the new areas for species distribution. The findings are in agreement with those of previous studies, indicating that in some regions, habitat suitability of plant species improves under climate change conditions (Feng et al., 2020; Li et al., 2019). The distribution of species under future climatic scenarios predicts that the area of species covering 20% of the earth’s surface will face the risk of extinction, and about 15%–37% of the species will be endangered (Thomas et al., 2004). One of the reasons for the endangered status of Satyrium is that mostSatyrium species are hermaphroditic. Some species rely on birds and other animals for long-distance transmission, the species population is small, and the quality of seed development is low because of long-distance pollination (Johnson et al., 2011). This study’s results provide a reliable basis for protecting Satyrium . People should effectively protect its native habitat and population. Nature reserves for Satyrium should be set up now according to the prediction results, and they should be strengthened to minimize human-made damage.
The results show that isothermality (bio3) and temperature seasonality (bio4) are the common factors in the three species, indicating that the main environmental variable affecting the appropriate distribution ofSatyrium is temperature. Zhao et. al. (2021) used the MaxEnt model to predict the potential suitable habitat of Chinese fir in China. Their results showed that temperature factors are more important than precipitation factors influencing habitat suitability for Chinese fir. Lou et al. (2015) used regression models to predict tea crop yield responses to climate change, finding that temperature plays a significant role in tea production and quality. Environmental variables like temperature can estimate plant distribution patterns (Deblauwe et al., 2016; Wang, R. et al., 2021). In regard to S. nepalense , precipitation is one of the environment variables influencing its geographic distribution.Satyrium is a perennial terrestrial orchid distributed in Southwest China (Deng et al., 2019). Terrestrial orchids are typically cold tolerant, live in low-temperature environments, and are highly distributed in areas with large amounts of annual rainfall (Phillips et al. 2011; Poff et al., 2016). More studies have shown that the dominant variables restricting geographical distribution of plants are energy supply, plenty of water, and cold tolerance (Zhou & Wang, 2000). Based on the prediction of the MaxEnt model, the area of the current potential suitable habitat of Satyrium is mainly located in Southwest China, which has a typical subtropical monsoon climate (Luo et al., 2021). Previous studies have indicated that precipitation is the main variable affecting plant growth, regeneration, nutrient cycles, and community productivity in different habitats (Miranda et al., 2011). Climate change can determine geographical distribution of species, and geographical distribution of species can respond to changes in climate (Warren et al., 2021). Global warming has changed the structures of terrestrial ecosystems, which have changed the habitats and geographical distribution functions of species in turn (Ghini et al., 2012). For instance, climate, topography, soil, human disturbance, and spatial constraints are significant to the distribution of many different spatial scales (Eiserhardt et al., 2011; Parisien et al., 2009). The environmental data used in the study included bioclimatic variables and topographic variables in WorldClim. We did not study soil type, land use, human activities, biological interaction, and other factors that influence the distribution ofSatyrium . The more factors that are included, the more accurate the prediction will be. Therefore, other factors affecting the potential suitable habitat of Satyrium should be studied in the future, with different niche prediction models predicting areas of potential suitable habitats. This will make the prediction of results more reliable.