*4.4. Limitations and Future Research Directions*

Predicting the shifts in the ranges of species under future global climates creates a major challenge for conservation biogeography [4,46]. Although SDM has been widely used in predicting the range shifts, each model is associated with the drawbacks that limited its predictive accuracy [19,29,47]. For example, the location dataset of *E. japonica* was compiled based on various sources, but may have a certain amount of sampling bias. Therefore, we created bias files within the models to limit sampling errors [29]. In addition, although BCC-CSM 1.1 has been recommended to be used in studies investigating the climate changes across China, the nature of climate change is uncertain, and hence the projected distribution/suitability of habitat are also uncertain [2,48]. Moreover, various important environmental factors that may affect the distribution of *E. japonica*, such as inter/intraspecific competition, predation, dispersal capabilities, anthropogenic influence, and geographical barriers, were not incorporated into our models because robust data were lacking. Therefore, future studies need to incorporate these factors into their analysis [18].

#### **5. Conclusions**

SDM has been extensively used to guide forest management under the threat of future global climate change [2,45]. Given our results and earlier biological information, we suggest that the distribution of *E. japonica* is mainly driven by the effects of the minimum temperature of the coldest month (Bio 6), annual precipitation (Bio 12), mean diurnal range (Bio 2), and annual mean temperature (Bio 1) on its fitness. Our results indicate that the temperate and subtropical regions of eastern China where the species had been recorded was highly suitable for *E. japonica* growth. Under climate change scenarios, the climatic niche of *E. japonica* expanded geographically further toward the north. The maps produced in our study give a quantitative view of the risks associated with regional climate that could impact *E. japonica* cultivation. Moreover, the methods proposed in this study may be adopted to quantify the distribution of other threatened and endangered species and may provide background data for field surveys as well as information that will support conservation and restoration efforts.

**Author Contributions:** J.T., K.Z. and L.S. collected the data; L.S. and K.Z. analyzed the data; L.S. and J.T. drafted the manuscript while consulting all coauthors. All authors commented on the manuscript and contributed to the final version. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research was funded by the Forestry Science and Technology Promotion and Demonstration Fund of Central Finance ([2018]TG08); and the Construction of Jiangsu Modern Agricultural Industry Technology System (JATS[2019]448).

**Conflicts of Interest:** The authors declare no conflict of interest.
