ACKNOWLEDGEMENTS
This work was supported by the Fundamental Research Funds of Chinese Academy of Forestry (CAFYBB2017ZF002), National Key R & D Program of China (2018YFC1200400) and National Natural Science Foundation of China (31971666). We thank Dr. Rodrigo J. Mercader (Department of Biology, Washburn University, Topeka, KS) and Dr. Andrew M. Liebhold (USDA Forest Service, Northern Research Station, Morgantown, WV) for their critical comments on an earlier version of the manuscript.