This study was supported by the National Key Research and Development Programme funded by the Ministry of Science and Technology of China (2016YFD0600202), the National Natural Science Foundation of China (31570447 and 31170426), and the Huitong Forest Ecological Station Programme funded by the State Forestry Administration of China. We thank the following postgraduates for their assistance in the field work: Zhaodan Liu, Yan Li, Renhui Li, Weixian Zeng, Mengmeng Gou, Hui Wei, Xiaoxiao Shen, Fangyong Yu, and Xinhao Huang. We are also grateful to the staff of the administration office of Paiyashan Forest State Farm, Jingzhou County, Hunan Province, for their local support.