Funding for this research was provided by:
Hunan province social science association think-tank foundation (ZK2017017)
Social science achievement evaluation committee general project in Hunan province (XSP17YBZC206)
Central South University of Forestry and Technology Presearch Project of National Social Science Fund (2016YY001)
Received: 5 November 2018
Accepted: 13 June 2019
First Online: 27 June 2019
Consent for publication
: Not applicable.
: The authors declare that they have no competing interests.