This paper was supported by Science Research of Hunan Provincial Education Department (Grant No. 16C1659), Natural Science Foundation of Hunan Province (Grant No. 13JJ2031, 13JJ4087), Teaching Reform Project of Central South University of Forestry and Technology (Grant No. 1020208), National Natural Science Foundation of China (Grant No. 61304208), Science and technology project of Hunan Province (Grant No. 2014SK2025), and the situation in Hunan province and decision-making consultation (Grant No. 2013BZZ54).