基金The research was supported by innovation research project of Chinese Academy of Sciences (KZCX3-SW-418), the 100-Young-Researcher-Project of Chinese Academy of Sciences, and by Nature Science Foundation of Liaoning Province (20021006). Acknowledgements We thank Professor Hexin Wang (Dalian University, China), Dr. Professor Zeng Dehui, and the graduate students in research group of Ecology and Management of Secondary Forest (Institute of Applied Ecology, Chinese Academy of Sciences) for their valuable discussion. We are grateful to Mr. Tao Yang (Institute of Applied Ecology, Chinese Academy of Sciences) for his field work. We also thank Dr. Professor Qingcheng Wang (Northeast Forestry University, China), Mr. Menqi Tu and Mr. Yuxiang Ge (Honghuaerji Forestry Bureau, Inner Mongolia, Hulunbeier, China) for providing the convenience during the field investigation.