Supported by Chongqing Natural Science Foundation Projects (CSTC-2008BA7032,CSTC-2010BB7003);the Fundamental Research Funds for the Central Universities (XDJK2009B032);the Doctoral Research Fund of Southwest University (SWU109020);the 948 Program of State Forestry Administration (2008-4-45);Chongqing Key Laboratory for the Protection and Restoration of Forest Ecology of the Three Gorges Reservoir Region (2008-01)