1. a Key Laboratory of Urban Environment and Health, Institute of Urban Environment , Chinese Academy of Sciences , Xiamen , 361021 , P.R. China
2. b State Key Laboratory of Urban and Regional Ecology, Research Center for Eco-Environmental Sciences , Chinese Academy of Sciences , Beijing , 100085 , China
3. c Department of Forestry and Natural Resources , Purdue University , West Lafayette , IN , 47906 , USA