1. a Department of Environmental Management , National Institute of Agro-Environmental Sciences , Tsukuba , 305 , Japan
2. b Macaulay Land Use Research Institute , Craigiebuckler, Aberdeen , AB9 2QJ , U.K.
3. c Department of Upland Farming , Kyushu National Agricultural Experiment Station , Miyakonojo , 885 , Japan
4. d Environmental Resources Division , Japan International Research Center for Agricultural Sciences , Tsukuba , 305 , Japan