Institute of Geographical Sciences and Natural Resources Research;
Chinese Academy of Sciences;
Beijing 100101;
P. R. China;
Graduate University;
chinese Academy of Sciences;
Beijing 100049;
P.R.China;
Center for Chinese Agricultural Policy (CCAP);
Beifing 10010;
P.R.China;
Center for Asian Pacific Studies;
Stanford Universitv;
95613;
. U.S.A;