Abstract: Stable carbon isotope technique has been playing many roles in the research of plant physio-logical ecology and global change ecology . For example, δ13C in leaves of some species is characterized with a certain photosynthesis pathway, or has some close relation with water use efficiency (WUE) . The δ13C recorded in tree righs can also be used to indicate the past climate changes. The fractio nation of δ13C from atmosphere to plants and the method for determining this value as well as some applications of such technique were briefly introduced in this paper .

Key words: population density, natural environment, man-land relationship, China.