Abstract: According to the buffers and urban fringes of Nanjing in 1988 and 2003, and by using landsat TM images and DEM data, 8 urban-rural gradient zones called Ⅰ,Ⅱ,Ⅲ， … …， Ⅷ in this city were marked off, and the forest distribution pattern as well as the land use strategies along these gradient zones were studied. The results showed that in each of these zones, there was a significant positive correlation between the coverage of mountainous area and forest, and the forest coverages were obviously higher in mountainous than in flat area, with a distribution pattern of Ⅰ＞Ⅱ，Ⅱ＜Ⅲ,Ⅲ≈Ⅳ,Ⅳ＞Ⅴ＞Ⅵ＞Ⅶ＞Ⅷ. In urbanizing area, there were three major land use types, i.e., urban building, ecological regulation (mainly forest stand), and agricultural production (mainly crop land). The potential value of a certain land use type became the leading cause of land use type selection. Inner city area had very low forest coverage because of its high exploitation value, and the ecological value of the outskirts within 10 km beyond the urban fringe was comparatively outstanding, with the forest coverage increased significantly. The forest coverage declined with the increasing distance to urban, because of the dominant station of the production value.

Key words: root biomass, root morphology, autotrophic respiration., nitrogen addition, forest ecosystem