Abstract: In this paper, an index system based on topography, vegetation, climate, and social-economic data was built to assess the ecological security of Wenchuan County in Sichuan Province, and Geographical Information System technology and Principal Component Analysis method were used for the ecological security assessment of 119 catchments in the County. The results showed that (1) the ecological security in the heavy debris flow regions was closely related to topography, and unreasonable human disturbance greatly affected the ecological security and ecosystem stability, (2) the areas of insecurity, relative insecurity, and critical security made up about 41.17% of the total area, and most of them were along Minjiang River, (3) the grading of ecological security index was consistent with the actual status by validation.

Key words: Cuscuta japonica, Parasitism, N content of hosts, Selection behavior, Secondary metabolites