Abstract: Based on quadrat investigation,this paper studied the species composition of alpine vegetation in permafrost region of Qinghai-Tibetan Plateau, calculated the diversity index and evenness index,and approached the effects of permafrost degradation on the species diversity. During the permafrost degradation,the family number and species richness decreased,and the hygrophytes and mesophytes were gradually replaced by meso-xerophytes and xerophytes. Permafrost degradation lowered the species diversity and primary productivity,giving negative effects on the stability of alpine grassland ecosystem. There was a close parabolic relationship between species diversity and primary productivity.

Key words: Spartina alterniflora, Emergy analysis, Added loop, Ecological engineering