Objective To analyze the dynamic changes of species composition and plant biodiversity at different succession stages in the burned area of Picea asperata- Abies fargesii forest on the northeastern edge of the Qinghai-Tibetan Plateau for providing a scientific reference for scientific management of plant communities in burned areas..

Method Using the method of space-for-time substitution, plant communities in four different succession stages were selected on the northern slope of Mount Dieshan, including5-year post-fire succession (5 a), 15-year post-fire succession (15 a), 23-year post-fire succession (23 a) and the climax forest community (Climax). The species composition of plant communities, and species important value, α diversity index and β diversity index were calculated.

Result 1) The species richness of the community and the number of plant decreased during the succession of plant community in the burned area. Among them, species richness and the number of plant (4 008 ± 298 individual ·400 m⁻²) in the community 5 a were the largest, but those in the Climax community were the least (1 759 ± 90 individual ·400 m⁻²). The Margalef index and the Shannon-Wiener index of the 5 a community in the herb layer, the Climax community in the shrub layer and the tree layer were the largest. 2) Based on the important value, the communities of 5 a, 15 a, 23 a and Climax in four different stages can be named as Rosa sweginzowii + Fargesia spathacea + Carex crebra, Lonicera tangutica + Salix heishuiensis + Carex crebra, Picea crassifolia-Betula albosinensis + Rosa sweginzowii + Carex crebra, Abies fargesii-Picea asperata + Lonicera tangutica + Carex crebra community, respectively. 3) The heterogeneity of herbaceous community at different succession stages were 5 a (0.07) ＜ 15 a (0.12) ＜ 23 a (0.19) ＜ Climax (0.22). 4) The plant abundance in stages 5 a, 15 a and 23 a presented the geometric progression distribution, indicating that the environmental conditions were conducive to herb growth and species with deterministic niche occupied a dominant role in community construction. The plant abundance in Climax stage showed an “S” distribution which belongs to late successional community because the "intermediate-type" species occupied the vast majority of the community. 5) According to the β diversity index, the shrub layer of 4 succession stages could be divided into initial shrub (5 a) and stable shrub (15 a, 23 a and Climax), and the herb layer could be divided into drastically changing layer (5 a and 15 a) and stable layer (23 a and Climax).

Conclusion With the succession of plant communities, the species richness decreases in the burned area of Picea asperata- Abies fargesii forest on the northeastern edge of the Qinghai-Tibetan Plateau, and the similarity between communities become closer. The succession of plant communities in the burned area is a positive succession, and the succession process is shrub- deciduous broad-leaved forest - coniferous forest - Picea asperata-Abies fargesii forest.