Abstract:

Many competing theories exist with respect to the mechanisms behind plant community assembly. Niche theory and neutral theory are among the two most widely proposed mechanisms. In this study， we focused on herbaceous communities at different successional stages in a burned area of Picea asperata-Abies fargesii forest on the northeastern margin of Qinghai-Tibetan Plateau. We aimed to elucidate the mechanism of community assembly through calculation of dispersal-niche continuum index （DNCI） and modified stochasticity ratio （MST）. Results show that， 1） DNCI between communities of 5， 15， 23 years and Climax were -22.6169， -21.7507 and -8.2594， respectively. These values were all significantly less than 0， and indicate that the main driving effect of herbaceous community assembly at different succession stages was the dispersal process； 2） MST values of both the 5 yr-Climax group and the 23 yr-Climax group were above the 50%， which indicated that the stochastic process dominated the community assembly in both groups. For the 15 yr-Climax group， the MST value of 15 yr was 0.6664， and the MST value of Climax vegetation was 0.4927， indicating that the plant community assembly of 15 yr is dominated by stochasticity， while the assembly of Climax community is deterministic； since the MST value of 15 yr is much higher than 50%， and the MST value of Climax is close to the threshold of 50%， it can also be shown that the community assembly of the 15 yr-Climax group is still dominated by stochasticity. In conclusion， in a burned area of P. asperata-A. fargesii forest on the northeastern margin of the Qinghai-Tibetan Plateau， stochasticity dispersal dominated the herbaceous community assembly.

Key words: herbaceous plant, community assembly, Picea asperata-Abies fargesii forest, burned area, northeastern margin of Qinghai-Tibetan Plateau