Abstract: Subalpine dark coniferous forest is the dominant vegetation in Miyaluo forest region of the western Sichuan. To better understand species composition and community structure of subalpine dark coniferous forest in the southeastern edge of the Tibetan Plateau, a 9.6 hm² forestdynamics plot was established in Sichuan Miyaluo Provincial Nature Reserve from 2016 to 2019, following the field protocol of the Center for Tropical Forest Science (CTFS) and the Chinese Forest Biodiversity Monitoring Network (CForBio). In this study, we analyzed the floristic types, species composition, community structure, and DBH size distribution on the basis of the data collected from all living woody plants with diameter at breast height (DBH) ≥1 cm. The results showed that there were 50055 living stems in total, including 24183 independent individuals and 25872 branching or sprouting stems, belonging to 32 species, 20 genera, and 14 families. The numbers of families and genera of temperate floristic elements accounted for 64.28% and 85.00%, respectively. Juniperus squamata, Picea asperata, Berberis dictyoneura,and Buddleja forrestii were the rare species, which together accounted for 12.50% of the total species richness. Ten species with importance value (IV) >2 had a total IV value of 90.54. The IV of top four dominant species, Abies fargesiivar. faxoniana, Betula utilis, Juniperus convallium, and Ribes luridumwas 30.55, 15.74, 9.95, and 8.80, respectively. When plot area was less than 1.6 hm², the number of species increased rapidly with the increasing area. When plot area reached 6.76 hm², all of the 32 species appeared. The mean DBH of all living individuals in the whole plot was 5.29 cm. The DBH size distribution of all living individuals showed an inverse “J” type. The stems with DBH <2.5 cm represented 59.63% of the total individuals in the whole plot.

Key words: forest dynamics plot, biodiversity, floristic type, importance value, DBH size distribution.