Abstract: The natural needle and broad-leaved mixed forest is a vertical zonal vegetation in the Shennongjia Mountains, with important ecological and economic values. To gain insights into the structure, dynamics, and the maintenance of species diversity of the natural mixed needle and broad-leaf forest community, a 1hm² forest plot was established in Shennongjia National Nature Reserve, Hubei Province. The species composition, sizeclass structure of diameter at breast height (DBH), and spatial distribution of dominant species were analyzed. A total of 5321 living individuals were recorded in the plot, belonging to 44 species, 26 genera, and 14 families. There were very few conifer species, with only Abies fargesii and Pinus armandii present in the plot. The total importance values of Abies fargesii, Crataegus wilsonii and Populus davidiana was 50.28%, and that of other broad-leaved species was 46.06%. The DBH class structure showed a reversed “J” shape with abundant saplings in the understory. Among the top three dominant species with respect to importance value, both Abies fargesii and Crataegus wilsonii had a DBH class structure of reversed “J” shape, indicating their regeneration status were good. On the contrary, the sizeclass structure of DBH of Populus davidiana was close to the normal distribution, the saplings were scarce, and the population had a tendency to decline.Abies fargesii,Crataegus wilsonii and Populus davidiana showed obvious habitat preference. With the increases of sampling scale size,Crataegus wilsonii and Populus davidiana did not change their aggregated distribution, while the spatial distribution of Abies fargesii changed from a clustered, via a random, to a uniform distribution. The species richness of broadleaved trees was higher than that of coniferous trees in the mixed needle and broad-leaved forest in Shennongjia. However, if only the top three dominant species on the importance value sorting list were considered, the importance values of needle and broad-leaved species were similar and the community structure was stable.

Key words: chlorophyll a, nutrient, Aureococcus anophagefferens