Aims The community assembly mechanisms are among the focal topics in ecological studies. In Changbai Mountains Nature Reserve, there is an intact primary broadleaved-Korean pine forest ecosystem. With increasing loss of species diversity in recent years, study that explores the community assembly mechanisms in this region is particularly important.
Methods This study was conducted in three large permanent plots, each of the size 5.2 hm 2, along suessional stages (secondary poplar and birch mixed forest, PBF; secondary mixed conifer and broad-leaved forest, CBF; and primary Tilia amurensis-Pinus koraiensis mixed forest, TKF) in Changbai Mountains. Six functional traits of major tree species were measured, including leaf area, specific leaf area, leaf thickness, leaf nitrogen content, leaf phosphorus content, and maximum tree height. Changes in the spatial values of community traints were analyzed at different spatial scales (5 m × 5 m, 10 m × 10 m, 20 m × 20 m, 30 m × 30 m, 40 m × 40 m, 50 m × 50 m and 60 m × 60 m). By comparing the observed values with expected values of null models, the community assembly mechanisms in temperate forests of Changbai Mountains were explored.
Important findings Results show that the size of species pool has an important impact on the outcome; in a larger species pool, the environmental filtration has a significant impact. At the plot level and for early and intermediate stages of succession, the observed spatial values of community traits do not significantly differ from the expected values. At the late successional stage, the observed spatial values of community traits were greater than the expected values. The analysis of multiple community functional diversity indices shows that the combined processes of habitat filtring and competitive exclusion are the main determinants of the species composition of the climax community in this region. In the early successional stage, large numbers of species are immigrated, and there are strong resource competitions among the species within a community. With progressing succession, some species are excluded, species maintained in the community show significant niche differentiations, and competition is the main mechanism species coexistence.