Niche characteristics and CCA ordination of dominant species of Thuja sutchuenensis community

Using Levins, MacArthur-Levins and Pearson index methods, niche breadth, niche overlap and canonical correspondence analysis (CCA) of top 20 tree and shrub species were studied in Thuja sutchuenensis community of Dabashan Mountain, southwestern China. Results showed that:1) Thuja sutchuenensis was a dominant species in the tree layer of the community with the maximum important value (0.225 1) and niche breadth (6.704 2), and had larger niche overlap than other species (O_ij>0.123 7). It indicates that Thuja sutchuenensis has stronger ability to adapt to the environment, to compete and utilize resources in the tree layer. 2) The living conditions of Thuja sutchuenensis in shrub layer was far from optimistic. Although owning the maximum important value (0.170 1), while its niche breadth only ranked 19th (1.853 0). Also, Thuja sutchuenensis had smaller niche overlap degree(O_ij < 0.482 3) than other species, but the other species had larger niche overlap degree with Thuja sutchuenensis. Consequently, the Thuja sutchuenensis had a weaker competition ability in the shrub layer. 3) Based on the advantage species CCA sequences in the tree layer, species (Thuja sutchuenensis, Cyclobalanopsis myrsinifolia) with broad niche breadth distributed in the center of the sequence diagram; individuals (Pinus armandii, Juglans cathayensis) with narrow niche breadth located in the periphery of the sequence diagram. Combined with the niche overlap, those species (Thuja sutchuenensis-Cyclobalanopsis multinervis, Thuja sutchuenensis-Lithocarpus fangii, Thuja sutchuenensis-Rhododendron sutchuenense, etc.) with high niche overlap degree usually close to each other in the sequence diagram. Concerning the 9 sequencing environmental factors, slope degree, pH and soil water content had great influence on the survival of Thuja sutchuenensis. 4) Habitat specialized and artificial destruction are two significant reasons to result in the narrow distribution range, patchlized shape, population renew difficulty and endangerment of Thuja sutchuenensis.