Abstract: Intraspecific and interspecific competition intensities of the Celtis sinensis stands from Laoshan National Forest Park and the Zijin Mountain in Nanjing, Jiangsu were quantitatively analyzed using Hegyi’s single-tree competition index model. Phylogenetic trees of the main tree species involved in the competition were constructed with the Phylomatic and PhyloCom. Meanwhile the modified M. Godron method was applied to analyze community stability of the C. sinensis stands.Results show that the intraspecific competition intensity of the C. sinensis trees decreases gradually with the trees growing and rising in diameter at breast height(DBH) class. C. sinensis compete with other trees in the forest, showing a decreasing order of Quercus acutissima > C. sinensis > Robinia pseudoacacia > Cornus walteri > Quercus variabilis in Zijin and of Broussonetia papyrifera > C. sinensis > Dalbergia hupeana > Robinia pseudoacacia > Platycarya strobilacea in Laoshan in competition intensity.  No matter  whether in Zijinshan or in Laoshan, the intraspecific competition is lower than the interspecific competition, which may be related to the biological characteristics, habitat heterogeneity and phylogeny of the dominant species of the forests. A power function relationship is found conforming to the one between competition intensity and DBH of the objective trees. When C. sinensis grows over 20 cm in DBH, its competition intensity changes little, so the model can be used to predict efficiently intraspecific and interspecific competition intensity within the forest. The analysis of community stability using the modified M. Godron method indicates that the C. sinensis stands, in both Zijin and Lanshan are still in an unstable state.

Key words: Celtis sinensis forest, competition intensity, community stability, Nanjing