Abstract: By the method of sampling plots investigation, the tree species composition of Thuja sutchuenensis community was studied, with the dominant tree species of the community ascertained by calculating the importance value. The overall association, interspecific association, and interspecific covariation of the dominant tree species were also studied. The results showed that an overall negative association was existed among 15 dominant tree species. The pairs with positive interspecific association were Quercus semecarpifolia-Carpinus fargesiana Q. semecarpifolia-Illicium fargesii, Cyclobalanopsis jenseniana-Q. phillyraeoides, Tsuga chinensis-Sorbus wilsoniana, C. cordata var. chinensis-Acer davidii, C. cordata var. chinensis-C. jenseniana, C. jenseniana-Macrocarpium chinense, and C. fargesiana- Illicium fargesii. The interspecific association of Q. semecarpifolia with A. davidii was negative, while that of T. sutchuenensis with other species was not significant. 26 pairs of species showed a significant positive interspecific covariation, and 12 pairs showed negative interspecific covariation. The similarity of environmental resources utilization could be the reason of the positive interspecific covariation.

Key words: Competition, Fraxinus mandshurica, Larix gmelini, Pure stand, Mixed stand