Characterization of the spatial distribution of tree species within forest stands is a focus of global research in forest ecology. The tree arrangement provides forestry ecologists significant information on ecological processes such as competition, facilitation, mortality, and dispersal, which tend to follow specific types of spatial patterns in a forest stand. Assessment of inter-and intraspecific interactions of tree species in forest stands that reduce growth and induce mortality, or enhance establishment and growth, has important consequences for both forest dynamics and management. In addition, the biomass ratio distribution of various dominant tree species is a synthetic reflection of the community structure and function in interspecific relationships, niche differentiation, and population dynamics. The objective of this study was to reveal spatial associations of dominant tree species in a subtropical evergreen deciduous broad-leaved forest in southeast China, and to quantitatively identify their ecological relationships and explain possible causes for their successful coexistence in these forest ecosystems. To accomplish the objective, niche breadth, niche overlap, and interspecific associations were used to analyze the inter-and intra-specific interactions of trees based on field data collected from forest permanent plots (1 hm²) in the National Nature Reserve of Mount Tianmu, Zhejiang Province. Furthermore, the biomass structure of the stand was studied at the community level. Field surveys of the forest permanent plots were conducted in 1996 and 2012, respectively. Field measurements showed that the niche breadth index of the dominant species Cyclocarya paliurus and Liquidambar acalycina decreased; on the contrary, that of Cyclobalanopsis myrsinifolia and Lithocarpus harlandii increased. Moreover, the niche overlap degree of the dominant species in 2012 was higher than that in 1996, which showed that the sharing and utilization of resources was higher in 2012. Species with similar biological features, ecological adaptability to the habitat, or a higher degree of niche overlap tended to be positively related, whereas those with different biological features, adaptability to the habitat, or existing interspecies competition tended to be negatively related. The test showed that positive correlations of the majority of the dominant species-pairs in 1996 and 2012, accounting for 48.48 and 71.21%, respectively, were followed by negative correlations of dominant species pairs accounting for 31.82% in both 1996 and 2012. Only some species pairs displayed no correlations in 1996. The results showed that all the dominant species showed similarity and niche overlap adaptability to the community environment and the ecological characteristics of the subtropical evergreen deciduous broad-leaved forest were affected by niche breadth, proportional similarity, and overlap in vegetation succession. The biomass of the trees in which diameter at breast height (DBH) was ≥ 10 cm decreased from 151.03 Mg in 1996 to 148.53 Mg in 2012. The biomass of the dominant species in which DBH was 5-10 cm in 2012 was 10.03 Mg, which suggested considerable potential growth. Our results explained the successful coexistence of dominant tree species at the study site and highlighted detailed tree-tree interactions of the species in the subtropical evergreen deciduous broad-leaved forest.