Recent studies have documented local鄄scale associations between tree species and habitat factors in forests worldwide. A 30 hm 2 plot (500 m 伊 600 m) was established in the Jiaohe Forestry Experimental Zone Bureau of Jilin province to study the long term dynamics of a broad鄄leaved Korean pine mixed forest. Within the plot, all free鄄standing trees and shrubs with a DBH of at least 1cm were identified, tagged and mapped, and their geographic coordinates recorded following a standard field protocol. One objective was to study mechanisms of the formation of spatial distribution patterns of understory tree species and to explore how environmental gradients influence these patterns in a broad鄄leaved Korean pine mixed forest. Based on the data from the 30 hm 2 plot, all trees with a DBH not greater than 5cm were defined as under storey trees. Only species represented by at least 300 individuals were chosen. 14 tree species representing 94. 32% of all understorey trees satisfied this condition. First, the spatial patterns of the 14 selected species were analysed at scale of 20m 伊20m cells, using Morisita忆 s index (I 啄). The results indicate that all 14 species show a clumped spatial distribution. Second, the spatial autocorrelations of the 14 species were studied at 15 distance classes using the spatial autocorrelation coefficient Moran忆s I. The results show a significant positive correlation at small distance classes and significant negative