Lishan Mountain，belonging to Zhongtiao Mountains，is situated in 35°16′30″-35°27′20″N, 111°51′10″-112°05′35 ″E in the southern Shanxi．It has a typical warm- temperate continental climate with abundant plant resources and high biodiversity. As an endemic to China, Juglans mandshurica is ranked the national third-class for protection of rare and endangered plants. Due to its multiple economic value, the species is shrinking and seriously influenced by human activities.
Interspecific segregation refers to extent of mosaic distributing among species, which is important to characterize community composition, structure and dynamics. In order to explore the pattern of the interspecific segregation in J. mandshurica communities, 35 quadratls were investigated in the field, and a distribution map was drawn for all trees and shrubs with an equal to or bigger than 1 cm basal diameter. The nearest neighbors of each individual were identified by using nearest neighbor method. The interspecific segregation for all species in these communities was studied by using χ2-test (including Fisher′s exact test for 2×2 contingency table), an N×N nearest-neighbor contingency table and a 2×2 nearest-neighbor contingency sub-table.
The results of χ2-test showed that there were 294 species-pair being significant segregation（P<0.05） and 6 species-pair being insignificant segregation（P>0.05）. Based on χ2 value to divide S, the interspecific segregation result indicated that there were 112 species-pair positive segregation, 28 species-pair negative and 160 species-pair random segregation accounting for 37.34%, 9.33%, and 53.33% respectively. Negative segregation appeared between dominant species and companioning species in the communities and companioning species had fewer individuals, lower coverage and similar habitat requirements with dominant species. Intensive interspecific competition resulted in mosaic distribution and fully exploiting competition for resources in speices such as J. mandshurica, Forsythia suspensa and Rhamnus davurica, Cotoneaster acutifolius. Therefore, they were apt to be negative segregation. The larger individuals being constructive or dominant species in the communities tended to be positive segregation with the other large trees and shrubs, due to their stronger capacity of adaptation and competition, such as Acer ginnala and Pyrus betulifolia. The constellation diagrams showed clearly the difference of interspecific segregation among the various species.
The result of χ2 test for N×N nearest-neighbor contingency table indicated that 25 species in the communities were mosaic distribution and overall non-segregation.
In addition, the results of species segregation suggested that the Juglans mandshurica communities in Lishan Mountain were in the early stage of succession, which was consistent with the fact that the communities were unstable due to the seriously disturbance of natural and human activities.