Interspecific segregation of species in tree and shrub layers of the Pinus bungeana Zucc. ex Endl. community in the Wulu Mountains, Shanxi Province, China

The Wulu Mountains, a part of the Luliang Mountain Range, are situated at 36 degree 23'45"--36 degree 38'20"N, 111 degree 08'--111 degree 18'E in western Shanxi Province, China. This area has a warm-temperate continental monsoon climate with abundant plant resources and high biodiversity. Appropriate conditions for the growth of Pinus bungeana Zucc. ex Endl. are limited within the Wulu Mountains which include only a part of the overall range of P. bungeana. Therefore, building nature reserves in which P. bungeana can be studied systematically is important both ecologically and academically, with the goal of studying this species in its warm temperate north China climate so it can be preserved in natural forests indefinitely. Interspecific relationships are an important factor affecting community composition, structure, function and dynamics. Interspecific segregation refers to the relative distributions of two or more related species. It reflects the degree of mixing of two species based on their interrelationships. For example, the less two species mix, the higher the degree of interspecific segregation exists. The segregation relationship between different species pairs can be helpful in revealing the phenomena of species interactions, community structure and dynamics. This relationship can be used to explore the impacts of environmental differences on species distribution. Practically, such study is the scientific foundation of species conservation, restoration and the reconstruction of degraded ecosystems. We established 55 quadrats within natural P. bungeana communities to study the intraspecific and interspecific competition relationships of nine tree species and patterns of interspecific segregation of all species in the tree and shrub layers of P. bungeana communities. Using ArcView GIS software and the nearest neighbor method, interspecific segregation was studied with an N x N nearest-neighbor contingency table, a 2 x 2 nearest-neighbor contingency sub-table, and Hegyi's competition index model for the individual tree species. The results indicate: (1) most of the species pairs are randomly segregated (80%), some species pairs are positively segregated (16.19%), and only a few species pairs are negatively segregated (3.81%). (2) There are some differences among different species in the interspecific segregation of all species. The larger individuals representing dominant species in the communities tended to be positively segregated with the other