| As one of the most important concepts of modern ecology, niche has allured ecologists to approach and been applied in every field of ecology since it was put forward in 1917. The theory and concept of niche has become the main idea to explain the interaction among organisms or between organisms and their environment, especially among interspecies competition, coexistence, resource allocation and resource utilization, and niche overlap, separation and replacement problems and so on.There were six dominant tree species named Pinus armandi, P. densata, Picea likiangensis Var. linzhiensis, Sabina saltuaila, Abies georgei Var. smithii and Quercus semicarpifolia occuping the arborous layer of the virgin forest scattering in the Sejilashan at the southeast of Tibet. A. georgei Var. smithii and P. likiangensis Var. linzhiensis occupied greater niche width, S. saltuaila and P. armandi occupied less niche width, P. densata and Q. semicarpifolia were in the middle of the complex environmental gradients. Among these trees, P. likiangensis Var. linzhiensis and Q. semicarpifolia shared the most niche overlap, P. likiangensis Var. linzhiensis and A. georgei Var. smithii shared the second, but the niche overlap of S. saltuaila and Q. semicarpifolia, S. saltuaila and P. armandi, S. saltuaila and P. densata was 0.We Selected the altitude, slope gradient, the slope aspect, slope site and A soil layer as the spatial resource axes and analyzed how these trees utilized the resource. In the 5-dimension resource space, A. georgei Var. smithii and P. densata occupied greater niche width; P. likiangensis Var. linzhiensis and Q. semicarpifolia after them; S. saltuaila and P. armandi have less niche width.Through measuring the dominant tree species' niche, we can have a sight about that the spatial distribution pattern, the ability of sharing resources, and relationship along these trees. This work was the preliminary work for further researching the especial forest ecosystem in this especial area.
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