Abstract: Mian Mountain is located in the northern of Taiyue Ranges and the middle south of Shanxi, at 36°50′N，112°5′E. In this paper, the niche breadth and niche overlapping of 25 dominant populations of vegetation in Mian Mountain, Shanxi, were studied by using Shannon-Weaver index and Portraits’s method. The result indicated that the niche breadth of Quercus liaotungensis (2.458 7), Prunus davidiana (2.342 2), Spiraea, pubescens (2.306 1), Carex lanceolata (2.518 7) and Artemisia brachyloba (2.218 2) were more than that of other species because these species had wide ecological amplitude, and extensive adaptation to environment, which were constructive or dominant species in the communities. There was not completely general overlapping among all 25 species because of their different biological characters and different adaptation to environment. In the arborous layer, there was less niche overlapping between species-pairs except Q. liaotungensis. The niche overlapping between Abelia biflora and S. pubescens (0.663), P. davidiana and Lespedeza bicolor (0.587) were more than that of other species-pairs in the shrub layer. The niche overlapping between C. lanceolata and Phlomis umbrosa (0.339), A. gmelinii and A. brachyloba (0.245) were more than that of the other species-pairs in the herb layer. The species-pairs having more niche overlapping had similar biological characters and similar adaptation to environment; on the contrary, those having less niche overlapping had different biological traits and different adaptation to environment. For example, A. biflora and S. pubescens, C. lanceolata and Phlomis umbrosa were shade-tolerant plants and had some shade tolerance, otherwise P. davidiana and L. bicolor, A. gmelinii and A. brachyloba were sun plants.

Key words: Mian Mountain, dominant population, niche breadth, general overlapping, specific overlapping