Abstract: Heng Mts., Shanxi is located in the ecotone of temperate grassland zone and warm-temperate deciduous broad-leaved forest zone according to China Vegetation Regionalization. Adopting Shannon-Wiener,the niche breadth index, the article classified constructive species on both slopes into 3 ecologic groups respectively. Artemisia brachyloba, Dendranthema chanetii, Carex lanceolata and Sanguisorba alpina of the south slope, and Carex lanceolata, Denfranthema zawwadskii, Poa sphondyloes,Siline jenisseensis and Sanguisorba alpina of the north slope occupy a broader niche, showing an apparent niche generalization. By contrast, Potentilla anserine, Spiraea trilobata, Ostryopsis davidiana and Hippophae rhamnoides subsp. sinensis of the south slope, Stipa bungeana, Puccinellia distans, Artemisia brachyloba, Polygonum viviparum, Anaphalis hancockii, Spiraea trilobata, Hippophae rhamnoides subsp. sinensis and Populus cathayana of the north slope occupy a much narrower niche, which is closely related to their environment. The 16 constructive populations of the south slope form 240 species counterparts, among which 100, that’s 41.9% of the total, have niche overlaps, indicating that there exits niche overlap among the 16 species of the south slope. The 21 constructive populations of the north slope form 420 species counterparts, among which 69, that’s 16.4% of the total, have niche overlaps, indicating that there does not exit an apparent niche overlap among the 21 species. The apparent separation in ecologic niche among populations suggests a significant difference as to their utility of recourses. All of the above are caused by the evenness the south slope while the sheerness the north, which leads to a continuous spreading of vegetation on the south and many discontinuities making overlap an rare occurrence on the north because of much sharper rise of elevation. By an overall comparison and contrast of niche breadth and niche overlap of the constructive species of each slope, an establishment of Hengshan Mts. as the borderline between temperate grassland zone and warmtemperate deciduous broad-leaved forest zone can achieved more objectively.

Key words: vegetation of both slopes of Hengshan, constructive species niche breadth, niche overlap