AbstractUsing quantitative analysis (DCA and TWINSPAN), the vegetation and plant species diversity patterns along the elevation gradient in Mt. Niubeiliang, Qinling Mountains were studied based on 51 plots along two altitudinal transects between 1500 m and 2800 m on northern and southern slopes. Plant communities varied continuously along the elevation gradient. From low to high elevation, mountain oak forest, mountain birch forest, subalpine fir forests and subalpine shrub occurred on both slopes. Relationship between communities and topographic variables were analyzed by detrended correspondence analysis (DCA). Elevation was the primary determinant of floristic composition in Mt. Niubeiliang, and followed by exposure. In terms of species diversity, different patterns existed among total number of species, woody species richness and herbaceous species richness, and also between southern and northern slopes. The total number of species changed unimodally with elevation on the southern slope, peaking at middle elevations. No significant relationship between total number of species and elevation was detected on the northern slope. Woody species richness changed similarly on both southern and northern slopes, keeping stable at low elevations and decreasing monotonically with the increasing elevation at high elevations. In contrast, no significant pattern of herbaceous plant richness existed along the elevation gradient. β diversity was higher at lower and higher elevations than in the mid-altitudinal zone, indicating a more homogeneous habitat at middle elevation than upper and lower elevations. Human disturbance at lower elevation and the timberline ecotone at higher elevations may contribute to the increase of β diversity in these areas.