Patterns of woody plant species diversity along environmental gradients on Mt.Taibai, Qinling Mountains

The variation of species diversity along ecological gradients is one of the focuses in the studies of biodiversity. Incorporating multiple interacting resource gradients, altitude gradient may be a decisive factor determining spatial patterns of species diversity. The Qinling Mountains represent the ecotone between warm temperate and subtropical zones in east China, and also play an important role in the study of vegetation differentiation between North and South China. Based on 83 plots of 600 m2 along two altitudinal transects between 1200 m and 3750 m a.s.l. on southern and northern slopes of Mt. Taibai, Qinling Mountains, Central China, we applied multivariate and traditional approaches to analyze the altitudinal patterns of woody plant diversity. The data matrix composed of 192 woody plants from 83 plots was subjected to TWINSPAN and DCA. The classification and ordination of the samples indicated that altitude and mean annual temperature (MAT) were the primary determinants of the floristic composition, followed by exposure and relative humidity (RH). In contrast, slope played a minor role in the determination of community distribution. Species richness and diversity of tree and shrub layers declined monotonically with elevation, which reflected decreasing temperature, while the evenness of each community changed little along the altitudinal gradient. With regards to environmental variables, species richness and diversity were primarily controlled by MAT and secondarily by RH. Species diversity was higher on the southern slope than on the northern slope of Mt. Taibai, and also higher in the shrub layer than in the canopy layer. β diversity decreased with the increasing of elevation on the southern slope, while it exhibited different patterns at higher and lower elevations on the northern slope: when lower than 2800 m, no significant relationship between altitude and diversity was detected, while at higher elevations, community dissimilarity decreased with the increasing elevation, indicating that communities at lower elevations had a higher rate of floristic turnover than those at higher elevations.