Altitudinal patterns of plant species diversity on the southern slope of Mt. Shennongjia, Hubei, China

The southern slope of Mt. Shennongjia has long been viewed as an important boundary for China's vegetation regional division. In order to explore the altitudinal patterns of plant species diversity in this area, we sampled 50 plots along an altitudinal gradient on the southern slope. Species richness, intensity of flora differentiation, floristic composition and life forms were analyzed. Quantitative classification and DCA ordination were also applied to the sample plots. Major results were: (1) the vertical vegetation spectrum was evergreen broad-leavee forest (below 900-1000 m a.s.l.), mixed deciduous and evergreen broad-leaved forest (1000-1700 m), deciduous forest (1600-2100 m), mixed coniferous and deciduous forest (2000-2400 m), and subalpine coniferous forest (above 2300 m a.s.l.). (2) Evergreen and deciduous broad-leaved tree species were almost equivalent in quantity and importance values in the basal vegetation zone. (3) The altitudinal pattern of plant species diversity showed a unimodal pattern, peaking at 1400-1500 m a.s.l. Mixed forest types have relatively higher α diversity and more intensive flora differentiation than the other types. (4) Temperate plants dominated the flora. With an increase of elevation, the number of cosmopolitan genera increased, while subtropical types and East Asian types decreased. Chinese endemic genera were limited to the area below 2000 m a.s.l. (5) Species richness of pteridophytes decreased with increasing elevation, while that of woody plants peaked in mixed evergreen and deciduous forest. Species richness of herbaceous did not correlate with elevation.