Vertical distribution patterns of the seed plant flora in the middle section on the southern slopes of the Tianshan Mountains in Xinjiang,China

Studies on the vertical distribution pattern of plant diversity and its maintenance mechanism can effectively reveal the distribution characteristics of plant species diversity and its environmental impact factors. Furthermore, such studies can provide a theoretical basis for the sustainable development and utilization of species resource protection areas. Based on field investigations, reference plant specimens, and related literature data, the floristic characteristics of wild seed plants along altitudinal gradients and the environmental impact factors in the middle section of the southern slopes of the Tianshan Mountains in Xinjiang (China) were systematically analyzed. Results showed that species richness at the family, genus, and species levels first increased and then decreased at the regional scale. Specifically, species richness showed a unimodal distribution, with the peak observed at mid to low elevations ranging from 1900 to 2000 m. Different plants life-forms demonstrated different change patterns along the altitudinal gradient. Plant diversity, including that of trees, annual herbs, vines, and parasitic plants, decreased with the increase in altitude. The richness of shrubs, perennial herbs, and biennial herbs showed unimodal change patterns. From the perspective of the geographical composition of flora, the cosmopolitan geographical components showed a slow unimodal trend along the elevational gradient; the temperate geographical components increased slowly along the elevational gradient; the ancient Mediterranea geographical components (T_dzh) showed a double-peak change pattern along the altitudinal gradient; the tropical geographical components (T_rd) showed a gradual decreasing trend with the increase in elevation; and the overall distribution trend of the East Asian geographical components (T_dy) demonstrated a double-peak distribution pattern with the increase in altitudinal gradient. These distribution patterns are compatible with the local climatic conditions as well as the changes in heat and moisture along the elevational gradient.