Floristic features and vegetation classification of the Hulun Buir Steppe in North China: Geography and climate-driven steppe diversification

摘要

This study aims to present a comprehensive description of the plant communities of the Hulun Buir Steppe based on floristically complete vegetation records as a baseline reference for future ecological and palaeoecological studies. We identify the main vegetation types in the Hulun Buir Steppe, provide their formal definitions and describe their species composition, habitat affinities and distributions. Floristic features (including floristic composition, life form and plant water ecotypes, floristic geographical elements) were also assessed. We recorded a total of 765 vascular plant taxa belonging to 68 families and 327 genera. The Hulun Buir Steppe indicates typical temperate steppe vegetation where the most frequent life form is hemicryptophytes with the maximum number of species. The most frequent water ecotype of Hulun Buir Steppe is typical-mesophytes. And the most frequent geographical element is the East Paleo-Arctic element. According to China vegetation classification system (China-VCS), the classification of 371 relevés resulted in assignment into 31 formations (Form.) grouped into threeVegetation-types and eleven Vegetation-subtypes. Hulun Buir Steppe vegetation classifications were described for the first time based on complete floristic data and community survey data. Our conclusions show that among the 765 vascular plant taxa, the main plant group among all vascular plants in terms of species numbers comprises dicotyledons, followed by monocotyledons and pteridophyta, with gymnosperms demonstrating the lowest numbers. The life forms are dominated by hemicryptophytes, the water ecological type is dominated by typical-mesophytes, and the floristic geographical element is dominated by the East Palaeo-Arctic element. Plant community types are diverse and can be conceptualized as meadow steppe, typical steppe and desert steppe. The vegetation types of the Hulun Buir Steppe are mainly affected by geographic variables and climatic factors: the geographic variables are mainly affected by the change in precipitation caused by the longitude gradient, while the climatic factors are mainly affected by the East Asian winter monsoon caused by the Siberian High and the East Asian Summer Monsoon caused by the Western Pacific Subtropical High. In addition, the surface runoff caused by forest snowmelt and seasonal rainfall, as well as the distance from the Greater Khingan Mountains, also affect the distribution of the Hulun Buir Steppe vegetation.