Species richness and composition of shrub-encroached grasslands in relation to environmental factors in northern China

Shrub encroachment has taken place in many of China’s northern grasslands. This study attempts to answer the following questions: which plant communities are present in these shrub-encroached grasslands (SEGs)? What are the species richness and composition of these communities? Which environmental factors determine the spatial distribution thereof? We investigated the community characteristics of 255 SEG plots with a size of 20 m × 20 m at 69 locations across grasslands in northern China. In each plot, paired 1-m2 quadrats were established within shrub patches and the neighbouring grassy matrix to record herb species composition. The quantitative characteristics (abundance, coverage and height) of herbs were measured in 0.25-m2 subquadrats, and soil samples were collected in the quadrats. Two-way indicator species analysis (TWINSPAN), detrended canonical analysis (DCA) and canonical correspondence analysis (CCA) were used for community clustering and ordination. The DCA and TWINSPAN results suggested that the SEGs in northern China can be divided into six community types: Potentilla fruticosa + Carex atrofusca, Spiraea hypericifolia + Festuca ovina, Caragana acanthophylla + Stipa sareptana, Caragana microphylla + Leymus chinensis, Caragana microphylla + Stipa klemenzii and Caragana tibetica + Cleistogenes songorica. At a regional scale, climate and soil nutrients controlled the spatial patterns of species richness and community composition of the SEGs in northern China. Temperature exerted a negative impact, whereas precipitation and nutrients had positive effects on species richness. Among the environmental factors used, climate was the major controller of the variations in community structure. These results provide new insights into the community composition of SEGs in China and enrich the global dataset of SEGs.