High grazing pressure accelerates changes in community assembly over time in a long-term grazing experiment in the desert steppe of northern China

Abstract

Abstract Although numerous studies have shown that grazing gives rise to community succession at the species level, there is a lack of discussion about how grazing drives community assembly based on plant functional traits in a long-term experiment. We find different grazing intensities lead to temporal effects on trait-mediated multidimensional community assembly processes, including community weighted trait mean (CWM), trait filtering, and trait distribution (divergence/convergence). CWM, trait filtering, and trait distribution of different traits transformed over the 16-years grazing experiment. Major findings include the following: (1) CWM changed rapidly under higher grazing intensity, and the removal of unsuitable traits from communities over time was accelerated with grazing intensity. (2) Patterns of trait filtering strongly depended on grazing intensity and trait types, most traits were filtered at high grazing intensity area, and relative effects of trait filtering in the community assembly process strengthened with grazing time. (3) Traits related to the cycling of biological matter more frequently diverged after long-term grazing, especially in higher grazing areas. This reflects the importance of resource capture partitioning within species, giving priority to maintaining the basic biological matter cycle of the ecosystem under the long-term nutrient deficiency experienced by plants with overgrazing. These results showed that community assembly in this vulnerable ecosystem experiencing intense grazing takes more than a decade to develop and maintain fundamental ecosystem functions, such as biological matter cycling. We are also reminded of the importance of establishing grazing intensity thresholds to maintain sustainable utilization of grasslands in the desert steppe.