Grazing livestock species composition influences community assembly and determines scale-dependent plant diversity

Grazing by domestic herbivores such as cattle and sheep is a major driver of grassland biodiversity. However, it remains unclear how livestock composition influences community dynamics and consequently shapes plant diversity across scales. Here, we conducted a 5-year livestock grazing experiment with continuous in situ vegetation monitoring by manipulating the grazing ratio of cattle and sheep in a meadow steppe of northern China. We found that all mixed grazing of cattle and sheep can continuously improve the α and β diversity of plants. Analysis of species dynamics within permanent quadrats showed that the number of newly colonizing species gradually increased as the proportion of grazing cattle increased, leading to higher plant α diversity under cattle-dominated grazing. By contrast, β diversity was higher under sheep-dominated grazing. Furthermore, linear mixed-effects models indicated that grazing effects on α diversity were primarily associated with shifts in community dominance, whereas β diversity responded to both community dominance and soil nitrogen heterogeneity, the latter playing a stronger role. These mechanisms were expressed differently by livestock species: relative to sheep, cattle more strongly promoted competitive release of dominant species, thereby increasing plant α diversity, while sheep were more effective at generating soil resource heterogeneity and enhancing environmental filtering, leading to higher plant β diversity. Our study provides important mechanistic insights into how livestock species composition affects plant diversity at different scales. This presents a novel perspective on the need for precision control of grazing livestock composition to optimize grassland management for diversity conservation.