Conclusions
The conclusion of this study is that the inter-specific relationship of dominant grass species is not only affected by grazing intensity, but also by initial population density and sampling scale. There are three results. First, the increase of grazing intensity generally increased the density of S. breviflora and C. songorica populations in a Inner Mongolian desert steppe. We also noted that this relationship was particularly sensitive to spatial scale, and observed that ‘density’ increased with the increase of our sampling scale (moving from 5 cm×5 cm to 100 cm×100 cm sampling quadrats). Secondly, with the increase of grazing intensity, the affinity of S. breviflora and C. songorica increased greatly at the small scale, though this affinity was not obvious when observing the entire plot, further suggesting that sampling size may induce bias in these measurements. Finally, with the increase of grazing intensity, the competition between S. breviflora and C. songorica increased first and then decreased, that is, heavy grazing led to the decrease of inter-specific competition between the two species. Inter-specific relationship is the basis for exploring the stability and evolution of plant communities. The change of inter-specific relationship of dominant grass species in desert steppe may further affect the stability and sustainability of grassland ecosystem, and our observations provide a theoretical basis for formulating reasonable and scientific grazing practices in S. breviflora desert steppe.