Cleistogenes songorica
Grazing intensity, spatial scale and their interaction had significant effects on the density of C. songorica population (Table 2,P < 0.05). The F value of spatial scale factor was larger (F = 374.19), which indicated that the response of density to spatial scale factor was more sensitive than that of grazing intensity.
The changes of population density under different grazing intensities and spatial scales were shown in Fig. 3. The density of C. songorica increased with the increase of grazing intensity (Fig. 3A), and there were significant differences between CK and HG, LG and HG, MG and HG (P < 0.05), which also indicated that the density difference of C. songorica only appeared in HG, implying that the heavy grazing did induce fragmentation of the plant habitat. Heavy grazing led to a significant increase in the density of C. songorica . Although there was no significant difference in the density among CK, LG and MG treatments, there was still a trend of density increase with the increase of grazing intensity. The error extension lines between each treatment were long, indicating that C. songorica distribution was highly variable between treatments. The density of C. songorica increased exponentially as the scale of our sampling increased (Fig. 3B). Except for 5 cm×5 cm and 10 cm×10 cm, 20 cm×20 cm and 50 cm×50 cm, there were significant differences between the other spatial scales (P < 0.05). In fact, there is an exponential correlation between density and spatial scale of C. songorica (density of C. songorica = 0.1412+0.0026×exp (1.4189×spatial scale of C. songorica ),r 2 = 0.9994).
Table 2 Variance analysis results of the Cleistogenes songorica population