Results
Diversity index calculation results and analysis of variance
The Simpson index analysis results show that compared with the control group sample, the test group showed a decline in the overall decline (Table 1) as the test group increased, and the differences between different gradients were significantly (Table 2). The differences between different research sites are significant, but the differences between seasons are not significant, and the laws of different research sites on gradients are different. Simpson of DL and HL showed a trend of first decreasing and then increasing on the grazing gradient, Simpson of EE showed an overall decreasing trend on the grazing gradient, Simpson of WA showed an overall fluctuating trend on the grazing gradient, and Simpson of SP showed an increasing trend on the grazing gradient, especially in the rainy season. Shannon index analysis showed that Shannon of WA showed the maximum value, while Shannon of SP showed the minimum value. In the study of grazing gradient, Shannon’s change characteristics were consistent with Simpson’s, that is, diversity index showed a significant negative correlation with grazing time, but the difference between seasons was not significant, and different research sites had different change rules on grazing gradient. For Simpson and Shannon indices, the interaction between the study site and grazing gradient, the study site and seasonal factor, and the seasonal factor and grazing gradient were all significant. In addition, the Pielou index of sites fluctuated across grazing gradients, but the differences between gradients were significant, while the differences between seasons were not significant. For Pielou index, the interaction between site and grazing gradient and seasonal factors and grazing gradient were significant. The interaction of the three factors of the study site, grazing gradient and seasonal factors had significant effects on the three diversity indexes.
Table1 Simpson, Shannon and Pielou index of each study sites along grazing gradients for dry season and rainy season. DL (Duo lun), EE (Er er duo si), HL (Hai La er), SP (Sha po tou), WA (Wu lan aodu).