Rotational grazing increases purple prairie clover frequency in the rangeland plant communities under semi-arid environment

Purple prairie clover (PPC, Dalea purpurea Vent.) is a grazing tolerant perennial legume with good nutritional quality and is widely distributed across North America. Deferred rotational grazing (DR) and continuous grazing (CG) are the most widespread grazing systems on North American grasslands. We conducted a 10 yr grazing study to assess the effects of environmental factors and grazing on the frequency of PPC in plant communities. The results showed that the frequency of PPC decreased and then increased with increasing precipitation under CG (P < 0.05), while there was no significant change under DR (P > 0.05). Meanwhile, PPC frequency increased with temperature under DR (P < 0.05), but did not change under CG (P > 0.05). Both grazing systems and the number of grazing years had a significant effect on PPC frequency (P < 0.05), and there is no interaction between those two factors (P > 0.05). We found that from 2011 to 2020, the growth rate of PPC population is 18.24% and 11.69% per year under DR and CG grazing, respectively. Moreover, after 10 yr of grazing, the PPC increase in DR was 22.86% higher than that of CG. Thus, selecting the DR grazing system can increase PPC and is an effective practice for coping with environmental changes.