Analysis of degradation response factors of a 17-year-old pasture in the source area of the Yellow River

To study the degradation of pastures in the alpine region, a 17-year-old pasture (dominant species was Elymus nutans) in the DaWu source area of the Yellow River was studied. We investigated the soil nutrients and plant community characteristics of pastures degraded to different degrees (severe degradation, moderate degradation, and non-degradation control area), which included 18 response factors. The results showed that there was no significant difference in soil nutrients among the non-degradation, moderate, and severe degradation pastures (P > 0.05). The difference in the coverage of E. nutans, Poaceae, and forbs between the moderate and severe degradation pastures was highly significant (P < 0.01). The plant diversity index in the moderate degradation area was higher than that of the other two pastures, and there was a significant difference in the Simpson index between the non-degradation and degradation pastures (P < 0.05). The different responses of 18 factors of the degraded pasture were analysed with the random forest method. Plant community characteristics such as E. nutans coverage and reproductive branch number were found to be more sensitive to degradation than the other response factors. Poaceae coverage less than 65% could not be used as an indicator to monitor the degradation of pastures. Soil organic matter content and total nitrogen content were insensitive to the degree of degradation, which indicated that the soil physical and chemical properties of pastures had stabilised during the past 17 years. Therefore, the coverage of Poaceae plants could be used as an important evaluation base for monitoring and investigating the degradation of pastures.