Evaluation Of Grassland Degradation In Mountainous Grassland On Northern Slope Of Tianshan Mountains

As an important livestock production base and a component of grassland ecosystem on the Northern Slope of Tianshan Mountain,the mountain grassland plays an extremely important role in regulating climate,developing livestock and maintaining ecological balance.In recent years,grassland has been degraded in different degrees due to overgrazing and unreasonable utilization.In this study,the representative Stipa Capillata and Festuca Ovina grassland in the middle and eastern part of the Northern Slope of the Tianshan Mountains were selected as the research object.According to the principle of index selection,frequency statistics and other methods were used to select degradation indexes from vegetation and soil,and principal component analysis was used to optimize degradation indexes.The grassland degradation evaluation system was established,and the grassland degradation grade based on the comprehensive grassland degradation index(GDI)was constructed by cluster analysis.The vegetation characteristics and soil physical and chemical properties of grassland with different degradation degrees were analyzed,and the adaptability changes of grassland vegetation and soil with the increase of grassland degradation degree were discussed.The results can provide scientific basis for rational utilization and sustainable development of grassland.The main conclusions are as follows:(1)Through principal component analysis on the two aspects of vegetation and soil index optimization,combined with the actual investigation,get coverage based on community,community density,aboveground biomass and underground biomass,soil bulk density,soil p H,soil organic matter,soil available nitrogen,available phosphorus and soil available potassium,a total of 10 indicators of evaluation system of grassland degradation.(2)The comprehensive calculation of grassland degradation index GDI showed that the value range of GDI was 0.150-0.802.The GDI index was clustered into four grades by cluster analysis.When GDI ﹥0.563,it is defined as no degradation.When0.377﹤GDI≦0.563,it was defined as mild degradation.When0.266﹤GDI≦0.377,it was defined as moderate degradation.When GDI≦0.266,it is defined as severe degradation.(3)The results of vegetation characteristics analysis under different degradation degrees showed that the important values of dominant species of Stipa Capillata and Festuca Ovina decreased with the increase of degradation degree,but the important values of perennial hybrid grass increased.The height,coverage and density of community decreased firstly,then increased and then decreased(P < 0.05).The height,coverage and density of each functional group did not show the same trend.The aboveground biomass first increased and then decreased.The underground biomass was significantly decreased(P <0.05),and the underground biomass was mainly concentrated in 0-10 cm soil layer.In terms of species diversity,species diversity and species richness increased first,then decreased,and then increased,while evenness increased first and then decreased,and there was no significant difference among the indices.(4)The results of soil physical and chemical properties analysis showed that the soil bulk density and p H value increased significantly with the increase of degradation degree(P < 0.05).The contents of soil organic matter and available phosphorus decreased gradually.The content of soil available nitrogen increased firstly and then decreased.The content of soil available potassium firstly decreased and then tended to be stable.