Study On The Determination Of Degradation Gradient In The Alpine Steppe Of Bayanbulak

In this paper,the Bayanbulak alpine steppe grassland was taken as the research object.Through field survey sampling and indoor analysis from 2015 to 2016,the composition and structure characteristics of the phytocoenosium,the physicochemical characteristics of the soil were analyzed and studied,and an indicator system for vegetation and soil was established.The grassland degeneration gradient was divided by using systematic cluster analysis method.The vegetation and soil factors under different degeneration gradient were conducted the fuzzy comprehensive evaluation,and then the difference evaluation coefficient of different degeneration degree was obtained,which provided a theoretical basis for the rational use and protection of grassland.Conclusions are as follows:1.The retrogressive succession process of Bayanbulak alpine steppe grassland can be divided into four gradients: Non-degradation grassland,Light-degradation grassland,Mid-degradation degraded grassland and Heavy-degradation grassland.With the intensification of grassland degradation,the composition and structure of the phytocoenosium changed significantly.The importance value of the main plant species Stipa purpurea decreased,and the vegetation height,coverage,density,and above-ground biomass gradually decreased.The similarity between sample plots within the same degeneration gradient was large,and the similarity between sample plots within different degeneration gradient was small.The index of the plant ? diversity decreased significantly,while the ? diversity index was gradually increasing;the niche overlap between species with large niche breadth was also larger.2.The physicochemical property of soil changed significantly within 0 cm to 10 cm of the soil surface.As the degradation degree of the grassland increased,the unit weight of the soil surface increased significantly with the water content decreasing significantly,and the soil organic matter and total nitrogen content continued to decline;the contents of alkali-hydrolysable nitrogen,rapidly available phosphorus and rapidly available potassium changed significantly,and the p H value and conductivity did not change significantly.3.Methods of filtrating and establishing the index system of vegetation and soil were different.The vegetation index system can use the one-way variance to filtrate the indicator with significant differences,whereas soil indicators needed to be conducted factor-analysis to extract factors with the characteristic value greater than 1,and then through the principal component to screen and select main indicators of contribution,finally the soil indicator system was established.4.Based on the fuzzy comprehensive evaluation of the vegetation-soil index system,the difference evaluation coefficients were obtained: Large Yurdusi alpine steppe grassland was slightly degraded with the index of 0.7046,moderately degraded of 0.6489,severely degraded of 0.5720.Small Yurdusi alpine steppe grassland was slightly degraded with the index of 0.8596,moderately degraded of 0.6714,and severely degraded of 0.5560.