Study On Succession Of Vegetation And Soil And Ecological Environmental Quality Assessment Of Desertification Grassland In Yanchi

Grassland ecosystem is the important natural resources and natural ecological barrier of Ningxia, is also a kind of typical ecological sensitive type, so its ecological status will make big effect on the entire western region. At present, the study on the ecological environmental quality and its evaluation system of the ecological sensitive types is less. Desertification grassland in Yanchi, Ningxia was taken as a study object, the desertification grassland is classified into four groups:the light desertification grassland, the moderate desertification grassland, the severe desertification grassland and the extreme desertification grassland. The typical plots which were selected for studying the characteristics of the vegetation and the soil by means of field investigation and laboratory analysis to reveal their space-time change rule and influence factors. Then establish the ecological environment quality evaluation index system of desertification grassland which suitable for the study region, and adopted comprehensive index method to evaluate the ecological environment quality of desertification grassland in study region, the main results were as follows:With the increasing of degree of grassland desertification, vegetation composition changed, perennial species gradually gave place to psammophyte annuals, shrubs and semi-shrubs increased at the beginning of the desertification, then reduced gradually.With grassland desertification aggravating, soil water content, organic matter, nitrogen content reduced; soil silt and clay fractions reduced, sand fractions increased, while changes of available phosphorus, available potassium, pH and salt content had no obvious trends. Overall, in study region, the dominant soil particle was sand, the soil moisture and nutrient contents were very low.The correlation among the indexes of the soil physical and chemical properties showed that:soil organic matter content and soil total nitrogen, alkali-hydrolysable nitrogen, water content index showed a significant positive correlation; and the bulk density was significantly negative correlation. Soil silt and clay fractions and soil water content, organic matter content, total nitrogen index showed a significant positive correlation. Total nitrogen and alkali-hydrolysable nitrogen, water content showed a significant positive correlation; and the bulk density was significantly negative correlation. Available potassium and available phosphorus were significant positive correlation. The correlation among the indexes of the soil properties and species diversity showed that the plant species richness index, Shannon-Wiener diversity index and soil moisture content showed significant positive correlation, species richness was significant positive correlation with soil organic matter. Simpson dominance index and soil water content were showed low significant positive correlation, total aboveground biomass was significantly negative correlation with soil pH.Built with16indexes were average temperature, rainfall, soil organic matter, available phosphorus, available potassium, bulk density, water content, total salt, silt and clay fractions content, vegetation coverage, total aboveground biomass,community density, community height, population density, farmer’s net income, amount of big livestock at Year-end as the ecological environment quality evaluation system of desertification grassland. Used comprehensive index method to evaluate the ecological environment quality of desertification grassland in Yanchi and divided into four ecological environment grade by the result of comprehensive evaluation. The results showed that the ecological environment quality of desertification grassland in study region were Ⅰ, Ⅱ, Ⅲ, Ⅳ grade. Used grey relationship evaluation to evaluate the ecological environment quality of the different degree of desertification grassland, the ranking of quality was:the light desertification grassland>the moderate desertification grassland>the extreme desertification grassland> the severe desertification grassland.Overall, in study region, the dominant soil particle was sand, the soil nutrient contents were very low.The desertification grassland ecological environment quality evaluation system was suitable for the study region,through the mathematical evaluation method and spatial statistics method to obtain the map of quality grade distribution, quality grade distribution and the region of ecological sensitivity transition position are highly correlated,and the distribution result is essential consistent with the actual eco-environment quality of the region.