Effects Of Different Grazing Intensities On Vegetation And Soil In Stipa Breviflora Desert Steppe

To explore the effects of different grazing intensities on vegetation characteristics and soil physical–chemical properties, plant community species composition, quantitative features, community diversity, the above ground biomass, litter, below ground biomass, soil machinery composition, soil compactness, soil bulk density, soil porosity, soil moisture content, soil total and light fraction organic carbon and nitrogen contents, soil total and available phosphorus, potassium contents and the trends along with the change of grazing intensity were studied through field investigation, sampling and laboratory analysis. We considered four different grazing intensities on a Stipa breviflora desert steppe: heavy grazing(HG), moderate grazing(MG), light grazing(LG), and an area fenced to exclude livestock grazing as the control(CK). Applying for the method of principal component analysis and fuzzy mathematics comprehensive evaluation, this paper had synthetically evaluated the 11 "grass" system indicators and 18 "soil" system indicators. This information should provide a scientific basis for protecting grassland, and for maintaining and improving the adaptive management of grassland ecological production functions. The results showed that:(1)Grazing changed the plant community species composition and its important value, community structure, community diversity. The plant community structure, productivity and diversity performance were not synchronous with increasing grazing intensity. Various plots were dominated by perennial herbaceous plants. Important values in all species showed a trend of dispersion first and then concentration with increasing grazing intensity. Annual or perennial herbs and dwarf shrubs appeared in heavy grazing intensity. The important value and proportion of fine forages grass was significantly decreased, the quality of grassland resources declined. Plant community height, coverage, biomass and litter were significantly reduced, while community density showed the opposite trend with increasing grazing intensity. Underground biomass from deep to shallow distributed in "T" shape. Margalef index in moderate grazing intensity was the largest. With increasing grazing intensity, Shannon-Wiener index, Simpson index and Pielou index all showed increasing trend.(2)The soil particle size was highest in silt content, the soil texture was sandy loam. Grazing made the soil particle coarse, the surface soil was more obvious. With increasing grazing intensity, 0–10 cm soil compactness showed increasing trend. Different grazing intensity had significantly effects on 0–30 cm soil bulk density and 0–40 cm soil porosity in each soil layer. The size sequence of 0–40 cm soil average moisture content was CK>LG >MG>HG.The phosphorus content of grassland in study area was relatively low. Different grazing intensity had significantly effect on only 0–10 cm soil total and available phosphorus contents. Soil total and available phosphorus contents showed decreasing trend with increasing grazing intensity. Different grazing intensity had no significantly effect on total potassium content, and had significantly effect on available potassium content.With increasing grazing intensity, soil carbon and nitrogen contents increased firstly and then decreased. 0–40 cm soil light fraction organic carbon and nitrogen contents were fluctuated in 0.26~1.92 g/kg, 0.02~0.13 g/kg, respectively. The soil total organic carbon and nitrogen stores of different grazing intensities in 0–40 cm were significantly different, expressed as LG>MG>CK>HG, LG>MG>HG>CK, respectively. The soil light fraction organic carbon and nitrogen stores in 0–40 cm were LG>MG>CK>HG. Compared with soil total organic carbon and nitrogen, light fraction organic carbon and nitrogen was more sensitive to different grazing intensities, with large variation range among different grazing intensities. Light and moderate grazing was contributed to the accumulation of soil organic carbon and nitrogen.(3)According to the investigation of vegetation characteristics and soil physical– chemical properties, the index system was established from two angles of "grass" system and "soil" system, principal component analysis and fuzzy mathematics comprehensive evaluation method were applied to synthetically evaluate and analyze the ecosystem’s health condition of Stipa breviflora desert steppe under different grazing intensity. The results were slightly different, but both of them reflected the disturbance of different grazing intensity made grassland ecosystem health change. With increasing grazing intensity, the principal component analysis of grassland ecosystem was 187.518, 173.507, 133.134 and 96.674 respectively. The ecosystem’s health condition of light, moderate and heavy grazing intensity of Stipa breviflora desert steppe were 92.53%, 71.00%, 51.55% of control. With increasing grazing intensity, the fuzzy mathematics comprehensive evaluation of grassland ecosystem was 0.800, 0.803, 0.745 and 0.678 respectively. The ecosystem’s health condition of light, moderate and heavy grazing intensity of Stipa breviflora desert steppe were 100.39%, 93.20%, 84.75% of control. The ecosystem’s health condition of light grazing intensity was better than control, which was conducive to the overall situation of grassland ecosystem. In conclusion, moderate grazing could improve the community diversity, the proportion of fine forage grass, soil nutrients, so that the grassland ecosystem was still in a healthy and stable state.