Classification of Range Site and Ecosystem Health Assessment in Hulunber Steppe
According to the vegetation, soil and terrain characteristics of grassland, Hulunber Steppe was divided into eight representative range sites in this experiment. A grazing gradient series of wavy high plains-the dark chestnut soil-Leymus chinensis meadow steppe range site was selected, and based on the quantitative division of grazing intensity, the influence under different grazing intensity (light grazing (LG), moderate grazing (MG) and heavy grazing (HG)) on grassland ecosystem structure and function were analyzed, and the illegibility mathematical method and CVOR (Condition, Vigor, Organization, and Resilience) method were used to evaluate the healthy condition of grassland ecosystem. The main results were as follows:(1) The different range sites could belong to the same grassland type, but all range sites have great difference in the numbers of the plant and the grassland productivity. Therefore, the determination of the rational grazing intensity should be founded on the rational division of range site.(2) The grazing intensity has great influence on grassland vegetation cover and the productivity, the change trend in different grazing gradient is:LG>MG>HG. As the grazing intensity increased, the quantity of plant root has no significant change (p>0.05), but showed a decreasing trend.(3) Grazing intensity has a significant influence on grassland biodiversity, when the grazing intensity increased, a diversity index decreased, and the value was biggest in the LG treatment, which supported the "moderate interference theory";βdiversity index increased with the increased of grazing intensity, which indicated the plant species composition changed with the increasing of grazing intensity, and promoted the retrograde succession in this grassland ecosystem.(4) With the increasing of grazing intensity, soil bulk density increased, the soil became more compacted, the also increased, but the clay decreased; with the increasing of the soil depth, the small gravel increased, while silt particle decreased; soil pH increased whereas soil organic matter, soil nitrogen and soil phosphorus significant (P<0.05) decreased with the increasing of grazing intensity, but the soil total potassium, available nitrogen, available phosphorus and available potassium had no obvious changes occurred under different grazing intensities (p>0.05).(5) The number of soil microorganisms reduced with the increasing of grazing intensity. The soil microorganisms biomass showed a decreased trend, but the change was not significant (p>0.05).(6) Plant community above-ground biomass, under-ground biomass, soil organic matter, soil total phosphate, soil total potassium, soil pH and soil sandy particle were selected to calculated the grassland ecosystem healthy indexes under different grazing intensities by the illegibility mathematical method and CVOR evaluation method. The evaluation values using illegibility mathematical method were as follows:the evaluation index is 1 in the LG treatment, it is 0.90 in MG treatment, while it is 0.62 in HG treatment; whereas the results by CVOR evaluation method were as follows:the evaluation value is 1 in LG treatment, and 0.87 in MG treatment, while it is 0.58 in HG treatment.