Community Ecological Effect Of Grazing On Stipa Krylovii Steppe

A continuous period of four years (2006-2009) rotational grazing experiment was carried out in the summer and autumn on Stipa krylovii steppe in the central part of Inner Mongolia. In this experiment 50 2-year-old Mongolian sheep were grazed on 22.5 hm2 experimental area that was divided into 6 small plots, of which 4 are different grazing intensity,1 for free grazing and 1 for control.Whole summer and autumn grazing period was divided into five grazing cycles, each lasting 22 days, which total is 110 days.The last day of each grazing cycle,plant above-biomass, plant height, plant density and so on were measured by quadrat. Soil and underground biomass sampling were placed in the period before and after grazing. Physical and chemical properties of soil and soil microbe were analysis in the laboratory. The cutting experiment and dominant plants moisture gradient pot experiments were also carried out in 2009.With combination of plant biomass, microorgan amount, soil nutrients, soil structure and the response of plants to water were investigated to know the ecological effects of different grazing intensity on plant communities and soil.With photography and geographic information systems,the effects of grazing on the distribution pattern of plant populations and communities in different grazing intensities experimental plots had also been studied.The results show that not only the impact of grazing on single plant and soil factors, also a comprehensive ecological effects of grazing. Heavy grazing makes the decrease of plant biomass, available nutrients and microbial activity, increase of soil bulk density, and also surface layer soil particle size coarser Moderate grazing makes the above-ground biomass emerge in the effects of compensatory growth of plants. However, different plant species show different effect. Under moderate grazing, the above-biomass of Stipa krylovii shows the increase trend and the cumulative effect with experimental time.Cleistogenes squarrosa shows opposite changes, which heavy grazing made above-ground biomass of Cleistogenes squarrosa increased reflecting Cleistogenes squarrosa will replace Stipa krylovii in the degradation process of community succession. On moisture gradient, the patience of bunchgrass stipa to water stress is more strong than rhizomatous grass, which shows Stipa plants more adapt to develop in the arid and semi arid areas.The photographic images and experimental data showed that different structures of patchiness of community were formed in different grazing areas and also the different gradient of the number of patch, area, population structure, plant abundance, circumference and above-ground biomas.Ass. Stipa kryloviia and population patch become fragmentation and individual plant become miniaturization due to different grazing intensity. However, the patches in enclosed control plot were still original Ass.Stipa krylovii and Ass. Leymus chinensis.This study showed that the changes of plant patch structure in community and population pattern were the basic for population colonization and recession during succession, and also the mechanism for the succession of plant communities on grassland.