Seasonal Regulation Of Grazing Intensity On Stipa Breviflora Community Characteristics And Spatial Heterogeneity

Response to seasonal regulation of grazing intensity on plant population and community characteristics of Stipa breviflora steppe were investigated during year2010～2011, which recorded the height, coverage and density of plant populations in order to calculate important value and diversity index. Plant of aboveground part in each treatment was cut, dried and weighed for the calculation of grassland productivity, meanwhile took back0～40cm soil samples, each10cm for a layer in the corresponding plots to laboratory for routine nutrients analysis. A representative plot by size100m×100m was selected in each treatment in2011, according to mechanical method,1m×1m quadrats laid per10m quadrats and detailed records of plant species, height, coverage, density and analyzed spatial heterogeneity of main plant population and community characteristics in each grazing treatment. Finally the relationship between treatments or treatment and plant population/soil nutrients was investigated using cluster and correspondence analysis to identify the optimal mode of seasonal regulation in different grazing intensity. The main results were as follows:1. Early banning grazing is conducive to plant population height and coverage, density of Stipa breviflora, that represented higher characteristics of plant populations for the regulation of banning grazing in spring+heavy grazing in summer+moderate grazing in autumn and banning grazing in spring+moderate grazing in summer+heavy grazing in autumn, while lower characteristics of plant populations for the regulation of continious heavy grazing or heavy grazing in spring and summer+moderate grazing in autumn. Moderate grazing intensity can effectively balance population status in the community, and correspondly increase population and individuals’numbers. The degree of species replacement reduced with increase of sampling area, which showing moderate grazing area> banning grazing in spring+heavy grazing in summer+moderate grazing in autumn area> heavy grazing area> heavy grazing in spring and summer+moderate grazing in autumn area> banning grazing in spring+moderate grazing in summer+heavy grazing in autumn area.2. Regulation of banning grazing in spring+heavy grazing in summer+moderate grazing in autumn, banning grazing in spring+moderate grazing in summer+heavy grazing in autumn and moderate grazing intensity increased community aboveground standing crop. The underground biomass declined with increase of soil layers deeper in different treatments, which showed "T" type, and was accordant to the declining pattern depicted by the exponential function. Moderate grazing intensity was benefit for underground biomass accumulation.3. Crude protein content showed a trend of "down-up-down ". regulation of banning grazing in spring+heavy grazing in summer+moderate grazing in autumn and moderate grazing intensity were more conducive to accumulation of community crude protein, crude fat, phosphorus and magnesium content; regulation of banning grazing in spring+moderate grazing in summer+heavy grazing in autumn can promote the improvement of plant calcium content.4. The isotropic and anisotropy space distribution of three main plant populations caused by random factors were larger in regulation of banning grazing in spring+moderate grazing in summer+heavy grazing in autumn which of plant spatial variability degree was also largest, and which of space heterogeneity caused mainly by structural factors. three main plant populations in different treatment were in distribution of mosaic patches; spatial variability of plant species number in regulation of banning grazing in spring+moderate grazing in summer+heavy grazing in autumn was larger by random factors, while regulation of banning grazing in spring+heavy grazing in summer+moderate grazing in autumn had the maximum degree of spatial variability, and enhanced with angle increasing; community coverage spatial variability of isotropic spatial distribution caused by random factors and maximum degree of spatial variability in heavy grazing treatment was larger; spatial variability of anisotropy spatial distribution caused by random factors was largest in regulation of banning grazing in spring+moderate grazing in summer+heavy grazing in autumn, which combined with heavy grazing intensity area had the maximum degree of spatial variability. Spatial distribution was mosaic patchy distribution.5. Available potassium in heavy grazing area> moderate grazing area; heavy grazing intensity accelerated the available N transfer rate of topsoil down to subsoil then caused a large number of phosphorus,.available P and potassium loss in topsoil;the organic matter content declined with soil layer increased.6. Compared to the community characteristics, banning grazing in spring+heavy grazing in summer+moderate grazing in autumn area and banning grazing in spring+moderate grazing in summer+heavy grazing in autumn area processing than the continious moderate grazing area, which all had a close relationship with the community characteristics of average height and density; the continious moderate grazing area was better than continious heavy grazing area and heavy grazing in spring and summer+ moderate grazing in autumn area, which had a close relationship with community coverage.7. The regulation of banning grazing in spring+heavy grazing in summer+moderate grazing in autumn was more reasonable.