The Optimal Stocking Rate on Grazing System in Inner Mongolia SteppeⅡ.Based on Relationship Between Stocking Rate and Aboveground Net Primary Productivity The Optimal Stocking Rates on Grazing System in Inner Mongolia SteppeⅠ.Based on Analysis of Liveweight Gain per Animal and Hectare and Benefit A study on optimal grazing rates in Stipa purpurea alpine grassland in Northern Tibet