Effects Of Different Grazing Intensities On Seasonal Pasture Soil Erosion And Breakeven On The Northern Slope Of Tianshan Mountains

The temporal and spatial pattern of soil erosion in pastoral areas,the influence degree of grazing disturbance on soil erosion and the breakeven characteristics between grazing activities and soil erosion were analyzed,which provided theoretical basis and practical support for soil and water conservation and ecological environment protection in pastoral areas.Taking the seasonal pasture in the middle part of the Northern Slope of Tianshan Mountain(NSTM)as the study area,using the methods of field investigation,Remote Sensing(RS),Geographic Information System(GIS),model simulation and mathematical statistics,based on the Chinese Soil Loss Equation,CSLE),Biome-BGC model,defoliation formulation and environmental economics theory,etc,quantitatively analyze the spatial and temporal pattern characteristics of soil erosion from 2000 to 2018,analyze the impact of grazing disturbance on soil erosion,clarify the relationship between grazing activities and soil erosion,and discuss the breakeven characteristics between grazing activities and soil erosion.The research results show that:(1)From 2000 to 2018,the grazing intensity on the NSTM generally increased.In the county,Urumqi county,Hutubi county and Changji city increased in fluctuation,while Fukang city and Shawan county changed slightly.The grazing intensity of seasonal pasture is 12.41 sheep/hm~2 in winter pasture>8.17sheep/hm~2 in spring and autumn pasture>5.19 sheep/hm~2 in summer pasture.From 2000 to 2018,the soil erosion modulus of pastures on the NSTM showed an overall upward trend,with 2007 as the watershed,which changed from fluctuating upward trend to fluctuating downward trend.Seasonal pasture in soil erosion modulus is summer pasture>winter pasture>spring and autumn pasture.The overall trend of soil erosion modulus in the county is consistent with that in the NSTM,but only Shawan County shows a fluctuating downward trend,with a multi-year average of soil erosion modulus 43.10 t/(hm~2·a)in Dabancheng district>34.08 t/(hm~2·a)in Changji city>33.49 t/(hm~2·a)in Fukang city>33.24 t/(hm~2·a)in Urumqi county>22.82t/(hm~2·a)in Hutubi county>21.52 t/(hm~2·a)in Manasi county>17.74 t/(hm~2·a)in Shawan county.With the increasing grazing intensity in seasonal pastures on the NSTM,the soil erosion modulus increases,and the correlation between grazing intensity and soil erosion modulus is spring and autumn ranch>winter ranch>summer ranch.(2)Biome-BGC model can well simulate the pasture biomass on the NSTM,with R~2 of 0.85 and RMSE of6.169 g C/(m~2·a).Under grazing disturbance,the biomass of pasture on the NSTM decreased,the value of biological measures increased,and the soil erosion modulus increased.The spatial pattern characteristics of pasture before and after grazing disturbance were consistent in seasonal pasture scale,but changed in county.The spatial pattern of soil erosion modulus is summer pasture>winter pasture>spring and autumn pasture.Before the county disturbance,the order is Urumqi county 45.26 t/(hm~2·a)>Changji city 42.25 t/(hm~2·a)>Fukang city 37.52 t/(hm~2·a)>Dabancheng 36.88 t/(hm~2·a)>Hutubi 33.20 t/(hm~2·a)>Manasi 21.79 County t/(hm~2·a)>Shawan County 16.04 t/(hm~2·a),After interference it changed into Urumqi county 48.68 t/(hm~2·a)>Fukang city 46.61 t/(hm~2·a)>Dabancheng district 45.01 t/(hm~2·a)>Changji city 44.49 t/(hm~2·a)>Hutubi county 34.65 t/(hm~2·a)>Manasi county 22.95 t/(hm~2·a)>Shawan county 21.16 t/(hm~2·a).In 2019,the average increase of pasture soil erosion modulus caused by grazing disturbance on the NSTM was 13.5%;Seasonal pastures increased by 20.65%in spring and autumn pastures,15.57%in summer pastures and 15.46%in winter pastures.The county growth rate is 31.93%in Shawan county>24.24%in Fukang city>22.04%in Dabancheng district>7.56%in Urumqi county>5.34%in Manas county>5.30%in Changji city>4.37%in Hutubi county.Soil erosion in seasonal pasture,spring and autumn pasture and Shawan county is mainly affected by grazing disturbance.(3)From 2000 to 2018,the trend of grazing economic benefit and soil erosion loss in every county on the NSTM is relatively stable,averaging 2.2×10~8 yuan/year and 4.9×10~8 yuan/year,respectively.Overall grazing benefit in Shawan county is 1.06×10~8 yuan>Urumqi county 0.40×10~8 yuan>Fukang city 0.37×10~8 yuan>Changji city 0.36×10~8 yuan>Hutubi county 0.25×10~8 yuan.The loss of soil erosion is 1.96×10~8 yuan in Urumqi county>1.01×10~8 yuan in Changji city>0.84×10~8 yuan in Fukang city>0.43×10~8 yuan in Hutubi county>0.14×10~8 yuan in Shawan county.The indexes of soil erosion loss are crop yield loss>soil erosion loss>land abandonment loss>water conservation loss.The threshold of comprehensive breakeven grazing scale of seasonal pastures on the NSTM is 12.25×10~4 heads in Shawan county>5.13×10~4 heads in Hutubi county>2.95×10~4 heads in Urumqi county>1.47×10~4 heads in Changji city>1.34×10~4 heads in Fukang city.