Dynamic Monitoring Study On Grassland Degradation And Grass-Livestock Balance In Gannan Tibetan Autonomous Prefecture From 2000 To 2019

As the world’s largest terrestrial ecosystem,grasslands play a very important role in promoting ecological and environmental improvement and socio-economic development.However,with global climate change and anthropogenic interventions,grassland ecosystems in Gannan Tibetan Autonomous Prefecture are showing a more obvious trend of degradation,which have seriously affected the local socio-ecological sustainable development and gradually attracted the attention of scholars.The degradation of grasslands is a systematic process with a long time series,which is not only reflected in the reduction of grassland cover and vegetation biomass,but also has a huge impact on the ecosystem.In order to solve the problem of grassland degradation,the national and local governments actively promote the"grass-livestock balance"system.Under the basic background of the rotational grazing system in Gannan Tibetan Autonomous Prefecture,traditional monitoring and research on grass-livestock balance only simply divide the year into cold and warm seasons,but no in-depth research has been conducted on the changes of grass-livestock balance during the cold and warm seasons.It makes the current grass-livestock balance monitoring lack of practical significance.This study used multi-source remote sensing data,statistical yearbook data and field research data to analyze the changes in grassland degradation,grassland-livestock balance and the spatial rationality of production in Gannan Tibetan Autonomous Prefecture from 2000 to 2019,and on this basis,provide corresponding suggestions for the sustainable development of grassland degradation and animal husbandry.Firstly,a time-series analysis was conducted based on the GPP and VC data with high spatial resolution obtained from the VPM model and linear fitting method,and the ecological characteristics of grassland degradation in the key degradation area-Maqu County were analyzed in conjunction with the field research data;Secondly,correlation analysis and linear fitting were conducted between the NPP data obtained from the VPM model and the grass production of the sample sites from the field research,and statistical secondly,the NPP data obtained from the VPM model were correlated and linearly fitted with the grass production at the sample sites from the field research,and the statistical datawere calculated to obtain the grass production and the actual livestock carrying capacity of the grassland in the growing season from 2000 to 2019,respectively,and the inter-month grass-livestock balance index was calculated and graded in the context of the rotational grazing system from 2000 to 2019 in the municipal,county and township areas of Gannan Tibetan Autonomous Prefecture to provide a basis for exploring the influence of human activities on grassland degradation.the spatial rationality of livestock production allocation and its changing trends in the county and township areas of Gannan Tibetan Autonomous Prefecture,to provide policy recommendations for attempting to address grassland degradation and sustainable development of livestock farming.The results of the study indicate that.（1）Based on GlobeLand data and land-use transfer matrix analysis,we obtained that the grassland area in Gannan Tibetan Autonomous Prefecture showed a continuous decrease from 2000 to 2020.the average value of grassland cover in Gannan Tibetan Autonomous Prefecture from 2000 to 2019 was 50.41%,showing a fluctuating upward trend at a rate of 0.025%·a^-1,with medium-low,medium and medium-high cover dominating.The mean value of grassland GPP in Gannan Tibetan Autonomous Prefecture from 2000 to 2019 was 713.46 g C·m^-2,showing a fluctuating upward trend at a rate of 0.356 g C·m^-2·a^-1.And the analysis of grassland degradation index constructed based on GPP and FVC data obtained that the degradation grade of grassland vegetation cover was predominantly undegraded in the three time periods from 2000 to 2009,2010 to 2019 and 2000 to 2019,accounting for 64.92%,66.13%and 65.74%of the grassland area respectively,and the proportion of grassland area with mild degradation grade was 35.08%,33.10%and 34.17%,with moderate degradation and moderate degradation distributed in both time periods from 2010 to 2019 and 2000to 2019,but with smaller areas.Grassland biomass degradation grade is more consistent with grassland cover degradation grade,which is mainly undegraded in all three time periods,accounting for 64.91%,55.89%and 61.37%of the grassland area respectively,and 35.09%,44.09%and 38.63%of the grassland area with mild degradation grade respectively.The combined grade of grassland degradation was mainly undegraded in all three periods,accounting for 64.92%,72.45%and 73.48%of the grassland area respectively,and the area of lightly degraded grassland accounted for 35.08%,27.15%and 26.47%respectively,with the grassland degradation areas concentrated in the western part of Maqu County.Combined with the Gannan Tibetan Autonomous Prefecture Grassland Monitoring Report and field research data,the manifestation of grassland degradation in Gannan Tibetan Autonomous Prefecture is mainly in the form of black soils and toxic weeds,and grassland sanding is mainly distributed near the Yellow River in the northwestern part of Magu County.Grassland degradation in Magu County is characterized by a decrease in cover and height,a decrease in fresh weight of grass production and an increase in the proportion of toxic weeds.The differences in grass height and fresh weight of grass production between the degraded and control groups were more obvious,while the differences in cover were not significant.（2）The inverse model of grassland above-ground biomass constructed based on the above-ground biomass collected from the sample sites and the NPP data calculated by the VPM model had good results（R²=0.92）.Grassland unit area yield and total grass production in Gannan Tibetan Autonomous Prefecture showed an increasing trend at3.60 g·m^-2·a^-1 and 14.60×10⁸ kg·a^-1 from 2000 to 2019.The inter-annual variation of actual livestock load in Gannan Tibetan Autonomous Prefecture from 2000 to 2019basically showed an increasing trend followed by a decreasing trend,among which,there were increasing trends during 2000～2001,2012～2013,2014～2015 and2018～2019,and decreasing trends in the rest of the years.The maximum and minimum values of actual livestock load occurred in 2001（942.40×10⁴ sheep units）and 2018（790.58×10⁴ sheep units）respectively.The temporal and spatial differences and variations in grass production and actual livestock carrying capacity are large at the county and township levels.（3）The inter-monthly grass-livestock balance of Gannan Tibetan Autonomous Prefecture from 2000 to 2019 was assessed based on the proposed concepts related to grass production,forage demand,forage stock and forage surplus.In the state level,except for April 2000,April and May 2009,which showed critical overload,forage balance and surplus respectively,the rest of the years showed a surplus state.There is a surplus of grass and animals.The inter-month variation in the balance of grass and livestock in the township is basically divided into three stages:January to May,June to August and September to December,with the frequency of overloads basically showing a"high-low-middle"trend.（4）The economic and ecological significance of the livestock production spatial rationality index is to weigh the balance between production factors（grass）and economic development（livestock）in the development of the grassland livestock industry.The mean values of the production space rationality index in Xiahe County（139.94）and Diebe County（72.50）are the largest and smallest values respectively.Only 32.63%of townships had reasonable mean values of the production space rationality index,while 26.32%and 41.05%of townships were too low and too high.（5）Based on the comprehensive analysis of grassland degradation,grass-livestock balance and spatial reasonableness of livestock production in Gannan Tibetan Autonomous Prefecture from 2000 to 2019,corresponding measures are proposed for the development of the grassland livestock industry:（1）Continue to implement the policy of“returning farmland to forest and grass”and“grassland ecological compensation mechanism”,and improve the government support and guarantee system.（2）Adjust the industrial structure,extend the industrial chain and increase economic benefits.（3）“storing grass”and“reducing livestock”in a two-pronged way.