Study On Ecological Carrying Capacity Of Alpine Grassland On Qinghai-Tibet Plateau

The Qinghai-Tibet Plateau?QTP?,with an average elevation exceeding 4000meters,is the highest plateau in the world,commonly referred to as“The roof of the world”and“Water tower of Asia”,considered as the most unique eco-region.Due to its geographical location and altitude,the QTP is sensitive to climate change and thus serves as“starter”of climate change and“indicator”of global change.The complex climate of the QTP breeds diverse ecosystem types.The alpine grassland,the most widely distributed on the QTP,accounting for 60%of the total area of the Plateau,is one of the most important natural pastures in China.The alpine grassland ecosystem on the QTP is vulnerable and has poor anti-interference ability.climate change and human activities further aggravated its vulnerability,which caused grassland degradation,increased desertification area and increased soil erosion intensity.Therefore,the big challenge facing alpine grassland on the QTP is how to use grassland rationally to reduce ecological risks and avoid environmental problems,which makes it necessary to study the ecological carrying capacity of alpine grassland,for providing scientific guidance for the ecological protection of the QTP.In previous studies,the ecological carrying capacity was the size of the population that could be supported indefinitely upon the available resources and services of that ecosystem,which quantitatively revealed the develop-ability of a region,but ignored the role of ecosystems in regional environmental maintenance.Considered the vulnerability of some certain areas,assessment of ecological carrying capacity based on ecological principles,which transformed the“black box hypothesis”between ecosystem environmental resource and carrying capacity into an“ecological hypothesis”,was proposed in this study.According to the main functions of the ecosystem of vulnerable areas,the ecosystem function module was constructed.The alpine grassland ecosystem on the QTP mainly considered its environmental maintenance function and natural regeneration function.The evaluation principle was the ability of the ecosystem to carry human activities on the basis of ensuring basic environmental maintenance functions and natural renewal functions.The environmental maintenance function module included soil and water conservation function module,wind proof and sand fixation function module,and a natural regeneration function module mainly focused on the update capability of the grassland main body.Using revised universal soil loss equation?RULSE?and revised universal wind loss equation?RWEQ?,and setting the threshold of soil erosion and soil wind erosion,the minimum vegetation coverage required for the environmental maintenance function of the grassland ecosystem in the Tibetan Plateau was obtained.Then,using the relationship between vegetation coverage and net primary production?NPP?,the NPP under the minimum vegetation cover required for soil and water conservation function(NPP_SWC)and the NPP under the minimum vegetation cover required for wind proof and sand fixation function(NPP_SF)were gotten.The natural regeneration module obtained the NPP required for natural regeneration(NPP_NR)of the ecosystem by summarizing empirical theory,grazing experimental results,and degradation trends.Potential NPP?PNPP?simulated by the BIOME4 model,minus the maximum value of the NPP_SWC,NPP_SF and NPP_NR was the NPP that can be utilized by humans?UNPP?.Finally,according to the standard hay coefficient,the daily output of sheep unit and other indexes,the carrying capacity of alpine grassland on the Tibetan Plateau was obtained.The results showed that:?1?It mainly considered the environmental maintenance function of preventing soil erosion and wind erosion.the effective vegetation coverage of the ecosystem to preventing soil water erosion on the QTP increased from northwest to southeast,and the vegetation coverage in southern and southeastern QTP needed to reach 70%above.From the perspective of preventing soil wind erosion,the effective vegetation coverage of the QTP should be no less than 30%,which was an important“threshold”for controlling soil wind erosion.When the average vegetation coverage was higher than this value,the soil wind erosion rate would be significantly reduced.?2?The UNPP of alpine grassland in the QTP was between 50⁴00 g m^-2 yr^-1,and the regional average was 167.49 g m^-2 yr^-1.The UNPP in the eastern part of the QTP was higher than that in the west.Places where natural grassland itself was not enough to support the environmental maintenance and natural regeneration functions were mainly distributed in Qiangtang Plateau lake basin alpine steppe region and Southern Xizang high mountain and valley shrub steppe region.?3?The average level of reasonable carrying capacity of alpine grassland on the QTP was 0.5 sheep units hm^-2yr^-1.The spatial distribution of carrying capacity of alpine grassland on the QTP varied greatly,showing a trend of increasing from northwest to southeast.Taking Golognaqu Plateau mountain alpine shrub-meadow region as the boundary,the carrying capacity in the east and south is greater than the average level,the carrying capacity in the western region is below average,and the areas that need to stop grazing are mostly distributed here.