| Desertification is the main cause of ecosystem degradation in many regions and one of the major environmental,social-economic problems facing the world.Desertification seriously erodes land resources and further affects the sustainable development of agriculture,animal husbandry and even economy.According to the "Ordos Declaration" issued by the 13 th Conference of the Parties in Ordos in 2017,the "United Nations Convention to Combat Desertification" pointed out that desertification is one of the main challenges that hinder global sustainable development,and it seriously threatens the ecosystem's ability to provide benefits to society.The Mu Us Desert is located in the transitional area from the Ordos Plateau to the Loess Plateau,and is a typical eco-environmental fragile area where agriculture,animal husbandry and forest interlace.With the development of agriculture and animal husbandry,energy development,and implementation of regional policy measures in the Mu Us Desert,the desertification situation and ecological environment have undergone significant changes in recent years.Therefore,exploring the impact of desertification on ecosystem services and assessing the effects of aerial seeding restoration from 1986 to 2015 can provide a theoretical basis for desertification prevention and control in the Mu Us Desert.In this study,the Mu Us Desert was used as the study area.Based on the measured data of vegetation coverage in 71 field sites,10 desertification remote sensing monitoring indexes were tested,and the most suitable index was selected for this area;and then the desertification dynamics in seven periods from 1986 to 2015 in the Mu Us Desert were inversed from the whole-desert scale and provincial scale.Based on the meteorological data,socio-economic data and policy investment data,the driving factors of the desertification change during this period were analyzed.Further more,based on the vegetation and soil samples from 32 aerial seeding restoration sites in Mu Us Desert,vegetation diversity,soil microbial diversity and soil multifunctionality were obtained through high-throughput sequencing and experimental test,and the effect of aerial seeding restoration was evaluated from three aspects: vegetation,soil microorganism and soil multifunctionality,and the driving factors and driving mode of soil multifunctionality were defined.Finally,based on remote sensing data,meteorological data and socio-economic data,the spatial quantification of ecosystem services in the Mu Us Desert was carried out,and the impact of desertification on ecosystem services was analyzed.The results are followed:(1)Among the 10 desertification remote sensing monitoring indexes selected through literature summary,the indexes reflecting the surface energy information and vegetation information have high accuracy for the desertification inversion.The Desertification Difference Index(DDI)not only reflects the surface radiation characteristics but also includes vegetation information,and has clear biophysical significance,can reflect the changes of surface coverage,water-heat combination and land desertification,and is the best remote sensing monitoring index of desertification in Mu Us Desert.(2)The overall desertification spatial pattern dynamics in the Mu Us Desert during the past 30 years showed a reversal trend in the central and eastern regions,and recovery and intensification occurred alternately in the western regions.From 1986 to 2015,the process of desertification at the whole-desert scale showed a trend of first deteriorating and then reversing.It continued to intensify from 1986 to 2005,and the area of heavily and severely desertified land increased during the process.After 2005,desertification gradually reversed,and the area of heavily desertified land decreased significantly,but until 2015,the desertification degree of whole-desert scale was still higher than that of 1986;the desertification process has a strong spatial heterogeneity at the provincial scale.Among them,the most obvious restoration of desertification is the five districts and counties in Shaanxi Province,which continued to reverse after 2000;Inner Mongolia Autonomous Region has coexisted with reversal and intensification since 1986;the overall desertification in Ningxia Autonomous Region showed a trend of intensifying and then reversing,and the desertification reached its strongest in 2005.(3)Desertification in the Mu Us Desert continued to intensify from 1986 to 2005,and reversed year after year after 2005.The main driving factor for the reversal was ecological restoration policies,while the driving force for desertification was socio-economic factors.Due to Inner Mongolia,Shaanxi and Ningxia provinces have differences in climatic conditions,socio-economic development and policy implementation,the desertification process and driving factors have significant spatial heterogeneity at the provincial scale.This study found the important role of ecological restoration policies in the reversal of desertification and quantified its contribution rate.We recommended that continue to invest in ecological restoration projects to continue the reversal of desertification and pay attention to the ecological sustainability in economic development.(4)Aerial seeding is an effective measure for vegetation restoration of active dunes in Mu Us Desert,which has substantially restored the plant diversity,soil microbial diversity and soil versatility of active dunes.The response of plant diversity and soil microbial diversity to restoration is rapid,plant diversity is the first to reach saturation,and the response of soil multifunctionality to restoration is lagged behind.On the 30-year restoration gradient,plants have a significant indirect effect on the restoration of soil multifunctionality through soil microorganisms,and the direct driving factor is mainly soil bacteria.It is recommended that future degraded land and ecosystem restoration measures and policies can draw on the successful experience of aerial seeding measures and give equal attention to vegetation and soil microorganisms in ecological restoration.(5)About ecosystem services of the Mu Us Desert,there is a significant synergy between the regulating services such as soil conservation,water retention and NPP,and there is also a significant synergy between provisioning services such as crop productivity and livestock productivity.A synergy relationship was also found between the two services of NPP and crop productivity.Soil conservation,water retention and NPP all showed an upward trend with the decrease of desertification,and the crop productivity and livestock productivity showed a non-significant hump relationship with desertification.It may be that the two provisioning services are realized through the input of human activities,which leads to their complicated relationship with desertification.In summary,this study explores the desertification dynamics,driving factors,ecosystem services,and the restoration of vegetation,soil,and soil microorganisms in the Mu Us Desert during 1986-2015 from the macro to the micro level,in a multi-level and multi-angle approach.This study describes the process of intensification and reversal of desertification,clarifies the positive effects of ecological restoration policies and negative effects of social-economic activities during this process,and finds the connecting role of soil microorganisms in the repair process.This paper provides a method for desertification monitoring and provides a theoretical basis for the preparation of corresponding prevention and control measures from the macro level;based on the successful experience of aerial seeding,it provides a new perspective from the micro level for the restoration of desertified land,finaly clarifies the impact of desertification on ecosystem services.It is hoped that this study can provide a scientific basis for desertification prevention and ecological restoration strategies in the Mu Us Desert,so as to enhance ecosystem services and human well-being in the region and achieve regional sustainable development. |
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