Research On The Temporal And Spatial Evolution Characteristics Of Supply And Demand Risks Of Ecosystem Services In The North And South Qinling Mountains In Shaanxi Province

Human beings are facing the risk that ecosystem service supply cannot meet the demand,due to the influence of global environmental change and human activities.The supply-demand risk of ecosystem services seriously threaten the well-being of residents and the sustainable development of social economy.Therefore,it is urgent to build a systematic,complete and operational index system to assess the supply-demand risk of ecosystem services and provide theoretical and technical support for the risk management of ecosystem services.This study systematically reviews the research progress of ecosystem services and ecological risk assessment,and constructs an index system of supply-demand risk of ecosystem services based on four indicators:the supply-demand ratio of ecosystem services,the trend of supply-demand ratio,the trend of ecosystem service supply,and the relationships of trade-offs and synergies between ecosystem services.Taking three key ecosystem services of freshwater,grain and soil conservation in the south and north region of Qinling Mountains in Shaanxi Province from 2001 to 2015 as the case study object,we firstly used model tools to map the supply and demand of ecosystem services quantitatively;secondly,we used linear tendency,the supply-demand ratio of ecosystem services,and correlation coefficient to analyze the spatial-temporal patterns of supply and demand of freshwater,grain and soil conservation services,and the levels of supply-demand balance status and its evolution trend in time and space,as well as the trade-off and synergies between ecosystem services.Finally,We mapped and analyzed the supply-demand risks of freshwater,grain and soil conservation services in the south and north of Qinling Mountains in Shaanxi Province based on the above study results and the constructed index system of supply-demand risk of ecosystem services.The main conclusions of this paper are as follows:(1)The spatial distributions of supply and demand of freshwater,grain and soil conservation services are not consistent and their time changes are not synchronous in the south and north regions of Qinling Mountains in Shaanxi Province.Among them,areas with large supply of fresh water services are mainly concentrated in the south region of Qinling Mountains,while areas with large demand for freshwater services are mainly concentrated in Guanzhong Plain in the north region of Qinling Mountains.In terms of time changes,there is no significant trend in freshwater supply,while freshwater demand shows a significant upward trend,with an upward rate of about 0.89× 108 m3/a.This kind of spatial-temporal pattern differences between supply and demand of ecosystem services is the basic reason for the supply-demand risk of ecosystem services.(2)The relationships between supply and demand of freshwater,grain and soil conservation services have obvious scale effects in the south and north region of Qinling Mountains in Shaanxi Province.On the whole region scale,the total supply of freshwater,grain and soil conservation services can meet the demand;on the prefecture city scale,the results show that the supply of ecosystem services in a few prefecture cities can not meet the demand;on the pixel scale,the deficit areas of freshwater,grain and soil conservation services(that is,the supply can not meet the demand)accounts for 8.2%,13.6%and 9%of the total area of the region respectively.Among them,freshwater and grain deficit pixels are mainly concentrated in urban built-up areas such as Xi'an and Hanzhong,while soil conservation service deficit areas are mainly concentrated in Qinling Mountains,distributed in patches.Therefore,we need to pay attention to this scale effect in the study of ecosystem service supply and demand and select the suitable scale to better identify the regions of ecosystem service deficit.(3)The supply-demand ratios of freshwater,grain and soil conservation services have different time varying patterns in the south and north regions of Qinling Mountains in Shaanxi Province.Among them,the supply-demand ratio of freshwater service mainly presents a "fluctuating type",which may be related to the large annual changes of freshwater supply;the supply-demand ratio of grain service mainly presents an upward trend,mainly because the grain demand presents a downward trend(only four types of grain are considered in this paper);the time changes mode of the supply-demand ratio of soil conservation service is relatively rich,including 'rapid rise-slow rise','rising-falling",falling-rising" and "falling-stable fluctuation-rising"type,which show obvious stage characteristics and time inflection points.It is of great significance for ecosystem service management to identify the time change patterns and obvious time inflection point of the supply-demand ratio of ecosystem services.(4)The high supply-demand risk areas of freshwater service are large and concentrated,mainly located in Xi'an city and the northeast of Xianyang city;The high supply-demand risk areas of grain service are relatively small,mainly located around the built-up areas of Xi'an city;The high supply-demand risk areas of soil conservation service are mainly scattered in Qinling Mountains,distributed in patches.For the management of the supply-demand risk of ecosystem services,it is necessary to formulate appropriate management strategies for different types of ecosystem services and supply-demand risk levels.Specifically,it can be managed from two aspects of ecosystem service supply and demand:for the supply regulation,we can adopt the redline of ecological protection for soil conservation service,and the cross regional allocation to increase the freshwater and grain supply;for the demand regulation,we can further improve the ecosystem service value theory,the environmental protection law,and ecological compensation policy.This study constructs an index system of supply-demand risk of ecosystem services based on four indicators:the supply-demand ratio of ecosystem services,the trend of supply-demand ratio,the trend of ecosystem service supply,and the relationships of trade-offs and synergies between ecosystem services.This research idea is helpful to further expand the study field of ecosystem services and enrich the research content of ecological risk assessment.The results of this study can not only provide decision support for ecosystem service management in the south and north region of Qinling Mountains in Shaanxi Province,but also provide theoretical and technical support for the assessment of supply-demand risk of ecosystem service in other regions.