Research On Ecosystem Services And Its Optimization In The Chongqing Main City

Mountain urban ecosystem can provide diverse ecosystem services(ESs)due to its unique and vertical ecological environment characteristics and diverse habitat types.Affected by endogenous instability and human disturbance in mountain areas,mountain urban ecosystem is characterized by fragility.At present,human activities such as global industrialization and urbanization have been advancing in an accelerated manner.However,the unreasonable exploitation and utilization of mountain natural resources have led to accelerated habitat loss,habitat fragmentation and ESs degradation,which seriously affect human well-being and threaten regional ecological security and sustainable development.The Chongqing main city(CMC)is a typical mountainous city.As one of the important growth engines for the Chengdu-Chongqing economic circle and the high-quality development in western China,CMC has experienced rapid socio-economic development and acute human-land relationship problems,which is facing the dual pressures of ecological protection and construction expansion.How to ensure the sustained and stable supply of ESs,and how to realize the coupling synergy management and optimization of multiple ESs in the processes of socio-economic development are urgent issues to be addressed for urban sustainable development.Therefore,taking CMC as the study area,micro-topographic characteristics of mountains were considered in this study to optimize the evaluation of biodiversity maintenance(BI),carbon fixation(CF),soil conservation(SC)and water conservation(WC).On these bases,this study identified ESs hotspots,quantitatively measured the spatio-temporal heterogeneity and intensity of the coupling synergy among key ESs and discussed the influence mechanisms.Taking into account multiple protection objectives of ESs,the protection priority areas with maximum benefits were scientifically identified,and a well-connected ecological security pattern was constructed.Finally,from the perspective of local-whole and point-line-surface,the optimization approaches and regulation strategies of ESs improvement were proposed in terms of both ecological protection pattern optimization and functional efficiency regulation.The main research contents and results of this paper were as follows:(1)Evaluation of key ESs in mountainous city of CMC.Based on the analysis of micro-topographic characteristics of mountains,combined with the quantitative survey of sample plots,coupled with In VEST model and Max Ent model,four key ESs were evaluated and optimized.Through the analysis of the spatio-temporal dynamic changes and hotspots differentiation,it can be seen that high-value ESs hotspots areas were concentrated in Jinyun,Zhongliang,Tongluo,Mingyue,Huaying,East Spring,Taozidang,Zhaishanping,Qiaoping and other mountainous areas.The Yangtze River and Jialing River outside the built-up areas were also high-value concentration areas of BI,while ESs in urban areas were extremely low.At administrative districts scale,ESs were relatively higher in Banan,Beibei and Yubei,while those in Yuzhong were the lowest.From 2000 to 2018,on the one hand,with the continuous advancement of urbanization,the disturbance of human activities gradually increased.On the other hand,with the strengthening of ecological protection,the overall BI of CMC had been improved by 0.074.Although ecological projects such as returning farmland to forestland had effectively ensured the carbon sequestration capacity of mountain vegetation,the overall CF of CMC showed a decreasing trend with the continuous expansion of urban scale.The SC hotspots were concentrated in mountainous areas with high vegetation coverage at an elevation of 200～700 m and a slope of 10～30°.The WC in mountainous areas was higher than that in flat areas.Affected by precipitation and other factors,SC and WC showed a general decreasing trend.Multiple ESs hotspots had strong selectivity to geomorphological conditions,and the distribution indices in mountainous areas were all greater than 1,showing obvious distribution advantages.The average distribution index presented a tendency to increase with an increase in terrain niche index(TNI)gradients.Generally,forestland was a major contributor to ESs,accounting for 91.00% of ESs hotspots.(2)Coupling synergy analysis of key ESs in mountainous city of CMC.At the entire scale,the relationships between ES pairs were synergistic,but the coupling synergy degree was low.Only the relationship between BI and CF exhibited primary synergistic relationship,with an average coupling synergy degree of 0.64.At local scale,the strong synergy areas were mainly concentrated in the high-high clusters,i.e.,mountainous areas,and the coupling synergy degree between BI,CF and WC were relatively higher.At administrative districts scale,the synergy area proportion and coupling synergy degree between ES pairs were higher in Beibei,Banan and Yubei,which were closely related to the higher proportion of forestland in these districts.From the perspective of the interaction of multiple ESs,ESs show different aggregation and combination forms at spatial and temporal scales,which could be divided into five types of ESs bundles(ESB).ESB1 was spatially clustered in Jinyun,Zhongliang,Tongluo,Mingyue,Huaying and southeastern mountainous areas,with forestland as the main land use type,accounting for 94.26%.ESB1 was especially characterized by high-quality synergy,with an average coupling synergy degree of 0.96.ESB2 was interlaced with ESB1,which showed relatively low SC due to topographic factors,with an average coupling synergy degree of 0.92.ESB3 was mainly located in the piedmont transition zone between mountains and flat areas with high SC.ESB4 was widely spread in the intermountain flat areas,the trough and valley at the top of anticline mountains,with a large proportion of cultivated land(96.26%)and an average coupling synergy degree of 0.63.ESB5 was concentrated in the central and surrounding urban groups and waters.The average ESs in this bundle were at the lowest level.(3)Influence mechanisms of key ESs in mountainous city of CMC.ESs were comprehensively affected by natural environment,socioeconomic and policies factors.The complex landforms combination and the unique and crisscrossing landscapes of mountains,rivers and cities resulted in a strongly nonlinear relationship between ESs and environmental factors.In general,ESs were deeply influenced by land use types and mountain micro-geomorphology types.Forestland had a profound impact on BI and CF.SC was mainly determined by geomorphological factors,while WC was more likely to be explained by natural environmental factors such as precipitation.Furthermore,ecological protection planning policies were confirmed to have a certain positive effect on ESs.The effects of environmental factors on the spatial differentiation of coupling synergy among ESs were not independent of each other.The interactions among influencing factors were mainly two-factor enhancement and nonlinear enhancement.Land use types had the strongest explanatory ability for the spatial differentiation of coupling synergy among ESs,with an average explanatory rate of 60.92%.Geomorphological factors were also key influencing factors,and the average coupling synergy degree in the middle of the slope of mountain micro-geomorphology types was higher than 0.5.The interactions between land use types and TNI or geomorphological types can significantly improve the explanatory ability of coupling synergy among ESs.The distance factors had profound impacts on the coupling synergy among ESs.The farther from the forestland and the closer to the construction land,the stronger the disturbance from human activities,and the lower the coupling synergy degree.(4)Optimization and regulation of key ESs in mountainous city of CMC.To optimize key ESs,the first step was to identify the protection priority areas.From the local scale,taking ESs hotspots and multi-functional coupling synergy hotspots as protection objects and quantifying protection costs with human footprints,the protection priority areas were identified using Marxan system protection planning tools.There was a spatial mismatch between the existing 42 nature protected areas and the protection priority areas,and the overlapping area was only 173.20 km~2.There were still 443.39km~2 of the protection priority areas that had not been included in the existing nature protected areas,so there was a protection gap.The existing nature protected areas still had common problems of high protection cost and low protection effectiveness.Only 5nature protected areas had an overlap rate of more than 50% with protection priority areas.From the point-line-surface multi-scale,taking the optimized protection priority areas as ecological sources,the basic ESPs were constructed based on Linkage Mapper and circuit theory,which consisted of 67 ecological sources with an area of 684.36 km~2,1203.16 km~2 buffer zones,115 ecological corridors,14 ecological pinch points and 24 ecological barrier points.Then,from the two aspects of ecological protection pattern optimization and functional efficiency regulation,the multi-scale ESs optimization approaches and regulation strategies were proposed based on the overall zoning management and control,key protection areas identification and optimization,and point-line-surface ecological network optimization.The scientific delineation of ecological-production-living spaces was conducive to the efficient and rational utilization of mountainous city space and to ensure the sustained and stable supply of ESs.Alleviating the disturbance of human activities to the key areas of ESs and actively promoting ecological sources protection and restoration through the optimization of nature protected system.Taking the river corridors as important supplementary corridors to strengthen ecological corridors construction and comprehensive improvement.Focusing on ecological pinch points management and ecological barrier points restoration through the identification of key restoration areas.Finally,the composite and networked ESPs of "two rivers,four mountains,multi-sources,multi-corridors,multi-points" were optimized,and ecological protection and restoration strategies were put forward according to local conditions to improve ESs.This study met the strategic demands of the national ecological civilization construction and sustainable development,and provided a scientific basis for ensuring the sustained and stable supply of key ESs and comprehensively optimizing ESs.The research results realized the practical transformation and decision-making application of basic theoretical knowledge,and provided a basic reference for the delineation of the ecological-production-living spaces,the optimization of the natural reserve system and ecological network.This study played an important role in spatial guidance and decision support for coordinating mountainous urban development and ecological protection planning.