| Ecosystem service research is the core of the ecosystem assessment and the basis for rational and effective use of natural resources,protection of the ecological environment,coordination of human-land relations,and socially sustainable development.How to effectively maintain the sustainability of the ecosystem and accurately weigh the supply of ecosystem services is a common challenge facing human society.The TGRA is an ecological security barrier area and an ecological economic area in the middle and lower reaches of the Yangtze River.It is also an important ecologically fragile area and biodiversity hotspot area in China.In recent years,under the implementation of a series of ecological projects such as water conservancy projects,natural forest protection and afforestation,the quality and stability of the surface cover and ecosystems in the TGRA have been consolidated and restored in some degree.However,the rugged and complicated geographical environment features of the reservoir area,global warming,and human activities have caused a significant impact on its fragile ecological environment.The ecological and environmental problems in the TGRA are long-term and urgent.To continuously improve the comprehensive benefits of ecosystem services in the area,the research on the dynamic changes of the ecosystem services in the area,and the formation mechanism should be strengthened.Reasonably regulating the trade-offs and synergies among multiple services,and integrating ecosystem service management into the policy-making process,have great practical significance and theoretical guidance.In this study,based on the remote sensing data,land-use change data,forest resource inventory data,sample survey and literature data of the TGRA,and comprehensive use of In VEST model,RUSLE model,and Arc GIS spatial analysis tools.The forest ecosystem services in the TGRA were evaluated at different spatial and temporal scales,from the regional scale ecosystem—forest—main dominant tree species(groups).Focus on evaluating the trade-offs and synergies of water retention,carbon sequestration and soil conservation at different scales in the TGRA,quantify the relationship between changes in natural factors and socio-economic factors and changes in ecosystem service supply capacity and explore the natural differences in the impact of processes and human activities on ecosystem services.Getis-Ord Gi* index,spatial correlation matrix,geographic detectors,and other spatial statistical analysis methods were used to analyze the spatial correlation of ecosystem services and their changes,as well as the trade-offs and synergies between different services.Finally,based on the analysis results,Founding the best balance between development and protection,to provide data support for the sustainable development of regional forests,formulate and implement differentiated forest resource protection and utilization policies,and to alleviate severe environmental problems and formulate human and nature.The harmonious development policy provided a scientific basis and proposes an optimization strategy based on the improvement of forest ecosystem services in the TGRA.The main research work and results of this article are as follows:(1)Characteristics of land use/cover change in the TGRA.During the 25 years from 1990 to 2015,the land use/cover structure in the TGRA has undergone significant changes.Overall,grassland and farmland areas have decreased,and forest land,construction land,waters,and unused land increased.The area of all woodland types increased,of which the area and percentage of coniferous forests have the largest increase,followed by coniferous and broad-leaved mixed forests and shrubs.The area of farmland fell the most,from 66.20% in1990 to 40.35 in 2015 %,and showing a decreasing trend year by year;due to the completion and operation of the Three Gorges Reservoir.The water area of the study area almost doubled between 1990 and 2015.The area of grassland increased first and then decreased during the whole study period,and the area was the largest in 2000.The area of unused land generally increased year by year.(2)Regional-scale dynamic assessment of ecosystem services and temporal and spatial evolution characteristics.From 1990 to 2015,water retention,carbon sequestration,and soil conservation services in the TGRA all had significant changes.The water retention showed a trend of first decreasing,then increasing,and then slightly decreasing;in terms of spatial distribution,the water retention was highest in the southern part of the reservoir head and the southern hinterland;in various typical ecosystems,the water retention was highest in coniferous forests,followed by coniferous and broad-leaved mixed forest,and the water retention of bare land and grassland were the smallest.From 1990 to 2015,the carbon reserves in the TGRA increased by 64.69 million tons,with an obvious increasing trend;in terms of spatial distribution,the regions with relatively large carbon density were the northeastern and southern margins.The order of carbon reserves of different ecosystem types is in turn leaf forest> cropland> coniferous and broad-leaved mixed forest> broad-leaved forest> shrubs>construction land> grassland> bare land> water area.Carbon reserves in most areas of the reservoir area increased to varying degrees,with spatial changes manifested in central and southern Yichang,northern Zigui,northeastern Badong,Wushan County,Yunyang County,eastern Wanxian and northern Banan.The carbon reserves in the main urban area,eastern Yichang,and the main roads and tributaries of the Yangtze River decreased significantly.In terms of soil conservation,among various typical ecosystems,forests(coniferous forests,coniferous and broad-leaved mixed forests,shrubs,and broad-leaved forests)had the highest soil retention,accounting for about 69% of the total soil retention in the study area.The ecosystem of the farmland was second,with soil conservation accounting for 29%.From 1990 to 2015,the soil conservation of the TGRA showed a gradual increase,with a total increase of6%;in terms of spatial distribution,soil retention had obvious differentiation,and its high-value areas were mainly distributed in the northern hinterland of the reservoir.From 1990 to 2015,a variety of ecosystem services in the Three Gorges Reservoir area have been improved and improved,which shows that the effective implementation of ecological projects such as returning farmland to forests and natural forest protection has greatly increased the proportion of forest land area,increased vegetation coverage,restored the structure of the ecosystem to a certain extent,and significantly improved various ecosystem services.The spatial heterogeneity attribution analysis of ecosystem services in this study is realized by the method of geo detector.Natural and social factors have a significant impact on ecosystem services..The slope was the main driving factor for the solution to the spatial heterogeneity of water retention services in the TGRA and had a negative correlation.Carbon storage was greatly affected by the proportion of forest land area,farmland area,and population density.Terrain factors and forest vegetation were the main factors affecting the spatial distribution pattern of soil conservation services in the TGRA.Natural and socio-economic impact factors had an interactive effect on the ecosystem services in the TGRA,and the influence of any two factors after interaction can be shown as the two-factor enhancement or nonlinear enhancement.(3)Regional-scale ecosystem service trade-offs and synergy.The geographical environment of the Three Gorges Reservoir area is complex,and there are great vertical differences in altitude.In the TGRA,ecosystem services not only show scale dependence,but also have spatial heterogeneity,the smaller the research scale,the higher the diversity of ecosystem trade-offs.The ecosystem services in the TGRA had complex non-linear relationships,and various ecosystem service trade-offs/synergies had regional differentiation characteristics and perform differently on different scales.At the regional scale,ecosystem services trade-off conflicts are mainly reflected in water conservation-carbon storage and water conservation-soil conservation.Soil conservation and carbon retention were in a synergistic relationship,while water retention and soil conservation,water retention,and carbon retention were all in a trade-off relationship.At the grid-scale,the distribution of soil retention and high carbon retention areas roughly coincided,and the relationship between the two was mainly synergistic.Water retention and soil retention were only in a synergistic relationship in Wuxi County,Kai County,Wulong County,and Jialing County in the northern part of the hinterland,while most other areas had a strong or weak trade-off relationship,and the weak trade-off was the main one.Water retention and carbon storage were only significantly positively related to Kaixian and Wuxi County in the northern hinterland.There was a synergy between services,and most other areas were in a trade-off relationship,and the area ratio of strong trade-offs to weak trade-offs was high as 67.41%,more than half of the total area of the reservoir area.(4)Spatiotemporal changes of forest ecosystem services in the reservoir head of the TGRA.During the second category of forest resource surveys from 1999 to 2017,the total water retention and unit area water retention of the forest ecosystem in the reservoir head of the TGRA increased by 29.63% and 20.85% respectively.The amount of water retention of different forest vegetation in various periods was the same as the area of forest vegetation types.From 1999 to 2017,the soil conservation of the forest ecosystem in the study area increased by56.723 million tons,an increase of 7.11%,and the soil conservation per unit area did not change much,only with an increase of 0.85%.The main reason for the increase of forest soil maintenance service function in the study area is the improvement of forest area and quality.The carbon reserves of forest vegetation in the study area increased by 4.2289 million tons,an increase of up to 42.56%,while the area of forest vegetation in the study area increased by only55,600 hectares,an increase of 7%.The significant increase in the carbon storage of forest vegetation in the study area was mainly due to the age of the forest increases.The storage volume per unit area also increased,so the biomass of forest vegetation showed an increasing trend.The area of the forest ecosystem in the study area accounted for a large proportion of middle-aged forests,the carbon storage density had not yet reached the maximum.With the growth of trees,these trees can also fix a certain amount of atmospheric carbon.If they were better nurtured and managed,the carbon fixation potential of forest vegetation still had a great increase in space.(5)The trade-off and synergies of ecosystem services of Pinus massoniana.The trade-off relationship is the main relationship between the three ecosystem services of Pinus massoniana Plantation in the study area.About 60.37% of the three ecosystem services of Pinus massoniana Plantation have different types and different degrees of benefit conflicts,which need to be managed.Soil thickness and forest age are the main factors that affect the water retention of Pinus massoniana plantation,altitude,landform,and slope are also the main factors that affect the water retention;The average DBH is the main factor that affects the carbon density of Pinus massoniana plantation,followed by the landform;The terrain factor is the main factor that affects the heterogeneity of soil conservation service space.Overall,The main relationship between the three ecosystem services of Pinus massoniana Plantation in the study area is the medium-low degree coordination and medium trade-off,and the overall ecosystem services benefit is still low.About 60.37% of Pinus massoniana X plantation ecosystem services have different types and different degrees of trade-offs.The proportion of areas with the synergistic relationship is about 39.63%.Among them,4.96% of the three ecosystem services of Pinus massoniana plantation are in the high or middle level,and there is a high synergistic effect between services.About 17.26% of the three ecosystems of Pinus massoniana Plantation have low service supply capacity,and there is a low synergy between services.The ecosystem service collaborative relationship of Pinus massoniana Plantation in the study area shows that the proportion of Pinus massoniana sample plots with a high level of ecosystem service in the reservoir head is very small,the overall ecological benefit of ecosystem service is still in the middle and low level,the proportion of high-quality forest area is small,and the service benefit supply situation is still severe.In the future,the forest resource management should take the low coordination forest land and the strong balance forest land as the key objects of forest supervision and benefit regulation,and further improve the ecosystem service supply capacity of the low and medium service capacity forest stands.The impact of natural and social factors on the ecosystem services of Pinus massoniana plantation is mainly mutual enhancement and non-linear enhancement,which is the result of multiple factors.Soil thickness and forest age are the main factors affecting the water conservation of Pinus massoniana plantation,and the terrain factors such as elevation,landform and slope are also the main factors affecting the water conservation of Pinus massoniana plantation;The average DBH is the main factor affecting the carbon density of Pinus massoniana plantation,followed by landform;The terrain factor is the main factor that affects the spatial heterogeneity of soil conservation services of Pinus massoniana plantation,and the slope has the highest explanatory power to the spatial heterogeneity of soil conservation services of Pinus massoniana plantation.In this study,three main ecosystem services in different time and space scales in the Three Gorges Reservoir area were evaluated and mapped comprehensively,which can provide data support and reference for regional and forest scale ecosystem service management,and help to better guide the implementation of ecological protection policies. |
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