Research On Regulating Forest Landscape Of The Three Gorges Reservoir Area Based On Ecosystem Service

Ecosystem service is a research hotpot of landscape planning and ecological restoration as it provides benefits to human survival and health.When people prefer one or several ecosystem services,other services would be decreased,which is ecosystem service trade-off.It is one of the great challenges of landscape planning and regulating to balance among ecosystem services to meet growing human demands.As a typical ecologically vulnerable area in China,an important ecological barrier in the middle and lower reaches of the Yangtze River,and one of the most ecological economic zones,the Three Gorges Reservoir Area（TGRA）has a significant influence to the human settlement and economic development inside and outside the reservoir area.However,the uncertainty of ecosystem structure and function increased due to the rugged topography and intensive anthropogenic activities over the past few decades.In this paper,the idea of"meeting human demands-regulating landscape configuration-predicting ecosystem services"was generated from the"structure-process-function"theory.The field measured data,multi-source remote sensing data and historical climate data were integrated.First,we used statistical analysis and spatial analysis to systematically study the landscape evolution of TGRA from 2000 to 2015.Then,five key ecosystem services were comprehensively defined and quantitatively assessed according to the ecosystem prossesses.Third,the relationships bwteen landscape configuration and ecosystem services were studied.Meanwhile,we demonstrated the relationships among ecosyteem services,and identified the spatial hotpots of ecosystem services trade-off.Fourth,we used the CA-Markov model to simulate and predict the future landscape configuration.In addition,we used these landscape maps to assess the ecosystem services in different scenarios.Last,we discussed the application of ecosystem services in landscape planning and provided some suggestions to regulate and optimize the forest ecosystem structure of the TGRA.Our results could provide the scientific basis and technical support for regulating forest ecosystem in future for meeting various human demands under ecosystem service trade-off in this region.Moreover,this paper could provide a quantitative reference for sustainable development management and national multidisciplinary decision-making in other ecologically vulnerable areas.The main conclusions of this study are as follows:（1）The topography and soil of the TGRA exhibited the spatial heterogeneity.It could be characterized by“high altitude and steep slope in east and north,low altitude and gentle slope in west and south”,while the soil organic carbon content increased with increasing altitude and slope.The climatic factors showed significantly the spatial heterogeneity,but changed insignificantly from 2000 to 2015.Among three climatic factors,the mean annual temperature（MAT）was high in middle and west but low in east,the mean annual precipitation（MAP）was large in middle but small in east and west,while the mean annual radiation（MAR）was large in north and small in south.During 2000²015,the MAT and the MAR increased,while the MAP decreased slowly.However,all of their change rates did not pass the t test at 95%confidence level.（2）The landscape configuration changed dramatically between 2000 and 2015,and the forest coverage increased linearly to 53.48%.Vegetations exhibited several significant distinct transformation phases.Most of forest types increased during 2000²005,while mixed forest increased during 2005²010.All landscapes and their changes exhibited significant spatial heterogeneity in the TGRA.Forests were mainly distributed in the mountainous areas in the east and southwest,while croplands were mainly distributed in the flat plateaus and valleys in the west.These distributions can contribute to reductions in soil loss and sediment production but increases in crop yield.Afforestation,returning cropland,water storing and urban expansion were four typical ecological processes in the TGRA.Ecological restoration activities such as returning croplands to forests mainly occurred in the zones of 500¹000m and 15²5°,while water storing and urban construction mainly occurred in the zones of<500m and 5¹0°.The process of landscape evolution in heterogeneous spaces effectively mitigated land conflicts between ecological restoration and economic development.Therefore,these landscape evaluations were targeted to different regions to reconcile the land use conflicts between ecological restoration and economic development.（3）The ecological and environmental factors had significantly impacted the spatial distribution of various landscapes.Correlation analysis results demonstrated the significant correlation among these factors,so we proposed two rotating principal components by the principal component analysis and the maximum variance rotation.We defined the first rotating principal component RC₁ as the topographic factor which mainly loaded by the elevation,the surface-height-fluctuation,the slope and soil organic carbon,and the second rotating principal component RC₂ as the climatic factor which mainly loaded by MAP,MAT and MAR.The linear regression results documented that the modelled R² of all vegetations were higher,while the model R² of all non-vegetation landscapes were lower.Topographic factors and climatic factors could effectively explain the spatial distribution of vegetations,but the non-vegetation landscape such as the construction land and bare land landscape were strongly interfered by human activities.（4）Five key ecosystem services slowly increased from 2000 to 2015,and exhibited significantly the spatial heterogeneity in horizontal and vertical distribution.First,the water purification was assessed by the non-point source pollution indicators and using the InVEST model.The pollutions of N and P were characterized by“high in west and south,low in east and north”,and decreased with increasing altitude and slope.Second,we used the RUSLE model to assess soil loss and retention.The mean annual soil loss of TGRA was about 35.72 t·ha^-1·yr^-1.The soil loss risk and retention capacity presented a spatial consistency.Third,the gas regulation was assessed by the NPP and using the CASA model.The mean annual NPP was about 560.52 gC·m^-2·yr^-1.Due to the interactions among climatic conditions,the NPP was high in the regions with the moderate altitude and slope along the both sides of the Yangtze River,but increased quickly in the regions with high altitude and steep slope.Lastly,we used the InVEST model to assess the habitat quality of terrestrial ecosystem and the recreation service which increased linearly and exponential,respectively.In addition,the response of recreation service was more sensitive to cultural landscapes than natural landscapes.（5）The response of ecosystem service was sensitive to the landscape evolution.Vegetation was a greater provider of regulating and support services,but provided less cultural services.Forests were the most important providers of ecosystem services in the TGRA,and the supply capacity varied among forest types for each ecosystem service.The redundancy analysis results documented that the cumulative variance of the two RDA axes was 95.94%.RDA1 would strongly explain the water purification,the soil retention and the habitat,and was positively correlated with forests,but negatively correlated with agricultural land.RDA2 would effectively explain the recreation service,and was highly positively related to construction land.Moreover,corresponding analysis results documented that ecological restorations significantly enhanced the services of water purification,soil retention,habitat quality and gas regulation,while the combined effect between ecological restorations and urban construction promoted the recreation service in the TGRA.（6）Ecosystem services were interrelated,but their cumulative effects and change rates presented a strong consistency.According to the correlation analysis results,the water purification,the soil retention,the gas regulation and the habitat quality were significantly and positively correlated,and they were significantly and negatively correlated with the recreation service.The redundancy analysis results demonstrated that the water purification,the soil retention and the habitat quality were highly synchronized.As local ecosystem service flows,the habitat quality and the recreation service presented a strong negative correlation.The former was seriously affected by the natural environment,while the latter was seriously affected by the social and economic conditions,resulting in the zero-sum game.As directional ecosystem service flows,the water purification and the soil retention were strongly synergistic.In addition,there was a strong synergy between directional and global ecosystem service flows,and they had significantly improved due the vegetation restorations.（7）The relationships among multiple ecosystem services could be attributed to trade-offs and synergies under the coupling of temporal and spatial scales,and were significantly affected by the temporal evolution and the spatial analysis scale.According to the temporal evolution of the correlation coefficients and their statistical significance,the synergy/trade-off relationships among ecosystem services became stronger,and the correlation gradually changed from irrelevant to significant during 2000²015.According to the correlation analysis,the correlation coefficients was smaller and passed the t test at 95%confidence level at the 1 km fishnet and watershed scale,was larger but did not pass the t test at 95%confidence level at the county scale.Moreover,the fishnet was the most suitable analysis scale for the local ecosystem service flow,while the watershed was the basic analysis unit for the directional ecosystem flow.（8）We used CA-Markov model to predict the landscape configuration of the TGRA in 2030,the results documented that the quantitative feature and spatial pattern of forests could significantly affect the performance of ecosystem services.Three quantitative demands,i.e.,ecological type（EG）,economic type（EM）and eco-economic type（EE）and three spatial hotspots of ecosystem services trade-off,i.e.,habitat quality（Hab）,recreation service（Rec）and directional ecosystem service flow（DF）,were combined to 9 scenarios.And the quantitative demands had more grater influences than the spatial hotspots for the future landscape of the TGRA.EG could effectively regulate the proportion of various forests,EM could effectively regulate the proportion of construction land,while EE has both of the above advantages.Predicting and comparing the differences of ecosystem services among 9 scenarios by variance analysis,EG_DF had larger water purification capabilities,EG_Hab and EG_DF had no significant difference at 95%confidence level in enhancing habitat quality but were significantly higher than other scenarios,EM_Rec significantly improved the recreation service.In summary,the quantitative demand was important for enhancing ecosystem services of the TGRA in future,while combing it and the spatial hotspot of ecosystem services trade-off could improve the supplies of ecosystem services.