Trade-offs And Synergies Analysis Of Forest Ecosystem Services In The Three Gorges Reservoir Area

The Three Gorges reservoir area(TGRA)is located at the upper and middle reach of the Yangtze River in China.The region displays complex topography with a diverse range of specie and community,it has always been a hot spot in China and the world.As one of the key areas of ecological environment protection of China,the ecological environment pressure is increasing in the TGRA,due to the influence of the construction of the Three Gorges Dam.Therefore,the forest ecosystem is not only an important guarantee for the ecological environment of the TGRA but also the main body of ecosystem services.Because of the uneven distribution of forest ecosystem services,the variety of services,and the long-term pursuit of interests in human beings,which lead to an imbalance between ecosystem services.Therefore,in order to correctly and comprehensively understand forest ecosystem services and the trade-offs and synergies between them,this paper used the ecosystem service function assessment norms and GIS spatial statistical methods to explore the dynamic changes of forest ecosystem service value in the TGRA from 1990 to 2015.In order to make the results more realistic,this paper combined the structural characteristics of the forest age to correct the basic parameters.On this basis,the correlation analysis,the tradeoffs-synergies degree model and the layer superposition are used to reveal the trade-offs and synergies between services and spatail-temporalvariations.The research results are as follows:(1)Contribution of different ecosystem service in the TGRA ranked as follows: Water conservation> carbon fixation and oxygen released > biodiversity conservation > soil conservation> atmosphere environmental purification > nutrient accumulation > action of forest against natural calamities.Different types of forest had the value trend as that of the TRGA,which showed the variation characteristics of “increase,decrease,increase”.The water conservation of high value was mostly distributed in the east of the TGRA.The soil conservation was better in the east of the TGRA,and the west end of the reservoir was lower.After 2005,the area of high-value carbon sequestration and oxygen released increased,which was along the Wuxi-Wulong line in a spatial scale,with higher in the southeast and lower in the northwest.The area of nutrient accumulation was gradually increasing,mainly distributed in the east and center of the TGRA.The spatial distribution of atmosphere environmental purification was similar as action of forest against natural calamities,and high-value areas were mainly distributed in the east of the TGRA and south of the center part.High-value areas of biodiversity conservation was distributed in east and weat of the TGRA.(2)During the period 1990-2015,the value of forest ecosystem services in the TGRA showed an upward trend on a timescale,growth characterized by “quick,slow,quick”,from 537.79 billion yuan to 306.742 billion yuan,with a growth rate of 99.46%.The geographical distribution of forest ecosystem service of the TGRA was along the Wuxi-Wulong line in a spatial scale,which was higher in the southeast and lower in the northwest.The variation range of forest ecosystem service value of the TGRA had grown rapidly in west while slowly in east from 1990 to 2015.(3)The trade-offs and synergies analysis of forest ecosystem services in the TGRA,synergies as a focus were showed between services.On the TGRA as a whole,the relationship between water conservation and various ecosystem services was dominated by synergies.However,on the east,center and end of the TGRA,which was dominated by trade-offs.An analysis of the relationship between indicators was found: Protecting fertilizer(protecting N,P,K,organic matter)was the main influencing factor that leaded to trade-offs between soil conservation and other ecological services.(4)The trade-offs and synergies showed changes between forest ecosystem services in the TGRA.As can be seen from the whole,the interrelationship between forest ecosystem services in the TGRA shows a positive development trend.The synergies between multiple services showed a trend of becoming stronge.The relationship among action of forest against natural calamities,carbon fixation,oxygen released,nutrient accumulation and atmosphere environmental purification had changed from trade-offs to synergies over time.Trade-off relationship increased over time among soil conservation,carbon fixation,oxygen released and nutrient accumulation.The negative correlation among action of forest against natural calamities soil conservation and biodiversity conservation was gradually changed into positive correlation.(5)This paper analyzed the spatial difference of trade-offs/synergies between ecosystem services by tradeoffs-synergies degree model.It was found that the relationship was mainly developed in the direction of synergies between forest ecosystem services in the TGRA.The trade-offs among water conservation,soil conservation and biodiversity conservation,as well as soil conservation,nutrient accumulation and action of forest against natural calamities were mostly distributed in in the east and center parts.The trade-offs among water,conservation carbon fixation,oxygen released,nutrient accumulation,atmosphere environmental purification and action of forest against natural calamities was mainly distributed in the south of Jiangjin and the southeastern part of Shizhu and Fengdu.The number of grids of synergistic effect among carbon fixation,oxygen released,nutrient accumulation,atmosphere environmental purification,action of forest against natural calamities and biodiversity conservation had reached more than 90%.(6)The trade-offs relationship between the main ecosystem services(water conservation,carbon fixation and oxygen released,biodiversity conservation and soil conservation)was widely distributed,especially in the strong trade-off area,accounting for 51.59% of the total forest area,which was distributed in the east and west of the TGRA.Weak trade-offs accounted for 13.29%,which mainly distributed in Yiling and Zigui and the center part of the TRGA.The synergistic area accounted for 35.13% of the total forest area.Strong synergy accounted for 10.25%,mainly distributed in the south of Jiangjin and Badong,and also included parts of Zigui and Yiling.Weak synergy accounted for 24.87%,mainly distributed in the center of the TGRA and scattered in the Xingshan.(7)In hotspot analysis,the scope of multiple services hot showed an increasing trend.Five high value ecosystem services were provided in five periods from 1990 to 2010.There were increased availability of 6 and 7 ecosystem services by 2015.The scope of multiple services hot region was mostly distributed in Badong,Xingshan,Zigui,Shizhu,Fengdu,Fuling and Wulong.From 1990 to 2015,the scope of multiple services hot region increased by 79.04%.The area of reduction of multiple services hot region was 14.37%.The TGRA implemented key forestry projects,such as the program of protective forest construction in the Yangtze River basin,natural forest resources protection project and the program of conversion farmland to forest or grassland.With the gradual increase of forest area,the total value of forest ecosystem services in the TGRA had been improved.The increase in the value of forest ecosystem services should not only pay attention to the growth of forest area,but also the increase in the value of unit area.This was of great significance in the TGRA and even the forest areas of the whole country.At the same time,by discussing the relationship between forest ecosystem services,we recognized the dynamics of trade-offs and synergies between forest ecosystem services in the TGRA,and the strength of the combination of service capabilities.The research results had a certain guiding significance for further understanding the function and value of forest ecosystem services in the TGRA and its protection and management of ecosystems.