The Study On Ecological Service Evaluation And Trade-off Analysis Of The Gain For Green Project Based On 3S Technology

The Grain for Green Program(GGP)was known as the largest ecological restoration project in the world,aiming to improve ecological environment and to benefit human well-being.However,a major challenge in ecosystem management for multiple ecosystem services(ESs)is the pervasive trade-offs between regulating services(e.g.,flood control)and provisioning service(e.g.,non-timber forest products).How to enhance the effect of GGP on ESs,as well as to mitigate the trade-off between regulating service and provisioning service are increasingly discussed by environmental managers and ecologists.Using the 3S technique(remote sensing,geography information systems and global positioning systems),filed-based sampling,household survey and ES model,we examined the GGP-driven land-use change between 2000 and 2015 and assessed its effects on ESs in a mountainous headwater of the northeast China,including Qingyuan Manchu Autonomous County,Xinbin Manchu Autonomous County and Fushun County.Then we identified the prioritizing areas(farmland retirement to achieve a high return on ESs),and compared the regulating service provide by the area with the realistic situation in 2015,trying to propose a reasonable landscape pattern for the GGP.Finally,we developed future scenarios for different proportional combinations of economic forest and ecological forest under the GGP,and analyze their effects on regulating services and provisioning services and their trade-offs to inform the decisions for afforestation types and spatial pattern.he results were as followed.(1)Between 2000 and 2015,the GGP-driven conversed area is 4209.7 ha,accounting for14.5% of the overall land-use change.The major type of the land use change is from farmland to forest,which is 3459 ha,accounting for 82.2% of the area of GGP.The GGP areas mainly distributed in the nearby riverbanks and western parts,which the area that degree of slope >15° only accounted for 12.6%.During the first around of GGP,the carbon storage increased from 1.5×105 to 5.1×105 t and the average carbon density increased from 36.48 t/ha to 121.2 t/ha.Soil erosion decreased from 17.1 t/ha·yr to 4.4 t/ha·yr,alleviating from mild level to slight level.Nitrogen concentration export decreased from 5.7 mg/L to 0.2 mg/L,improving from class III to class I.Flood mitigation service increased by 62.6 mm.Although the improvement in concerned regulating services had been observed,steep-sloped farmlands with a total area of 6160.9 ha were still cultivated.(2)Through analysis of alternative scenarios that developed in an effort to prioritize the conversion of steep-slope and riparian farmlands,we estimated the total amount of the concerned regulating services.The result indicated that,except for carbon storage,the other regulating services under the two alternative scenarios greatly improved as compared with those under the current status in 2015.The greatest flood mitigation service was observed forthe conversion of steep-slope farmlands to forest(55.8 mm),followed by that of riparian buffer farmlands to forest(36.2 mm)and the realistic situation in 2015(26.1 mm);the similar order was also found for sediment retention service.The greatest water purification service was observed for the conversion of riparian buffer farmlands to forest(8.1 mg/L),followed by that of steep-slope farmlands to forest(6.5 mg/L)and the realistic situation in 2015(5.2mg/L).This result indicated that retirement of riparian buffer farmlands can improve water purification service better,whereas retirement of slope-steep farmlands can promote sediment retention and seasonal water yield services better.There farmlands are supposed to be retired preferentially in the new round of GGP.(3)We modelled the future scenarios for different proportional combinations(10%,20%to 77%)of economic forest and ecological forest under the GGP.Although the total amount of production provision increased with afforestation area of economic forest increasing,the production per unit area deceased.Meanwhile,carbon storage and flood mitigation declined and soil erosion and export of nitrogen concentration increased.This result indicated that production provision increased,but at the expense of decreases in regulating services.In conclusion,we recommend that the afforestation proportion of economic forest should be not beyond 50%,depending on the site condition and prioritizing areas for ecological protection.