The Evolutionary Characteristics And Interaction Mechanisms Of Ecological Service Functions Under Vegetation Rehabilitation On The Loess Hilly Region Of China

The Loess Hilly Region of China,which form a typical fragile habitat,were used as the earliest pilot area for the grain-for-green project and as a key area for monitoring ecological environment construction.Currently,ecological restoration work in the region has shifted from a phase of comprehensive promotion to a phase of achievement consolidation and improvement.A systematic,comprehensive,and accurate assessment of the eco-service functions of local ecological restoration projects would facilitate regional ecological security assessment,sustainable development forecasting,and green GDP accounting,and would provide a scientific guidance for further implementation and management of the grain-for-green project under the new situation.Therefore,in this study,the abandoned grasslands?AG?and artificial Robinia pseudoacacia?RP?communities that restored for 10,18,28,and 43-years in Loess Hilly Region were taken as the research objects,and the slope farmland was taken as the control.By using fixed-station observation,field experiment,and indoor analysis methods,the plant characteristics,soil properties,and the physical quantity and value of the eco-service functions in the AG and RP communities were measured at the sample land scale;the dynamic changes,correlation,trade-off,and synergy of eco-service functions in the AG and RP communities were clarified;and the driving factors and mechanisms of the eco-service function in the AG and RP communities were further elucidated.At last,based on the assessment of eco-service function,this study predicted the future development of the AG and RP communities,and put forward corresponding management advice.The main research contents and results are as follows:?1?Vegetation types and restoration time play a decisive role in improving the functions of ecological support services and ecological regulation services of artificial vegetationBased on the calculation of physical quantity,the AG and RP communities were valued at 5000¹5,000 and 7500¹0,000 yuan·hm^-2·a^-1,respectively,with regard to biodiversity conservation function;at 57.21⁹6.88 and 1431.78²635.70 yuan·hm^-2·a^-1,respectively,with regard to nutrient accumulation function;at 1064.03⁶566.29 and 4460.99¹0,480.36 yuan·hm^-2·a^-1,respectively,with regard to soil conservation function;at9458.99²8,426.81 and 25,648.10³7,308.24 yuan·hm^-2·a^-1,respectively,with regard to water conservation function;at 1205.54²145.51 and 10,216.54¹6,469.90 yuan·hm^-2·a^-1,respectively,with regard to carbon fixation and oxygen release function;and at 62.14³03.43 and 885.80²,588.08 yuan·hm^-2·a^-1,respectively,with regard to air quality purification function.Under the same restoration age,both physical quantities and values of the ecological support functions and ecological regulation functions were greater for the RP communities than for the AG communities,except for biodiversity conservation function at18 and 28 years of restoration.As restoration years increased,the biodiversity and biodiversity value of the AG communities first increased and then decreased,whereas the physical quantities and values of other five ecological service functions increased significantly.Meanwhile,the biodiversity and biodiversity value of the RP communities first decreased and then increased with restoration years,whereas the physical quantity and value of nutrient accumulation and other three ecological regulation functions first increased with restoration years,and only those of soil conservation increased significantly with restoration years.?2?The evolution characteristics of the correlation,trade-off,and synergy of eco-service functions in the artificial vegetations are clarified,and both of them are greatly affected by the restoration time.Correlation analysis revealed that,during the first 28 years of restoration,there were significant positive pairwise correlations?R²>0.70?between the six eco-service functions in the AG communities.In contrast,biodiversity conservation was significantly and negatively correlated?-0.78>R²>-0.99?with the other five eco-service functions during 28⁴3 years of restoration in the AG communities and during the first 28 years of restoration in the RP communities,and there were significant positive pairwise correlations?R²>0.72?between the other five eco-service functions.During 28⁴3 years of restoration,the biodiversity conservation and soil conservation functions in the RP communities were significantly and positively correlated with each other?R²=0.88?,but significantly and negatively correlated with the other four service functions?-0.62>R²>-0.99?.The root mean square errors between the eco-service functions were 0.000⁰.583 and0.003⁰.714 for the AG and RP communities,respectively,with both fluctuating as restoration years increased.The largest trade-off existed between water conservation function and the other five eco-service functions,with the relative gains shifting in favor of water conservation function,whereas the trade-off between carbon fixation and oxygen release function,nutrient accumulation function,and air quality purification function was relatively small.A time model for the trade-off and synergy relationships of the eco-service functions revealed that,for the AG communities,the trade-off between each eco-service function and the other five eco-service functions increased with restoration years,and the difference between recovery 28 years and recovery 43 years was not significant.In contrast,the trade-offs significantly increased and then decreased with restoration years in the RP communities.This indicated that the trade-off between the eco-service functions of the AG communities gradually tended to stabilize,whereas the RP communities generally remained in a dynamic and unstable state.?3?Vegetation characteristics and soil properties jointly drive the improvement of ecological service function,and the influence of vegetation factors on ecological service function is greater than that of soil factorsThe vegetation characteristics and soil physicochemical properties and biological activities were affected by both vegetation types and restoration years,and these changes significantly affected the eco-service functions.The vegetation factors had the greatest impact on the eco-service functions,followed by the soil physicochemical properties,and the biological activity of the soil had a relatively small impact on eco-service function.With regard to vegetation properties,litter thickness,total leaf nitrogen content,and litter water holding capacity were the main vegetation factors that affected the eco-service functions of the AG communities,whereas vegetation coverage,leaf area,and specific leaf area were the main factors that affected the eco-service functions of the RP communities.With regard to soil properties,nutrient contents had the greatest impact on the eco-service functions of the AG communities,whereas soil erodibility and water contents had the greatest impact on the eco-service functions of the RP communities.With regard to soil biological activity,the soil microbial biomass and nitrogen-phosphorus ratio of enzymatic activity had the greatest impact on the eco-service functions of both the AG and RP communities.?4?The composition and development trend of the ecological service function in artificial forest-grass vegetations are different,among which the sustainable ability of the AG community is greater than that of the RP community,resulting in their different management modesThe eco-service function of the AG community was dominated by water conservation function,biodiversity conservation function,and soil conservation function,accounting for51.70⁶3.13%,15.65³3.56%and 6.32¹4.58%,respectively.The eco-service function of the RP community was dominated by water conservation function,carbon fixation and oxygen release function,and soil conservation function,accounting for 47.25⁴9.34%,18.43²4.09%and 8.47¹4.49%,respectively.The eco-service function values of the RP communities were significantly greater than those of the AG communities,and the eco-service functions of the AG communities increased continuously with increasing restoration time,whereas those of the RP communities decreased at 43 years of restoration.Model simulation analysis suggested that the eco-service functions of the RP communities would be smaller than those of the AG communities after 58 years of restoration,and a scenario analysis of area ratio revealed that vegetation-related eco-service functions decreased as the relative area of the RP communities increased and that the eco-service functions of the mixed vegetation would be lower at 58 years of restoration than those of the AG communities.Therefore,the AG communities was more beneficial to long-term continuous increases in eco-service functions.However,management measures should be taken to increase the vegetation productivity of the AG communities.Although the eco-service functions of RP communities may be greatly improved on a short term,the improvement sustainability is not substantial,and posterior management should focus on water carrying capacity by adopting management measures,such as compact planting,branch trimming,intermediate cutting,supplementary planting,and mixed afforestation,that effectively reduce vegetation water consumption.