| Human survival and development depend on ecosystem services,and land use change and natural resource utilization under the influence of human activities affect ecosystem services.The Three Gorges Reservoir area is one of the most important ecological protection areas in China.With the promotion of the Three Gorges Project,the Project of Returned Farmland to Forest and the Natural Forest Protection Project,the land use pattern and ecosystem services in the Three Gorges Reservoir area have undergone significant changes.Lanlingxi watershed,as a demonstration site of scientific and technological support for the conversion of farmland to forest in China,has formed the "three belts" model of ecological protection forest belt,ecological economic forest belt and landscape forest belt and the spatial pattern of land use in the hilly area of the Three Gorges Reservoir area.In this study,we analyzed the spatiotemporal changes of land use in Lanlingxi watershed in recent 20 years,and evaluated and explored the processes and mechanisms of ecosystem service changes,including ecosystem supply,supporting and regulating functions.It can provide experience and case support for ecosystem management,resource allocation,ecological safety maintenance,ecological compensation and ecological restoration at the watershed and regional scale,and also provide theoretical basis and data support for the optimization model and configuration structure of the Three Gorges Reservoir Area,such as the conversion of farmland to forest,ecological protection and restoration,agricultural and forestry structure adjustment,etc.This article is based on remote sensing image data,meteorological data,statistical yearbook data and DEM data,in zigui county LanLingXi small watershed as the study area through the use of the land use dynamic degree,partition type transfer,elevation,slope slope to partition,comprehensive analysis of the small watershed landscape pattern index method from 2000 to 2020,spatial and temporal change of land use,With the support of 3S technology,the RUSLE model and CASA model were used to evaluate the functions of product supply,water and soil conservation,carbon fixation and oxygen release,and the spatial distribution and change trend of each function were analyzed from different angles of land use type partition,elevation partition and slope direction partition.Specific research results are as follows:(1)From 2000 to 2020,the implementation of the policy of returning farmland to forest has led to great changes in land use in the small watershed of Lanlingxi,with a large number of farmland being transferred to tea plantation and citrus,and the area of construction land,broadleaved forest and mixed coniferous and broad-leaved forest increasing continuously.The most frequent land use type transfer occurred in the region below 600 m and between 5 degrees and 35 degrees of slope.Taking 600 m as the dividing line,the dominance of patches decreases in the range less than 600 m,the landscape fragmentation increases,and the degree of disturbance by human activities becomes greater and greater.In the area above 600 m,the landscape complexity and fragmentation degree of public welfare forest protection decreased,and the connectivity degree increased.(2)With the transfer and change of land use in the small watershed of Lanlingxi in the past 20 years,the main supply of farmland in the small watershed has changed to the double supply of tea garden and citrus.The total product supply capacity first decreased and then increased year by year,and exceeded the total product supply in 2000.The product supply capacity is mainly concentrated in the area below 600 m above sea level,and the total product supply within 200-600 m accounts for more than 73%of the total.The product supply in the area of 5 degree to 25 degree accounts for more than 75%of the total area.The area below 35 degrees develops garden economy vigorously,the area above 35 degrees develops public welfare forest,the reasonable agricultural and forestry structure,improves the ecological environment quality at the same time the product supply ability is also strengthened continuously,realizes the economic benefit and the ecological benefit balance.(3)According to RUSLE model analysis,soil erosion in Lanlingxi small watershed is mainly distributed in two striped areas of southwest mountainous region,which is caused by large vertical slope,steep terrain,bare surface and strong rainfall scouring intensity in the mountainous region.In the past 20 years of comprehensive management,the overall potential soil erosion modulus and actual soil erosion modulus of Lanlingxi watershed gradually decreased,and the overall erosion intensity gradually decreased from strong erosion to light erosion.The total soil erosion was effectively reduced by 55,415 t,and the total soil erosion was one fifth of that in 2000.(4)The results of NPP calculated by CASA model show that the net primary productivity per unit area of Lanlingxi watershed decreases from southwest to northeast.From 2000 to 2020,the NPP of Lanlingxi watershed increased,and the net primary productivity increased from 452.84 gC m-2 a-1 in 2000 to 588.22 gC m-2 a-1.The total amount of NPP increased from 6916.04 t in 2000 to 8983.65 t in 2020,increasing by 2067.6 t.Tea plantation was the second largest type of NPP,and mixed coniferous and broad-leaved forest had the highest NPP.The total amount of NPP was the largest in the range of 200 m to 400 m elevation,and the total amount of NPP in the range of 25 degrees to 35 degrees accounted for more than 60%,which were the main distribution areas of tea plantation and citrus.During the 20 years,the annual carbon sequestration and oxygen release increased by 919.06 t and 2460.54t respectively.Twenty years,the implementation of the policy of returning farmland to forest and tianbao engineering greatly improved the ecological environment of LanLingXi watershed,high natural forest protection is given priority to ecological shelter belt,predominantly agroforestry ecological economic forest in central,low for landscape forest ecological protection type-"three belts" model increases on the whole product supply capacity,soil and water conservation capacity and carbon oxygen releasing ability,Water and soil conservation services and carbon sequestration and oxygen release services have increased by 80%and 29%,respectively,achieving both economic and ecological benefits. |
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